動態代理(一)

代理模式是Java的一種設計模式,開發中可能會有一種場景,某個類的方法需要補充,但是由於不想在原有的類基礎上改動,該如何做呢,如下:

接口:
public interface ProxyUserService{
    String getUserMobile(String name);
}
public class ProxyUserServiceImpl implements ProxyUserService{
    @Override
    public String getUserMobile(String name) {
        return name;
    }

}
public class ProxyUserServiceStaticImpl implements ProxyUserService{
    private ProxyUserService proxyUserService;

    public ProxyUserServiceStaticImpl(ProxyUserService proxyUserService) {
        this.proxyUserService = proxyUserService;
    }

    @Override
    public String getUserMobile(String name) {
        //before
        String result = roxyUserService.getUserMobile(name);
        //after
        return result;
    }

}

上面可以看出,ProxyUserServiceStaticImpl實現了ProxyUserService接口,構造方法中用ProxyUserService子類初始化,在創建ProxyUserServiceStaticImpl對象時,構造方法中傳入ProxyUserServiceImpl實例即可,它的getUserMobile方法其實是對ProxyUserServiceImpl類的一種功能增強.Java中有木有其他方法來幫助我們實現這一功能呢?下面就來談談jdk動態代理、cglib動態代理.

jdk動態代理

public class ProxyUserServiceProxy implements InvocationHandler{
    /**
     * 被代理對象
     */
    private Object target;
    private static final Logger logger = LoggerFactory.getLogger(ProxyUserServiceProxy.class);

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

    /**
     *
     * @param proxy 代理對象
     * @param method 被調用的方法
     * @param args 方法的參數
     * @return
     * @throws Throwable
     */
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        //執行前預處理
        Object result = method.invoke(target,args);//調用被代理類中的方法
        //執行後處理
        return result;
    }

    public static void main(String[] args) {
        ProxyUserServiceImpl  proxyUserServiceImpl= new ProxyUserServiceImpl();
        ProxyUserServiceProxy proxyUserServiceProxy = new ProxyUserServiceProxy(proxyUserServiceImpl);
        ProxyUserService proxyUserService = (ProxyUserService)Proxy.newProxyInstance(proxyUserServiceImpl.getClass().getClassLoader(),proxyUserServiceImpl.getClass().getInterfaces(),proxyUserServiceProxy);
        logger.info(proxyUserService.getUserMobile("18883845677"));
    }
}

ProxyUserServiceProxy代理類實現了InvocationHandler接口,重寫invoke方法,在調用被代理類方法前後可以實現需要的邏輯.

cglib動態代理

public class ProxyUserServiceCgLib implements MethodInterceptor{
    private static final Logger logger = LoggerFactory.getLogger(ProxyUserServiceCgLib.class);
    //回調方法
    @Override
    public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
        //執行前預處理
        Object returnObj = methodProxy.invokeSuper(o,objects);
        //執行完處理
        return returnObj;
    }

    public static void main(String[] args) {
        ProxyUserServiceCgLib proxyUserServiceCgLib = new ProxyUserServiceCgLib();
        Enhancer enhancer = new Enhancer();
        //對目標對象創建子類對象
        enhancer.setSuperclass(ProxyUserServiceImpl.class);
        //設置回調
        enhancer.setCallback(proxyUserServiceCgLib);
        ProxyUserService proxyUserService = (ProxyUserService) enhancer.create();
       logger.info(proxyUserService.getUserMobile("18888488585"));

    }
}

ProxyUserServiceCgLib實現了MethodInterceptor接口,重寫intercept方法,在其中實現具體邏輯.

總結

1. jdk代理的目標對象必須實現接口
2. cglib代理的目標對象可以不實現接口
3. 如果目標對象沒有實現接口,使用cglib