Java中的一些代理技术

使用cglib,asm 对接口进行拦截,这里需要调用Invoke方法

        final IUserService userService=new UserService();

        Enhancer enhancer=new Enhancer();
        enhancer.setSuperclass(IUserService.class);
        enhancer.setCallback(new MethodInterceptor() {

            @Override
            public Object intercept(Object arg0, Method arg1, Object[] arg2,
                    MethodProxy arg3) throws Throwable {
                System.out.println(arg1.getName());

                return arg3.invoke(userService, arg2);
            }
        });
        IUserService proxy= (IUserService) enhancer.create();
        System.out.println(proxy.getNameById(3));

        final IUserService userService=new UserService();

        Enhancer enhancer=new Enhancer();
        enhancer.setSuperclass(UserService.class);
        enhancer.setCallback(new MethodInterceptor() {

            @Override
            public Object intercept(Object arg0, Method arg1, Object[] arg2,
                    MethodProxy arg3) throws Throwable {
                System.out.println(arg1.getName());

                return arg3.invoke(userService, arg2);
            }
        });
        IUserService proxy= (IUserService) enhancer.create();
        System.out.println(proxy.getNameById(3));

拦截一些自开发类(自己控制类的创建)，非其他框架生成的，就不需要代理中引用的Target了

        Enhancer enhancer=new Enhancer();
        enhancer.setSuperclass(UserService.class);
        enhancer.setCallback(new MethodInterceptor() {

            @Override
            public Object intercept(Object arg0, Method arg1, Object[] arg2,
                    MethodProxy arg3) throws Throwable {
                System.out.println(arg1.getName());

                return arg3.invokeSuper(arg0, arg2);
            }
        });
        IUserService proxy= (IUserService) enhancer.create();
        System.out.println(proxy.getNameById(3));

使用动态代理,只支持接口

        final IUserService userService=new UserService();
       IUserService proxy2=(IUserService) Proxy.newProxyInstance(this.getClass().getClassLoader(), new Class[]{ IUserService.class}, new InvocationHandler() {

            @Override
            public Object invoke(Object proxy, Method method, Object[] args)
                    throws Throwable {
                    System.out.println(method.getName());
                    return method.invoke(userService, args);
            }
        });

使用Enhancer与动态代理，拦截Request，注意Enhancer需要设置类加载器

package cn.haoda.web.filter;

import java.io.IOException;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import cn.haoda.web.filter.imp.UserService;

import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;

/**
 * Servlet Filter implementation class Filter1
 */
public class Filter1 implements Filter {

    /**
     * Default constructor.
     */
    public Filter1() {
        // TODO Auto-generated constructor stub
    }

    /**
     * @see Filter#destroy()
     */
    public void destroy() {
        // TODO Auto-generated method stub
    }

    /**
     * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
     */
    public void doFilter(final ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException {
        // TODO Auto-generated method stub
        // place your code here

        // pass the request along the filter chain

        final HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) resp;

        Enhancer enhancer=new Enhancer();
        enhancer.setSuperclass(HttpServletRequest.class);
        enhancer.setClassLoader(this.getClass().getClassLoader()); //需要指定这句不然会报错
        enhancer.setCallback(new MethodInterceptor() {

            @Override
            public Object intercept(Object arg0, Method arg1, Object[] arg2,
                    MethodProxy arg3) throws Throwable {
                System.out.println("Enhancer->" +arg1.getName());

                return arg3.invoke(request, arg2);
            }
        });

        ServletRequest proxyReq=(ServletRequest) Proxy.newProxyInstance(this.getClass().getClassLoader(), request.getClass().getInterfaces(), new InvocationHandler() {

            @Override
            public Object invoke(Object proxy, Method method, Object[] args)
                    throws Throwable {
                System.out.println("动态代理->" +method.getName());
                return method.invoke(request, args);
            }
        });

        chain.doFilter((HttpServletRequest)enhancer.create(), response);
        //chain.doFilter(proxyReq, response);
    }

    /**
     * @see Filter#init(FilterConfig)
     */
    public void init(FilterConfig fConfig) throws ServletException {
        // TODO Auto-generated method stub
    }

}

参考：
http://llying.iteye.com/blog/220452
http://stackoverflow.com/questions/11574049/cglib-with-spring-throws-illegalaccesserror
关于类加载器:http://www.ibm.com/developerworks/cn/java/j-lo-classloader/