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cglib入门

��羊 — Tue, 26 Oct 2010 06:27:00 GMT

代理��控制讉K��的类提供了一�U�可行的途径�Q�他为目标类引入一个中间层�Q�JDK1.3后也有动态代理，不过性能不是很好�Q?.6有所加强�?

CGLIB是一个强大的代码生成包，在ASM上徏立，在一些开源工具中�l�常可以看到他的�w�媄�Q�比如hibernate,spring�?/div>

CGLIB底层通过字节码处理框架ASM来将字节码生成新的类�Q�在spring AOP中不强制使用CGLIB�Q�默认是JDK动态代理�?/div>

CGLIB 包情况：

net.sf.cglib.core:底层字节码处理类�Q�大部分与ASM有关�?/div>

net.sf.cglib.transform:�~�译期或�q�行期和�c�L��件的转换

net.sf.cglib.proxy�Q�实现创��Z��理和�Ҏ��拦截器的�c?/div>

net.sf.cglib.reflect:实现快速放��?/div>

net.sf.cglib.util:工具�?/div>

net.sf.cglib.beans:javabean相关工具�c?/div>

通过CGLIB创徏动态代理，本质上，他是动态的生成目标�cȝ��子类�Q�覆盖目标类所有不是final的方法，�q�给他们讄��好callback,因此�Q�原有类的每个方法调用就会变成自定义的拦截方法�?/div>

创徏动态代理时通常要用到如下api:net.sf.cglib.proxy.Callback�q�个接口�Q�他是很关键的一个接口，所有被net.sf.cglib.proxy.Enhancer�c�调用的回调借口都要�l�承�q�个接口

如：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;

}

�q�个是基与方法的回调�Q�第一个参数是代理对象�Q�第二个是被拦截的方法对象，�W�三个是�Ҏ��参数�Q�第四个是方法的代理对象�?/div>

public class MyClass {

public void method1() {

System.out.println("method1");

}

public void method2() {

System.out.println("method2");

}

拦截器：

public class MethodInterceptImpl implements MethodInterceptor {

public Object intercept(Object arg0, Method arg1, Object[] arg2,

MethodProxy arg3) throws Throwable {

System.out.println(arg1.getName()+"--intercept");

arg3.invokeSuper(arg0, arg2);// �q�里其实也可以用原来的方法对象来执行�Q�但是性能上不如cglib的方法代理类

return null;

}

public class MainTest {

public static void main(String[] args) {

simpleTest();

}

private static void simpleTest() {

Enhancer en = new Enhancer();

en.setCallback(new MethodInterceptImpl());

en.setSuperclass(MyClass.class);

MyClass m = (MyClass) en.create();

m.method1();

m.method2();

}

�l�果�Q�method1--intercept

method1

method2--intercept

method2

现实��目中可能存在某些需求，比如method1需要拦截，而method2不需要拦截。那我们可以对callback做下选择,使用net.sf.cglib.proxy.CallbackFilter做一些过滤�?/div>

public class MethodFilterImpl implements CallbackFilter {

private final static int execute = 0;

private final static int unexecute = 1;

public int accept(Method method) {

String methodName = method.getName();

if("method1".equals(methodName)){

return execute;

}

return unexecute;

}

调用的时候需要给callback讄��好烦引位�|�，因�ؓaccept的返回值就是callbacks数组的烦引位�|��?/div>

private static void filterTest() {

Enhancer en = new Enhancer();

Callback[] callbacks = new Callback[] { new MethodInterceptImpl(),

NoOp.INSTANCE };//�q�里拦截器的索引位置要与filter里的讄��一�?/div>

en.setCallbacks(callbacks);

en.setSuperclass(MyClass.class);

en.setCallbackFilter(new MethodFilterImpl());

MyClass m = (MyClass) en.create();

m.method1();

m.method2();

}

�q�里callbacks[1]�q�个位置使用了NoOp�q�个回调接口

public interface NoOp extends Callback

{

/**

* A thread-safe singleton instance of the NoOp callback.

public static final NoOp INSTANCE = new NoOp() { };

}

�q�个callback其实��是直接把�Q务委�z��q�个�Ҏ��在父�c�M��的实玎ͼ�其实也等同于没做什么额外的事情

执行�l�果�Q�method1--intercept

method1

method2

method2 �q�未被MethodInterceptImpl拦截

}

��羊 2010-10-26 14:27 发表评论

使用Annotation来完成spring aop

��羊 — Mon, 25 Oct 2010 08:52:00 GMT

spring AOP中，可以通过annotation来简化XML上的配置�Q�可以很灉|��的��切面切入到自己想要的�Ҏ��上，而不需要象aop:config里一定要切入到特定命名方法上

使用annotation来表�C�pointcut�Q�需要在xml里配�|�org.springframework.aop.support.annotation.AnnotationMatchingPointcut�Q?/div>

如：

class="org.springframework.aop.support.annotation.AnnotationMatchingPointcut">

value="com.hengtian.fxfundsystem.aop.annotation.UseAOPAnnotation">

value="com.hengtian.fxfundsystem.aop.annotation.TimeoutAnnotation" />

�W�一个参数是标在目标�c�M��的annotation,�W�二天参数是标注在方法上的Annotation

因此�Q�首先要在自��q��工程里定�?个annotation�Q�一个�ؓTimeoutAnnotation�Q�一个�ؓUseAOPAnnotation

@Target({ElementType.TYPE })//表示�c�L��?/div>

@Retention(RetentionPolicy.RUNTIME)

@Inherited

public @interface UseAOPAnnotation {

}

@Target({ElementType.METHOD})//表示�Ҏ��标注

@Retention(RetentionPolicy.RUNTIME)

public @interface TimeoutAnnotation {

/**

* 默认�?-1)�Q�表�C�Z��启用��时

public static final long DefaultValue = -1;

/**

* ��时旉��Q�单位是ms

* @return

long value() default DefaultValue;

}

在需要AOP的类上��?/div>

@UseAOPAnnotation

@Component("StrongDuck")

public class StrongDuck {

@TimeoutAnnotation(70000)

public void say(){

System.out.println("I am a strong duck");

}

timeout通知�Q?/div>

public class TimeoutAdvice implements MethodInterceptor {

* (non-Javadoc)

* @see

* org.aopalliance.intercept.MethodInterceptor#invoke(org.aopalliance.intercept

* .MethodInvocation)

public Object invoke(final MethodInvocation methodInvocation)

throws Throwable {

Method targetMethod = methodInvocation.getMethod();

TimeoutAnnotation timeoutAnnotation = targetMethod

.getAnnotation(TimeoutAnnotation.class);

if (timeoutAnnotation != null) {

long waitTime = timeoutAnnotation.value();

if (waitTime != TimeoutAnnotation.DefaultValue) {

Future task = ThreadManager.ExecutorService

.submit(encapsulateSyncToAsync(methodInvocation));

return getAsyncResult(waitTime, task);

}

return methodInvocation.proceed();

}

XML中配�|�拦截器�Q?/div>

class="org.springframework.aop.framework.autoproxy.DefaultAdvisorAutoProxyCreator">

true

�q�样�Q�spring��׃��Z��生成aop代理�c�d��现AOP

��羊 2010-10-25 16:52 发表评论

JDK代理

��羊 — Sun, 24 Oct 2010 16:20:00 GMT

JDK代理以前性能不怎么��P��?.6版本却有很大提升

/**

* 行�ؓ接口

* @author Administrator

public interface Study {

public void doStudy();

}

/**

* 目标对象

* @author Administrator

public class StudyImpl implements Study {

@Override

public void doStudy() {

System.out.println("study jdk proxy");

}

/**

* 代理�c?/div>

* @author Administrator

public class JDKProxy implements InvocationHandler {

private Study s;

public JDKProxy(Study s) {

this.s = s;

}

@Override

public Object invoke(Object proxy, Method method, Object[] args)

throws Throwable {

System.out.println("before jdkproxy");

method.invoke(s, args);

System.out.println("after jdkproxy");

return null;

}

应用中进行调用：

public class Test {

public static void main(String[] args) throws SecurityException,

NoSuchMethodException, IllegalArgumentException,

InstantiationException, IllegalAccessException,

InvocationTargetException {

Class clazz = StudyImpl.class;//获取目标�cȝ��Class对象

Study st = new StudyImpl();//实例化一个目标类

Class proxClass = Proxy.getProxyClass(clazz.getClassLoader(), clazz

.getInterfaces());//通过Proxy静态方法，获取一个于目标�c�d��现同��h��口的Class对象�Q�也可以说是兄弟�c?/div>

Constructor c = proxClass

.getConstructor(new Class[] { InvocationHandler.class });//�l�这个类一个指定的公开的构造方�?/div>

Study ds = (Study) c.newInstance(new Object[] { new JDKProxy(st) });//实例化一个代理类

}

��羊 2010-10-25 00:20 发表评论

AOP日记

��羊 — Sun, 24 Oct 2010 15:48:00 GMT

最�q�在学着�ȝ��Q�因为常感觉做完东西�Q�长久不用，�q�段旉��忘�Q�下�ơ想复习下都不行�?/div>

AOP�Q�面向方面编�E�，我们�pȝ��中有很多�l��g�l�成�Q�每一个组件负责一部分业务功能,

但是�q�些�l��g往往又带有一部分核心功能外的附加功能�Q�而且是重复代码，如：日志�Q�安全，事务�Q?通过AOP�Q�实现这些附加功能的可重复利用�?/div>

AOP其实可以看作是代理模式的扩展,写一个简单的代理

public class ProxySubject implements ProxyInterface {

private Subject innerObj;// 真正的对�?/div>

@Override

public void handle() {

innerObj = new Subject();

// 做额外的事情

innerObj.handle();// 真正的处理业�?/div>

// 做额外的事情

}

Aop中叫代理�c�Mؓadvice,可以有多个连接�v来，一个事仉��

实现AOP�Q�还需要涉及到JAVA的反��，通过反射�Q�获取method对象�Q��ƈ执行�Ҏ��Q�AOP规范包里有个接口

public interface MethodInterceptor extends Interceptor {

*Implement this method to perform extra treatments before and

* after the invocation. Polite implementations would certainly

* like to invoke {@link Joinpoint#proceed()}.

* @param invocation the method invocation joinpoint

* @return the result of the call to {@link

* Joinpoint#proceed()}, might be intercepted by the

* interceptor.

* @throws Throwable if the interceptors or the

* target-object throws an exception.

Object invoke(MethodInvocation invocation) throws Throwable;

�?/p>

通过 MethodInvocation�?getMethod()获得�Ҏ��对象�Q��ƈ执行

�q�样�Q�如果你一个类中有很多�Ҏ��Q�就可以通过�q�么一�?/p>

AOP中生成代理类�?�U�方式，

1.静态编译时期，源代码生成，为每个符合条件的�cȝ��成一个代理类

2.静态字节码增强通过ASM/CGLIB分析字节码，生成代理�c?/p>

3.动态字节码增强�Q�spring aop��是�q�样,ASM/CGLIB或者JDK的动态代�?/p>

AOP的原理可以理解�ؓ代理模式+攑ְ�+自动字节码生�?/p>

Spring中动态代理有2�U�方式，一�U�是通过CGLIB�Q�一�U�是JDK�?/p>

什么时候采用JDK什么时候采用CGLIB动态生成，主要取决于你又没实现接口�Q�JDK动态代理需要目标类实现某接口，而CGLIB则是生成目标�cȝ��子类

public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {

if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) {

Class targetClass = config.getTargetClass();

if (targetClass == null) {

throw new AopConfigException("TargetSource cannot determine target class: " +

"Either an interface or a target is required for proxy creation.");

}

if (targetClass.isInterface()) {

return new JdkDynamicAopProxy(config);

}

if (!cglibAvailable) {

throw new AopConfigException(

"Cannot proxy target class because CGLIB2 is not available. " +

"Add CGLIB to the class path or specify proxy interfaces.");

}

return CglibProxyFactory.createCglibProxy(config);

}

else {

return new JdkDynamicAopProxy(config);

}

�q�个是DefaultAopProxyFactory里创��Z��理类的方�?/p>

��羊 2010-10-24 23:48 发表评论