java实现动态代理的三种方法

绪论：以下三种java实现动态代理的的方式，分别为基于jdk的，基于cglib的和基于javassist的，其中需要注意的两点

一：基于jdk实现的动态代理需要实现父类，而其他两种不需要

二：其中基于cglib的需要额外的jar包依赖，pom的依赖如下

<!-- https://mvnrepository.com/artifact/cglib/cglib -->
<dependency>
    <groupId>cglib</groupId>
    <artifactId>cglib</artifactId>
    <version>2.2</version>
</dependency>

为了方便，测试类写在了一起，代码如下：

package info.lumanman.mybatis.entry.proxy;

public class People implements PeopleInterface{

	public String getInfo(int age){
		System.out.println("执行中--张三的年龄："+age);
		return "张三的年龄："+age;
	}
}

package info.lumanman.mybatis.entry.proxy;

public interface PeopleInterface {

	public String getInfo(int age);
}

package info.lumanman.mybatis.entry.proxy;

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

import org.junit.Test;

import javassist.util.proxy.MethodFilter;
import javassist.util.proxy.MethodHandler;
import javassist.util.proxy.ProxyFactory;
import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;

public class ProxyTest {

	@Test
	public void testJdkProxy() {
		 final People people=new People();
		PeopleInterface proxy=(PeopleInterface) Proxy.newProxyInstance(ProxyTest.class.getClassLoader(), 
				People.class.getInterfaces(), new InvocationHandler() {
			public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
				System.out.println("代理前");
				Object result=method.invoke(people, args);
				System.out.println("代理后");
				return result;
			}
		});
		
		String result=proxy.getInfo(18);
		System.out.println("执行结果："+result);
	}
	
	@Test
	public void testCglibProxy() {
		People people=new People();
		
		Enhancer enhancer=new Enhancer();
		enhancer.setSuperclass(people.getClass());
		enhancer.setCallback(new MethodInterceptor() {
			public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
				System.out.println("前置处理");
				Object result=proxy.invokeSuper(obj, args);
				System.out.println("后置处理");
				return result;
			}
		});
		People proxy=(People)enhancer.create();
		
		String result= proxy.getInfo(19);
		System.out.println("执行结果："+result);
	}
	
	@Test
	public void testJavassistProxy() throws Exception {
		ProxyFactory factory=new ProxyFactory();
		factory.setSuperclass(People.class);
		factory.setFilter(new MethodFilter() {//过滤器可以对方法进行过滤，不加也行
			
			public boolean isHandled(Method m) {
				//if(m.getName().equals("execute")){
					return true;
				//}
				//return false;
			}
		});
		
		factory.setHandler(new MethodHandler() {
			
			public Object invoke(Object self, Method thisMethod, Method proceed, Object[] args) throws Throwable {
				System.out.println("前置处理");
				Object result=proceed.invoke(self, args);
				System.out.println("后置处理");
				return result;
			}
		});
		
		Class<?> c=factory.createClass();
		People proxy=(People) c.newInstance();
		String result= proxy.getInfo(19);
		System.out.println("执行结果："+result);
	}

}

参考：《mybatis技术内幕》