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package com.youthlin.rpc.core;

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

/**
 * guava: com.google.common.reflect.AbstractInvocationHandler
 * 创建: youthlin.chen
 * 时间: 2017-11-28 10:00
 */
public abstract class AbstractInvocationHandler implements InvocationHandler {
    private static final Object[] NO_ARGS = {};

    /**
     * {@inheritDoc}
     * 
     * 

     * {@code proxy.hashCode()} delegates to {@link AbstractInvocationHandler#hashCode}
     * 
{@code proxy.toString()} delegates to {@link AbstractInvocationHandler#toString}
     * 
{@code proxy.equals(argument)} returns true if: 
     * {@code proxy} and {@code argument} are of the same type
     * 
and {@link AbstractInvocationHandler#equals} returns true for the {@link
     * InvocationHandler} of {@code argument}
     * 
     * 
other method calls are dispatched to {@link #handleInvocation}.
     * 
     */
    @Override
    public final Object invoke(Object proxy, Method method, Object[] args)
            throws Throwable {
        if (args == null) {
            args = NO_ARGS;
        }
        if (args.length == 0 && method.getName().equals("hashCode")) {
            return hashCode();
        }
        if (args.length == 1
                && method.getName().equals("equals")
                && method.getParameterTypes()[0] == Object.class) {
            Object arg = args[0];
            return proxy.getClass().isInstance(arg) && equals(Proxy.getInvocationHandler(arg));
        }
        if (args.length == 0 && method.getName().equals("toString")) {
            return toString();
        }
        return handleInvocation(proxy, method, args);
    }

    /**
     * {@link #invoke} delegates to this method upon any method invocation on the proxy instance,
     * except {@link Object#equals}, {@link Object#hashCode} and {@link Object#toString}. The result
     * will be returned as the proxied method's return value.
     * 
     * 
Unlike {@link #invoke}, {@code args} will never be null. When the method has no parameter,
     * an empty array is passed in.
     */
    protected abstract Object handleInvocation(Object proxy, Method method, Object[] args)
            throws Throwable;

    /**
     * By default delegates to {@link Object#equals} so instances are only equal if they are
     * identical. {@code proxy.equals(argument)} returns true if: 

     * {@code proxy} and {@code argument} are of the same type
     * 
and this method returns true for the {@link InvocationHandler} of {@code argument}
     * 
     * Subclasses can override this method to provide custom equality.
     */
    @Override
    public boolean equals(Object obj) {
        return super.equals(obj);
    }

    /**
     * By default delegates to {@link Object#hashCode}. The dynamic proxies' {@code hashCode()} will
     * delegate to this method. Subclasses can override this method to provide custom equality.
     */
    @Override
    public int hashCode() {
        return super.hashCode();
    }

    /**
     * By default delegates to {@link Object#toString}. The dynamic proxies' {@code toString()} will
     * delegate to this method. Subclasses can override this method to provide custom string
     * representation for the proxies.
     */
    @Override
    public String toString() {
        return super.toString();
    }
}