代理模式

介绍

  提供一种代理来对原有对象的访问。

  应用实例：Spring AOP、日志、事务控制。

demo

1、定义一个接口和实现

public interface IService {
    /**
     * 获取名称为name 的年龄
     * @param name
     * @return
     */
    public Integer getAge(String name);
}

public class ServiceImpl implements IService {
    @Override
    public Integer getAge(String name) {
        if (Objects.equals("jack",name)){
            return 18;
        } else if (Objects.equals("ma",name)){
            return 24;
        }
        return 20;
    }
}

2、实现接口方法的拦截，打印参数和返回结果等信息

1. JDK 动态代理
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang3.time.StopWatch;

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

@Slf4j
public class MyInvocationHandler implements InvocationHandler {

    private IService iService;

    public MyInvocationHandler(IService iService) {
        this.iService = iService;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        if (Objects.equals("getAge",method.getName())){

            StopWatch stopWatch = new StopWatch();

            log.info("{}.{} start,args:{}",iService.getClass(),method.getName(),args);
            stopWatch.start();
            int age = (int)method.invoke(iService, args);
            stopWatch.stop();
            log.info("{}.{} end success,execTime:{},result:{}",iService.getClass(),method.getName(),stopWatch.getTime(),age);
        }
        return null;
    }
}

2. CGLIB代理
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang3.time.StopWatch;
import org.springframework.cglib.proxy.*;

import java.lang.reflect.Method;
import java.util.Objects;

@Slf4j
public class CglibInvocationHandler implements MethodInterceptor {

    private Object target;

    public CglibInvocationHandler(Object target) {
        this.target = target;
    }

    @Override
    public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
        if (Objects.equals("getAge", method.getName())) {

            StopWatch stopWatch = new StopWatch();

            log.info("{}.{} start,args:{}", target.getClass(), method.getName(), objects);
            stopWatch.start();
            int age = (int) method.invoke(target, objects);
            stopWatch.stop();
            log.info("{}.{} end success,execTime:{},result:{}", target.getClass(), method.getName(), stopWatch.getTime(), age);
        }
        return null;
    }

    public static Object getProxy(Object target) {
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(target.getClass());
        enhancer.setCallback(new CglibInvocationHandler(target));
        return enhancer.create();
    }
}

3、测试

import java.lang.reflect.Proxy;

public class ProxyTest {
    public static void main(String[] args) {
        //jdk 动态代理
        IService iService = new ServiceImpl();
        MyInvocationHandler myInvocationHandler = new MyInvocationHandler(iService);

        IService service = (IService) Proxy.newProxyInstance(ClassLoader.getSystemClassLoader(), new Class[]{IService.class}, myInvocationHandler);
        service.getAge("jack");

        //cglib 动态代理
       /* IService iService = new ServiceImpl();
        IService service = (IService) CglibInvocationHandler.getProxy(iService);
        service.getAge("jack");*/
    }
}

4、运行结果

image.png

最后

JDK动态代理的对象必须要实现接口，所以对于一些没有实现接口要被代理的对象，不适用JDK动态代理；cglib是通过继承被代理类，重写方法，织入通知通过动态字节码生成代理类，所以被final修饰的类是不能用cglib动态代理的。Spring的动态代理选择的方式也是根据这个条件来的。

// org.springframework.aop.framework.DefaultAopProxyFactory
@Override
    public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
        if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) {
            Class<?> targetClass = config.getTargetClass();
            if (targetClass == null) {
                throw new AopConfigException("TargetSource cannot determine target class: " +
                        "Either an interface or a target is required for proxy creation.");
            }
            if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
                return new JdkDynamicAopProxy(config);
            }
            return new ObjenesisCglibAopProxy(config);
        }
        else {
            return new JdkDynamicAopProxy(config);
        }
    }