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

/* MBeanServerInvocationHandler.java -- Provides a proxy for a bean.
   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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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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terms of your choice, provided that you also meet, for each linked
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package javax.management;

import gnu.javax.management.Translator;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

/**
 * <p>
 * Provides a proxy for a management bean.  The methods
 * of the given interface are fulfilled by redirecting the
 * calls over an {@link MBeanServerConnection} to the bean
 * specified by the supplied {@link ObjectName}.
 * </p>
 * <p>
 * The {@link java.lang.reflect.InvocationHandler} also makes
 * provision for {@link MXBean}s by providing type conversion
 * according to the rules defined for these beans.  The input
 * parameters are converted to their equivalent open type before
 * calling the method, and then the return value is converted
 * back from its open type to the appropriate Java type.  For
 * example, a method that takes an {@link Enum} as input and
 * returns a {@link java.util.List} will have the input value
 * converted from an {@link Enum} to a {@link String}, while
 * the return value will be converted from its return type
 * (an appropriately typed array) to a {@link java.util.List}.
 * </p>
 * <p>
 * The proxy has special cases for the {@link Object#equals(Object)},
 * {@link Object#hashCode()} and {@link Object#toString()} methods.
 * Unless they are specified explictly by the interface, the
 * following behaviour is provided for these methods by the proxy:
 * </p>
 * <ul>
 * <li><code>equals(Object)</code> returns true if the other object
 * is an {@link MBeanServerInvocationHandler} with the same
 * {@link MBeanServerConnection} and {@link ObjectName}.  If an
 * interface class was specified on construction for one of the
 * proxies, then the same class must have also been specified
 * for the other.</li>
 * <li><code>hashCode()</code> returns the same value for
 * equivalent proxies.</li>
 * <li><code>toString()</code> returns a textual representation
 * of the proxy.</li>
 * </ul>
 * 
 * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
 * @since 1.5
 */
public class MBeanServerInvocationHandler
  implements InvocationHandler
{

  /**
   * The connection used to make the calls.
   */
  private MBeanServerConnection conn;

  /**
   * The name of the bean to perform operations on.
   */
  private ObjectName name;

  /**
   * True if this proxy is for an {@link MXBean}.
   */
  private boolean mxBean;

  /**
   * The interface class associated with the bean.
   */
  private Class<?> iface;

  /**
   * Constructs a new {@link MBeanServerInvocationHandler}
   * which forwards methods to the supplied bean via the
   * given {@link MBeanServerConnection}.  This constructor
   * is used in preference to
   * {@link JMX#newMBeanProxy(MBeanServerConnection, ObjectName,
   * Class<T>)} if you wish to make your own call to
   * {@link java.lang.reflect.Proxy#newInstance(ClassLoader,
   * Class[], java.lang.reflect.InvocationHandler)} with
   * a different {@link ClassLoader}.  Calling this constructor
   * is equivalent to <code>MBeanServerInvocationHandler(conn,
   * name, false)</code>.  The other constructor should be used
   * instead if the bean being proxied is an {@link MXBean}.
   *
   * @param conn the connection through which methods will
   *             be forwarded to the bean.
   * @param name the name of the bean to use to provide the
   *             actual calls.
   */
  public MBeanServerInvocationHandler(MBeanServerConnection conn,
				      ObjectName name)
  {
    this(conn, name, false);
  }

  /**
   * Constructs a new {@link MBeanServerInvocationHandler}
   * which forwards methods to the supplied bean via the
   * given {@link MBeanServerConnection}.  This constructor
   * is used in preference to
   * {@link JMX#newMBeanProxy(MBeanServerConnection, ObjectName,
   * Class<T>)} if you wish to make your own call to
   * {@link java.lang.reflect.Proxy#newInstance(ClassLoader,
   * Class[], java.lang.reflect.InvocationHandler)} with
   * a different {@link ClassLoader}.  
   *
   * @param conn the connection through which methods will
   *             be forwarded to the bean.
   * @param name the name of the bean to use to provide the
   *             actual calls.
   * @param mxBean true if the bean being proxied is an
   *               {@link MXBean}.
   * @since 1.6
   */
  public MBeanServerInvocationHandler(MBeanServerConnection conn,
				      ObjectName name, boolean mxBean)
  {
    this.conn = conn;
    this.name = name;
    this.mxBean = mxBean;
  }

  /**
   * Returns the connection through which the calls to the bean
   * will be made.
   * 
   * @return the connection being used to forward the calls to
   *         the bean.
   * @since 1.6
   */
  public MBeanServerConnection getMBeanServerConnection()
  {
    return conn;
  }

  /**
   * Returns the name of the bean to which method calls are made.
   *
   * @return the bean which provides the actual method calls.
   * @since 1.6
   */
  public ObjectName getObjectName()
  {
    return name;
  }

  /**
   * Called by the proxy class whenever a method is called.  The method
   * is emulated by retrieving an attribute from, setting an attribute on
   * or invoking a method on the server connection as required.  Translation
   * between the Java data types supplied as arguments to the open types used
   * by the bean is provided, as well as translation of the return value back
   * in to the appropriate Java type if the bean is an {@link MXBean}.
   *
   * @param proxy the proxy on which the method was called.
   * @param method the method which was called.
   * @param args the arguments supplied to the method.
   * @return the return value from the method.
   * @throws Throwable if an exception is thrown in performing the
   *                   method emulation.
   */
  public Object invoke(Object proxy, Method method, Object[] args)
    throws Throwable
  {
    String mName = method.getName();
    Class<?> proxyClass = proxy.getClass();
    if (mName.equals("toString"))
      {
	if (inInterface(mName, proxyClass))
	  return conn.invoke(name,mName,null,null);
	else
	  return proxyClass.getName() + "[name=" + name 
	    + ", conn=" + conn + "]";
      }
    if (mName.equals("hashCode"))
      {
	if (inInterface(mName, proxyClass))
	  return conn.invoke(name,mName,null,null);
	else
	  return conn.hashCode() + name.hashCode()
	    + (iface == null ? 0 : iface.hashCode());
      }
    if (mName.equals("equals"))
      {
	if (inInterface(mName, proxyClass, Object.class))
	  return conn.invoke(name,mName,new Object[]{args[0]},
			     new String[]{"java.lang.Object"});
	else
	  {
	    if (args[0].getClass() != proxy.getClass())
	      return false;
	    InvocationHandler ih = Proxy.getInvocationHandler(args[0]);
	    if (ih instanceof MBeanServerInvocationHandler)
	      {
		MBeanServerInvocationHandler h =
		  (MBeanServerInvocationHandler) ih;
		return conn.equals(h.getMBeanServerConnection())
		  && name.equals(h.getObjectName())
		  && (iface == null ? h.iface == null 
		      : iface.equals(h.iface));
	      }
	    return false;
	  }
      }
    if (NotificationEmitter.class.isAssignableFrom(proxyClass))
      {
	if (mName.equals("addNotificationListener"))
	  {
	    conn.addNotificationListener(name,
					 (NotificationListener) args[0],
					 (NotificationFilter) args[1],
					 args[2]);
	    return null;
	  }
	if (mName.equals("getNotificationInfo"))
	  return conn.getMBeanInfo(name).getNotifications();
	if (mName.equals("removeNotificationListener"))
	  {
	    if (args.length == 1)
	      conn.removeNotificationListener(name, 
					      (NotificationListener)
					      args[0]);
	    else
	      conn.removeNotificationListener(name, 
					      (NotificationListener)
					      args[0],
					      (NotificationFilter)
					      args[1], args[2]);
	    return null;
	  }
      }
    String[] sigs;
    if (args == null)
      sigs = null;
    else
      {
	sigs = new String[args.length];
	for (int a = 0; a < args.length; ++a)
	  sigs[a] = args[a].getClass().getName();
      }
    String attrib = null;
    if (mName.startsWith("get"))
      attrib = mName.substring(3);
    else if (mName.startsWith("is"))
      attrib = mName.substring(2);
    if (attrib != null)
      {
	Object val = conn.getAttribute(name, attrib);
	if (mxBean)
	  return Translator.toJava(val, method);
	else
	  return val;
      }
    else if (mName.startsWith("set"))
      {
	Object arg;
	if (mxBean)
	  arg = Translator.fromJava(args, method)[0];
	else
	  arg = args[0];
	conn.setAttribute(name, new Attribute(mName.substring(3), arg));
	return null;
      }
    if (mxBean)
      return Translator.toJava(conn.invoke(name, mName, 
					   Translator.fromJava(args,method),
					   sigs), method);
    else
      return conn.invoke(name, mName, args, sigs);
  }

  /**
   * Returns true if this is a proxy for an {@link MXBean}
   * and conversions must be applied to input parameters
   * and return types, according to the rules for such beans.
   *
   * @return true if this is a proxy for an {@link MXBean}.
   * @since 1.6
   */
  public boolean isMXBean()
  {
    return mxBean;
  }

  /**
   * <p>
   * Returns a proxy for the specified bean.  A proxy object is created
   * using <code>Proxy.newProxyInstance(iface.getClassLoader(),
   * new Class[] { iface }, handler)</code>.  The
   * {@link javax.management.NotificationEmitter} class is included as the
   * second element of the array if <code>broadcaster</code> is true.
   * <code>handler</code> refers to the invocation handler which forwards
   * calls to the connection, which is created by a call to
   * <code>new MBeanServerInvocationHandler(conn, name)</code>. 
   * </p>
   * <p>
   * <strong>Note</strong>: use of the proxy may result in
   * {@link java.io.IOException}s from the underlying
   * {@link MBeanServerConnection}.
   * As of 1.6, the use of {@link JMX#newMBeanProxy(MBeanServerConnection,
   * ObjectName,Class)} and {@link JMX#newMBeanProxy(MBeanServerConnection,
   * ObjectName,Class,boolean)} is preferred.
   * </p>
   *
   * @param conn the server connection to use to access the bean.
   * @param name the {@link javax.management.ObjectName} of the
   *             bean to provide a proxy for.
   * @param iface the interface for the bean being proxied.
   * @param broadcaster true if the proxy should implement
   *                    {@link NotificationEmitter}.
   * @return a proxy for the specified bean.
   * @see JMX#newMBeanProxy(MBeanServerConnection,ObjectName,Class)
   */
  // Suppress warnings as we know an instance of T will be returned.
  @SuppressWarnings("unchecked")
  public static <T> T newProxyInstance(MBeanServerConnection conn,
				       ObjectName name, Class<T> iface,
				       boolean broadcaster)
  {
    if (broadcaster)
      return (T) Proxy.newProxyInstance(iface.getClassLoader(),
					new Class[] { iface,
						      NotificationEmitter.class },
					new MBeanServerInvocationHandler(conn,name));
    else
      return (T) Proxy.newProxyInstance(iface.getClassLoader(),
					new Class[] { iface },
					new MBeanServerInvocationHandler(conn,name));
  }

  /**
   * Returns true if the specified method is specified
   * by one of the proxy's interfaces.
   *
   * @param name the name of the method to search for.
   * @param proxyClass the class of the proxy.
   * @param args the arguments to the method.
   * @return true if one of the interfaces specifies the
   *         given method.
   */
  private boolean inInterface(String name, Class<?> proxyClass,
			      Class<?>... args)
  {
    for (Class<?> iface : proxyClass.getInterfaces())
      {
	try
	  {
	    iface.getMethod(name, args);
	    return true;
	  }
	catch (NoSuchMethodException e)
	  {
	    /* Ignored; this interface doesn't specify
	       the method. */
	  }
      }
    return false;
  }
  
}