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MyBatis之Mapper与动态代理简介说明

下文笔者讲述mybatis的动态代理简介说明，如下所示

动态代理

代理是一种设计模式
一个类A，设计一个拥有同样接口的代理类P
负责为A进行统一的预处理、过滤、事后处理等
例：

interface Base {void work1();void work2();
}
class A implements Base {public void work1() { System.out.println("work1"); }public void work2() { System.out.println("work2"); }
}class P extends A {public void work1() {long start = new Date().getTime();try {super.work1();} finally {long end = new Date().getTime();System.out.println(end-start);}}public void work2() {.....}
}

当我们需为某一个方法扩展功能时，我们只需编写一个代理类，即可扩展其功能

public class MyProxy 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("begin");try {return method.invoke(target, args);  } finally {System.out.println("end");}}  public static void main(String[] args) {  MyProxy proxy = new MyProxy();  Base x = (Base) proxy.bind(new A());  x.work1();  }  
}  

Mapper与动态代理

 
public class MapperProxy implements InvocationHandler {// 生成某个接口的mapperpublic static  T newInstance(Class clazz) {MapperProxy proxy = new MapperProxy<>();// 动态代理return (T) Proxy.newProxyInstance(clazz.getClassLoader(), new Class[] { clazz }, proxy);}// 调用mapper方法时实际执行的内容@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {System.out.println("invoke " + method.getName());return null;}
}拥有一个newInstance方法
来生成一个指定的mapper
实现了invoke方法
指定在调用mapper方法时执行的事情public static void main(String args[]) throws Exception {ArticleMapper mapper = MapperProxy.newInstance(ArticleMapper.class);mapper.findById(888);
}