动态代理

1.proxy代理模式

      代理模式为其他对象提供一种代理，并以控制对这个对象的访问。通过代理可以实现对象的延迟加载和对象的访问控制，在具体调用的前后执行特殊处理或者是完全改变具体实现。代理模式能够协调调用者和被调用者，在一定程度上降低了系统的耦合度。

 

      代理模式结构图如下：

 

2.java动态代理

      jdk通过InvocationHandler和Proxy来实现对接口的动态代理，cglib用于对具体类实现动态代理，其内部是通过创建具体类的子类来实现动态代理的，所以不支持对final类及final方法动态代理，对final类动态代理会报:java.lang.IllegalArgumentException: Cannot subclass final class class javaProxy.HelloWordImpl;对非final类的动态代理，其final方法则不会执行动态代理，直接调用具体类的final方法，其他方法则执行动态代理。

    具体代码示例：

//接口定义

 public interface HelloWord {

public void sayHelloWord();

public void sayHelloWord(String name);

public String getHelloWord();

public String getHelloWord(String name);

}

 

//接口具体实现

public class HelloWordImpl implements HelloWord {

 

@Override

public void sayHelloWord() {

System.out.println("HelloWord");

}

 

@Override

public void sayHelloWord(String name) {

System.out.println("HelloWord " + name);

}

 

@Override

public final String getHelloWord() {

return "HelloWord";

}

 

@Override

public String getHelloWord(String name) {

return "HelloWord " + name;

}

}

 

//jdk动态代理

public class HelloWordInvocationHandler implements InvocationHandler {

Object targe;

 

public HelloWordInvocationHandler(Object targe){

this.targe = targe;

}

 

@Override

public Object invoke(Object proxy, Method method, Object[] args)

throws Throwable {

doBefore(method, args);

Object result = method.invoke(targe, args);

doAfter(method, args, result);

return result;

}

 

private void doBefore(Method method, Object[] args){

StringBuilder sb = new StringBuilder("javaProxy doBefore: ");

sb.append(method.getName()).append('(');

if(args != null){

for(Object arg : args)

sb.append(arg).append(',');

}

if(sb.charAt(sb.length()-1) == ',')

sb.deleteCharAt(sb.length()-1);

sb.append(')');

System.out.println(sb.toString());

}

 

private void doAfter(Method method, Object[] args, Object result){

StringBuilder sb = new StringBuilder("javaProxy doAfter: ");

sb.append(method.getName()).append('(');

if(args != null){

for(Object arg : args)

sb.append(arg).append(',');

}

if(sb.charAt(sb.length()-1) == ',')

sb.deleteCharAt(sb.length()-1);

sb.append(')').append(" result:").append(result);

System.out.println(sb.toString());

}

}

 

//cglib动态代理

public class HelloWordCglibProxy implements MethodInterceptor{    

    public Object getProxyInstance(Class targetClass) {    

        Enhancer enhancer = new Enhancer();    

        enhancer.setSuperclass(targetClass);    

        enhancer.setCallback(this);  

        return enhancer.create(); 

    }    

      

    @Override  

    public Object intercept(Object target, Method method, Object[] args, MethodProxy proxy) throws Throwable {  

    doBefore(method, args);

        Object result = proxy.invokeSuper(target, args);  

        doAfter(method, args, result);

        return result;  

    } 

    

    private void doBefore(Method method, Object[] args){

StringBuilder sb = new StringBuilder("cglibProxy doBefore: ");

sb.append(method.getName()).append('(');

if(args != null){

for(Object arg : args)

sb.append(arg).append(',');

}

if(sb.charAt(sb.length()-1) == ',')

sb.deleteCharAt(sb.length()-1);

sb.append(')');

System.out.println(sb.toString());

}

 

private void doAfter(Method method, Object[] args, Object result){

StringBuilder sb = new StringBuilder("cglibProxy doAfter: ");

sb.append(method.getName()).append('(');

if(args != null){

for(Object arg : args)

sb.append(arg).append(',');

}

if(sb.charAt(sb.length()-1) == ',')

sb.deleteCharAt(sb.length()-1);

sb.append(')').append(" result:").append(result);

System.out.println(sb.toString());

}

}

 

//测试类

public class HelloWordTest {

public static void main(String... args) throws Exception{

System.out.println("--------------java Proxy--------------");

HelloWordInvocationHandler handler = new HelloWordInvocationHandler(new HelloWordImpl());

Class proxyClass = Proxy.getProxyClass(

HelloWord.class.getClassLoader(), new Class[] { HelloWord.class });

HelloWord helloWord1 = (HelloWord) proxyClass.

        getConstructor(new Class[] { InvocationHandler.class }).

        newInstance(new Object[] { handler });

helloWord1.sayHelloWord();

helloWord1.sayHelloWord("beautiful girl");

 

HelloWord helloWord2 = (HelloWord) Proxy.newProxyInstance(HelloWord.class.getClassLoader(),

                new Class[] { HelloWord.class },

                handler);

helloWord2.getHelloWord();

helloWord2.getHelloWord("beautiful girl");

 

 

System.out.println("");

System.out.println("");

System.out.println("");

 

System.out.println("--------------cglib Proxy--------------");

HelloWordCglibProxy cglibProxy = new HelloWordCglibProxy();

HelloWordImpl helloWordImpl = (HelloWordImpl)cglibProxy.getProxyInstance(HelloWordImpl.class);

helloWordImpl.sayHelloWord();

helloWordImpl.sayHelloWord("beautiful girl");

helloWordImpl.getHelloWord();

helloWordImpl.getHelloWord("beautiful girl");

}

}

 

输入如下：

--------------java Proxy--------------

javaProxy doBefore: sayHelloWord()

HelloWord

javaProxy doAfter: sayHelloWord() result:null

javaProxy doBefore: sayHelloWord(beautiful girl)

HelloWord beautiful girl

javaProxy doAfter: sayHelloWord(beautiful girl) result:null

javaProxy doBefore: getHelloWord()

javaProxy doAfter: getHelloWord() result:HelloWord

javaProxy doBefore: getHelloWord(beautiful girl)

javaProxy doAfter: getHelloWord(beautiful girl) result:HelloWord beautiful girl

 

 

 

--------------cglib Proxy--------------

cglibProxy doBefore: sayHelloWord()

HelloWord

cglibProxy doAfter: sayHelloWord() result:null

cglibProxy doBefore: sayHelloWord(beautiful girl)

HelloWord beautiful girl

cglibProxy doAfter: sayHelloWord(beautiful girl) result:null

cglibProxy doBefore: getHelloWord(beautiful girl)

cglibProxy doAfter: getHelloWord(beautiful girl) result:HelloWord beautiful girl