java动态代理是一个挺有意思的东西，他有时候可以被使用的很灵活。像rpc的调用，调用方只是定义的一个接口，动态代理让他匹配上对应的不同接口；mybatis内部的实现，编码时，只是实现了mapper层的接口和sql的xml的配置，动态代理把他们连起来。记得之前在一家公司，他们使用thrift做rpc的解决方案，每个项目都得管理thrift的连接和关闭，代码考来考去，在spring下还得不断new对象。后来参照mybatis的实现方式，使用动态代理，做成spring注入的方式，方便很多，程序员只需要加些配置就好了。
先来一个动态代理的简单实例：
/**
* Created by sten on 7/12/16.
*/
public interface Person { void eat() ;
} /**
* Created by sten on 7/12/16.
*/
public class Chinese implements Person { @Override
public void eat() {
System.out.print("eat fish.");
}
} /**
* Created by sten on 7/12/16.
*/
public class InvocationTest implements InvocationHandler { private Person person ; public InvocationTest(Person person) {
this.person = person ;
} @Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
return method.invoke(person, args);
}
} /**
* Created by sten on 7/12/16.
*/
public class Main { public static void main(String[] args) { Chinese chinese = new Chinese() ; Person person = (Person) Proxy.newProxyInstance(Person.class.getClassLoader(),
new Class[]{Person.class},
new InvocationTest(chinese)); person.eat();
} }
这是一般动态代理的范式，Chinese代理Person的实现，接口person每个方法的调用，实际执行的方法是InvocationTest.invoke, 当然，还有动态代理还有其他实现方式。
这里实现简单实现下mybatis的动态代理：
假设解析完mapper和xml，知道每个mapper的方法对应的sql了，通过类名和方法名，就可以执行sql
/**
* Created by sten on 7/12/16.
*/
public class SqlMap { private Map<String, String> map = new HashedMap() ; public SqlMap() {
map.put("Class1.method1","select sql1") ;
map.put("Class1.method2","delete sql1") ;
map.put("Class1.method3","update sql1") ;
map.put("Class1.method4","insert sql1") ;
map.put("Class2.method1","select sql2") ;
map.put("Class2.method2","delete sql2") ;
map.put("Class2.method3","update sql2") ;
map.put("Class2.method4","insert sql2") ;
} public String getSql(String classNameMethodName) {
return map.get(classNameMethodName) ;
} }
假设定义的一个mapper
/**
* Created by sten on 7/12/16.
*/
public interface Class1 { String method1() ; String method2() ; String method3() ; String method4() ;
}
InvocationHandler的实现
/**
* Created by sten on 7/12/16.
*/
public class InvocationSql implements InvocationHandler { private Class interfaceObject ; private SqlMap sqlMap ; public InvocationSql(Class interfaceObject, SqlMap sqlMap) {
this.interfaceObject = interfaceObject ;
this.sqlMap = sqlMap ;
} @Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { String key = interfaceObject.getClass().getName() + "." + method.getName() ;
String value = sqlMap.getSql(key) ; return value ;
}
}
根据mapper接口生成对象
/**
* Created by sten on 7/12/16.
*/
public class TargetProxy<T> { public T getTarget(Class<T> interfaceObject, SqlMap sqlMap) { InvocationSql invocationSql = new InvocationSql(interfaceObject, sqlMap) ; return (T)newProxyInstance(interfaceObject.getClassLoader(),new Class[] {interfaceObject},
invocationSql) ;
} }
执行生成的对象
/**
* Created by sten on 7/12/16.
*/
public class Bitis { public static void main(String[] args) { TargetProxy targetProxy = new TargetProxy() ; Class1 class1 = (Class1) targetProxy.getTarget(Class1.class, new SqlMap()); class1.method1() ;
} }