gcc/libjava/classpath/javax/management/Descriptor.java

/* Descriptor.java -- Metadata container.
   Copyright (C) 2007 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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02110-1301 USA.

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permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
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exception statement from your version. */

package javax.management;

import java.io.Serializable;

/**
 * <p>
 * Provides metadata for a management element as a series
 * of fields, formed from name-value pairs.  Descriptors
 * are usually attached to one of the <code>Info</code>
 * classes, such as {@link MBeanAttributeInfo}.
 * </p>
 * <p>
 * Field names are not case-sensitive, but are case-preserving
 * (in that the same use of case will be returned by
 * {@link #getFields()} and {@link #getFieldNames()}).
 * The type of the value should match the type returned
 * by the <code>getType()</code> method of the associated
 * <code>Info</code> object.  In the case of {@link MXBean}s,
 * this should be the mapped type returned by the mapping rules.
 * </p>
 * <p>
 * The contents of a descriptor may be immutable, in which
 * case, attempts to change the contents of the descriptor
 * will cause an exception to be thrown.  Immutable descriptors
 * are usually instances or subclasses of {@link ImmutableDescriptor},
 * while mutable descriptors are usually instances or subclasses
 * of {@link javax.management.modelmbean.DescriptorSupport}.
 * </p>
 * <p>
 * A series of field names are predefined, but additional
 * ones can be added as needed.  Predefined names never include
 * a period ('.'), and so additional names may safely avoid
 * conflicts by including this character.  It is recommended that
 * additional names make use of the same syntax as Java package
 * names e.g. <code>gnu.classpath.ImportantMetadata</code>.
 * </p>
 * <p>
 * The predefined names are as follows:
 * </p>
 * <table>
 * <th>
 * <td>Name</td><td>Type</td><td>Used In</td><td>Meaning</td>
 * </th>
 * <tr>
 * <td>defaultValue</td><td>Object</td><td>{@link MBeanAttributeInfo},
 * {@link MBeanParameterInfo}</td><td>Default value for an attribute
 * or parameter.</td>
 * </tr>
 * <tr>
 * <td>deprecated</td><td>String</td><td>Any</td><td>The annotated element
 * has been deprecated.  Conventially, the field's value takes the form
 * of the version in which the element was deprecated, followed by an
 * explaination.</td>
 * </tr>
 * <tr>
 * <td>descriptionResourceBundleBaseName</td><td>String</td><td>Any</td>
 * <td>The base name for the bundle in which the <code>descriptionResourceKey</code>
 * can be found.</td>
 * </tr>
 * <tr>
 * <td>descriptionResourceKey</td><td>String</td><td>Any</td>
 * <td>The name of the resource key which contains a localized description of
 * this element.</td>
 * </tr>
 * <tr>
 * <td>enabled</td><td>String</td><td>{@link MBeanAttributeInfo},
 * {@link MBeanNotificationInfo}, {@link MBeanOperationInfo}</td>
 * <td>Specifies whether the annotated element is currently enabled or
 * not, via a value of either <code>"true"</code> or <code>"false"</code>.
 * </tr>
 * <tr>
 * <td>immutableInfo</td><td>String</td><td>{@link MBeanInfo}</td>
 * <td>If the value of this field is <code>"true"</code>, this means that
 * the annotated element will not change and thus may be cached.</td>
 * </tr>
 * <tr>
 * <td>infoTimeout</td><td>String or Long</td><td>{@link MBeanInfo}</td>
 * <td>If this field is present, and non-zero, it will contain a value
 * in milliseconds for which the value of the annotated element will
 * remain unchanged, allowing it to be safely cached for that period.</td>
 * </tr>
 * <tr>
 * <td>interfaceClassName</td><td>String</td><td>{@link MBeanInfo}</td>
 * <td>The Java interface name associated with the bean, as returned
 * by {@link Class#getName()}.</td>
 * </tr>
 * <tr>
 * <td>legalValues</td><td>Set<?></td><td>{@link MBeanAttributeInfo},
 * {@link MBeanParameterInfo}</td><td>Legal values for an attribute
 * or parameter.</td>
 * </tr>
 * <tr>
 * <td>maxValue</td><td>Object</td><td><td>{@link MBeanAttributeInfo},
 * {@link MBeanParameterInfo}</td><td>Maximum legal value for an attribute
 * or parameter.</td>
 * </tr>
 * <tr>
 * <td>metricType</td><td>String</td><td>{@link MBeanAttributeInfo},
 * {@link MBeanOperationInfo}</td><td>Specifies the type of metric represented
 * by the annotated element.  This will be either <code>"counter"</code>
 * (an increasing value, which will only be reset and never decrease)
 * or <code>"gauge"</code> (an increasing and decreasing value).</td>
 * </tr>
 * <tr>
 * <td>minValue</td><td>Object</td><td>{@link MBeanAttributeInfo},
 * {@link MBeanParameterInfo}</td><td>Minimum legal value for an attribute
 * or parameter.</td>
 * </tr>
 * <tr>
 * <td>mxbean</td><td>String</td><td>{@link MBeanInfo}</td>
 * <td>Specifies whether the annotated element is an {@link MXBean} or
 * not, via a value of either <code>"true"</code> or <code>"false"</code>.
 * </tr>
 * <tr>
 * <td>openType</td><td>{@link javax.management.openmbean.OpenType}</td>
 * <td>{@link MBeanAttributeInfo}, {@link MBeanOperationInfo}</td>,
 * {@link MBeanNotificationInfo}, {@link MBeanParameterInfo}</td>
 * <td>Specifies the open type of the attribute or parameter, the return
 * value of the operation or the user data of the notification respectively.
 * This is present on <code>Open*Info</code> instances and for {@link MXBean}s.</td>
 * <tr>
 * <td>originalType</td><td>String</td><td>{@link MBeanAttributeInfo},
 * {@link MBeanOperationInfo}, {@link MBeanParameterInfo}</td>
 * <td>The original Java type of an element which has been converted
 * to another type according to the {@link MXBean} typing rules.
 * For example, {@link java.lang.management.MemoryType} becomes a
 * String after conversion.  This field would contain
 * <code>"java.lang.management.MemoryType"</code> to represent the
 * earlier type of an element with the converted type.</td>
 * </tr>
 * <tr>
 * <td>severity</td><td>Integer or String</td>
 * <td>{@link MBeanNotificationInfo}</td><td>Represents the severity
 * of the notification, ranging from 1 (most severe) to 6 (least
 * severe), with 0 representing unknown severity.</td>
 * </tr>
 * <tr>
 * <td>since</td><td>String</td><td>Any</td>
 * <td>The version in which this field was introduced.</td>
 * </tr>
 * <tr>
 * <td>units</td><td>String</td><td>{@link MBeanAttributeInfo},
 * {@link MBeanOperationInfo}, {@link MBeanParameterInfo}</td>
 * <td>The units used by the value of an attribute or parameter,
 * or the return value of an operation, such as <code>"bytes"</code>,
 * <code>"milliseconds"</code> or <code>"kilogrammes"</code>.
 * </tr>
 * </table>
 * <p>Some names are also defined as part of the Model MBeans package.
 * See {@link javax.management.modelmbean.ModelMBeanInfo}.</p>
 *
 * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
 * @since 1.5
 */
public interface Descriptor
  extends Serializable, Cloneable
{

  /**
   * Returns a clone of this descriptor, which can then be modified
   * independently of this descriptor.  If the descriptor is
   * immutable, it is sufficient to return this instance.
   *
   * @return a clone of this descriptor.
   * @throws RuntimeOperationsException if creation of the new
   *                                    descriptor fails for any
   *                                    reason.
   */
  Object clone()
    throws RuntimeOperationsException;

  /**
   * <p>
   * Returns true if this descriptor is equivalent to the
   * supplied object.  This is true if the following holds:
   * </p>
   * <ul>
   * <li>The given object is also a {@link Descriptor}.</li>
   * <li>Has the same field names, independent of case.</li>
   * <li>Has the same values, based on the following:
   * <ul>
   * <li>If one value is <code>null</code>, the other must be.</li>
   * <li>If one value is a primitive array, the other must be a
   * primitive array of the same type with the same elements.</li>
   * <li>If one value is an {@link Object} array, the other
   * must be and {@link java.util.Arrays#deepEquals(Object[],Object[])}
   * must return true.</li>
   * <li>Otherwise, {@link Object#equals(Object)} must return true.</li>
   * </ul>
   *
   * @param obj the object to compare according to the above.
   * @return true if the above holds.
   * @see Object#equals(Object)
   * @see Object#hashCode()
   * @since 1.6
   */
  boolean equals(Object obj);

  /**
   * Returns the field names of the descriptor.  If the
   * descriptor is empty, an empty array is returned.
   *
   * @return the field names as an array of Strings.
   */
  String[] getFieldNames();

  /**
   * <p>
   * Returns all the field name and value pairs, in the
   * form <code>name=value</code>.  The value is converted
   * to a String as follows:
   * </p>
   * <ul>
   * <li>If the value is a String, it is used as is.</li>
   * <li>If the value is <code>null</code>, the printed
   * value will be empty.</li>
   * <li>Otherwise, the value will be converted to a
   * String using its {@link Object#toString()} method,
   * and included as <code>"(" + string + ")"</code>.</li>
   * </ul>
   * <p>If the descriptor is empty, an empty array is returned.</p>
   *
   * @return the field names and values as an array of Strings.
   * @see #setFields(String[],Object[])
   */
  String[] getFields();

  /**
   * Returns the value of the specified field, or <code>null</code>
   * if no value is present for the given field name.
   *
   * @param name the field name.
   * @return the value of the field, or <code>null</code> if there
   *         is no value present.
   * @throws RuntimeOperationsException if the field name is illegal.
   */
  Object getFieldValue(String name);

  /**
   * Returns the values corresponding to the fields named in
   * the specified array, in the same order.  If an empty
   * array is supplied, an empty array is returned.  A value
   * of <code>null</code> leads to behaviour equivalent to
   * {@link #getFields()}.  Field values are obtained as specified
   * in {@link #getFieldValue(String)}, with <code>null</code>
   * being returned if the field is not present.  This applies
   * even if the given field name is <code>null</code> or
   * the empty string.
   *
   * @param names an array of field names whose values should
   *              be returned.
   * @return the values of the specified fields.
   * @see #getFields()
   * @see #getFieldValue(String)
   */
  Object[] getFieldValues(String... names);

  /**
   * <p>
   * Returns the hash code of the descriptor.  The hashcode
   * is computed as the sum of the hashcodes for each field,
   * which in turn is calculated as the sum of
   * the hashcode of the name, <code>n</code>, computed
   * using <code>n.toLowerCase().hashCode()</code>, and the
   * hashcode of the value, <code>v</code>, computed
   * using:
   * </p>
   * <ul>
   * <li>If <code>v</code> is <code>null</code>, then the
   * hash code is 0.</li>
   * <li>If <code>v</code> is a primitive array, then the
   * hash code is computed using the appropriate method
   * from {@link java.util.Arrays}.</li>
   * <li>If <code>v</code> is an {@link java.lang.Object}
   * array, then the hash code is computed using the
   * {@link java.util.Arrays#deepHashCode(Object[])} method.</li>
   * <li>Otherwise, the hashcode is equal to
   * <code>v.hashCode()</code>.
   * </ul>
   *
   * @return a hashcode for this descriptor.
   * @since 1.6
   * @see Object#equals(Object)
   * @see Object#hashCode()
   */
  int hashCode();

  /**
   * Returns true if all the fields have legal values, given
   * their names.  Validity is determined by the implementation.
   *
   * @return true if the values are legal.
   * @throws RuntimeOperationsException if the validity check
   *                                    fails for some reason.
   */
  boolean isValid()
    throws RuntimeOperationsException;

  /**
   * Removes a field from the descriptor.  If the field name
   * is illegal or not found, this method fails silently.
   *
   * @param name the name of the field to remove.
   * @throws RuntimeOperationsException if the field exists
   *                                    and the descriptor is
   *                                    immutable.  This wraps
   *                                    an {@link UnsupportedOperationException}.
   */
  void removeField(String name);

  /**
   * Attempts to set the specified field to the supplied
   * value.  If the field does not exist, it will be created.
   * If the field value given is invalid, then an exception will
   * be thrown.  Validity is determined by the implementation
   * of the descriptor.
   *
   * @param name the field to set.  Can not be <code>null</code>
   *             or empty.
   * @param value the value to use, the validity of which is
   *              determined by the implementation.
   * @throws RuntimeOperationsException if the name or value is
   *                                    illegal (wrapping a
   *                                    {@link IllegalArgumentException})
   *                                    or if the descriptor is
   *                                    immutable (wrapping a
   *                                    {@link UnsupportedOperationException}.
   */
  void setField(String name, Object value)
    throws RuntimeOperationsException;

  /**
   * Sets the field named in the first array to the corresponding
   * value specified in the second.  The array sizes must match.
   * Empty arrays have no effect.  An invalid value will cause
   * an exception to be thrown.
   *
   * @param names the names of the fields to change.  Neither
   *              the array or its elements may be <code>null</code>.
   * @param values the values to use.  The array must not be
   *               <code>null</code>.  The value of the elements
   *               depends on the validity constraints of the
   *               implementation.
   * @throws RuntimeOperationsException if the arrays differ in
   *                                    length, or a name or value is
   *                                    illegal (wrapping a
   *                                    {@link IllegalArgumentException})
   *                                    or if the descriptor is
   *                                    immutable (wrapping a
   *                                    {@link UnsupportedOperationException}.
   * @see #setField(String,Object)
   */
  void setFields(String[] names, Object[] values);

}