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 * 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).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 *
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package java.rmi.server;

import java.io.InvalidObjectException;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.rmi.Remote;
import java.rmi.RemoteException;
import java.rmi.UnexpectedException;
import java.rmi.activation.Activatable;
import java.security.PrivilegedAction;
import java.util.Map;
import java.util.WeakHashMap;
import sun.rmi.server.Util;
import sun.rmi.server.WeakClassHashMap;


An implementation of the InvocationHandler interface for
use with Java Remote Method Invocation (Java RMI).  This invocation
handler can be used in conjunction with a dynamic proxy instance as a
replacement for a pregenerated stub class.

Applications are not expected to use this class directly. A remote object exported to use a dynamic proxy with UnicastRemoteObject or Activatable has an instance of this class as that proxy's invocation handler. 
Author: Ann Wollrath
Since:  1.5
/**
 * An implementation of the <code>InvocationHandler</code> interface for
 * use with Java Remote Method Invocation (Java RMI).  This invocation
 * handler can be used in conjunction with a dynamic proxy instance as a
 * replacement for a pregenerated stub class.
 *
 * <p>Applications are not expected to use this class directly.  A remote
 * object exported to use a dynamic proxy with {@link UnicastRemoteObject}
 * or {@link Activatable} has an instance of this class as that proxy's
 * invocation handler.
 *
 * @author  Ann Wollrath
 * @since   1.5
 **/
public class RemoteObjectInvocationHandler
    extends RemoteObject
    implements InvocationHandler
{
    private static final long serialVersionUID = 2L;

    // set to true if invocation handler allows finalize method (legacy behavior)
    private static final boolean allowFinalizeInvocation;

    static {
        String propName = "sun.rmi.server.invocationhandler.allowFinalizeInvocation";
        String allowProp = java.security.AccessController.doPrivileged(
            new PrivilegedAction<String>() {
                @Override
                public String run() {
                    return System.getProperty(propName);
                }
            });
        if ("".equals(allowProp)) {
            allowFinalizeInvocation = true;
        } else {
            allowFinalizeInvocation = Boolean.parseBoolean(allowProp);
        }
    }

    
A weak hash map, mapping classes to weak hash maps that map
method objects to method hashes.

/**
     * A weak hash map, mapping classes to weak hash maps that map
     * method objects to method hashes.
     **/
    private static final MethodToHash_Maps methodToHash_Maps =
        new MethodToHash_Maps();

    
Creates a new RemoteObjectInvocationHandler constructed
with the specified RemoteRef.

Params:
  • ref – the remote ref
Throws:
/**
     * Creates a new <code>RemoteObjectInvocationHandler</code> constructed
     * with the specified <code>RemoteRef</code>.
     *
     * @param ref the remote ref
     *
     * @throws NullPointerException if <code>ref</code> is <code>null</code>
     **/
    public RemoteObjectInvocationHandler(RemoteRef ref) {
        super(ref);
        if (ref == null) {
            throw new NullPointerException();
        }
    }

    
Processes a method invocation made on the encapsulating
proxy instance, proxy, and returns the result.

RemoteObjectInvocationHandler implements this method
as follows:

If method is one of the following methods, it
is processed as described below:

    

  • Object.hashCode: Returns the hash code value for the proxy. 
  • Object.equals: Returns true
if the argument (args[0]) is an instance of a dynamic
proxy class and this invocation handler is equal to the invocation
handler of that argument, and returns false otherwise.

  • Object.toString: Returns a string representation of the proxy. 


Otherwise, a remote call is made as follows:

    

  • If proxy is not an instance of the interface Remote, then an IllegalArgumentException is thrown. 
  • Otherwise, the invoke method is invoked on this invocation handler's RemoteRef, passing
proxy, method, args, and the
method hash (defined in section 8.3 of the "Java Remote Method
Invocation (RMI) Specification") for method, and the
result is returned.

  • If an exception is thrown by RemoteRef.invoke and
that exception is a checked exception that is not assignable to any
exception in the throws clause of the method
implemented by the proxy's class, then that exception is wrapped in an UnexpectedException and the wrapped exception is thrown. Otherwise, the exception thrown by invoke is thrown by this method.



The semantics of this method are unspecified if the
arguments could not have been produced by an instance of some
valid dynamic proxy class containing this invocation handler.

Params:
  • proxy – the proxy instance that the method was invoked on
  • method – the Method instance corresponding to the
interface method invoked on the proxy instance
  • args – an array of objects containing the values of the
arguments passed in the method invocation on the proxy instance, or
null if the method takes no arguments
Throws:
  • Throwable – the exception to throw from the method invocation
on the proxy instance
Returns:the value to return from the method invocation on the proxy
instance
/**
     * Processes a method invocation made on the encapsulating
     * proxy instance, <code>proxy</code>, and returns the result.
     *
     * <p><code>RemoteObjectInvocationHandler</code> implements this method
     * as follows:
     *
     * <p>If <code>method</code> is one of the following methods, it
     * is processed as described below:
     *
     * <ul>
     *
     * <li>{@link Object#hashCode Object.hashCode}: Returns the hash
     * code value for the proxy.
     *
     * <li>{@link Object#equals Object.equals}: Returns <code>true</code>
     * if the argument (<code>args[0]</code>) is an instance of a dynamic
     * proxy class and this invocation handler is equal to the invocation
     * handler of that argument, and returns <code>false</code> otherwise.
     *
     * <li>{@link Object#toString Object.toString}: Returns a string
     * representation of the proxy.
     * </ul>
     *
     * <p>Otherwise, a remote call is made as follows:
     *
     * <ul>
     * <li>If <code>proxy</code> is not an instance of the interface
     * {@link Remote}, then an {@link IllegalArgumentException} is thrown.
     *
     * <li>Otherwise, the {@link RemoteRef#invoke invoke} method is invoked
     * on this invocation handler's <code>RemoteRef</code>, passing
     * <code>proxy</code>, <code>method</code>, <code>args</code>, and the
     * method hash (defined in section 8.3 of the "Java Remote Method
     * Invocation (RMI) Specification") for <code>method</code>, and the
     * result is returned.
     *
     * <li>If an exception is thrown by <code>RemoteRef.invoke</code> and
     * that exception is a checked exception that is not assignable to any
     * exception in the <code>throws</code> clause of the method
     * implemented by the <code>proxy</code>'s class, then that exception
     * is wrapped in an {@link UnexpectedException} and the wrapped
     * exception is thrown.  Otherwise, the exception thrown by
     * <code>invoke</code> is thrown by this method.
     * </ul>
     *
     * <p>The semantics of this method are unspecified if the
     * arguments could not have been produced by an instance of some
     * valid dynamic proxy class containing this invocation handler.
     *
     * @param proxy the proxy instance that the method was invoked on
     * @param method the <code>Method</code> instance corresponding to the
     * interface method invoked on the proxy instance
     * @param args an array of objects containing the values of the
     * arguments passed in the method invocation on the proxy instance, or
     * <code>null</code> if the method takes no arguments
     * @return the value to return from the method invocation on the proxy
     * instance
     * @throws  Throwable the exception to throw from the method invocation
     * on the proxy instance
     **/
    public Object invoke(Object proxy, Method method, Object[] args)
        throws Throwable
    {
        if (! Proxy.isProxyClass(proxy.getClass())) {
            throw new IllegalArgumentException("not a proxy");
        }

        if (Proxy.getInvocationHandler(proxy) != this) {
            throw new IllegalArgumentException("handler mismatch");
        }

        if (method.getDeclaringClass() == Object.class) {
            return invokeObjectMethod(proxy, method, args);
        } else if ("finalize".equals(method.getName()) && method.getParameterCount() == 0 &&
            !allowFinalizeInvocation) {
            return null; // ignore
        } else {
            return invokeRemoteMethod(proxy, method, args);
        }
    }

    
Handles java.lang.Object methods.

/**
     * Handles java.lang.Object methods.
     **/
    private Object invokeObjectMethod(Object proxy,
                                      Method method,
                                      Object[] args)
    {
        String name = method.getName();

        if (name.equals("hashCode")) {
            return hashCode();

        } else if (name.equals("equals")) {
            Object obj = args[0];
            InvocationHandler hdlr;
            return
                proxy == obj ||
                (obj != null &&
                 Proxy.isProxyClass(obj.getClass()) &&
                 (hdlr = Proxy.getInvocationHandler(obj)) instanceof RemoteObjectInvocationHandler &&
                 this.equals(hdlr));

        } else if (name.equals("toString")) {
            return proxyToString(proxy);

        } else {
            throw new IllegalArgumentException(
                "unexpected Object method: " + method);
        }
    }

    
Handles remote methods.

/**
     * Handles remote methods.
     **/
    private Object invokeRemoteMethod(Object proxy,
                                      Method method,
                                      Object[] args)
        throws Exception
    {
        try {
            if (!(proxy instanceof Remote)) {
                throw new IllegalArgumentException(
                    "proxy not Remote instance");
            }

            // Verify that the method is declared on an interface that extends Remote
            Class<?> decl = method.getDeclaringClass();
            if (!Remote.class.isAssignableFrom(decl)) {
                throw new RemoteException("Method is not Remote: " + decl + "::" + method);
            }

            return ref.invoke((Remote) proxy, method, args,
                              getMethodHash(method));
        } catch (Exception e) {
            if (!(e instanceof RuntimeException)) {
                Class<?> cl = proxy.getClass();
                try {
                    method = cl.getMethod(method.getName(),
                                          method.getParameterTypes());
                } catch (NoSuchMethodException nsme) {
                    throw (IllegalArgumentException)
                        new IllegalArgumentException().initCause(nsme);
                }
                Class<?> thrownType = e.getClass();
                for (Class<?> declaredType : method.getExceptionTypes()) {
                    if (declaredType.isAssignableFrom(thrownType)) {
                        throw e;
                    }
                }
                e = new UnexpectedException("unexpected exception", e);
            }
            throw e;
        }
    }

    
Returns a string representation for a proxy that uses this invocation
handler.

/**
     * Returns a string representation for a proxy that uses this invocation
     * handler.
     **/
    private String proxyToString(Object proxy) {
        Class<?>[] interfaces = proxy.getClass().getInterfaces();
        if (interfaces.length == 0) {
            return "Proxy[" + this + "]";
        }
        String iface = interfaces[0].getName();
        if (iface.equals("java.rmi.Remote") && interfaces.length > 1) {
            iface = interfaces[1].getName();
        }
        int dot = iface.lastIndexOf('.');
        if (dot >= 0) {
            iface = iface.substring(dot + 1);
        }
        return "Proxy[" + iface + "," + this + "]";
    }

    
Throws:
  • InvalidObjectException – unconditionally
/**
     * @throws InvalidObjectException unconditionally
     **/
    private void readObjectNoData() throws InvalidObjectException {
        throw new InvalidObjectException("no data in stream; class: " +
                                         this.getClass().getName());
    }

    
Returns the method hash for the specified method.  Subsequent calls
to "getMethodHash" passing the same method argument should be faster
since this method caches internally the result of the method to
method hash mapping.  The method hash is calculated using the
"computeMethodHash" method.

Params:
  • method – the remote method
Returns:the method hash for the specified method
/**
     * Returns the method hash for the specified method.  Subsequent calls
     * to "getMethodHash" passing the same method argument should be faster
     * since this method caches internally the result of the method to
     * method hash mapping.  The method hash is calculated using the
     * "computeMethodHash" method.
     *
     * @param method the remote method
     * @return the method hash for the specified method
     */
    private static long getMethodHash(Method method) {
        return methodToHash_Maps.get(method.getDeclaringClass()).get(method);
    }

    
A weak hash map, mapping classes to weak hash maps that map
method objects to method hashes.

/**
     * A weak hash map, mapping classes to weak hash maps that map
     * method objects to method hashes.
     **/
    private static class MethodToHash_Maps
        extends WeakClassHashMap<Map<Method,Long>>
    {
        MethodToHash_Maps() {}

        protected Map<Method,Long> computeValue(Class<?> remoteClass) {
            return new WeakHashMap<Method,Long>() {
                public synchronized Long get(Object key) {
                    Long hash = super.get(key);
                    if (hash == null) {
                        Method method = (Method) key;
                        hash = Util.computeMethodHash(method);
                        put(method, hash);
                    }
                    return hash;
                }
            };
        }
    }
}