cglib用法
CGLib动态代理的介绍及用法(单回调、多回调、不处理、固定值、懒加载)
参照: https://blog.csdn.net/difffate/article/details/70552056
前面介绍了代理模式,讲了动态代理常见的实现方式,包含了JDK的动态代理和CGLib的动态代理。本文将介绍下CGLib动态代理及几种用法。CGLib(Code Generation Library)是一个高效的代码生成库,底层实现是使用asm来转换字节码生成类。在生成代理类的场景中,由于JDK动态代理必须要求源对象有实现接口,而实际场景中,并不是所有类都有实现接口,因此使用CGLib可以用在未实现接口的类上。
值得注意的几点是:
1)使用CGLib代理的类不能是final修饰的,因为代理类需要继承主题类;
2)final修饰的方法不会被切入;
3)如果主题类的构造函数不是默认空参数的,那么在使用Enhancer类create的时候,选择create(java.lang.Class[] argumentTypes, java.lang.Object[] arguments) 方法。
接下来认识实现动态代理最重要的一个接口 MethodInteceptor
- package net.sf.cglib.proxy;
- /**
- * General-purpose {@link Enhancer} callback which provides for "around advice".
- * @author Juozas Baliuka <a href="mailto:baliuka@mwm.lt">baliuka@mwm.lt</a>
- * @version $Id: MethodInterceptor.java,v 1.8 2004/06/24 21:15:20 herbyderby Exp $
- */
- public interface MethodInterceptor
- extends Callback
- {
- /**
- * All generated proxied methods call this method instead of the original method.
- * The original method may either be invoked by normal reflection using the Method object,
- * or by using the MethodProxy (faster).
- * @param obj "this", the enhanced object
- * @param method intercepted Method
- * @param args argument array; primitive types are wrapped
- * @param proxy used to invoke super (non-intercepted method); may be called
- * as many times as needed
- * @throws Throwable any exception may be thrown; if so, super method will not be invoked
- * @return any value compatible with the signature of the proxied method. Method returning void will ignore this value.
- * @see MethodProxy
- */
- public Object intercept(Object obj, java.lang.reflect.Method method, Object[] args,
- MethodProxy proxy) throws Throwable;
- }
MethodInterceptor,从名字上方法拦截器,就是对方法做切入的。intercept方式的4个参数分别对应增强对象、调用方法、方法参数以及调用父类方法的代理。使用MethodProxy速度会更快,所以后面将用
下面介绍几种用法,这里使用spring包中cglib,其实和引单独的cglib包是一样,只不过spring为了版本不冲突,将cglib包含在自己的包中。
先定义一个主题对象
- /**
- * Create by zxb on 2017/4/23
- */
- public class DBQuery {
- public DBQuery() {
- }
- public DBQuery(Integer i) {
- System.out.println("Here's in DBQuery Constructor");
- }
- public String getElement(String id) {
- return id + "_CGLib";
- }
- public List<String> getAllElements() {
- return Arrays.asList("Hello_CGLib1", "Hello_CGLib2");
- }
- public String methodForNoop() {
- return "Hello_Noop";
- }
- public String methodForFixedValue(String param) {
- return "Hello_" + param;
- }
- public final String sayHello() {
- return "Hello Everyone!";
- }
- }
(一)单回调
切入类:
- /**
- * Create by zxb on 2017/4/22
- */
- public class DBQueryProxy implements MethodInterceptor {
- public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
- System.out.println("Here in interceptor !");
- return methodProxy.invokeSuper(o, objects);
- }
- }
测试类:
- public class TestCGLibProxy {
- public static void main(String[] args) {
- DBQueryProxy dbQueryProxy = new DBQueryProxy();
- Enhancer enhancer = new Enhancer();
- enhancer.setSuperclass(DBQuery.class);
- enhancer.setCallback(dbQueryProxy);
- // DBQuery dbQuery = (DBQuery)enhancer.create(new Class[]{Integer.class}, new Object[]{1});
- DBQuery dbQuery = (DBQuery) enhancer.create();
- System.out.println(dbQuery.getElement("Hello"));
- System.out.println();
- System.out.println(dbQuery.getAllElements());
- System.out.println();
- System.out.println(dbQuery.sayHello());
- }
- }
执行结果:
(二)多回调
在前面的基础上,加个切入类,并通过CallbackFilter来决定是使用哪个切入类
- /**
- * Create by zxb on 2017/4/22
- */
- public class DBQueryProxy2 implements MethodInterceptor {
- public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
- System.out.println("Here in interceptor 2!");
- return methodProxy.invokeSuper(o, objects);
- }
- }
测试类:
- /**
- * Create by zxb on 2017/4/22
- */
- public class TestCGLibProxy {
- public static void main(String[] args) {
- DBQueryProxy dbQueryProxy = new DBQueryProxy();
- DBQueryProxy2 dbQueryProxy2 = new DBQueryProxy2();
- Enhancer enhancer = new Enhancer();
- enhancer.setSuperclass(DBQuery.class);
- enhancer.setCallbacks(new Callback[]{dbQueryProxy, dbQueryProxy2});
- enhancer.setCallbackFilter(new CallbackFilter() {
- public int accept(Method method) {
- if (method.getName().equals("getElement")) {
- return 0;
- } else {
- return 1;
- }
- }
- });
- DBQuery dbQuery = (DBQuery) enhancer.create();
- System.out.println("========Inteceptor By DBQueryProxy ========");
- System.out.println(dbQuery.getElement("Hello"));
- System.out.println();
- System.out.println("========Inteceptor By DBQueryProxy2 ========");
- System.out.println(dbQuery.getAllElements());
- }
- }
执行结果:
(三)不处理
利用枚举常量 Callback noopCb = NoOp.INSTANCE;
测试类:
- public class TestCGLibProxy {
- public static void main(String[] args) {
- DBQueryProxy dbQueryProxy = new DBQueryProxy();
- DBQueryProxy2 dbQueryProxy2 = new DBQueryProxy2();
- Callback noopCb = NoOp.INSTANCE;
- Enhancer enhancer = new Enhancer();
- enhancer.setSuperclass(DBQuery.class);
- enhancer.setCallbacks(new Callback[]{dbQueryProxy, dbQueryProxy2, noopCb});
- enhancer.setCallbackFilter(new CallbackFilter() {
- public int accept(Method method) {
- if (method.getName().equals("getElement")) {
- return 0;
- } else if (method.getName().equals("getAllElements")) {
- return 1;
- } else {
- return 2;
- }
- }
- });
- DBQuery dbQuery = (DBQuery) enhancer.create();
- System.out.println("========Inteceptor By DBQueryProxy ========");
- System.out.println(dbQuery.getElement("Hello"));
- System.out.println();
- System.out.println("========Inteceptor By DBQueryProxy2 ========");
- System.out.println(dbQuery.getAllElements());
- System.out.println();
- System.out.println("========Return Original Value========");
- System.out.println(dbQuery.methodForNoop());
- }
- }
执行结果:
(四)固定值
需要实现FixedValue接口,会忽略原来函数的返回值,使用固定值来替换。
- /**
- * 返回固定的值
- * Create by zxb on 2017/4/23
- */
- public class DBQueryProxyFixedValue implements FixedValue {
- public Object loadObject() throws Exception {
- System.out.println("Here in DBQueryProxyFixedValue ! ");
- return "Fixed Value";
- }
- }
测试类:
- public class TestCGLibProxy {
- public static void main(String[] args) {
- DBQueryProxy dbQueryProxy = new DBQueryProxy();
- DBQueryProxy2 dbQueryProxy2 = new DBQueryProxy2();
- Callback noopCb = NoOp.INSTANCE;
- Callback fixedValue = new DBQueryProxyFixedValue();
- Enhancer enhancer = new Enhancer();
- enhancer.setSuperclass(DBQuery.class);
- enhancer.setCallbacks(new Callback[]{dbQueryProxy, dbQueryProxy2, noopCb, fixedValue});
- enhancer.setCallbackFilter(new CallbackFilter() {
- public int accept(Method method) {
- if (method.getName().equals("getElement")) {
- return 0;
- } else if (method.getName().equals("getAllElements")) {
- return 1;
- } else if (method.getName().equals("methodForNoop")) {
- return 2;
- } else if (method.getName().equals("methodForFixedValue")) {
- return 3;
- } else {
- return 0;
- }
- }
- });
- DBQuery dbQuery = (DBQuery) enhancer.create();
- System.out.println("========Inteceptor By DBQueryProxy ========");
- System.out.println(dbQuery.getElement("Hello"));
- System.out.println();
- System.out.println("========Inteceptor By DBQueryProxy2 ========");
- System.out.println(dbQuery.getAllElements());
- System.out.println();
- System.out.println("========Return Original Value========");
- System.out.println(dbQuery.methodForNoop());
- System.out.println();
- System.out.println("========Return Fixed Value========");
- System.out.println(dbQuery.methodForFixedValue("myvalue"));
- }
- }
执行结果:
(五)懒加载
CGLib的懒加载,可以用在一些不需要立即加载完整对象实例的场景,比如说Hibernate中的查询对象,如果这个对象有关联其他对象,这个时候不会马上将关联对象一起查询出来关联,要等到调用到这个关联对象时才去做查询。利用CGLib的懒加载机制,可以很好的实现这个需求。需要了解2个接口,LazyLoader和Dispatcher。这两个接口的定义如下:
- public interface LazyLoader extends Callback {
- Object loadObject() throws Exception;
- }
- public interface Dispatcher extends Callback {
- Object loadObject() throws Exception;
- }
它们都继承了Callback接口,都有一个loadObject的方法,区别在于LazyLoader只有在第一次调用时,会执行loadObject获取对象,而Dispatcher会在每次调用时都触发loadObject方法,不理解?没关系,后面代码示例上可以看到明显的区别。假定有个学生类(Student),学术类包含2门课的课程表对象,分别是英语课程表(EnglishSchedule)和数学课程表(MathSchedule),它们都是课程表类的实例
- /**
- * 课程表
- * Create by zxb on 2017/4/23
- */
- @Data
- @NoArgsConstructor
- @AllArgsConstructor
- public class Schedule {
- private String courseName;
- private Date courseTime;
- }
EnglishSchedule属性的加载依赖于ScheduleLazyLoader
- /**
- * Create by zxb on 2017/4/23
- */
- public class ScheduleLazyLoader implements LazyLoader {
- public Object loadObject() throws Exception {
- System.out.println("before LazyLoader init...you can query from db...");
- Schedule schedule = new Schedule();
- schedule.setCourseName("English");
- Calendar calendar = Calendar.getInstance();
- calendar.set(2017,3,28);
- schedule.setCourseTime(calendar.getTime());
- System.out.println("after LazyLoader init...");
- return schedule;
- }
- }
MathSchedule属性的加载依赖于ScheduleDispatcher
- /**
- * Create by zxb on 2017/4/23
- */
- public class ScheduleDispatcher implements Dispatcher {
- public Object loadObject() throws Exception {
- System.out.println("before Dispatcher init...you can query from db...");
- Schedule schedule = new Schedule();
- schedule.setCourseName("Math");
- Calendar calendar = Calendar.getInstance();
- calendar.set(2017,4,1);
- schedule.setCourseTime(calendar.getTime());
- System.out.println("after Dispatcher init...");
- return schedule;
- }
- }
学生类:
定义时,需要对EnglishSchedule和MathSchedule先初始为动态代理的对象
- package org.zheng.proxy.cglib.lazyload;
- import lombok.Data;
- import org.springframework.cglib.proxy.Enhancer;
- /**
- * Create by zxb on 2017/4/23
- */
- @Data
- public class Student {
- private int id;
- private String name;
- /**
- * 英语课时间表
- */
- private Schedule EnglishSchedule;
- /**
- * 数学课时间表
- */
- private Schedule MathSchedule;
- public Student(int id, String name) {
- this.id = id;
- this.name = name;
- this.EnglishSchedule = createEnglishSchedule();
- this.MathSchedule = createMathSchedule();
- }
- private Schedule createEnglishSchedule() {
- Enhancer enhancer = new Enhancer();
- enhancer.setSuperclass(Schedule.class);
- enhancer.setCallback(new ScheduleLazyLoader());
- return (Schedule) enhancer.create();
- }
- private Schedule createMathSchedule() {
- Enhancer enhancer = new Enhancer();
- enhancer.setSuperclass(Schedule.class);
- enhancer.setCallback(new ScheduleDispatcher());
- return (Schedule) enhancer.create();
- }
- }
测试类:
- /**
- * 延迟加载属性
- * Create by zxb on 2017/4/23
- */
- public class LazyLoadTest {
- public static void main(String[] args) {
- Student student = new Student(666, "XiaoMing");
- System.out.println("id=" + student.getId());
- System.out.println("name=" + student.getName());
- // LazyLoader 只有第一次,Dispatcher是每次都会进loadObject的方法
- System.out.println("========First Get EnglishSchedule ========");
- System.out.println(student.getEnglishSchedule());
- System.out.println();
- System.out.println("========First Get MathSchedule ========");
- System.out.println(student.getMathSchedule());
- System.out.println();
- System.out.println("========Second Get EnglishSchedule ========");
- System.out.println(student.getEnglishSchedule());
- System.out.println();
- System.out.println("========Second Get MathSchedule ========");
- System.out.println(student.getMathSchedule());
- }
- }
执行结果:
可以看到第二次取懒加载对象的时候,实现LoadLazy接口不会重新执行loadObject,而实现Dispatcher的会重新执行LoadObject方法:)
以上,就是使用CGLib的几种常见用法。
项目完整代码:
https://github.com/difffate/JavaProject
最新文章
- Metaio在Unity3D中报错 Start: failed to load tracking configuration: TrackingConfigGenerated.xml 解决方法
- setValue和setObject的区别
- LINQ To DataSet 示例
- SQL查询语句执行的顺序是-----------------
- ThroughRain学期冲刺总结
- 算法最坏,平均和最佳情况(Worst, Average and Best Cases)-------geeksforgeeks 翻译
- AngularJS——grunt神器的安装
- LOL(英雄联盟)系统鼠标速度锁定工具
- BUG: scheduling while atomic: events/0/4/总结
- STM32 PWM波
- easyui&;8Jquery ztree树插件
- 深入C#.NET数据类型
- C#枚举的简单使用
- jquery获取url的方式
- WPF Image控件的绑定
- Eclipse设置默认的换行长度
- codeforces#525 Div2---ABC
- 学习笔记(5)——实验室集群LVS监控Web界面配置
- 读高性能JavaScript编程 第一章
- select默认下拉箭头改变、option样式清除
热门文章
- java8快速实现分组、过滤、list转map
- String.valueOf()和toString()的区别
- 代码反向生成数据库注释更新sql
- jvm(1):内存结构
- HTML的页面结构
- AcWing 790. 数的三次方根
- [linux] Ubuntu18.04 安装mysql密码不对
- OPGL+VS2017+GLFW+GLEW配置详细步骤
- 【C语言】一堆数组中存放了10个小于100的整数,请编程对所有数据按照从小到大的顺序进行排序,若个位数相等,则按照十位从小到大的顺序排序,输出排序后的结果
- ONESHELL