Java:代理模式
静态代理
Java代理模式是很有用的模式,之前阿里的面试官问我AOP是怎么实现的,说了半天没说清楚,后来才发现原来叫代理模式...代理模式的核心思想是,在方法外面再包装一层,这样执行的时候,当然可以在实际执行的方法前面和后面加别的函数了...
首先要定义一个接口:
interface Handler{
public void handle();
}
然后这个接口有个实现,就略了;关键是还要加一个代理实现:
class Proxy implements Handler{
HandlerImpl impl = new HandlerImpl();
@Override
public void handle(){
//before
this.impl.handle();
//after
}
}
这样实际在使用的过程中,用这个代理而不是直接的实现,就可以在handle处理前后做一些文章了。
动态代理
JDK提供了Proxy接口可以用来实现动态代理,以下是一个例子,先定义接口和实现:
public interface Handler {
public void handle(String param);
}
public class DefaultHandler implements Handler{
@Override
public void handle(String param) {
System.out.println("Handling=>" + param);
}
}
然后定义代理类:
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
public class DynamicHandlerProxy implements InvocationHandler{
private Object target;
public Object bind(Object target){
this.target = target;
return Proxy.newProxyInstance(target.getClass().getClassLoader(), target.getClass().getInterfaces(), this);
}
@Override
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
System.out.println(proxy.getClass());
Object result = null;
this.before();
result = method.invoke(target, args);
this.after();
return result;
}
public void before(){
System.out.println("----before----");
}
public void after(){
System.out.println("----after----");
}
}
...
DynamicHandlerProxy proxy1 = new DynamicHandlerProxy();
Handler handler = (Handler) proxy1.bind(new DefaultHandler());
handler.handle("My name is Han Meimei!");
Cglib动态代理
JDK提供的代理只能针对于接口,cglib可支持类。定义一个普通类:
public class CglibHandler {
public void handle(String args){
System.out.println("This is from a class:" + args);
}
public void another(){
System.out.println("another!");
}
}
下面实现代理:
public class CglibHandlerProxy implements MethodInterceptor{
private Object target;
@Override
public Object intercept(Object proxy, Method method, Object[] args, MethodProxy arg3) throws Throwable {
Object result = null;
this.before();
result = method.invoke(target, args);
this.after();
return result;
}
public Object getInstance(Object target){
this.target = target;
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(target.getClass());
enhancer.setCallback(this);
return enhancer.create();
}
public void before(){
System.out.println("----before----");
}
public void after(){
System.out.println("----after----");
}
}
...
CglibHandlerProxy proxy2 = new CglibHandlerProxy();
CglibHandler handler1 = (CglibHandler)proxy2.getInstance(new CglibHandler());
handler1.handle("Cglib proxy");
handler1.another();