【原创】学习CGLIB动态代理中遇到的问题

代码清单1 CGLIB动态代理

 package wulj.proxy.cglibProxy;

 import java.lang.reflect.Method;

 import net.sf.cglib.proxy.Enhancer;
 import net.sf.cglib.proxy.MethodInterceptor;
 import net.sf.cglib.proxy.MethodProxy;

 public class CglibProxyExample implements MethodInterceptor {

     /**
      * 代理逻辑方法
      * @param proxy 代理对象
      * @param method 方法
      * @param args 方法参数
      * @param methodProxy 方法代理
      * @return 代理逻辑返回
      * @throws Throwable 异常
      *
      */
     @Override
     public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
         System.out.println("调用真实对象前");
         //CGLIB反射调用真实对象方法
         Object result = methodProxy.invokeSuper(proxy, args);
         System.out.println("调用真实对象后");
         return result;
     }

     /**
      * 生成CGLIB代理对象
      * @param cls     Class类
      * @return  Class类的CGLIB代理对象
      */
     public Object getProxy(Class<?> cls){
         //CGLIB enhancer 增强类对象
         Enhancer enhancer = new Enhancer();
         //设置增强类型
         enhancer.setSuperclass(cls);
         //定义代理逻辑对象为当前对象，要求当前对象实现MethodInterceptor方法
         enhancer.setCallback(this);
         //生成并返回代理对象
         return enhancer.create();

     }

 }

代码清单2 真实对象

 package wulj.proxy;

 public class ReflectServiceImpl {
     private String name = "";
     public void sayHello(String name){
         System.out.println(name);
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }

 }

代码清单3 测试类

 package wulj.proxy.cglibProxy;

 import wulj.reflect.ReflectServiceImpl;

 public class TestCGLIbProxyMain {

     public static void main(String[] args) {
         CglibProxyExample cpe = new CglibProxyExample();
         ReflectServiceImpl obj = (ReflectServiceImpl) cpe.getProxy(ReflectServiceImpl.class);//获得代理对象
         obj.sayHello("hello，world!");//调用逻辑处理方法
     }
 }

原本只引入了cglib-3.2.5.jar,执行main方法时报错如下：

Exception in thread "main" java.lang.NoClassDefFoundError: org/objectweb/asm/Type
    at net.sf.cglib.core.TypeUtils.parseType(TypeUtils.java:184)
    at net.sf.cglib.core.KeyFactory.<clinit>(KeyFactory.java:72)
    at net.sf.cglib.proxy.Enhancer.<clinit>(Enhancer.java:72)
    at wulj.proxy.cglibProxy.CglibProxyExample.getProxy(CglibProxyExample.java:37)
    at wulj.proxy.cglibProxy.TestCGLIbProxyMain.main(TestCGLIbProxyMain.java:9)
Caused by: java.lang.ClassNotFoundException: org.objectweb.asm.Type
    at java.net.URLClassLoader.findClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    ... 5 more

报错显示有找不到的类，上网查了一下知道了很多java字节码操作和分析的第三方类库都引用了asm.jar文件，由于工程不是Maven管理的，无法解决依赖传递问题，所以要手动引入asm.jar文件。把asm.jar文件添加到项目路径里，运行，然后就正常了，此处参考：https://www.cnblogs.com/gl-developer/p/7115644.html

引入asm-3.3.1.jar后执行main方法是，又报下面的错：　

Exception in thread "main" java.lang.ExceptionInInitializerError
    at wulj.proxy.cglibProxy.CglibProxyExample.getProxy(CglibProxyExample.java:37)
    at wulj.proxy.cglibProxy.TestCGLIbProxyMain.main(TestCGLIbProxyMain.java:9)
Caused by: java.lang.IllegalStateException: Unable to load cache item
    at net.sf.cglib.core.internal.LoadingCache.createEntry(LoadingCache.java:79)
    at net.sf.cglib.core.internal.LoadingCache.get(LoadingCache.java:34)
    at net.sf.cglib.core.AbstractClassGenerator$ClassLoaderData.get(AbstractClassGenerator.java:116)
    at net.sf.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:291)
    at net.sf.cglib.core.KeyFactory$Generator.create(KeyFactory.java:221)
    at net.sf.cglib.core.KeyFactory.create(KeyFactory.java:174)
    at net.sf.cglib.core.KeyFactory.create(KeyFactory.java:153)
    at net.sf.cglib.proxy.Enhancer.<clinit>(Enhancer.java:73)
    ... 2 more
Caused by: java.lang.IncompatibleClassChangeError: class net.sf.cglib.core.DebuggingClassWriter has interface org.objectweb.asm.ClassVisitor as super class
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(Unknown Source)
    at java.security.SecureClassLoader.defineClass(Unknown Source)
    at java.net.URLClassLoader.defineClass(Unknown Source)
    at java.net.URLClassLoader.access$100(Unknown Source)
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at net.sf.cglib.core.DefaultGeneratorStrategy.getClassVisitor(DefaultGeneratorStrategy.java:30)
    at net.sf.cglib.core.DefaultGeneratorStrategy.generate(DefaultGeneratorStrategy.java:24)
    at net.sf.cglib.core.AbstractClassGenerator.generate(AbstractClassGenerator.java:329)
    at net.sf.cglib.core.AbstractClassGenerator$ClassLoaderData$3.apply(AbstractClassGenerator.java:93)
    at net.sf.cglib.core.AbstractClassGenerator$ClassLoaderData$3.apply(AbstractClassGenerator.java:91)
    at net.sf.cglib.core.internal.LoadingCache$2.call(LoadingCache.java:54)
    at java.util.concurrent.FutureTask.run(Unknown Source)
    at net.sf.cglib.core.internal.LoadingCache.createEntry(LoadingCache.java:61)
    ... 9 more

参考：http://blog.csdn.net/yuanlaishinizhu/article/details/12998847，找到解决方案，原因是：cglib版本为3.0以上，org.objectweb.asm版本为3.1.0时，版本冲突，报错java.lang.IncompatibleClassChangeError: class net.sf.cglib.core.DebuggingClassWriter has interface org.objectweb.asm.ClassVisitor as super class

使用cglib 2.2 可解决此问题,该版本中的DebuggingClassWriter的父类为ClassWriter

执行main方法：问题解决：

调用真实对象前
hello，world!
调用真实对象后