src/java.management/share/classes/javax/management/openmbean/package.html - master - githubmirror/jdk17u-dev

src/java.management/share/classes/javax/management/openmbean/package.html
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<title>javax.management.openmbean package</title>
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    <p>Provides the open data types and Open MBean descriptor classes.
      An <em>Open MBean</em> is an MBean where the types of attributes
      and of operation parameters and return values are built using a
      small set of predefined Java classes.  Open MBeans facilitate
      operation with remote management programs that do not necessarily
      have access to application-specific types, including non-Java
      programs.</p>

    <p>Every MBean has an {@link javax.management.MBeanInfo
      MBeanInfo} with information about the MBean itself, and its
      attributes, operations, constructors, and notifications.  In an
      Open MBean, this <code>MBeanInfo</code> implements the {@link
      javax.management.openmbean.OpenMBeanInfo OpenMBeanInfo}
      interface, usually by being an instance of {@link
      javax.management.openmbean.OpenMBeanInfoSupport
      OpenMBeanInfoSupport}.</p>

    <p>The attribute information returned by {@link
      javax.management.MBeanInfo#getAttributes()
      MBeanInfo.getAttributes} for an Open MBean is an array of
      objects implementing {@link
      javax.management.openmbean.OpenMBeanAttributeInfo
      OpenMBeanAttributeInfo}, usually instances of {@link
      javax.management.openmbean.OpenMBeanAttributeInfoSupport
      OpenMBeanAttributeInfoSupport}.  In addition to the usual
      information about attributes, an
      <code>OpenMBeanAttributeInfo</code> specifies the {@link
      javax.management.openmbean.OpenType OpenType} of the attribute.
      The possible <code>OpenType</code> values are predefined, which
      is what ensures that remote managers will understand them.</p>

    <p>Similar remarks apply to the parameter types of operations and
      constructors, and to the return types of operations.</p>

    <p>There is a distinction between an attribute's Java language
      type, as returned by {@link
      javax.management.MBeanAttributeInfo#getType() getType()}, and
      its <code>OpenType</code>, as returned by {@link
      javax.management.openmbean.OpenMBeanAttributeInfo#getOpenType()
      getOpenType()}.  For example, if the Java language type is
      <code>java.lang.String</code>, the <code>OpenType</code> will be
      {@link javax.management.openmbean.SimpleType#STRING
      SimpleType.String}.  If the Java language type is {@link
      javax.management.openmbean.CompositeData}, the
      <code>OpenType</code> will be a {@link
      javax.management.openmbean.CompositeType CompositeType} that
      describes the items in the <code>CompositeData</code> instances
      for the attribute.</p>

    <h2><a id="constraints">Default values and constraints</a></h2>

    <p>In Open MBeans, attributes and parameters can have default values
      and/or constraints associated with them in the {@code
      OpenMBeanAttributeInfo} or {@code OpenMBeanParameterInfo}.
      There are two ways to specify these constraints.  Either the
      values are directly specified as parameters to one of the
      constructors of {@code OpenMBeanAttributeInfoSupport} or
      {@code OpenMBeanParameterInfoSupport}, for example
      {@link
      javax.management.openmbean.OpenMBeanParameterInfoSupport#OpenMBeanParameterInfoSupport(
      String, String, OpenType, Object, Object[])}; or the values are
      specified in a {@link javax.management.Descriptor Descriptor} given
      as a parameter to one of the constructors.</p>

    <p>When a {@code Descriptor} is used, the fields of interest are
      these:</p>

    <ul>

      <li>{@code defaultValue} defines the value returned by
	{@link javax.management.openmbean.OpenMBeanParameterInfo#getDefaultValue()
	getDefaultValue()};

      <li>{@code minValue} defines the value returned by {@link
	javax.management.openmbean.OpenMBeanParameterInfo#getMinValue() getMinValue()};

      <li>{@code maxValue} defines the value returned by {@link
	javax.management.openmbean.OpenMBeanParameterInfo#getMaxValue() getMaxValue()};

      <li>{@code legalValues} defines the values returned by {@link
	javax.management.openmbean.OpenMBeanParameterInfo#getLegalValues() getLegalValues()}.

    </ul>

    <p>For {@code defaultValue}, {@code minValue}, and {@code
      maxValue}, the associated value must either be of the Java type
      corresponding to {@code openType}, or be a string that can be
      converted into that type.  The conversion uses the static method
      {@code valueOf(String)} if it finds one; otherwise a constructor
      with a single {@code String} parameter if it finds one; otherwise
      it fails.</p>

    <p>For {@code legalValues}, the associated value must be either
      an array or a {@code Set}, and the elements of the array or set
      must be convertible as described for {@code defaultValue} etc.</p>

    <p>The following conditions must be met for these fields:</p>

    <ul>
      <li>the values must be of the appropriate type, or be strings
	that can be converted to the appropriate type as explained
	above;

      <li>if {@code legalValues} is present then neither {@code
	minValue} nor {@code maxValue} must be present;

      <li>if {@code defaultValue} is present then it must satisfy the
	constraints defined by {@code legalValues}, {@code minValue}, or
	{@code maxValue} when any of these is also present;

      <li>if {@code minValue} and {@code maxValue} are both present
	then {@code minValue} must not be greater than {@code maxValue}.
    </ul>

    @see <a href="https://jcp.org/aboutJava/communityprocess/mrel/jsr160/index2.html">
      JMX Specification, version 1.4</a>

    @since 1.5

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