methodhandle

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JDK中的动态代理，通过实现InvocationHandler代理实现代理类的方法，

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public interface InvocationHandler {
    /**
     * Processes a method invocation on a proxy instance and returns
     * the result.  This method will be invoked on an invocation handler
     * when a method is invoked on a proxy instance that it is
     * associated with.
     *
     * @param   proxy the proxy instance that the method was invoked on
     *
     * @param   method the {@code Method} instance corresponding to
     * the interface method invoked on the proxy instance.  The declaring
     * class of the {@code Method} object will be the interface that
     * the method was declared in, which may be a superinterface of the
     * proxy interface that the proxy class inherits the method through.
     *
     * @param   args an array of objects containing the values of the
     * arguments passed in the method invocation on the proxy instance,
     * or {@code null} if interface method takes no arguments.
     * Arguments of primitive types are wrapped in instances of the
     * appropriate primitive wrapper class, such as
     * {@code java.lang.Integer} or {@code java.lang.Boolean}.
     *
     * @return  the value to return from the method invocation on the
     * proxy instance.  If the declared return type of the interface
     * method is a primitive type, then the value returned by
     * this method must be an instance of the corresponding primitive
     * wrapper class; otherwise, it must be a type assignable to the
     * declared return type.  If the value returned by this method is
     * {@code null} and the interface method's return type is
     * primitive, then a {@code NullPointerException} will be
     * thrown by the method invocation on the proxy instance.  If the
     * value returned by this method is otherwise not compatible with
     * the interface method's declared return type as described above,
     * a {@code ClassCastException} will be thrown by the method
     * invocation on the proxy instance.
     *
     * @throws  Throwable the exception to throw from the method
     * invocation on the proxy instance.  The exception's type must be
     * assignable either to any of the exception types declared in the
     * {@code throws} clause of the interface method or to the
     * unchecked exception types {@code java.lang.RuntimeException}
     * or {@code java.lang.Error}.  If a checked exception is
     * thrown by this method that is not assignable to any of the
     * exception types declared in the {@code throws} clause of
     * the interface method, then an
     * {@link UndeclaredThrowableException} containing the
     * exception that was thrown by this method will be thrown by the
     * method invocation on the proxy instance.
     *
     * @see     UndeclaredThrowableException
     */
    public Object invoke(Object proxy, Method method, Object[] args)
        throws Throwable;
}

InvocationHandler中的invoker方法是对代理类的所有method生效，如果要应对复杂的代理需求，
将会使这个方法过于庞大，所以可以通过自定义接口MethodHandler为每一个方法实现不同的代理逻辑。

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public interface MethodHandler {
    Object invoke(Object[] args) throws Throwable;
}

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public class HttpHelperHandler implements InvocationHandler {
    private Map<Method, MethodHandler> methodHandlerMap;
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        MethodHandler methodHandler = methodHandlerMap.get(method);
        if (methodHandler != null) {
            return methodHandler.invoke(args);
        } else {
            return method.invoke(proxy,args);
        }
    }
}

这种方式更加灵活