java InvocationHandler用法举例

1、被代理对象

public interface AccountChange {
     AccountChange deposit (double value);
     AccountChange withdraw (double value);
     double getBalance ();
}

　　

2、代理

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

public class ExampleInvocationHandler implements InvocationHandler {


    private double balance;

    @Override
    public Object invoke (Object proxy, Method method, Object[] args) throws Throwable {

        
        if ("deposit".equals(method.getName())) {
            Double value = (Double) args[0];
            System.out.println("deposit: " + value);
            balance = balance + value;
            return proxy;
        }
        if ("withdraw".equals(method.getName())) {
            Double value = (Double) args[0];
            System.out.println("withdraw: " + value);
            balance = balance - value;
            return proxy;
        }
        if ("getBalance".equals(method.getName())) {
           // System.out.println("getBalance: " + balance);
            return balance;
        }
        return null;
    }

}

　　

3、测试

import java.io.Serializable;
import java.lang.reflect.Proxy;

public class MyTest {
    public static void main(String[] args){
        MyTest myTest = new MyTest();
        myTest.proxyTest();
    }

    public void proxyTest(){
        AccountChange accountChange = (AccountChange) Proxy.newProxyInstance(this.getClass().getClassLoader(), new Class[] {AccountChange.class, Serializable.class},
                new ExampleInvocationHandler());


        AccountChange ac = accountChange.deposit(100);
        System.out.println("Balance: " + accountChange.getBalance());
        System.out.println("Balance: " + ac.getBalance());
        System.out.println("  " );
        accountChange.withdraw(40);
        System.out.println("Balance: " + accountChange.getBalance());
    }
}

　　

调用AccountChange对象（被代理）的任何一个方法，都会自动调用代理对象的invoke()方法，并且invoke()方法能获取到被代理对象正在被调用的方法和参数。