java 之 动态代理学习示例

import java.lang.reflect.Method;public interface Advice {public void beforeMethod(Method method);public void afterMethod(Method method);}

import java.lang.reflect.Method;public class MyAdvice implements Advice {long beginTime = 0;public void beforeMethod(Method method) {System.out.println("start.........................");beginTime = System.currentTimeMillis();}public void afterMethod(Method method) {System.out.println("end...........................");long endTime = System.currentTimeMillis();System.out.println(method.getName()+" running time of "+(endTime-beginTime));}}

import java.lang.reflect.Constructor;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.lang.reflect.Proxy;import java.util.ArrayList;import java.util.Collection;import org.omg.CORBA.portable.InvokeHandler;public class ProxyTest {/** * 创建动态代理类 * 查看其方法列表信息 * class Proxy${ * InvocationHandler handler; * add(Object object) { * return handler.invoke(Object proxy,Method method, Object[] args); * } * } * hashCode,equals,toString 委托给了handler,invoke调用，return null * @param args * @throws Exception  */public static void main(String[] args) throws Exception {//拿到代理类字节码Class clazzProxy1 = Proxy.getProxyClass(Collection.class.getClassLoader(), Collection.class);//拿到构造方法Constructor constructor = clazzProxy1.getConstructor(InvocationHandler.class);class MyInvocationHandler implements InvocationHandler {@Overridepublic Object invoke(Object proxy, Method method, Object[] args)throws Throwable {return null;}}//实例化代理对象/*Collection proxy1 = (Collection) constructor.newInstance(new MyInvocationHandler());//invocationHandler Proxy类里实现的toString() invoke--->return null;//此处结果：null. proxy1!=nullSystem.out.println(proxy1);proxy1.clear();*///此处报错，因为invoke放回的是null,相当于void,而size方法是有返回值的// java.lang.NullPointerException//proxy1.size();/*Collection proxy2 = (Collection) constructor.newInstance(new InvocationHandler() {@Overridepublic Object invoke(Object proxy, Method method, Object[] args)throws Throwable {// TODO Auto-generated method stubreturn null;}});*//*Collection proxy3 = (Collection) Proxy.newProxyInstance(Collection.class.getClassLoader(), new Class[]{Collection.class},new InvocationHandler() {ArrayList<String> arrayList = new ArrayList<String>();@Overridepublic Object invoke(Object proxy, Method method, Object[] args)throws Throwable {long beginTime = System.currentTimeMillis();Object retVal = method.invoke(arrayList, args);long endTime = System.currentTimeMillis();System.out.println(method.getName()+" is running of  "+(endTime-beginTime));return retVal;}});proxy3.add("aaa");proxy3.add("bbb");proxy3.add("ccc");System.out.println(proxy3.size());*/final ArrayList target = new  ArrayList();Collection proxy4 = (Collection) getProxy(target, new MyAdvice());proxy4.add("aaa");System.out.println(proxy4.size());System.out.println(proxy4.getClass().getName());}public static void getMethodList() {//代理类字节码Class clazzProxy1 = Proxy.getProxyClass(Collection.class.getClassLoader(), Collection.class);System.out.println(clazzProxy1);System.out.println("------------------------构造方法列表-----------------------------");//代理类构造方法Constructor[] constructors = clazzProxy1.getConstructors();for(Constructor constructor:constructors) {String name = constructor.getName();StringBuilder sBuilder = new StringBuilder(name);sBuilder.append('(');Class[] clazzParams = constructor.getParameterTypes();for(Class clazzParam:clazzParams) {sBuilder.append(clazzParam.getName()).append(",");}if(clazzParams!=null&&clazzParams.length!=0) {sBuilder.deleteCharAt(sBuilder.length()-1);}sBuilder.append(')');//打印各个构造方法System.out.println(sBuilder.toString());}System.out.println("------------------------方法列表-----------------------------");//代理类构造方法Method[] methods = clazzProxy1.getMethods();for(Method method:methods) {String name = method.getName();StringBuilder sBuilder = new StringBuilder(name);sBuilder.append('(');Class[] clazzParams = method.getParameterTypes();for(Class clazzParam:clazzParams) {sBuilder.append(clazzParam.getName()).append(",");}if(clazzParams!=null&&clazzParams.length!=0) {sBuilder.deleteCharAt(sBuilder.length()-1);}sBuilder.append(')');//打印各个构造方法System.out.println(sBuilder.toString());}}public static Object getProxy(final Object target, final Advice advice) {Object proxy = Proxy.newProxyInstance(target.getClass().getClassLoader(), target.getClass().getInterfaces(),new InvocationHandler() {@Overridepublic Object invoke(Object proxy, Method method, Object[] args)throws Throwable {advice.beforeMethod(method);Object retVal = method.invoke(target, args);advice.afterMethod(method);return retVal;}});return proxy;}}

advice 把执行逻辑封装到一个类里边，AOP的做法。