Java中的代理模式

1. 静态代理

接口

public interface ICeo {void meeting(String name) throws InterruptedException;
}

目标类

public class Ceo implements ICeo{public void meeting(String name) throws InterruptedException {Thread.sleep(2000);System.out.println("和"+name+"谈成了34亿的项目");}
}

代理类

public class CeoProxy implements ICeo{private Ceo ceo;public CeoProxy(Ceo ceo) {this.ceo = ceo;}@Overridepublic void meeting(String name) throws InterruptedException {System.out.println("秘书登记来访: "+name);StopWatch stopWatch = new StopWatch();stopWatch.start();ceo.meeting(name);stopWatch.stop();double totalTimeMillis = stopWatch.getTotalTimeSeconds();System.out.println("耗时: "+totalTimeMillis);}
}

测试

public class CeoTest {public static void main(String[] args) throws InterruptedException {Ceo ceo = new Ceo();CeoProxy ceoProxy = new CeoProxy(ceo);ceoProxy.meeting("XXX");}
}

2. JDK动态代理

接口

public interface IDao {void select();
}

目标类

public class UserDao implements IDao{@Overridepublic void select() {try {Thread.sleep(2000);System.out.println("select ----");} catch (InterruptedException e) {throw new RuntimeException(e);}}
}

动态代理类

public class JdkProxy implements InvocationHandler {private Object target;public JdkProxy(Object target) {this.target = target;}@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {StopWatch stopWatch = new StopWatch();System.out.println("前置方法");stopWatch.start();Object obj = method.invoke(target, args);stopWatch.stop();System.out.println("后置方法");System.out.println("耗时: "+stopWatch.getTotalTimeSeconds());return obj;}
}

测试

public class DaoTest {public static void main(String[] args) {UserDao userDao = new UserDao();IDao dao = (IDao) Proxy.newProxyInstance(UserDao.class.getClassLoader(), UserDao.class.getInterfaces(), new JdkProxy(new UserDao()));dao.select();}
}

总结:

1. 动态生成代理类
2. 通过实现接口生成代理类(目标接口必须实现接口)
3. 代理类是实现接口的方式
4. 调用目标类使用反射调用
5. 目标类调用本类方法只会代理一次

3. CGLib动态代理

目标类

public class ZlmDao {public void select(){try {Thread.sleep(2000);System.out.println("select ---");} catch (InterruptedException e) {throw new RuntimeException(e);}}
}

代理类

public class CglibProxy implements MethodInterceptor {@Overridepublic Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {StopWatch stopWatch = new StopWatch();stopWatch.start();System.out.println("前置增强");Object result = proxy.invokeSuper(obj, args);stopWatch.stop();System.out.println("后置增强");System.out.println("耗时: "+stopWatch.getTotalTimeSeconds());return result;}
}

测试

public class ZlmDaoTest {public static void main(String[] args) {//实例化增强器Enhancer enhancer = new Enhancer();//设置需要代理的目标类enhancer.setSuperclass(ZlmDao.class);//设置拦截对象回调的实现类enhancer.setCallback(new CglibProxy());//生成代理类ZlmDao zlmDao = (ZlmDao) enhancer.create();zlmDao.select();}
}

总结

1. 通过ASM第三方框架动态代理
2. 无需接口(final修饰的类和方法除外)
3. 代理类通过继承目标类的方式实现代理
4. 调用目标类,使用子类调用父类的方式直接调用
5. invokeSuper目标类中调用本类方法会再次代理
6. incoke目标类中调用本来方法只会调用一次