Java动态代理实现接口方法

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最近正在看Mybatis源码，重点研究了自定义Mapper接口里方法实现如何与xml配置文件进行绑定，最后了解到是通过java动态代理实现了接口方法。

主要使用了Proxy.newProxyInstance(loader, interfaces, invocationHandler方法来实现实例化，第一个参数为classLoader,第二个参数为要实例化的接口，第三个是InvocationHanler接口，需要实现此接口来实现方法的具体操作。例：

public void proxyTest() throws ClassNotFoundException,InstantiationException, IllegalAccessException {MethodProxy invocationHandler = new MethodProxy();Object newProxyInstance = Proxy.newProxyInstance(IUserService.class.getClassLoader(),new Class[] { IUserService.class }, invocationHandler);IUserService userService = (IUserService) newProxyInstance;User query = userService.query();System.out.println("query result->" + query.toString());}

执行结果：

具体代码实现如下（仅为了说明实现方式，请忽略结构层次和命名规范）：

public class MethodProxy implements InvocationHandler {@Overridepublic Object invoke(Object proxy, Method method, Object[] args)throws Throwable {// TODO Auto-generated method stubSystem.out.println("执行前");if (Object.class.equals(method.getDeclaringClass())) {try {return method.invoke(this, args);} catch (Throwable t) {t.printStackTrace();}} else {//System.out.println("调用方法名："+method.getName());return run(method, args);}System.out.println("执行后");return null;}UserDao dao = null;//具体实现通过方法名绑定。public Object run(Method method,Object[] args){if(dao == null){dao = new UserDao();}Object ret = null;String name = method.getName();if(name.equals("add")){dao.add(args);}else if(name.equals("delete")){dao.delete();}else if(name.equals("query")){ret = dao.query();}return ret;}class UserDao {public void add(Object[] args){System.out.println("dao add");for (Object object : args) {System.out.print(object+",");}}public void delete(){System.out.println("dao delete");}public User query(){return new User("123", "济南", 22, "备注");}}}

public interface IUserService {public void add(User user);public User query();public void delete(int id);}

public class User {private String id;private String username;private int age;private String remarks;public User(String id, String username, int age, String remarks) {super();this.id = id;this.username = username;this.age = age;this.remarks = remarks;} ……       @Override       public String toString() {           return "User [id=" + id + ", username=" + username + ", age=" + age                + ", remarks=" + remarks + "]";    }｝

本demo所展示的是具体接口的实现方法，为保证通用性，则可通过泛型实现接口实例化的通用方法。（参考mybatis-src）

例地：

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