Java代理示例：静态代理、jdk动态代理、cglib动态代理

Bertha 。 2022-02-23 01:54 365阅读 0赞

# 1 接口及其实现 #

public interface Greeting {
        
        void sayHello(String name);
    }
    ---------------------------------------------
    public class GreetingImpl implements Greeting {
        
        @Override
        public void sayHello(String name) {
        
            System.out.println( "Hello! " + name );
        }
    }

# 2 静态代理 #

public class GreetingProxy implements Greeting {
        
    
        private GreetingImpl greeting;
    
        public GreetingProxy(GreetingImpl greeting){
        
            this.greeting = greeting;
        }
    
        @Override
        public void sayHello(String name) {
        
            before();
            greeting.sayHello(name);
            after();
        }
    
        private void before(){
        
            System.out.println("Before");
        }
    
        private void after(){
        
            System.out.println("After");
        }
    }

# 3 JDK动态代理 #

import java.lang.reflect.InvocationHandler;
    import java.lang.reflect.Method;
    import java.lang.reflect.Proxy;
    
    // 1. 首先实现一个InvocationHandler，方法调用会被转发到该类的invoke()方法。
    public class JDKDynamicProxy implements InvocationHandler {
        
    
        // 目标对象
        private Object target;
    
        public JDKDynamicProxy(Object target){
        
            this.target = target;
        }
    
        // 2. 然后在需要使用Hello的时候，通过JDK动态代理获取Hello的代理对象。
        @SuppressWarnings("unchecked")
        public <T>T getProxy() {
        
            // 会返回一个实现了指定接口的代理对象，对该对象的所有方法调用都会转发给InvocationHandler.invoke()方法
            return (T) Proxy.newProxyInstance(
                    target.getClass().getClassLoader(),  // 指定代理对象的类加载器；
                    target.getClass().getInterfaces(),  // 代理对象需要实现的接口，可以同时指定多个接口
                    this // 自定义的InvocationHandler，即方法调用的实际处理者，代理对象的方法调用都会转发到这里
            );
        }
    
        @Override
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        
            before(); // 前置处理
            Object result = method.invoke(target,args);
            after(); // 后置处理
            return result;
        }
    
        private void before(){
        
            System.out.println("Before");
        }
    
        private void after(){
        
            System.out.println("After");
        }
    }

# 4 CGLIB动态代理 #

## 4.1 pom.xml ##

<dependency>
                <groupId>cglib</groupId>
                <artifactId>cglib</artifactId>
                <version>2.2.2</version>
            </dependency>

## 4.2 Java实现 ##

import net.sf.cglib.proxy.Enhancer;
    import net.sf.cglib.proxy.MethodInterceptor;
    import net.sf.cglib.proxy.MethodProxy;
    
    import java.lang.reflect.Method;
    
    public class CGLibDynamicProxy implements MethodInterceptor {
        
    
        private static CGLibDynamicProxy instance = new CGLibDynamicProxy();
    
        private CGLibDynamicProxy(){
        }
    
        public static CGLibDynamicProxy getInstance(){
        
            return instance;
        }
    
        @SuppressWarnings("unchecked")
        public <T>T getProxy(Class<T> cls) {
        
            return (T) Enhancer.create(cls,this);
        }
    
        @Override
        public Object intercept(Object target, Method method, Object[] args, MethodProxy proxy) throws Throwable {
        
            before();
            Object result = proxy.invokeSuper(target,args);
            after();
            return result;
        }
    
        private void before(){
        
            System.out.println("Before");
        }
    
        private void after(){
        
            System.out.println("After");
        }
    }

# 5 测试代码 #

public class MainProxy {
        
        public static void main(String[] args) {
        
            // staitcProxy();
            jdkDynamicProxy();
            // cglibDynamicProxy();
        }
    
        private static void staitcProxy(){
        
            Greeting greeting = new GreetingProxy(new GreetingImpl());
            greeting.sayHello("jtzen9");
        }
    
        private static void jdkDynamicProxy(){
        
            JDKDynamicProxy jdkDynamicProxy = new JDKDynamicProxy(new GreetingImpl());
            Greeting greeting = jdkDynamicProxy.getProxy();
            greeting.sayHello("jtzen9");
        }
    
        private static void cglibDynamicProxy(){
        
            Greeting greeting = CGLibDynamicProxy.getInstance().getProxy(GreetingImpl.class);
            greeting.sayHello("jtzen9");
        }
    }