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src/java.base/share/classes/java/nio/charset/Charset.java
983 строки
38 KB
Todd V. Jonker
8319817: Charset constructor should make defensive copy of aliases
14 авг 2024, 16:01
14 авг 2024, 16:01
edd6437
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/* * Copyright (c) 2000, 2023, 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.nio.charset; import jdk.internal.misc.ThreadTracker; import jdk.internal.misc.VM; import jdk.internal.util.StaticProperty; import jdk.internal.vm.annotation.Stable; import sun.nio.cs.ThreadLocalCoders; import java.nio.ByteBuffer; import java.nio.CharBuffer; import java.nio.charset.spi.CharsetProvider; import java.security.AccessController; import java.security.PrivilegedAction; import java.util.Arrays; import java.util.Collections; import java.util.Iterator; import java.util.Locale; import java.util.Map; import java.util.NoSuchElementException; import java.util.ServiceConfigurationError; import java.util.ServiceLoader; import java.util.Set; import java.util.SortedMap; import java.util.TreeMap; /** * A named mapping between sequences of sixteen-bit Unicode <a * href="../../lang/Character.html#unicode">code units</a> and sequences of * bytes. This class defines methods for creating decoders and encoders and * for retrieving the various names associated with a charset. Instances of * this class are immutable. * * <p> This class also defines static methods for testing whether a particular * charset is supported, for locating charset instances by name, and for * constructing a map that contains every charset for which support is * available in the current Java virtual machine. Support for new charsets can * be added via the service-provider interface defined in the {@link * java.nio.charset.spi.CharsetProvider} class. * * <p> All of the methods defined in this class are safe for use by multiple * concurrent threads. * * * <h2><a id="names">Charset names</a></h2> * * <p> Charsets are named by strings composed of the following characters: * * <ul> * * <li> The uppercase letters {@code 'A'} through {@code 'Z'} * (<code>'\u0041'</code> through <code>'\u005a'</code>), * * <li> The lowercase letters {@code 'a'} through {@code 'z'} * (<code>'\u0061'</code> through <code>'\u007a'</code>), * * <li> The digits {@code '0'} through {@code '9'} * (<code>'\u0030'</code> through <code>'\u0039'</code>), * * <li> The dash character {@code '-'} * (<code>'\u002d'</code>, <small>HYPHEN-MINUS</small>), * * <li> The plus character {@code '+'} * (<code>'\u002b'</code>, <small>PLUS SIGN</small>), * * <li> The period character {@code '.'} * (<code>'\u002e'</code>, <small>FULL STOP</small>), * * <li> The colon character {@code ':'} * (<code>'\u003a'</code>, <small>COLON</small>), and * * <li> The underscore character {@code '_'} * (<code>'\u005f'</code>, <small>LOW LINE</small>). * * </ul> * * A charset name must begin with either a letter or a digit. The empty string * is not a legal charset name. Charset names are not case-sensitive; that is, * case is always ignored when comparing charset names. Charset names * generally follow the conventions documented in <a * href="http://www.ietf.org/rfc/rfc2278.txt"><i>RFC 2278: IANA Charset * Registration Procedures</i></a>. * * <p> Every charset has a <i>canonical name</i> and may also have one or more * <i>aliases</i>. The canonical name is returned by the {@link #name() name} method * of this class. Canonical names are, by convention, usually in upper case. * The aliases of a charset are returned by the {@link #aliases() aliases} * method. * * <p><a id="hn">Some charsets have an <i>historical name</i> that is defined for * compatibility with previous versions of the Java platform.</a> A charset's * historical name is either its canonical name or one of its aliases. The * historical name is returned by the {@code getEncoding()} methods of the * {@link java.io.InputStreamReader#getEncoding InputStreamReader} and {@link * java.io.OutputStreamWriter#getEncoding OutputStreamWriter} classes. * * <p><a id="iana"> </a>If a charset listed in the <a * href="http://www.iana.org/assignments/character-sets"><i>IANA Charset * Registry</i></a> is supported by an implementation of the Java platform then * its canonical name must be the name listed in the registry. Many charsets * are given more than one name in the registry, in which case the registry * identifies one of the names as <i>MIME-preferred</i>. If a charset has more * than one registry name then its canonical name must be the MIME-preferred * name and the other names in the registry must be valid aliases. If a * supported charset is not listed in the IANA registry then its canonical name * must begin with one of the strings {@code "X-"} or {@code "x-"}. * * <p> The IANA charset registry does change over time, and so the canonical * name and the aliases of a particular charset may also change over time. To * ensure compatibility it is recommended that no alias ever be removed from a * charset, and that if the canonical name of a charset is changed then its * previous canonical name be made into an alias. * * * <h2><a id="standard">Standard charsets</a></h2> * * * <p> Every implementation of the Java platform is required to support the * following standard charsets. Consult the release documentation for your * implementation to see if any other charsets are supported. The behavior * of such optional charsets may differ between implementations. * * <blockquote><table class="striped" style="width:80%"> * <caption style="display:none">Description of standard charsets</caption> * <thead> * <tr><th scope="col" style="text-align:left">Charset</th><th scope="col" style="text-align:left">Description</th></tr> * </thead> * <tbody> * <tr><th scope="row" style="vertical-align:top">{@code US-ASCII}</th> * <td>Seven-bit ASCII, a.k.a. {@code ISO646-US}, * a.k.a. the Basic Latin block of the Unicode character set</td></tr> * <tr><th scope="row" style="vertical-align:top"><code>ISO-8859-1 </code></th> * <td>ISO Latin Alphabet No. 1, a.k.a. {@code ISO-LATIN-1}</td></tr> * <tr><th scope="row" style="vertical-align:top">{@code UTF-8}</th> * <td>Eight-bit UCS Transformation Format</td></tr> * <tr><th scope="row" style="vertical-align:top">{@code UTF-16BE}</th> * <td>Sixteen-bit UCS Transformation Format, * big-endian byte order</td></tr> * <tr><th scope="row" style="vertical-align:top">{@code UTF-16LE}</th> * <td>Sixteen-bit UCS Transformation Format, * little-endian byte order</td></tr> * <tr><th scope="row" style="vertical-align:top">{@code UTF-16}</th> * <td>Sixteen-bit UCS Transformation Format, * byte order identified by an optional byte-order mark</td></tr> * </tbody> * </table></blockquote> * * <p> The {@code UTF-8} charset is specified by <a * href="http://www.ietf.org/rfc/rfc2279.txt"><i>RFC 2279</i></a>; the * transformation format upon which it is based is specified in * Amendment 2 of ISO 10646-1 and is also described in the <a * href="http://www.unicode.org/standard/standard.html"><i>Unicode * Standard</i></a>. * * <p> The {@code UTF-16} charsets are specified by <a * href="http://www.ietf.org/rfc/rfc2781.txt"><i>RFC 2781</i></a>; the * transformation formats upon which they are based are specified in * Amendment 1 of ISO 10646-1 and are also described in the <a * href="http://www.unicode.org/standard/standard.html"><i>Unicode * Standard</i></a>. * * <p> The {@code UTF-16} charsets use sixteen-bit quantities and are * therefore sensitive to byte order. In these encodings the byte order of a * stream may be indicated by an initial <i>byte-order mark</i> represented by * the Unicode character <code>'\uFEFF'</code>. Byte-order marks are handled * as follows: * * <ul> * * <li><p> When decoding, the {@code UTF-16BE} and {@code UTF-16LE} * charsets interpret the initial byte-order marks as a <small>ZERO-WIDTH * NON-BREAKING SPACE</small>; when encoding, they do not write * byte-order marks. </p></li> * * <li><p> When decoding, the {@code UTF-16} charset interprets the * byte-order mark at the beginning of the input stream to indicate the * byte-order of the stream but defaults to big-endian if there is no * byte-order mark; when encoding, it uses big-endian byte order and writes * a big-endian byte-order mark. </p></li> * * </ul> * * In any case, byte order marks occurring after the first element of an * input sequence are not omitted since the same code is used to represent * <small>ZERO-WIDTH NON-BREAKING SPACE</small>. * * <p> Every instance of the Java virtual machine has a default charset, which * is {@code UTF-8} unless changed in an implementation specific manner. Refer to * {@link #defaultCharset()} for more detail. * * <p> The {@link StandardCharsets} class defines constants for each of the * standard charsets. * * <h2>Terminology</h2> * * <p> The name of this class is taken from the terms used in * <a href="http://www.ietf.org/rfc/rfc2278.txt"><i>RFC 2278</i></a>. * In that document a <i>charset</i> is defined as the combination of * one or more coded character sets and a character-encoding scheme. * (This definition is confusing; some other software systems define * <i>charset</i> as a synonym for <i>coded character set</i>.) * * <p> A <i>coded character set</i> is a mapping between a set of abstract * characters and a set of integers. US-ASCII, ISO 8859-1, * JIS X 0201, and Unicode are examples of coded character sets. * * <p> Some standards have defined a <i>character set</i> to be simply a * set of abstract characters without an associated assigned numbering. * An alphabet is an example of such a character set. However, the subtle * distinction between <i>character set</i> and <i>coded character set</i> * is rarely used in practice; the former has become a short form for the * latter, including in the Java API specification. * * <p> A <i>character-encoding scheme</i> is a mapping between one or more * coded character sets and a set of octet (eight-bit byte) sequences. * UTF-8, UTF-16, ISO 2022, and EUC are examples of * character-encoding schemes. Encoding schemes are often associated with * a particular coded character set; UTF-8, for example, is used only to * encode Unicode. Some schemes, however, are associated with multiple * coded character sets; EUC, for example, can be used to encode * characters in a variety of Asian coded character sets. * * <p> When a coded character set is used exclusively with a single * character-encoding scheme then the corresponding charset is usually * named for the coded character set; otherwise a charset is usually named * for the encoding scheme and, possibly, the locale of the coded * character sets that it supports. Hence {@code US-ASCII} is both the * name of a coded character set and of the charset that encodes it, while * {@code EUC-JP} is the name of the charset that encodes the * JIS X 0201, JIS X 0208, and JIS X 0212 * coded character sets for the Japanese language. * * <p> The native character encoding of the Java programming language is * UTF-16. A charset in the Java platform therefore defines a mapping * between sequences of sixteen-bit UTF-16 code units (that is, sequences * of chars) and sequences of bytes. </p> * * * @spec http://www.iana.org/assignments/character-sets Character Sets * @spec https://www.rfc-editor.org/info/rfc2278 * RFC 2278: IANA Charset Registration Procedures * @spec https://www.rfc-editor.org/info/rfc2279 * RFC 2279: UTF-8, a transformation format of ISO 10646 * @spec https://www.rfc-editor.org/info/rfc2781 * RFC 2781: UTF-16, an encoding of ISO 10646 * @author Mark Reinhold * @author JSR-51 Expert Group * @since 1.4 * * @see CharsetDecoder * @see CharsetEncoder * @see java.nio.charset.spi.CharsetProvider * @see java.lang.Character */ public abstract class Charset implements Comparable<Charset> { /* -- Static methods -- */ /** * Checks that the given string is a legal charset name. </p> * * @param s * A purported charset name * * @throws IllegalCharsetNameException * If the given name is not a legal charset name */ private static void checkName(String s) { int n = s.length(); if (n == 0) { throw new IllegalCharsetNameException(s); } for (int i = 0; i < n; i++) { char c = s.charAt(i); if (c >= 'A' && c <= 'Z') continue; if (c >= 'a' && c <= 'z') continue; if (c >= '0' && c <= '9') continue; if (c == '-' && i != 0) continue; if (c == '+' && i != 0) continue; if (c == ':' && i != 0) continue; if (c == '_' && i != 0) continue; if (c == '.' && i != 0) continue; throw new IllegalCharsetNameException(s); } } /* The standard set of charsets */ private static final CharsetProvider standardProvider = new sun.nio.cs.StandardCharsets(); private static final String[] zeroAliases = new String[0]; // Cache of the most-recently-returned charsets, // along with the names that were used to find them // private static volatile Object[] cache1; // "Level 1" cache private static volatile Object[] cache2; // "Level 2" cache private static void cache(String charsetName, Charset cs) { cache2 = cache1; cache1 = new Object[] { charsetName, cs }; } // Creates an iterator that walks over the available providers, ignoring // those whose lookup or instantiation causes a security exception to be // thrown. Should be invoked with full privileges. // private static Iterator<CharsetProvider> providers() { return new Iterator<>() { ClassLoader cl = ClassLoader.getSystemClassLoader(); ServiceLoader<CharsetProvider> sl = ServiceLoader.load(CharsetProvider.class, cl); Iterator<CharsetProvider> i = sl.iterator(); CharsetProvider 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 CharsetProvider next() { if (!getNext()) throw new NoSuchElementException(); CharsetProvider n = next; next = null; return n; } public void remove() { throw new UnsupportedOperationException(); } }; } 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 Charset lookupViaProviders(final String charsetName) { // The runtime startup sequence looks up standard charsets as a // consequence of the VM's invocation of System.initializeSystemClass // in order to, e.g., set system properties and encode filenames. At // that point the application class loader has not been initialized, // however, so we can't look for providers because doing so will cause // that loader to be prematurely initialized with incomplete // information. // if (!VM.isBooted()) return null; Object key = tryBeginLookup(); if (key == null) { // Avoid recursive provider lookups return null; } try { return AccessController.doPrivileged( new PrivilegedAction<>() { public Charset run() { for (Iterator<CharsetProvider> i = providers(); i.hasNext();) { CharsetProvider cp = i.next(); Charset cs = cp.charsetForName(charsetName); if (cs != null) return cs; } return null; } }); } finally { endLookup(key); } } /* The extended set of charsets */ private static class ExtendedProviderHolder { static final CharsetProvider[] extendedProviders = extendedProviders(); // returns ExtendedProvider, if installed @SuppressWarnings("removal") private static CharsetProvider[] extendedProviders() { return AccessController.doPrivileged(new PrivilegedAction<>() { public CharsetProvider[] run() { CharsetProvider[] cps = new CharsetProvider[1]; int n = 0; ServiceLoader<CharsetProvider> sl = ServiceLoader.loadInstalled(CharsetProvider.class); for (CharsetProvider cp : sl) { if (n + 1 > cps.length) { cps = Arrays.copyOf(cps, cps.length << 1); } cps[n++] = cp; } return n == cps.length ? cps : Arrays.copyOf(cps, n); }}); } } private static Charset lookupExtendedCharset(String charsetName) { if (!VM.isBooted()) // see lookupViaProviders() return null; CharsetProvider[] ecps = ExtendedProviderHolder.extendedProviders; for (CharsetProvider cp : ecps) { Charset cs = cp.charsetForName(charsetName); if (cs != null) return cs; } return null; } private static Charset lookup(String charsetName) { if (charsetName == null) throw new IllegalArgumentException("Null charset name"); Object[] a; if ((a = cache1) != null && charsetName.equals(a[0])) return (Charset)a[1]; // We expect most programs to use one Charset repeatedly. // We convey a hint to this effect to the VM by putting the // level 1 cache miss code in a separate method. return lookup2(charsetName); } private static Charset lookup2(String charsetName) { Object[] a; if ((a = cache2) != null && charsetName.equals(a[0])) { cache2 = cache1; cache1 = a; return (Charset)a[1]; } Charset cs; if ((cs = standardProvider.charsetForName(charsetName)) != null || (cs = lookupExtendedCharset(charsetName)) != null || (cs = lookupViaProviders(charsetName)) != null) { cache(charsetName, cs); return cs; } /* Only need to check the name if we didn't find a charset for it */ checkName(charsetName); return null; } /** * Tells whether the named charset is supported. * * @param charsetName * The name of the requested charset; may be either * a canonical name or an alias * * @return {@code true} if, and only if, support for the named charset * is available in the current Java virtual machine * * @throws IllegalCharsetNameException * If the given charset name is illegal * * @throws IllegalArgumentException * If the given {@code charsetName} is null */ public static boolean isSupported(String charsetName) { return (lookup(charsetName) != null); } /** * Returns a charset object for the named charset. * * @param charsetName * The name of the requested charset; may be either * a canonical name or an alias * * @return A charset object for the named charset * * @throws IllegalCharsetNameException * If the given charset name is illegal * * @throws IllegalArgumentException * If the given {@code charsetName} is null * * @throws UnsupportedCharsetException * If no support for the named charset is available * in this instance of the Java virtual machine */ public static Charset forName(String charsetName) { Charset cs = lookup(charsetName); if (cs != null) return cs; throw new UnsupportedCharsetException(charsetName); } /** * Returns a charset object for the named charset. If the charset object * for the named charset is not available or {@code charsetName} is not a * legal charset name, then {@code fallback} is returned. * * @param charsetName * The name of the requested charset; may be either * a canonical name or an alias * * @param fallback * fallback charset in case the charset object for the named * charset is not available or {@code charsetName} is not a legal * charset name. May be {@code null} * * @return A charset object for the named charset, or {@code fallback} * in case the charset object for the named charset is not * available or {@code charsetName} is not a legal charset name * * @throws IllegalArgumentException * If the given {@code charsetName} is {@code null} * * @since 18 */ public static Charset forName(String charsetName, Charset fallback) { try { Charset cs = lookup(charsetName); return cs != null ? cs : fallback; } catch (IllegalCharsetNameException icne) { return fallback; } } // Fold charsets from the given iterator into the given map, ignoring // charsets whose names already have entries in the map. // private static void put(Iterator<Charset> i, Map<String,Charset> m) { while (i.hasNext()) { Charset cs = i.next(); m.putIfAbsent(cs.name(), cs); } } /** * Constructs a sorted map from canonical charset names to charset objects. * * <p> The map returned by this method will have one entry for each charset * for which support is available in the current Java virtual machine. If * two or more supported charsets have the same canonical name then the * resulting map will contain just one of them; which one it will contain * is not specified. </p> * * <p> The invocation of this method, and the subsequent use of the * resulting map, may cause time-consuming disk or network I/O operations * to occur. This method is provided for applications that need to * enumerate all of the available charsets, for example to allow user * charset selection. This method is not used by the {@link #forName * forName} method, which instead employs an efficient incremental lookup * algorithm. * * <p> This method may return different results at different times if new * charset providers are dynamically made available to the current Java * virtual machine. In the absence of such changes, the charsets returned * by this method are exactly those that can be retrieved via the {@link * #forName forName} method. </p> * * @return An immutable, case-insensitive map from canonical charset names * to charset objects */ @SuppressWarnings("removal") public static SortedMap<String,Charset> availableCharsets() { return AccessController.doPrivileged( new PrivilegedAction<>() { public SortedMap<String,Charset> run() { TreeMap<String,Charset> m = new TreeMap<>( String.CASE_INSENSITIVE_ORDER); put(standardProvider.charsets(), m); CharsetProvider[] ecps = ExtendedProviderHolder.extendedProviders; for (CharsetProvider ecp :ecps) { put(ecp.charsets(), m); } for (Iterator<CharsetProvider> i = providers(); i.hasNext();) { CharsetProvider cp = i.next(); put(cp.charsets(), m); } return Collections.unmodifiableSortedMap(m); } }); } private @Stable static Charset defaultCharset; /** * Returns the default charset of this Java virtual machine. * * <p> The default charset is {@code UTF-8}, unless changed in an * implementation specific manner. * * @implNote An implementation may override the default charset with * the system property {@code file.encoding} on the command line. If the * value is {@code COMPAT}, the default charset is derived from * the {@code native.encoding} system property, which typically depends * upon the locale and charset of the underlying operating system. * * @return A charset object for the default charset * @see <a href="../../lang/System.html#file.encoding">file.encoding</a> * @see <a href="../../lang/System.html#native.encoding">native.encoding</a> * * @since 1.5 */ public static Charset defaultCharset() { if (defaultCharset == null) { synchronized (Charset.class) { // do not look for providers other than the standard one Charset cs = standardProvider.charsetForName(StaticProperty.fileEncoding()); if (cs != null) defaultCharset = cs; else defaultCharset = sun.nio.cs.UTF_8.INSTANCE; } } return defaultCharset; } /* -- Instance fields and methods -- */ private final String name; // tickles a bug in oldjavac private final String[] aliases; // tickles a bug in oldjavac private Set<String> aliasSet; /** * Initializes a new charset with the given canonical name and alias * set. * * @param canonicalName * The canonical name of this charset * * @param aliases * An array of this charset's aliases, or null if it has no aliases * * @throws IllegalCharsetNameException * If the canonical name or any of the aliases are illegal */ protected Charset(String canonicalName, String[] aliases) { String[] as = aliases == null ? zeroAliases : VM.isSystemDomainLoader(getClass().getClassLoader()) ? aliases : Arrays.copyOf(aliases, aliases.length); // Skip checks for the standard, built-in Charsets we always load // during initialization. if (canonicalName != "ISO-8859-1" && canonicalName != "US-ASCII" && canonicalName != "UTF-8") { checkName(canonicalName); for (int i = 0; i < as.length; i++) { checkName(as[i]); } } this.name = canonicalName; this.aliases = as; } /** * Returns this charset's canonical name. * * @return The canonical name of this charset */ public final String name() { return name; } /** * Returns a set containing this charset's aliases. * * @return An immutable set of this charset's aliases */ public final Set<String> aliases() { Set<String> set = this.aliasSet; if (set == null) { set = Set.of(aliases); this.aliasSet = set; } return set; } /** * Returns this charset's human-readable name for the default locale. * * <p> The default implementation of this method simply returns this * charset's canonical name. Concrete subclasses of this class may * override this method in order to provide a localized display name. </p> * * @return The display name of this charset in the default locale */ public String displayName() { return name; } /** * Tells whether or not this charset is registered in the <a * href="http://www.iana.org/assignments/character-sets">IANA Charset * Registry</a>. * * @return {@code true} if, and only if, this charset is known by its * implementor to be registered with the IANA * @spec http://www.iana.org/assignments/character-sets Character Sets */ public final boolean isRegistered() { return !name.startsWith("X-") && !name.startsWith("x-"); } /** * Returns this charset's human-readable name for the given locale. * * <p> The default implementation of this method simply returns this * charset's canonical name. Concrete subclasses of this class may * override this method in order to provide a localized display name. </p> * * @param locale * The locale for which the display name is to be retrieved * * @return The display name of this charset in the given locale */ public String displayName(Locale locale) { return name; } /** * Tells whether or not this charset contains the given charset. * * <p> A charset <i>C</i> is said to <i>contain</i> a charset <i>D</i> if, * and only if, every character representable in <i>D</i> is also * representable in <i>C</i>. If this relationship holds then it is * guaranteed that every string that can be encoded in <i>D</i> can also be * encoded in <i>C</i> without performing any replacements. * * <p> That <i>C</i> contains <i>D</i> does not imply that each character * representable in <i>C</i> by a particular byte sequence is represented * in <i>D</i> by the same byte sequence, although sometimes this is the * case. * * <p> Every charset contains itself. * * <p> This method computes an approximation of the containment relation: * If it returns {@code true} then the given charset is known to be * contained by this charset; if it returns {@code false}, however, then * it is not necessarily the case that the given charset is not contained * in this charset. * * @param cs * The given charset * * @return {@code true} if the given charset is contained in this charset */ public abstract boolean contains(Charset cs); /** * Constructs a new decoder for this charset. * * @return A new decoder for this charset */ public abstract CharsetDecoder newDecoder(); /** * Constructs a new encoder for this charset. * * @return A new encoder for this charset * * @throws UnsupportedOperationException * If this charset does not support encoding */ public abstract CharsetEncoder newEncoder(); /** * Tells whether or not this charset supports encoding. * * <p> Nearly all charsets support encoding. The primary exceptions are * special-purpose <i>auto-detect</i> charsets whose decoders can determine * which of several possible encoding schemes is in use by examining the * input byte sequence. Such charsets do not support encoding because * there is no way to determine which encoding should be used on output. * Implementations of such charsets should override this method to return * {@code false}. </p> * * @return {@code true} if, and only if, this charset supports encoding */ public boolean canEncode() { return true; } /** * Convenience method that decodes bytes in this charset into Unicode * characters. * * <p> An invocation of this method upon a charset {@code cs} returns the * same result as the expression * * {@snippet lang=java : * cs.newDecoder() * .onMalformedInput(CodingErrorAction.REPLACE) * .onUnmappableCharacter(CodingErrorAction.REPLACE) * .decode(bb); * } * * except that it is potentially more efficient because it can cache * decoders between successive invocations. * * <p> This method always replaces malformed-input and unmappable-character * sequences with this charset's default replacement byte array. In order * to detect such sequences, use the {@link * CharsetDecoder#decode(java.nio.ByteBuffer)} method directly. </p> * * @param bb The byte buffer to be decoded * * @return A char buffer containing the decoded characters */ public final CharBuffer decode(ByteBuffer bb) { try { return ThreadLocalCoders.decoderFor(this) .onMalformedInput(CodingErrorAction.REPLACE) .onUnmappableCharacter(CodingErrorAction.REPLACE) .decode(bb); } catch (CharacterCodingException x) { throw new Error(x); // Can't happen } } /** * Convenience method that encodes Unicode characters into bytes in this * charset. * * <p> An invocation of this method upon a charset {@code cs} returns the * same result as the expression * * {@snippet lang=java : * cs.newEncoder() * .onMalformedInput(CodingErrorAction.REPLACE) * .onUnmappableCharacter(CodingErrorAction.REPLACE) * .encode(bb); * } * * except that it is potentially more efficient because it can cache * encoders between successive invocations. * * <p> This method always replaces malformed-input and unmappable-character * sequences with this charset's default replacement string. In order to * detect such sequences, use the {@link * CharsetEncoder#encode(java.nio.CharBuffer)} method directly. </p> * * @param cb The char buffer to be encoded * * @return A byte buffer containing the encoded characters */ public final ByteBuffer encode(CharBuffer cb) { try { return ThreadLocalCoders.encoderFor(this) .onMalformedInput(CodingErrorAction.REPLACE) .onUnmappableCharacter(CodingErrorAction.REPLACE) .encode(cb); } catch (CharacterCodingException x) { throw new Error(x); // Can't happen } } /** * Convenience method that encodes a string into bytes in this charset. * * <p> An invocation of this method upon a charset {@code cs} returns the * same result as the expression * * {@snippet lang=java : * cs.encode(CharBuffer.wrap(s)); * } * * @param str The string to be encoded * * @return A byte buffer containing the encoded characters */ public final ByteBuffer encode(String str) { return encode(CharBuffer.wrap(str)); } /** * Compares this charset to another. * * <p> Charsets are ordered by their canonical names, without regard to * case. </p> * * @param that * The charset to which this charset is to be compared * * @return A negative integer, zero, or a positive integer as this charset * is less than, equal to, or greater than the specified charset */ public final int compareTo(Charset that) { return (name().compareToIgnoreCase(that.name())); } /** * Computes a hashcode for this charset. * * @return An integer hashcode */ public final int hashCode() { return name().hashCode(); } /** * Tells whether or not this object is equal to another. * * <p> Two charsets are equal if, and only if, they have the same canonical * names. A charset is never equal to any other type of object. </p> * * @return {@code true} if, and only if, this charset is equal to the * given object */ public final boolean equals(Object ob) { if (!(ob instanceof Charset)) return false; if (this == ob) return true; return name.equals(((Charset)ob).name()); } /** * Returns a string describing this charset. * * @return A string describing this charset */ public final String toString() { return name(); } }