src/java.base/share/classes/java/net/URL.java - master - niceSOFT/openjdk21

src/java.base/share/classes/java/net/URL.java
1 967 строк75 KB
Jonathan Gibbons
8305206: Add @spec tags in java.base/java.* (part 1)
04 апр 2023, 03:09
04 апр 2023, 03:09c6bd489
/*
 * Copyright (c) 1995, 2022, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.net;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.net.spi.URLStreamHandlerProvider;
import java.nio.file.Path;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Hashtable;
import java.io.InvalidObjectException;
import java.io.ObjectStreamException;
import java.io.ObjectStreamField;
import java.io.ObjectInputStream.GetField;
import java.util.Iterator;
import java.util.Locale;
import java.util.NoSuchElementException;
import java.util.ServiceConfigurationError;
import java.util.ServiceLoader;

import jdk.internal.access.JavaNetURLAccess;
import jdk.internal.access.SharedSecrets;
import jdk.internal.misc.ThreadTracker;
import jdk.internal.misc.VM;
import sun.net.util.IPAddressUtil;
import sun.security.util.SecurityConstants;
import sun.security.action.GetPropertyAction;

/**
 * Class {@code URL} represents a Uniform Resource
 * Locator, a pointer to a "resource" on the World
 * Wide Web. A resource can be something as simple as a file or a
 * directory, or it can be a reference to a more complicated object,
 * such as a query to a database or to a search engine. More
 * information on the types of URLs and their formats can be found at:
 * <a href=
 * "http://web.archive.org/web/20051219043731/http://archive.ncsa.uiuc.edu/SDG/Software/Mosaic/Demo/url-primer.html">
 * <i>Types of URL</i></a>
 * <p>
 * In general, a URL can be broken into several parts. Consider the
 * following example:
 * <blockquote><pre>
 *     http://www.example.com/docs/resource1.html
 * </pre></blockquote>
 * <p>
 * The URL above indicates that the protocol to use is
 * {@code http} (HyperText Transfer Protocol) and that the
 * information resides on a host machine named
 * {@code www.example.com}. The information on that host
 * machine is named {@code /docs/resource1.html}. The exact
 * meaning of this name on the host machine is both protocol
 * dependent and host dependent. The information normally resides in
 * a file, but it could be generated on the fly. This component of
 * the URL is called the <i>path</i> component.
 * <p>
 * A URL can optionally specify a "port", which is the
 * port number to which the TCP connection is made on the remote host
 * machine. If the port is not specified, the default port for
 * the protocol is used instead. For example, the default port for
 * {@code http} is {@code 80}. An alternative port could be
 * specified as:
 * <blockquote><pre>
 *     http://www.example.com:1080/docs/resource1.html
 * </pre></blockquote>
 * <p>
 * The syntax of {@code URL} is defined by  <a
 * href="http://www.ietf.org/rfc/rfc2396.txt"><i>RFC&nbsp;2396: Uniform
 * Resource Identifiers (URI): Generic Syntax</i></a>, amended by <a
 * href="http://www.ietf.org/rfc/rfc2732.txt"><i>RFC&nbsp;2732: Format for
 * Literal IPv6 Addresses in URLs</i></a>. The Literal IPv6 address format
 * also supports scope_ids. The syntax and usage of scope_ids is described
 * <a href="Inet6Address.html#scoped">here</a>.
 * <p>
 * A URL may have appended to it a "fragment", also known
 * as a "ref" or a "reference". The fragment is indicated by the sharp
 * sign character "#" followed by more characters. For example,
 * <blockquote><pre>
 *     http://www.example.com/index.html#chapter1
 * </pre></blockquote>
 * <p>
 * This fragment is not technically part of the URL. Rather, it
 * indicates that after the specified resource is retrieved, the
 * application is specifically interested in that part of the
 * document that has the tag {@code chapter1} attached to it. The
 * meaning of a tag is resource specific.
 * <p>
 * An application can also specify a "relative URL",
 * which contains only enough information to reach the resource
 * relative to another URL. Relative URLs are frequently used within
 * HTML pages. For example, if the contents of the URL:
 * <blockquote><pre>
 *     http://www.example.com/index.html
 * </pre></blockquote>
 * contained within it the relative URL:
 * <blockquote><pre>
 *     FAQ.html
 * </pre></blockquote>
 * it would be a shorthand for:
 * <blockquote><pre>
 *     http://www.example.com/FAQ.html
 * </pre></blockquote>
 * <p>
 * The relative URL need not specify all the components of a URL. If
 * the protocol, host name, or port number is missing, the value is
 * inherited from the fully specified URL. The file component must be
 * specified. The optional fragment is not inherited.
 *
 * <h2><a id="constructor-deprecation"></a>Constructing instances of {@code URL}</h2>
 *
 * The {@code java.net.URL} constructors are deprecated.
 * Developers are encouraged to use {@link URI java.net.URI} to parse
 * or construct a {@code URL}. In cases where an instance of {@code
 * java.net.URL} is needed to open a connection, {@link URI} can be used
 * to construct or parse the URL string, possibly calling {@link
 * URI#parseServerAuthority()} to validate that the authority component
 * can be parsed as a server-based authority, and then calling
 * {@link URI#toURL()} to create the {@code URL} instance.
 * <p>
 * The URL constructors are specified to throw
 * {@link MalformedURLException} but the actual parsing/validation
 * that is performed is implementation dependent. Some parsing/validation
 * may be delayed until later, when the underlying {@linkplain
 * URLStreamHandler stream handler's implementation} is called.
 * Being able to construct an instance of {@code URL} doesn't
 * provide any guarantee about its conformance to the URL
 * syntax specification.
 * <p>
 * The URL class does not itself encode or decode any URL components
 * according to the escaping mechanism defined in RFC2396. It is the
 * responsibility of the caller to encode any fields, which need to be
 * escaped prior to calling URL, and also to decode any escaped fields,
 * that are returned from URL. Furthermore, because URL has no knowledge
 * of URL escaping, it does not recognise equivalence between the encoded
 * or decoded form of the same URL. For example, the two URLs:<br>
 * <pre>    http://foo.com/hello world/ and http://foo.com/hello%20world</pre>
 * would be considered not equal to each other.
 * <p>
 * Note, the {@link java.net.URI} class does perform escaping of its
 * component fields in certain circumstances. The recommended way
 * to manage the encoding and decoding of URLs is to use {@link java.net.URI},
 * and to convert between these two classes using {@link #toURI()} and
 * {@link URI#toURL()}.
 * <p>
 * The {@link URLEncoder} and {@link URLDecoder} classes can also be
 * used, but only for HTML form encoding, which is not the same
 * as the encoding scheme defined in RFC2396.
 *
 * @apiNote
 *
 * <a id="integrity"></a>
 * Applications working with file paths and file URIs should take great
 * care to use the appropriate methods to convert between the two.
 * The {@link Path#of(URI)} factory method and the {@link File#File(URI)}
 * constructor can be used to create {@link Path} or {@link File}
 * objects from a file URI. {@link Path#toUri()} and {@link File#toURI()}
 * can be used to create a {@link URI} from a file path, which can be
 * converted to URL using {@link URI#toURL()}.
 * Applications should never try to {@linkplain #URL(String, String, String)
 * construct} or {@linkplain #URL(String) parse} a {@code URL}
 * from the direct string representation of a {@code File} or {@code Path}
 * instance.
 * <p>
 * Before constructing a {@code URL} from a {@code URI}, and depending
 * on the protocol involved, applications should consider validating
 * whether the URI authority {@linkplain URI#parseServerAuthority()
 * can be parsed as server-based}.
 * <p>
 * Some components of a URL or URI, such as <i>userinfo</i>, may
 * be abused to construct misleading URLs or URIs. Applications
 * that deal with URLs or URIs should take into account
 * the recommendations advised in <a
 * href="https://tools.ietf.org/html/rfc3986#section-7">RFC3986,
 * Section 7, Security Considerations</a>.
 * <p>
 * All {@code URL} constructors may throw {@link MalformedURLException}.
 * In particular, if the underlying {@link URLStreamHandler}
 * implementation rejects, or is known to reject, any of the parameters,
 * {@link MalformedURLException} may be thrown.
 * Typically, a constructor that calls the stream handler's {@linkplain
 * URLStreamHandler#parseURL(URL, String, int, int) parseURL method} may
 * throw {@code MalformedURLException} if the underlying stream handler
 * implementation of that method throws {@code IllegalArgumentException}.
 * However, which checks are performed, or not, by the stream handlers
 * is implementation dependent, and callers should not rely on such
 * checks for full URL validation.
 *
 * @spec https://www.rfc-editor.org/info/rfc2396
 *      RFC 2396: Uniform Resource Identifiers (URI): Generic Syntax
 * @spec https://www.rfc-editor.org/info/rfc2732
 *      RFC 2732: Format for Literal IPv6 Addresses in URL's
 * @spec https://www.rfc-editor.org/info/rfc3986
 *      RFC 3986: Uniform Resource Identifier (URI): Generic Syntax
 * @author  James Gosling
 * @since 1.0
 */
public final class URL implements java.io.Serializable {

    static final String BUILTIN_HANDLERS_PREFIX = "sun.net.www.protocol";
    @java.io.Serial
    static final long serialVersionUID = -7627629688361524110L;

    /**
     * The property which specifies the package prefix list to be scanned
     * for protocol handlers.  The value of this property (if any) should
     * be a vertical bar delimited list of package names to search through
     * for a protocol handler to load.  The policy of this class is that
     * all protocol handlers will be in a class called <protocolname>.Handler,
     * and each package in the list is examined in turn for a matching
     * handler.  If none are found (or the property is not specified), the
     * default package prefix, sun.net.www.protocol, is used.  The search
     * proceeds from the first package in the list to the last and stops
     * when a match is found.
     */
    private static final String protocolPathProp = "java.protocol.handler.pkgs";

    /**
     * The protocol to use (ftp, http, nntp, ... etc.) .
     * @serial
     */
    private String protocol;

    /**
     * The host name to connect to.
     * @serial
     */
    private String host;

    /**
     * The protocol port to connect to.
     * @serial
     */
    private int port = -1;

    /**
     * The specified file name on that host. {@code file} is
     * defined as {@code path[?query]}
     * @serial
     */
    private String file;

    /**
     * The query part of this URL.
     */
    private transient String query;

    /**
     * The authority part of this URL.
     * @serial
     */
    private String authority;

    /**
     * The path part of this URL.
     */
    private transient String path;

    /**
     * The userinfo part of this URL.
     */
    private transient String userInfo;

    /**
     * # reference.
     * @serial
     */
    private String ref;

    /**
     * The host's IP address, used in equals and hashCode.
     * Computed on demand. An uninitialized or unknown hostAddress is null.
     */
    private transient InetAddress hostAddress;

    /**
     * The URLStreamHandler for this URL.
     */
    transient URLStreamHandler handler;

    /* Our hash code.
     * @serial
     */
    private int hashCode = -1;

    private transient UrlDeserializedState tempState;

    /**
     * Creates a {@code URL} object from the specified
     * {@code protocol}, {@code host}, {@code port}
     * number, and {@code file}.<p>
     *
     * {@code host} can be expressed as a host name or a literal
     * IP address. If IPv6 literal address is used, it should be
     * enclosed in square brackets ({@code '['} and {@code ']'}), as
     * specified by <a
     * href="http://www.ietf.org/rfc/rfc2732.txt">RFC&nbsp;2732</a>;
     * However, the literal IPv6 address format defined in <a
     * href="http://www.ietf.org/rfc/rfc2373.txt"><i>RFC&nbsp;2373: IP
     * Version 6 Addressing Architecture</i></a> is also accepted.<p>
     *
     * Specifying a {@code port} number of {@code -1}
     * indicates that the URL should use the default port for the
     * protocol.<p>
     *
     * If this is the first URL object being created with the specified
     * protocol, a <i>stream protocol handler</i> object, an instance of
     * class {@code URLStreamHandler}, is created for that protocol:
     * <ol>
     * <li>If the application has previously set up an instance of
     *     {@code URLStreamHandlerFactory} as the stream handler factory,
     *     then the {@code createURLStreamHandler} method of that instance
     *     is called with the protocol string as an argument to create the
     *     stream protocol handler.
     * <li>If no {@code URLStreamHandlerFactory} has yet been set up,
     *     or if the factory's {@code createURLStreamHandler} method
     *     returns {@code null}, then the {@linkplain java.util.ServiceLoader
     *     ServiceLoader} mechanism is used to locate {@linkplain
     *     java.net.spi.URLStreamHandlerProvider URLStreamHandlerProvider}
     *     implementations using the system class
     *     loader. The order that providers are located is implementation
     *     specific, and an implementation is free to cache the located
     *     providers. A {@linkplain java.util.ServiceConfigurationError
     *     ServiceConfigurationError}, {@code Error} or {@code RuntimeException}
     *     thrown from the {@code createURLStreamHandler}, if encountered, will
     *     be propagated to the calling thread. The {@code
     *     createURLStreamHandler} method of each provider, if instantiated, is
     *     invoked, with the protocol string, until a provider returns non-null,
     *     or all providers have been exhausted.
     * <li>If the previous step fails to find a protocol handler, the
     *     constructor reads the value of the system property:
     *     <blockquote>{@systemProperty
     *         java.protocol.handler.pkgs
     *     }</blockquote>
     *     If the value of that system property is not {@code null},
     *     it is interpreted as a list of packages separated by a vertical
     *     slash character '{@code |}'. The constructor tries to load
     *     the class named:
     *     <blockquote>{@code
     *         <package>.<protocol>.Handler
     *     }</blockquote>
     *     where {@code <package>} is replaced by the name of the package
     *     and {@code <protocol>} is replaced by the name of the protocol.
     *     If this class does not exist, or if the class exists but it is not
     *     a subclass of {@code URLStreamHandler}, then the next package
     *     in the list is tried.
     * <li>If the previous step fails to find a protocol handler, then the
     *     constructor tries to load a built-in protocol handler.
     *     If this class does not exist, or if the class exists but it is not a
     *     subclass of {@code URLStreamHandler}, then a
     *     {@code MalformedURLException} is thrown.
     * </ol>
     *
     * <p>Protocol handlers for the following protocols are guaranteed
     * to exist on the search path:
     * <ul>
     * <li>{@code http}</li>
     * <li>{@code https}</li>
     * <li>{@code file}</li>
     * <li>{@code jar}</li>
     * </ul>
     * Protocol handlers for additional protocols may also be  available.
     * Some protocol handlers, for example those used for loading platform
     * classes or classes on the class path, may not be overridden. The details
     * of such restrictions, and when those restrictions apply (during
     * initialization of the runtime for example), are implementation specific
     * and therefore not specified
     *
     * <p>No validation of the inputs is performed by this constructor.
     *
     * @param      protocol   the name of the protocol to use.
     * @param      host       the name of the host.
     * @param      port       the port number on the host.
     * @param      file       the file on the host
     * @throws     MalformedURLException  if an unknown protocol or the port
     *                  is a negative number other than -1, or if the
     *                  underlying stream handler implementation rejects,
     *                  or is known to reject, the {@code URL}
     * @spec https://www.rfc-editor.org/info/rfc2373 RFC 2373: IP Version 6 Addressing Architecture
     * @spec https://www.rfc-editor.org/info/rfc2732 RFC 2732: Format for Literal IPv6 Addresses in URL's
     * @see        java.lang.System#getProperty(java.lang.String)
     * @see        java.net.URL#setURLStreamHandlerFactory(
     *                  java.net.URLStreamHandlerFactory)
     * @see        java.net.URLStreamHandler
     * @see        java.net.URLStreamHandlerFactory#createURLStreamHandler(
     *                  java.lang.String)
     * @deprecated Use {@link URI#toURL()} to construct an instance of URL. See the note on
     * <a href="#constructor-deprecation">constructor deprecation</a> for more
     * details.
     */
    @Deprecated(since = "20")
    public URL(String protocol, String host, int port, String file)
        throws MalformedURLException
    {
        this(protocol, host, port, file, null);
    }

    /**
     * Creates a URL from the specified {@code protocol}
     * name, {@code host} name, and {@code file} name. The
     * default port for the specified protocol is used.
     * <p>
     * This constructor is equivalent to the four-argument
     * constructor with the only difference of using the
     * default port for the specified protocol.
     *
     * No validation of the inputs is performed by this constructor.
     *
     * @param      protocol   the name of the protocol to use.
     * @param      host       the name of the host.
     * @param      file       the file on the host.
     * @throws     MalformedURLException  if an unknown protocol is specified,
     *                        or if the underlying stream handler implementation
     *                        rejects, or is known to reject, the {@code URL}
     * @see        java.net.URL#URL(java.lang.String, java.lang.String,
     *                  int, java.lang.String)
     * @deprecated Use {@link URI#toURL()} to construct an instance of URL. See the note on
     * <a href="#constructor-deprecation">constructor deprecation</a> for more
     * details.
     */
    @Deprecated(since = "20")
    public URL(String protocol, String host, String file)
            throws MalformedURLException {
        this(protocol, host, -1, file);
    }

    /**
     * Creates a {@code URL} object from the specified
     * {@code protocol}, {@code host}, {@code port}
     * number, {@code file}, and {@code handler}. Specifying
     * a {@code port} number of {@code -1} indicates that
     * the URL should use the default port for the protocol. Specifying
     * a {@code handler} of {@code null} indicates that the URL
     * should use a default stream handler for the protocol, as outlined
     * for:
     *     {@link java.net.URL#URL(java.lang.String, java.lang.String, int,
     *                      java.lang.String)}
     *
     * <p>If the handler is not null and there is a security manager,
     * the security manager's {@code checkPermission}
     * method is called with a
     * {@code NetPermission("specifyStreamHandler")} permission.
     * This may result in a SecurityException.
     *
     * No validation of the inputs is performed by this constructor.
     *
     * @param      protocol   the name of the protocol to use.
     * @param      host       the name of the host.
     * @param      port       the port number on the host.
     * @param      file       the file on the host
     * @param      handler    the stream handler for the URL.
     * @throws     MalformedURLException  if an unknown protocol or the port
     *                    is a negative number other than -1,
     *                    or if the underlying stream handler implementation
     *                    rejects, or is known to reject, the {@code URL}
     * @throws     SecurityException
     *        if a security manager exists and its
     *        {@code checkPermission} method doesn't allow
     *        specifying a stream handler explicitly.
     * @see        java.lang.System#getProperty(java.lang.String)
     * @see        java.net.URL#setURLStreamHandlerFactory(
     *                  java.net.URLStreamHandlerFactory)
     * @see        java.net.URLStreamHandler
     * @see        java.net.URLStreamHandlerFactory#createURLStreamHandler(
     *                  java.lang.String)
     * @see        SecurityManager#checkPermission
     * @see        java.net.NetPermission
     * @deprecated
     * Use {@link #of(URI, URLStreamHandler)} to construct an instance of URL
     * associated with a custom protocol handler.
     * See the note on <a href="#constructor-deprecation">constructor deprecation</a>
     * for more details.
     */
    @Deprecated(since = "20")
    public URL(String protocol, String host, int port, String file,
               URLStreamHandler handler) throws MalformedURLException {
        if (handler != null) {
            @SuppressWarnings("removal")
            SecurityManager sm = System.getSecurityManager();
            if (sm != null) {
                // check for permission to specify a handler
                checkSpecifyHandler(sm);
            }
        }

        protocol = lowerCaseProtocol(protocol);
        this.protocol = protocol;
        if (host != null) {

            /**
             * if host is a literal IPv6 address,
             * we will make it conform to RFC 2732
             */
            if (host.indexOf(':') >= 0 && !host.startsWith("[")) {
                host = "["+host+"]";
            }
            this.host = host;

            if (port < -1) {
                throw new MalformedURLException("Invalid port number :" +
                                                    port);
            }
            this.port = port;
            authority = (port == -1) ? host : host + ":" + port;
        }

        int index = file.indexOf('#');
        this.ref = index < 0 ? null : file.substring(index + 1);
        file = index < 0 ? file : file.substring(0, index);
        int q = file.lastIndexOf('?');
        if (q != -1) {
            this.query = file.substring(q + 1);
            this.path = file.substring(0, q);
            this.file = path + "?" + query;
        } else {
            this.path = file;
            this.file = path;
        }

        // Note: we don't do full validation of the URL here. Too risky to change
        // right now, but worth considering for future reference. -br
        if (handler == null &&
            (handler = getURLStreamHandler(protocol)) == null) {
            throw new MalformedURLException("unknown protocol: " + protocol);
        }
        this.handler = handler;
        if (host != null && isBuiltinStreamHandler(handler)) {
            String s = IPAddressUtil.checkExternalForm(this);
            if (s != null) {
                throw new MalformedURLException(s);
            }
        }
        if ("jar".equalsIgnoreCase(protocol)) {
            if (handler instanceof sun.net.www.protocol.jar.Handler) {
                // URL.openConnection() would throw a confusing exception
                // so generate a better exception here instead.
                String s = ((sun.net.www.protocol.jar.Handler) handler).checkNestedProtocol(file);
                if (s != null) {
                    throw new MalformedURLException(s);
                }
            }
        }
    }

    /**
     * Creates a {@code URL} object from the {@code String}
     * representation.
     * <p>
     * This constructor is equivalent to a call to the two-argument
     * constructor with a {@code null} first argument.
     *
     * @param      spec   the {@code String} to parse as a URL.
     * @throws     MalformedURLException  if no protocol is specified, or an
     *               unknown protocol is found, or {@code spec} is {@code null},
     *               or the parsed URL fails to comply with the specific syntax
     *               of the associated protocol, or the
     *               underlying stream handler's {@linkplain
     *               URLStreamHandler#parseURL parseURL method} throws
     *               {@code IllegalArgumentException}
     * @see        java.net.URL#URL(java.net.URL, java.lang.String)
     * @deprecated Use {@link URI#toURL()} to construct an instance of URL. See the note on
     * <a href="#constructor-deprecation">constructor deprecation</a> for more
     * details.
     */
    @Deprecated(since = "20")
    public URL(String spec) throws MalformedURLException {
        this(null, spec);
    }

    /**
     * Creates a URL by parsing the given spec within a specified context.
     *
     * The new URL is created from the given context URL and the spec
     * argument as described in
     * RFC2396 &quot;Uniform Resource Identifiers : Generic Syntax&quot; :
     * <blockquote><pre>
     *          &lt;scheme&gt;://&lt;authority&gt;&lt;path&gt;?&lt;query&gt;#&lt;fragment&gt;
     * </pre></blockquote>
     * The reference is parsed into the scheme, authority, path, query and
     * fragment parts. If the path component is empty and the scheme,
     * authority, and query components are undefined, then the new URL is a
     * reference to the current document. Otherwise, the fragment and query
     * parts present in the spec are used in the new URL.
     * <p>
     * If the scheme component is defined in the given spec and does not match
     * the scheme of the context, then the new URL is created as an absolute
     * URL based on the spec alone. Otherwise the scheme component is inherited
     * from the context URL.
     * <p>
     * If the authority component is present in the spec then the spec is
     * treated as absolute and the spec authority and path will replace the
     * context authority and path. If the authority component is absent in the
     * spec then the authority of the new URL will be inherited from the
     * context.
     * <p>
     * If the spec's path component begins with a slash character
     * &quot;/&quot; then the
     * path is treated as absolute and the spec path replaces the context path.
     * <p>
     * Otherwise, the path is treated as a relative path and is appended to the
     * context path, as described in RFC2396. Also, in this case,
     * the path is canonicalized through the removal of directory
     * changes made by occurrences of &quot;..&quot; and &quot;.&quot;.
     * <p>
     * For a more detailed description of URL parsing, refer to RFC2396.
     *
     * @implSpec Parsing the URL includes calling the {@link
     * URLStreamHandler#parseURL(URL, String, int, int) parseURL} method on the
     * selected handler.
     *
     * @param      context   the context in which to parse the specification.
     * @param      spec      the {@code String} to parse as a URL.
     * @throws     MalformedURLException  if no protocol is specified, or an
     *               unknown protocol is found, or {@code spec} is {@code null},
     *               or the parsed URL fails to comply with the specific syntax
     *               of the associated protocol, or the
     *               underlying stream handler's {@linkplain
     *               URLStreamHandler#parseURL parseURL method} throws
     *               {@code IllegalArgumentException}
     * @see        java.net.URL#URL(java.lang.String, java.lang.String,
     *                  int, java.lang.String)
     * @see        java.net.URLStreamHandler
     * @see        java.net.URLStreamHandler#parseURL(java.net.URL,
     *                  java.lang.String, int, int)
     * @deprecated Use {@link URI#toURL()} to construct an instance of URL. See the note on
     * <a href="#constructor-deprecation">constructor deprecation</a> for more
     * details.
     */
    @Deprecated(since = "20")
    public URL(URL context, String spec) throws MalformedURLException {
        this(context, spec, null);
    }

    /**
     * Creates a URL by parsing the given spec with the specified handler
     * within a specified context. If the handler is null, the parsing
     * occurs as with the two argument constructor.
     *
     * @implSpec Parsing the URL includes calling the {@link
     * URLStreamHandler#parseURL(URL, String, int, int) parseURL} method on the
     * selected handler.
     *
     * @param      context   the context in which to parse the specification.
     * @param      spec      the {@code String} to parse as a URL.
     * @param      handler   the stream handler for the URL.
     * @throws     MalformedURLException  if no protocol is specified, or an
     *               unknown protocol is found, or {@code spec} is {@code null},
     *               or the parsed URL fails to comply with the specific syntax
     *               of the associated protocol, or the
     *               underlying stream handler's {@linkplain
     *               URLStreamHandler#parseURL(URL, String, int, int)
     *               parseURL method} throws {@code IllegalArgumentException}
     * @throws     SecurityException
     *        if a security manager exists and its
     *        {@code checkPermission} method doesn't allow
     *        specifying a stream handler.
     * @see        java.net.URL#URL(java.lang.String, java.lang.String,
     *                  int, java.lang.String)
     * @see        java.net.URLStreamHandler
     * @see        java.net.URLStreamHandler#parseURL(java.net.URL,
     *                  java.lang.String, int, int)
     * @deprecated
     * Use {@link #of(URI, URLStreamHandler)} to construct an instance of URL
     * associated with a custom protocol handler.
     * See the note on <a href="#constructor-deprecation">constructor deprecation</a>
     * for more details.
     */
    @Deprecated(since = "20")
    public URL(URL context, String spec, URLStreamHandler handler)
        throws MalformedURLException
    {
        String original = spec;
        int i, limit, c;
        int start = 0;
        String newProtocol = null;
        boolean aRef=false;
        boolean isRelative = false;

        // Check for permission to specify a handler
        if (handler != null) {
            @SuppressWarnings("removal")
            SecurityManager sm = System.getSecurityManager();
            if (sm != null) {
                checkSpecifyHandler(sm);
            }
        }

        try {
            limit = spec.length();
            while ((limit > 0) && (spec.charAt(limit - 1) <= ' ')) {
                limit--;        //eliminate trailing whitespace
            }
            while ((start < limit) && (spec.charAt(start) <= ' ')) {
                start++;        // eliminate leading whitespace
            }

            if (spec.regionMatches(true, start, "url:", 0, 4)) {
                start += 4;
            }
            if (start < spec.length() && spec.charAt(start) == '#') {
                /* we're assuming this is a ref relative to the context URL.
                 * This means protocols cannot start w/ '#', but we must parse
                 * ref URL's like: "hello:there" w/ a ':' in them.
                 */
                aRef=true;
            }
            for (i = start ; !aRef && (i < limit) &&
                     ((c = spec.charAt(i)) != '/') ; i++) {
                if (c == ':') {
                    String s = lowerCaseProtocol(spec.substring(start, i));
                    if (isValidProtocol(s)) {
                        newProtocol = s;
                        start = i + 1;
                    }
                    break;
                }
            }

            // Only use our context if the protocols match.
            protocol = newProtocol;
            if ((context != null) && ((newProtocol == null) ||
                            newProtocol.equalsIgnoreCase(context.protocol))) {
                // inherit the protocol handler from the context
                // if not specified to the constructor
                if (handler == null) {
                    handler = context.handler;
                }

                // If the context is a hierarchical URL scheme and the spec
                // contains a matching scheme then maintain backwards
                // compatibility and treat it as if the spec didn't contain
                // the scheme; see 5.2.3 of RFC2396
                if (context.path != null && context.path.startsWith("/"))
                    newProtocol = null;

                if (newProtocol == null) {
                    protocol = context.protocol;
                    authority = context.authority;
                    userInfo = context.userInfo;
                    host = context.host;
                    port = context.port;
                    file = context.file;
                    path = context.path;
                    isRelative = true;
                }
            }

            if (protocol == null) {
                throw new MalformedURLException("no protocol: "+original);
            }

            // Get the protocol handler if not specified or the protocol
            // of the context could not be used
            if (handler == null &&
                (handler = getURLStreamHandler(protocol)) == null) {
                throw new MalformedURLException("unknown protocol: "+protocol);
            }

            this.handler = handler;

            i = spec.indexOf('#', start);
            if (i >= 0) {
                ref = spec.substring(i + 1, limit);
                limit = i;
            }

            /*
             * Handle special case inheritance of query and fragment
             * implied by RFC2396 section 5.2.2.
             */
            if (isRelative && start == limit) {
                query = context.query;
                if (ref == null) {
                    ref = context.ref;
                }
            }

            handler.parseURL(this, spec, start, limit);

        } catch(MalformedURLException e) {
            throw e;
        } catch(Exception e) {
            MalformedURLException exception = new MalformedURLException(e.getMessage());
            exception.initCause(e);
            throw exception;
        }
    }

    /**
     * Creates a URL from a URI, as if by invoking {@code uri.toURL()}, but
     * associating it with the given {@code URLStreamHandler}, if allowed.
     *
     * @apiNote
     * Applications should consider performing additional integrity
     * checks before constructing a {@code URL} and opening a connection.
     * See the <a href=#integrity>API note</a> in the class level API
     * documentation.
     *
     * @implSpec The implementation of this method includes calling the {@link
     * URLStreamHandler#parseURL(URL, String, int, int) parseURL} method on the
     * selected handler.
     *
     * @param uri the {@code URI} from which the returned {@code URL} should
     *           be built
     * @param handler a custom protocol stream handler for
     *                      the returned {@code URL}. Can be {@code null},
     *                      in which case the default stream handler for
     *                      the protocol if any, will be used.
     *
     * @return a new {@code URL} instance created from the given {@code URI}
     *   and associated with the given {@code URLStreamHandler}, if any
     *
     * @throws NullPointerException if {@code uri} is {@code null}
     *
     * @throws IllegalArgumentException if no protocol is specified
     *         (the {@linkplain URI#getScheme() uri scheme} is {@code null}), or
     *         if the {@code URLStreamHandler} is not {@code null} and can not be
     *         set for the given protocol
     *
     * @throws  MalformedURLException if an unknown protocol is found,
     *          or the given URI fails to comply with the specific
     *          syntax of the associated protocol, or the
     *          underlying stream handler's {@linkplain
     *          URLStreamHandler#parseURL(URL, String, int, int)
     *          parseURL method} throws {@code IllegalArgumentException}
     *
     * @throws SecurityException
     *        if a security manager exists and its
     *        {@code checkPermission} method doesn't allow
     *        specifying a stream handler
     *
     * @see java.net.URI#toURL()
     *
     * @since 20
     */
    public static URL of(URI uri, URLStreamHandler handler)
        throws MalformedURLException {
        if (!uri.isAbsolute()) {
            throw new IllegalArgumentException("URI is not absolute");
        }

        String protocol = uri.getScheme();

        // fast path for canonical jrt:/... URLs
        //
        // In general we need to go via Handler.parseURL, but for the jrt
        // protocol we enforce that the Handler is not overridable and can
        // optimize URI to URL conversion.
        //
        // Case-sensitive comparison for performance; malformed protocols will
        // be handled correctly by the slow path.
        if (handler == null && protocol.equals("jrt") && !uri.isOpaque()
                && uri.getRawAuthority() == null
                && uri.getRawFragment() == null) {

            String query = uri.getRawQuery();
            String path = uri.getRawPath();
            String file = (query == null) ? path : path + "?" + query;

            // URL represent undefined host as empty string while URI use null
            String host = uri.getHost();
            if (host == null) {
                host = "";
            }

            int port = uri.getPort();

            return new URL("jrt", host, port, file, null);
        }

        // slow path (will work for non-canonical forms of jrt: too)

        if ("url".equalsIgnoreCase(protocol)) {;
            String uristr = uri.toString();
            try {
                URI inner = new URI(uristr.substring(4));
                if (inner.isAbsolute()) {
                    protocol = inner.getScheme();
                }
            } catch (URISyntaxException use) {
                throw new MalformedURLException(use.getMessage());
            }
        }

        if (handler != null && !isOverrideable(protocol)) {
            throw new IllegalArgumentException("Can't override URLStreamHandler for protocol "
                    + protocol);
        }

        return new URL((URL)null, uri.toString(), handler);
    }

    /*
     * Returns true if specified string is a valid protocol name.
     */
    private boolean isValidProtocol(String protocol) {
        int len = protocol.length();
        if (len < 1)
            return false;
        char c = protocol.charAt(0);
        if (!Character.isLetter(c))
            return false;
        for (int i = 1; i < len; i++) {
            c = protocol.charAt(i);
            if (!Character.isLetterOrDigit(c) && c != '.' && c != '+' &&
                c != '-') {
                return false;
            }
        }
        return true;
    }

    /*
     * Checks for permission to specify a stream handler.
     */
    private void checkSpecifyHandler(@SuppressWarnings("removal") SecurityManager sm) {
        sm.checkPermission(SecurityConstants.SPECIFY_HANDLER_PERMISSION);
    }

    /**
     * Sets the specified 8 fields of the URL. This is not a public method so
     * that only URLStreamHandlers can modify URL fields. URLs are otherwise
     * constant.
     *
     * @param protocol the name of the protocol to use
     * @param host the name of the host
     * @param port the port number on the host
     * @param authority the authority part for the url
     * @param userInfo the username and password
     * @param path the file on the host
     * @param ref the internal reference in the URL
     * @param query the query part of this URL
     * @since 1.3
     */
    void set(String protocol, String host, int port,
             String authority, String userInfo, String path,
             String query, String ref) {
        synchronized (this) {
            this.protocol = protocol;
            this.host = host;
            this.port = port;
            this.file = query == null ? path : path + "?" + query;
            this.userInfo = userInfo;
            this.path = path;
            this.ref = ref;
            /* This is very important. We must recompute this after the
             * URL has been changed. */
            hashCode = -1;
            hostAddress = null;
            this.query = query;
            this.authority = authority;
        }
    }

    /**
     * Returns the address of the host represented by this URL.
     * A {@link SecurityException} or an {@link UnknownHostException}
     * while getting the host address will result in this method returning
     * {@code null}
     *
     * @return an {@link InetAddress} representing the host
     */
    synchronized InetAddress getHostAddress() {
        if (hostAddress != null) {
            return hostAddress;
        }

        if (host == null || host.isEmpty()) {
            return null;
        }
        try {
            hostAddress = InetAddress.getByName(host);
        } catch (UnknownHostException | SecurityException ex) {
            return null;
        }
        return hostAddress;
    }


    /**
     * Gets the query part of this {@code URL}.
     *
     * @return  the query part of this {@code URL},
     * or <CODE>null</CODE> if one does not exist
     * @since 1.3
     */
    public String getQuery() {
        return query;
    }

    /**
     * Gets the path part of this {@code URL}.
     *
     * @return  the path part of this {@code URL}, or an
     * empty string if one does not exist
     * @since 1.3
     */
    public String getPath() {
        return path;
    }

    /**
     * Gets the userInfo part of this {@code URL}.
     *
     * @return  the userInfo part of this {@code URL}, or
     * <CODE>null</CODE> if one does not exist
     * @since 1.3
     */
    public String getUserInfo() {
        return userInfo;
    }

    /**
     * Gets the authority part of this {@code URL}.
     *
     * @return  the authority part of this {@code URL}
     * @since 1.3
     */
    public String getAuthority() {
        return authority;
    }

    /**
     * Gets the port number of this {@code URL}.
     *
     * @return  the port number, or -1 if the port is not set
     */
    public int getPort() {
        return port;
    }

    /**
     * Gets the default port number of the protocol associated
     * with this {@code URL}. If the URL scheme or the URLStreamHandler
     * for the URL do not define a default port number,
     * then -1 is returned.
     *
     * @return  the port number
     * @since 1.4
     */
    public int getDefaultPort() {
        return handler.getDefaultPort();
    }

    /**
     * Gets the protocol name of this {@code URL}.
     *
     * @return  the protocol of this {@code URL}.
     */
    public String getProtocol() {
        return protocol;
    }

    /**
     * Gets the host name of this {@code URL}, if applicable.
     * The format of the host conforms to RFC 2732, i.e. for a
     * literal IPv6 address, this method will return the IPv6 address
     * enclosed in square brackets ({@code '['} and {@code ']'}).
     *
     * @return  the host name of this {@code URL}.
     */
    public String getHost() {
        return host;
    }

    /**
     * Gets the file name of this {@code URL}.
     * The returned file portion will be
     * the same as <CODE>getPath()</CODE>, plus the concatenation of
     * the value of <CODE>getQuery()</CODE>, if any. If there is
     * no query portion, this method and <CODE>getPath()</CODE> will
     * return identical results.
     *
     * @return  the file name of this {@code URL},
     * or an empty string if one does not exist
     */
    public String getFile() {
        return file;
    }

    /**
     * Gets the anchor (also known as the "reference") of this
     * {@code URL}.
     *
     * @return  the anchor (also known as the "reference") of this
     *          {@code URL}, or <CODE>null</CODE> if one does not exist
     */
    public String getRef() {
        return ref;
    }

    /**
     * Compares this URL for equality with another object.<p>
     *
     * If the given object is not a URL then this method immediately returns
     * {@code false}.<p>
     *
     * Two URL objects are equal if they have the same protocol, reference
     * equivalent hosts, have the same port number on the host, and the same
     * file and fragment of the file.<p>
     *
     * Two hosts are considered equivalent if both host names can be resolved
     * into the same IP addresses; else if either host name can't be
     * resolved, the host names must be equal without regard to case; or both
     * host names equal to null.<p>
     *
     * Since hosts comparison requires name resolution, this operation is a
     * blocking operation. <p>
     *
     * Note: The defined behavior for {@code equals} is known to
     * be inconsistent with virtual hosting in HTTP.
     *
     * @param   obj   the URL to compare against.
     * @return  {@code true} if the objects are the same;
     *          {@code false} otherwise.
     */
    public boolean equals(Object obj) {
        if (!(obj instanceof URL u2))
            return false;

        return handler.equals(this, u2);
    }

    /**
     * Creates an integer suitable for hash table indexing.<p>
     *
     * The hash code is based upon all the URL components relevant for URL
     * comparison. As such, this operation is a blocking operation.
     *
     * @return  a hash code for this {@code URL}.
     */
    public synchronized int hashCode() {
        if (hashCode != -1)
            return hashCode;

        hashCode = handler.hashCode(this);
        return hashCode;
    }

    /**
     * Compares two URLs, excluding the fragment component.<p>
     *
     * Returns {@code true} if this {@code URL} and the
     * {@code other} argument are equal without taking the
     * fragment component into consideration.
     *
     * @param   other   the {@code URL} to compare against.
     * @return  {@code true} if they reference the same remote object;
     *          {@code false} otherwise.
     */
    public boolean sameFile(URL other) {
        return handler.sameFile(this, other);
    }

    /**
     * Constructs a string representation of this {@code URL}. The
     * string is created by calling the {@code toExternalForm}
     * method of the stream protocol handler for this object.
     *
     * @return  a string representation of this object.
     * @see     java.net.URL#URL(java.lang.String, java.lang.String, int,
     *                  java.lang.String)
     * @see     java.net.URLStreamHandler#toExternalForm(java.net.URL)
     */
    public String toString() {
        return toExternalForm();
    }

    /**
     * Constructs a string representation of this {@code URL}. The
     * string is created by calling the {@code toExternalForm}
     * method of the stream protocol handler for this object.
     *
     * @return  a string representation of this object.
     * @see     java.net.URL#URL(java.lang.String, java.lang.String,
     *                  int, java.lang.String)
     * @see     java.net.URLStreamHandler#toExternalForm(java.net.URL)
     */
    public String toExternalForm() {
        return handler.toExternalForm(this);
    }

    /**
     * Returns a {@link java.net.URI} equivalent to this URL.
     * This method functions in the same way as {@code new URI (this.toString())}.
     * <p>Note, any URL instance that complies with RFC 2396 can be converted
     * to a URI. However, some URLs that are not strictly in compliance
     * can not be converted to a URI.
     *
     * @throws    URISyntaxException if this URL is not formatted strictly according to
     *            RFC2396 and cannot be converted to a URI.
     *
     * @return    a URI instance equivalent to this URL.
     * @since 1.5
     */
    public URI toURI() throws URISyntaxException {
        URI uri = new URI(toString());
        if (authority != null && isBuiltinStreamHandler(handler)) {
            String s = IPAddressUtil.checkAuthority(this);
            if (s != null) throw new URISyntaxException(authority, s);
        }
        return uri;
    }

    /**
     * Returns a {@link java.net.URLConnection URLConnection} instance that
     * represents a connection to the remote object referred to by the
     * {@code URL}.
     *
     * <P>A new instance of {@linkplain java.net.URLConnection URLConnection} is
     * created every time when invoking the
     * {@linkplain java.net.URLStreamHandler#openConnection(URL)
     * URLStreamHandler.openConnection(URL)} method of the protocol handler for
     * this URL.</P>
     *
     * <P>It should be noted that a URLConnection instance does not establish
     * the actual network connection on creation. This will happen only when
     * calling {@linkplain java.net.URLConnection#connect() URLConnection.connect()}.</P>
     *
     * <P>If for the URL's protocol (such as HTTP or JAR), there
     * exists a public, specialized URLConnection subclass belonging
     * to one of the following packages or one of their subpackages:
     * java.lang, java.io, java.util, java.net, the connection
     * returned will be of that subclass. For example, for HTTP an
     * HttpURLConnection will be returned, and for JAR a
     * JarURLConnection will be returned.</P>
     *
     * @return     a {@link java.net.URLConnection URLConnection} linking
     *             to the URL.
     * @throws     IOException  if an I/O exception occurs.
     * @see        java.net.URL#URL(java.lang.String, java.lang.String,
     *             int, java.lang.String)
     */
    public URLConnection openConnection() throws java.io.IOException {
        return handler.openConnection(this);
    }

    /**
     * Same as {@link #openConnection()}, except that the connection will be
     * made through the specified proxy; Protocol handlers that do not
     * support proxying will ignore the proxy parameter and make a
     * normal connection.
     *
     * Invoking this method preempts the system's default
     * {@link java.net.ProxySelector ProxySelector} settings.
     *
     * @param      proxy the Proxy through which this connection
     *             will be made. If direct connection is desired,
     *             Proxy.NO_PROXY should be specified.
     * @return     a {@code URLConnection} to the URL.
     * @throws     IOException  if an I/O exception occurs.
     * @throws     SecurityException if a security manager is present
     *             and the caller doesn't have permission to connect
     *             to the proxy.
     * @throws     IllegalArgumentException will be thrown if proxy is null,
     *             or proxy has the wrong type
     * @throws     UnsupportedOperationException if the subclass that
     *             implements the protocol handler doesn't support
     *             this method.
     * @see        java.net.URL#URL(java.lang.String, java.lang.String,
     *             int, java.lang.String)
     * @see        java.net.URLConnection
     * @see        java.net.URLStreamHandler#openConnection(java.net.URL,
     *             java.net.Proxy)
     * @since      1.5
     */
    public URLConnection openConnection(Proxy proxy)
        throws java.io.IOException {
        if (proxy == null) {
            throw new IllegalArgumentException("proxy can not be null");
        }

        // Create a copy of Proxy as a security measure
        Proxy p = proxy == Proxy.NO_PROXY ? Proxy.NO_PROXY : sun.net.ApplicationProxy.create(proxy);
        @SuppressWarnings("removal")
        SecurityManager sm = System.getSecurityManager();
        if (p.type() != Proxy.Type.DIRECT && sm != null) {
            InetSocketAddress epoint = (InetSocketAddress) p.address();
            if (epoint.isUnresolved())
                sm.checkConnect(epoint.getHostName(), epoint.getPort());
            else
                sm.checkConnect(epoint.getAddress().getHostAddress(),
                                epoint.getPort());
        }
        return handler.openConnection(this, p);
    }

    /**
     * Opens a connection to this {@code URL} and returns an
     * {@code InputStream} for reading from that connection. This
     * method is a shorthand for:
     * <blockquote><pre>
     *     openConnection().getInputStream()
     * </pre></blockquote>
     *
     * @return     an input stream for reading from the URL connection.
     * @throws     IOException  if an I/O exception occurs.
     * @see        java.net.URL#openConnection()
     * @see        java.net.URLConnection#getInputStream()
     */
    public final InputStream openStream() throws java.io.IOException {
        return openConnection().getInputStream();
    }

    /**
     * Gets the contents of this URL. This method is a shorthand for:
     * <blockquote><pre>
     *     openConnection().getContent()
     * </pre></blockquote>
     *
     * @return     the contents of this URL.
     * @throws     IOException  if an I/O exception occurs.
     * @see        java.net.URLConnection#getContent()
     */
    public final Object getContent() throws java.io.IOException {
        return openConnection().getContent();
    }

    /**
     * Gets the contents of this URL. This method is a shorthand for:
     * <blockquote><pre>
     *     openConnection().getContent(classes)
     * </pre></blockquote>
     *
     * @param classes an array of Java types
     * @return     the content object of this URL that is the first match of
     *               the types specified in the classes array.
     *               null if none of the requested types are supported.
     * @throws     IOException  if an I/O exception occurs.
     * @see        java.net.URLConnection#getContent(Class[])
     * @since 1.3
     */
    public final Object getContent(Class<?>[] classes)
    throws java.io.IOException {
        return openConnection().getContent(classes);
    }

    /**
     * The URLStreamHandler factory.
     */
    private static volatile URLStreamHandlerFactory factory;

    /**
     * Sets an application's {@code URLStreamHandlerFactory}.
     * This method can be called at most once in a given Java Virtual
     * Machine.
     *
     *<p> The {@code URLStreamHandlerFactory} instance is used to
     *construct a stream protocol handler from a protocol name.
     *
     * <p> If there is a security manager, this method first calls
     * the security manager's {@code checkSetFactory} method
     * to ensure the operation is allowed.
     * This could result in a SecurityException.
     *
     * @param      fac   the desired factory.
     * @throws     Error  if the application has already set a factory.
     * @throws     SecurityException  if a security manager exists and its
     *             {@code checkSetFactory} method doesn't allow
     *             the operation.
     * @see        java.net.URL#URL(java.lang.String, java.lang.String,
     *             int, java.lang.String)
     * @see        java.net.URLStreamHandlerFactory
     * @see        SecurityManager#checkSetFactory
     */
    public static void setURLStreamHandlerFactory(URLStreamHandlerFactory fac) {
        synchronized (streamHandlerLock) {
            if (factory != null) {
                throw new Error("factory already defined");
            }
            @SuppressWarnings("removal")
            SecurityManager security = System.getSecurityManager();
            if (security != null) {
                security.checkSetFactory();
            }
            handlers.clear();

            // safe publication of URLStreamHandlerFactory with volatile write
            factory = fac;
        }
    }

    private static final URLStreamHandlerFactory defaultFactory = new DefaultFactory();

    private static class DefaultFactory implements URLStreamHandlerFactory {
        private static final String PREFIX = "sun.net.www.protocol.";

        public URLStreamHandler createURLStreamHandler(String protocol) {
            // Avoid using reflection during bootstrap
            switch (protocol) {
                case "file":
                    return new sun.net.www.protocol.file.Handler();
                case "jar":
                    return new sun.net.www.protocol.jar.Handler();
                case "jrt":
                    return new sun.net.www.protocol.jrt.Handler();
            }
            String name = PREFIX + protocol + ".Handler";
            try {
                Object o = Class.forName(name).getDeclaredConstructor().newInstance();
                return (URLStreamHandler)o;
            } catch (Exception e) {
                // For compatibility, all Exceptions are ignored.
                // any number of exceptions can get thrown here
            }
            return null;
        }
    }

    private static URLStreamHandler lookupViaProperty(String protocol) {
        String packagePrefixList =
                GetPropertyAction.privilegedGetProperty(protocolPathProp);
        if (packagePrefixList == null) {
            // not set
            return null;
        }

        String[] packagePrefixes = packagePrefixList.split("\\|");
        URLStreamHandler handler = null;
        for (int i=0; handler == null && i<packagePrefixes.length; i++) {
            String packagePrefix = packagePrefixes[i].trim();
            try {
                String clsName = packagePrefix + "." + protocol + ".Handler";
                Class<?> cls = null;
                try {
                    cls = Class.forName(clsName);
                } catch (ClassNotFoundException e) {
                    ClassLoader cl = ClassLoader.getSystemClassLoader();
                    if (cl != null) {
                        cls = cl.loadClass(clsName);
                    }
                }
                if (cls != null) {
                    @SuppressWarnings("deprecation")
                    Object tmp = cls.newInstance();
                    handler = (URLStreamHandler)tmp;
                }
            } catch (Exception e) {
                // any number of exceptions can get thrown here
            }
        }
        return handler;
    }

    private static Iterator<URLStreamHandlerProvider> providers() {
        return new Iterator<>() {

            ClassLoader cl = ClassLoader.getSystemClassLoader();
            ServiceLoader<URLStreamHandlerProvider> sl =
                    ServiceLoader.load(URLStreamHandlerProvider.class, cl);
            Iterator<URLStreamHandlerProvider> i = sl.iterator();

            URLStreamHandlerProvider next = null;

            private boolean getNext() {
                while (next == null) {
                    try {
                        if (!i.hasNext())
                            return false;
                        next = i.next();
                    } catch (ServiceConfigurationError sce) {
                        if (sce.getCause() instanceof SecurityException) {
                            // Ignore security exceptions
                            continue;
                        }
                        throw sce;
                    }
                }
                return true;
            }

            public boolean hasNext() {
                return getNext();
            }

            public URLStreamHandlerProvider next() {
                if (!getNext())
                    throw new NoSuchElementException();
                URLStreamHandlerProvider n = next;
                next = null;
                return n;
            }
        };
    }

    private static class ThreadTrackHolder {
        static final ThreadTracker TRACKER = new ThreadTracker();
    }

    private static Object tryBeginLookup() {
        return ThreadTrackHolder.TRACKER.tryBegin();
    }

    private static void endLookup(Object key) {
        ThreadTrackHolder.TRACKER.end(key);
    }

    @SuppressWarnings("removal")
    private static URLStreamHandler lookupViaProviders(final String protocol) {
        Object key = tryBeginLookup();
        if (key == null) {
            throw new Error("Circular loading of URL stream handler providers detected");
        }
        try {
            return AccessController.doPrivileged(
                new PrivilegedAction<>() {
                    public URLStreamHandler run() {
                        Iterator<URLStreamHandlerProvider> itr = providers();
                        while (itr.hasNext()) {
                            URLStreamHandlerProvider f = itr.next();
                            URLStreamHandler h = f.createURLStreamHandler(protocol);
                            if (h != null)
                                return h;
                        }
                        return null;
                    }
                });
        } finally {
            endLookup(key);
        }
    }

    /**
     * Returns the protocol in lower case. Special cases known protocols
     * to avoid loading locale classes during startup.
     */
    static String lowerCaseProtocol(String protocol) {
        if (protocol.equals("jrt")) {
            return "jrt";
        } else if (protocol.equals("file")) {
            return "file";
        } else if (protocol.equals("jar")) {
            return "jar";
        } else {
            return protocol.toLowerCase(Locale.ROOT);
        }
    }

    /**
     * Non-overrideable protocols: "jrt" and "file"
     *
     * Character-based comparison for performance reasons; also ensures
     * case-insensitive comparison in a locale-independent fashion.
     */
    static boolean isOverrideable(String protocol) {
        if (protocol.length() == 3) {
            if ((Character.toLowerCase(protocol.charAt(0)) == 'j') &&
                    (Character.toLowerCase(protocol.charAt(1)) == 'r') &&
                    (Character.toLowerCase(protocol.charAt(2)) == 't')) {
                return false;
            }
        } else if (protocol.length() == 4) {
            if ((Character.toLowerCase(protocol.charAt(0)) == 'f') &&
                    (Character.toLowerCase(protocol.charAt(1)) == 'i') &&
                    (Character.toLowerCase(protocol.charAt(2)) == 'l') &&
                    (Character.toLowerCase(protocol.charAt(3)) == 'e')) {
                return false;
            }
        }
        return true;
    }

    /**
     * A table of protocol handlers.
     */
    static Hashtable<String,URLStreamHandler> handlers = new Hashtable<>();
    private static final Object streamHandlerLock = new Object();

    /**
     * Returns the Stream Handler.
     * @param protocol the protocol to use
     */
    static URLStreamHandler getURLStreamHandler(String protocol) {

        URLStreamHandler handler = handlers.get(protocol);

        if (handler != null) {
            return handler;
        }

        URLStreamHandlerFactory fac;
        boolean checkedWithFactory = false;
        boolean overrideableProtocol = isOverrideable(protocol);

        if (overrideableProtocol && VM.isBooted()) {
            // Use the factory (if any). Volatile read makes
            // URLStreamHandlerFactory appear fully initialized to current thread.
            fac = factory;
            if (fac != null) {
                handler = fac.createURLStreamHandler(protocol);
                checkedWithFactory = true;
            }

            if (handler == null && !protocol.equalsIgnoreCase("jar")) {
                handler = lookupViaProviders(protocol);
            }

            if (handler == null) {
                handler = lookupViaProperty(protocol);
            }
        }

        if (handler == null) {
            // Try the built-in protocol handler
            handler = defaultFactory.createURLStreamHandler(protocol);
        }

        synchronized (streamHandlerLock) {
            URLStreamHandler handler2 = null;

            // Check again with hashtable just in case another
            // thread created a handler since we last checked
            handler2 = handlers.get(protocol);

            if (handler2 != null) {
                return handler2;
            }

            // Check with factory if another thread set a
            // factory since our last check
            if (overrideableProtocol && !checkedWithFactory &&
                (fac = factory) != null) {
                handler2 = fac.createURLStreamHandler(protocol);
            }

            if (handler2 != null) {
                // The handler from the factory must be given more
                // importance. Discard the default handler that
                // this thread created.
                handler = handler2;
            }

            // Insert this handler into the hashtable
            if (handler != null) {
                handlers.put(protocol, handler);
            }
        }
        return handler;
    }

    /**
     * @serialField    protocol String the protocol to use (ftp, http, nntp, ... etc.)
     *
     * @serialField    host String the host name to connect to
     *
     * @serialField    port int the protocol port to connect to
     *
     * @serialField    authority String the authority part of this URL
     *
     * @serialField    file String the specified file name on that host. {@code file} is
     *                 defined as {@code path[?query]}
     *
     * @serialField    ref String the fragment part of this URL
     *
     * @serialField    hashCode int the hashCode of this URL
     *
     */
    @java.io.Serial
    private static final ObjectStreamField[] serialPersistentFields = {
        new ObjectStreamField("protocol", String.class),
        new ObjectStreamField("host", String.class),
        new ObjectStreamField("port", int.class),
        new ObjectStreamField("authority", String.class),
        new ObjectStreamField("file", String.class),
        new ObjectStreamField("ref", String.class),
        new ObjectStreamField("hashCode", int.class), };

    /**
     * WriteObject is called to save the state of the URL to an
     * ObjectOutputStream. The handler is not saved since it is
     * specific to this system.
     *
     * @serialData the default write object value. When read back in,
     * the reader must ensure that calling getURLStreamHandler with
     * the protocol variable returns a valid URLStreamHandler and
     * throw an IOException if it does not.
     *
     * @param  s the {@code ObjectOutputStream} to which data is written
     * @throws IOException if an I/O error occurs
     */
    @java.io.Serial
    private synchronized void writeObject(java.io.ObjectOutputStream s)
        throws IOException
    {
        s.defaultWriteObject(); // write the fields
    }

    /**
     * readObject is called to restore the state of the URL from the
     * stream.  It reads the components of the URL and finds the local
     * stream handler.
     *
     * @param  s the {@code ObjectInputStream} from which data is read
     * @throws IOException if an I/O error occurs
     * @throws ClassNotFoundException if a serialized class cannot be loaded
     */
    @java.io.Serial
    private synchronized void readObject(java.io.ObjectInputStream s)
            throws IOException, ClassNotFoundException {
        GetField gf = s.readFields();
        String protocol = (String)gf.get("protocol", null);
        if (getURLStreamHandler(protocol) == null) {
            throw new IOException("unknown protocol: " + protocol);
        }
        String host = (String)gf.get("host", null);
        int port = gf.get("port", -1);
        String authority = (String)gf.get("authority", null);
        String file = (String)gf.get("file", null);
        String ref = (String)gf.get("ref", null);
        int hashCode = gf.get("hashCode", -1);
        if (authority == null
                && ((host != null && !host.isEmpty()) || port != -1)) {
            if (host == null)
                host = "";
            authority = (port == -1) ? host : host + ":" + port;
        }
        tempState = new UrlDeserializedState(protocol, host, port, authority,
               file, ref, hashCode);
    }

    /**
     * Replaces the de-serialized object with an URL object.
     *
     * @return a newly created object from deserialized data
     *
     * @throws ObjectStreamException if a new object replacing this
     * object could not be created
     */
   @java.io.Serial
   private Object readResolve() throws ObjectStreamException {

        URLStreamHandler handler = null;
        // already been checked in readObject
        handler = getURLStreamHandler(tempState.getProtocol());

        URL replacementURL = null;
        if (isBuiltinStreamHandler(handler.getClass().getName())) {
            replacementURL = fabricateNewURL();
        } else {
            replacementURL = setDeserializedFields(handler);
        }
        return replacementURL;
    }

    private URL setDeserializedFields(URLStreamHandler handler) {
        URL replacementURL;
        String userInfo = null;
        String protocol = tempState.getProtocol();
        String host = tempState.getHost();
        int port = tempState.getPort();
        String authority = tempState.getAuthority();
        String file = tempState.getFile();
        String ref = tempState.getRef();
        int hashCode = tempState.getHashCode();


        // Construct authority part
        if (authority == null
            && ((host != null && !host.isEmpty()) || port != -1)) {
            if (host == null)
                host = "";
            authority = (port == -1) ? host : host + ":" + port;

            // Handle hosts with userInfo in them
            int at = host.lastIndexOf('@');
            if (at != -1) {
                userInfo = host.substring(0, at);
                host = host.substring(at+1);
            }
        } else if (authority != null) {
            // Construct user info part
            int ind = authority.indexOf('@');
            if (ind != -1)
                userInfo = authority.substring(0, ind);
        }

        // Construct path and query part
        String path = null;
        String query = null;
        if (file != null) {
            // Fix: only do this if hierarchical?
            int q = file.lastIndexOf('?');
            if (q != -1) {
                query = file.substring(q+1);
                path = file.substring(0, q);
            } else
                path = file;
        }

        // Set the object fields.
        this.protocol = protocol;
        this.host = host;
        this.port = port;
        this.file = file;
        this.authority = authority;
        this.ref = ref;
        this.hashCode = hashCode;
        this.handler = handler;
        this.query = query;
        this.path = path;
        this.userInfo = userInfo;
        replacementURL = this;
        return replacementURL;
    }

    private URL fabricateNewURL()
                throws InvalidObjectException {
        // create URL string from deserialized object
        URL replacementURL = null;
        String urlString = tempState.reconstituteUrlString();

        try {
            replacementURL = new URL(urlString);
        } catch (MalformedURLException mEx) {
            resetState();
            InvalidObjectException invoEx = new InvalidObjectException(
                    "Malformed URL:  " + urlString);
            invoEx.initCause(mEx);
            throw invoEx;
        }
        replacementURL.setSerializedHashCode(tempState.getHashCode());
        resetState();
        return replacementURL;
    }

    boolean isBuiltinStreamHandler(URLStreamHandler handler) {
       Class<?> handlerClass = handler.getClass();
       return isBuiltinStreamHandler(handlerClass.getName())
                 || VM.isSystemDomainLoader(handlerClass.getClassLoader());
    }

    private boolean isBuiltinStreamHandler(String handlerClassName) {
        return (handlerClassName.startsWith(BUILTIN_HANDLERS_PREFIX));
    }

    private void resetState() {
        this.protocol = null;
        this.host = null;
        this.port = -1;
        this.file = null;
        this.authority = null;
        this.ref = null;
        this.hashCode = -1;
        this.handler = null;
        this.query = null;
        this.path = null;
        this.userInfo = null;
        this.tempState = null;
    }

    private void setSerializedHashCode(int hc) {
        this.hashCode = hc;
    }

    static {
        SharedSecrets.setJavaNetURLAccess(
                new JavaNetURLAccess() {
                    @Override
                    public URLStreamHandler getHandler(URL u) {
                        return u.handler;
                    }
                }
        );
    }
}

final class UrlDeserializedState {
    private final String protocol;
    private final String host;
    private final int port;
    private final String authority;
    private final String file;
    private final String ref;
    private final int hashCode;

    public UrlDeserializedState(String protocol,
                                String host, int port,
                                String authority, String file,
                                String ref, int hashCode) {
        this.protocol = protocol;
        this.host = host;
        this.port = port;
        this.authority = authority;
        this.file = file;
        this.ref = ref;
        this.hashCode = hashCode;
    }

    String getProtocol() {
        return protocol;
    }

    String getHost() {
        return host;
    }

    String getAuthority () {
        return authority;
    }

    int getPort() {
        return port;
    }

    String getFile () {
        return file;
    }

    String getRef () {
        return ref;
    }

    int getHashCode () {
        return hashCode;
    }

    String reconstituteUrlString() {

        // pre-compute length of StringBuilder
        int len = protocol.length() + 1;
        if (authority != null && !authority.isEmpty())
            len += 2 + authority.length();
        if (file != null) {
            len += file.length();
        }
        if (ref != null)
            len += 1 + ref.length();
        StringBuilder result = new StringBuilder(len);
        result.append(protocol);
        result.append(":");
        if (authority != null && !authority.isEmpty()) {
            result.append("//");
            result.append(authority);
        }
        if (file != null) {
            result.append(file);
        }
        if (ref != null) {
            result.append("#");
            result.append(ref);
        }
        return result.toString();
    }
}