分析Spring源代码之，DI的兑现

分析Spring源代码之，DI的实现

(转)

分析Spring源代码之，DI的实现

2012/1/3 by tony

??????????????? 接着上次的讲，以下这个sample

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1. package?com.hyron.tony;??
2. import?org.springframework.beans.factory.BeanFactory;??
3. import?org.springframework.beans.factory.xml.XmlBeanFactory;??
4. import?org.springframework.core.io.ClassPathResource;??
5. ??
6. public?class?Test?{??
7. ??
8. ????public?static?void?main(String[]?args)throws?Exception?{??
9. ????????BeanFactory?factory?=?new?XmlBeanFactory(new?ClassPathResource("applicationContext.xml"));??
10. ????????GreetingService?greetingService?=?(GreetingService)factory.getBean("greetingService");??
11. ????????greetingService.sayGreeting();??
12. ????}??
13. ??
14. }??

Bean的实时启动，就是以下这行代码：

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1. (GreetingService)factory.getBean("greetingService");??

他的执行树如下：

Factory.getBean

--?XmlBeanFactory

--AbstractAutowireCapableBeanFactory

--?AbstractBeanFactory 在其中找到如下方法

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1. //---------------------------------??
2. ????//?Implementation?of?BeanFactory?interface??
3. ????//---------------------------------??
4. ??
5. ????public?Object?getBean(String?name)?throws?BeansException?{??
6. ????????return?doGetBean(name,?null,?null,?false);??
7. ????}??

?

doGetBean的方法声明：

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1. /**?
2. ?????*?Return?an?instance,?which?may?be?shared?or?independent,?of?the?specified?bean.?
3. ?????*?@param?name?the?name?of?the?bean?to?retrieve?
4. ?????*?@param?requiredType?the?required?type?of?the?bean?to?retrieve?
5. ?????*?@param?args?arguments?to?use?if?creating?a?prototype?using?explicit?arguments?to?a?
6. ?????*?static?factory?method.?It?is?invalid?to?use?a?non-null?args?value?in?any?other?case.?
7. ?????*?@param?typeCheckOnly?whether?the?instance?is?obtained?for?a?type?check,?
8. ?????*?not?for?actual?use?
9. ?????*?@return?an?instance?of?the?bean?
10. ?????*?@throws?BeansException?if?the?bean?could?not?be?created?
11. ?????*/??
12. ????@SuppressWarnings("unchecked")??
13. ????protected?<T>?T?doGetBean(??
14. ????????????final?String?name,?final?Class<T>?requiredType,?final?Object[]?args,?boolean?typeCheckOnly)??
15. ????????????throws?BeansException?{??
16. }??

?

我真觉得有时候研究人家代码真不如看人家注释，特别是很好的开源架构，代码是好得很

doGetBean方法中比较有意思的代码如下：

//将beanName前面可能的&符号滤掉

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1. final?String?beanName?=?transformedBeanName(name);??

?

//得到已经登记过的单例Object，而不是再次生成它

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1. Object?sharedInstance?=?getSingleton(beanName);??

?

它的具体代码如下：

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1. /**?
2. ?????*?Return?the?(raw)?singleton?object?registered?under?the?given?name.?
3. ?????*?<p>Checks?already?instantiated?singletons?and?also?allows?for?an?early?
4. ?????*?reference?to?a?currently?created?singleton?(resolving?a?circular?reference).?
5. ?????*?@param?beanName?the?name?of?the?bean?to?look?for?
6. ?????*?@param?allowEarlyReference?whether?early?references?should?be?created?or?not?
7. ?????*?@return?the?registered?singleton?object,?or?<code>null</code>?if?none?found?
8. ?????*/??
9. ????protected?Object?getSingleton(String?beanName,?boolean?allowEarlyReference)?{??
10. ????????Object?singletonObject?=?this.singletonObjects.get(beanName);??
11. ????????if?(singletonObject?==?null)?{??
12. ????????????synchronized?(this.singletonObjects)?{??
13. ????????????????singletonObject?=?this.earlySingletonObjects.get(beanName);??
14. ????????????????if?(singletonObject?==?null?&&?allowEarlyReference)?{??
15. ????????????????????ObjectFactory?singletonFactory?=?this.singletonFactories.get(beanName);??
16. ????????????????????if?(singletonFactory?!=?null)?{??
17. ????????????????????????singletonObject?=?singletonFactory.getObject();??
18. ????????????????????????this.earlySingletonObjects.put(beanName,?singletonObject);??
19. ????????????????????????this.singletonFactories.remove(beanName);??
20. ????????????????????}??
21. ????????????????}??
22. ????????????}??
23. ????????}??
24. ????????return?(singletonObject?!=?NULL_OBJECT???singletonObject?:?null);??
25. ????}??

?

其中有一点比较有意思，就是singletonFactories是在哪里塞入的

以下：

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1. /**?
2. ?????*?Add?the?given?singleton?factory?for?building?the?specified?singleton?
3. ?????*?if?necessary.?
4. ?????*?<p>To?be?called?for?eager?registration?of?singletons,?e.g.?to?be?able?to?
5. ?????*?resolve?circular?references.?
6. ?????*?@param?beanName?the?name?of?the?bean?
7. ?????*?@param?singletonFactory?the?factory?for?the?singleton?object?
8. ?????*/??
9. ????protected?void?addSingletonFactory(String?beanName,?ObjectFactory?singletonFactory)?{??
10. ????????Assert.notNull(singletonFactory,?"Singleton?factory?must?not?be?null");??
11. ????????synchronized?(this.singletonObjects)?{??
12. ????????????if?(!this.singletonObjects.containsKey(beanName))?{??
13. ????????????????this.singletonFactories.put(beanName,?singletonFactory);??
14. ????????????????this.earlySingletonObjects.remove(beanName);??
15. ????????????????this.registeredSingletons.add(beanName);??
16. ????????????}??
17. ????????}??
18. ????}??

?

这个方法被执行与createBean

createBean的执行其实是在doGetBean方法内本身

接下来从一个BeanFactory中获得对象的instance

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1. /**?
2. ?????*?Get?the?object?for?the?given?bean?instance,?either?the?bean?
3. ?????*?instance?itself?or?its?created?object?in?case?of?a?FactoryBean.?
4. ?????*?@param?beanInstance?the?shared?bean?instance?
5. ?????*?@param?name?name?that?may?include?factory?dereference?prefix?
6. ?????*?@param?beanName?the?canonical?bean?name?
7. ?????*?@param?mbd?the?merged?bean?definition?
8. ?????*?@return?the?object?to?expose?for?the?bean?
9. ?????*/??
10. ????protected?Object?getObjectForBeanInstance(??
11. ????????????Object?beanInstance,?String?name,?String?beanName,?RootBeanDefinition?mbd)?{??
12. ??
13. ????????//?Don't?let?calling?code?try?to?dereference?the?factory?if?the?bean?isn't?a?factory.??
14. ????????if?(BeanFactoryUtils.isFactoryDereference(name)?&&?!(beanInstance?instanceof?FactoryBean))?{??
15. ????????????throw?new?BeanIsNotAFactoryException(transformedBeanName(name),?beanInstance.getClass());??
16. ????????}??
17. ??
18. ????????//?Now?we?have?the?bean?instance,?which?may?be?a?normal?bean?or?a?FactoryBean.??
19. ????????//?If?it's?a?FactoryBean,?we?use?it?to?create?a?bean?instance,?unless?the??
20. ????????//?caller?actually?wants?a?reference?to?the?factory.??
21. ????????if?(!(beanInstance?instanceof?FactoryBean)?||?BeanFactoryUtils.isFactoryDereference(name))?{??
22. ????????????return?beanInstance;??
23. ????????}??
24. ??
25. ????????Object?object?=?null;??
26. ????????if?(mbd?==?null)?{??
27. ????????????object?=?getCachedObjectForFactoryBean(beanName);??
28. ????????}??
29. ????????if?(object?==?null)?{??
30. ????????????//?Return?bean?instance?from?factory.??
31. ????????????FactoryBean<?>?factory?=?(FactoryBean<?>)?beanInstance;??
32. ????????????//?Caches?object?obtained?from?FactoryBean?if?it?is?a?singleton.??
33. ????????????if?(mbd?==?null?&&?containsBeanDefinition(beanName))?{??
34. ????????????????mbd?=?getMergedLocalBeanDefinition(beanName);??
35. ????????????}??
36. ????????????boolean?synthetic?=?(mbd?!=?null?&&?mbd.isSynthetic());??
37. ????????????object?=?getObjectFromFactoryBean(factory,?beanName,?!synthetic);??
38. ????????}??
39. ????????return?object;??
40. ????}??

?

否则的话，失败的话，则从BeanFacory中动态生成对象实例

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1. //?Fail?if?we're?already?creating?this?bean?instance:??
2. ????????????//?We're?assumably?within?a?circular?reference.??
3. ????????????if?(isPrototypeCurrentlyInCreation(beanName))?{??
4. ????????????????throw?new?BeanCurrentlyInCreationException(beanName);??
5. ????????????}??
6. ??
7. ????????????//?Check?if?bean?definition?exists?in?this?factory.??
8. ????????????BeanFactory?parentBeanFactory?=?getParentBeanFactory();??
9. ????????????if?(parentBeanFactory?!=?null?&&?!containsBeanDefinition(beanName))?{??
10. ????????????????//?Not?found?->?check?parent.??
11. ????????????????String?nameToLookup?=?originalBeanName(name);??
12. ????????????????if?(args?!=?null)?{??
13. ????????????????????//?Delegation?to?parent?with?explicit?args.??
14. ????????????????????return?(T)?parentBeanFactory.getBean(nameToLookup,?args);??
15. ????????????????}??
16. ????????????????else?{??
17. ????????????????????//?No?args?->?delegate?to?standard?getBean?method.??
18. ????????????????????return?parentBeanFactory.getBean(nameToLookup,?requiredType);??
19. ????????????????}??
20. ????????????}??

?以上这段代码真的很让人费解，什么是BeanFactory,什么是FactoryBean

?

接下来，如果在失败，就直接createBean

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1. //?Create?bean?instance.??
2. ????????if?(mbd.isSingleton())?{??
3. ????????????sharedInstance?=?getSingleton(beanName,?new?ObjectFactory<Object>()?{??
4. ????????????????public?Object?getObject()?throws?BeansException?{??
5. ????????????????????try?{??
6. ????????????????????????return?createBean(beanName,?mbd,?args);??
7. ????????????????????}??
8. ????????????????????catch?(BeansException?ex)?{??
9. ????????????????????????//?Explicitly?remove?instance?from?singleton?cache:?It?might?have?been?put?there??
10. ????????????????????????//?eagerly?by?the?creation?process,?to?allow?for?circular?reference?resolution.??
11. ????????????????????????//?Also?remove?any?beans?that?received?a?temporary?reference?to?the?bean.??
12. ????????????????????????destroySingleton(beanName);??
13. ????????????????????????throw?ex;??
14. ????????????????????}??
15. ????????????????}??
16. ????????????});??
17. ????????????bean?=?getObjectForBeanInstance(sharedInstance,?name,?beanName,?mbd);??
18. ????????}??

其中createBean是写在父类中的抽象类 AbstractAutowireCapableBeanFactory中

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1. /**?
2. ?????*?Central?method?of?this?class:?creates?a?bean?instance,?
3. ?????*?populates?the?bean?instance,?applies?post-processors,?etc.?
4. ?????*?@see?#doCreateBean?
5. ?????*/??
6. ????@Override??
7. ????protected?Object?createBean(final?String?beanName,?final?RootBeanDefinition?mbd,?final?Object[]?args)??
8. ????????????throws?BeanCreationException?{??
9. ??
10. ????????if?(logger.isDebugEnabled())?{??
11. ????????????logger.debug("Creating?instance?of?bean?'"?+?beanName?+?"'");??
12. ????????}??
13. ????????//?Make?sure?bean?class?is?actually?resolved?at?this?point.??
14. ????????resolveBeanClass(mbd,?beanName);??
15. ??
16. ????????//?Prepare?method?overrides.??
17. ????????try?{??
18. ????????????mbd.prepareMethodOverrides();??
19. ????????}??
20. ????????catch?(BeanDefinitionValidationException?ex)?{??
21. ????????????throw?new?BeanDefinitionStoreException(mbd.getResourceDescription(),??
22. ????????????????????beanName,?"Validation?of?method?overrides?failed",?ex);??
23. ????????}??
24. ??
25. ????????try?{??
26. ????????????//?Give?BeanPostProcessors?a?chance?to?return?a?proxy?instead?of?the?target?bean?instance.??
27. ????????????Object?bean?=?resolveBeforeInstantiation(beanName,?mbd);??
28. ????????????if?(bean?!=?null)?{??
29. ????????????????return?bean;??
30. ????????????}??
31. ????????}??
32. ????????catch?(Throwable?ex)?{??
33. ????????????throw?new?BeanCreationException(mbd.getResourceDescription(),?beanName,??
34. ????????????????????"BeanPostProcessor?before?instantiation?of?bean?failed",?ex);??
35. ????????}??
36. ??
37. ????????Object?beanInstance?=?doCreateBean(beanName,?mbd,?args);??
38. ????????if?(logger.isDebugEnabled())?{??
39. ????????????logger.debug("Finished?creating?instance?of?bean?'"?+?beanName?+?"'");??
40. ????????}??
41. ????????return?beanInstance;??
42. ????}??

?

其中真正反射生成对象instance的是

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1. protected?Object?doCreateBean(final?String?beanName,?final?RootBeanDefinition?mbd,?final?Object[]?args)???

这个方法分成两部分：

第一，生成对象instance的Wapper，用到了包装者模式

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1. if?(instanceWrapper?==?null)?{??
2. ????????????instanceWrapper?=?createBeanInstance(beanName,?mbd,?args);??
3. ????????}??

第二，实例化对象instance

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1. //?Initialize?the?bean?instance.??
2. ????????Object?exposedObject?=?bean;??
3. ????????try?{??
4. ????????????populateBean(beanName,?mbd,?instanceWrapper);??
5. ????????????if?(exposedObject?!=?null)?{??
6. ????????????????exposedObject?=?initializeBean(beanName,?exposedObject,?mbd);??
7. ????????????}??
8. ????????}??
9. ????????catch?(Throwable?ex)?{??
10. ????????????if?(ex?instanceof?BeanCreationException?&&?beanName.equals(((BeanCreationException)?ex).getBeanName()))?{??
11. ????????????????throw?(BeanCreationException)?ex;??
12. ????????????}??
13. ????????????else?{??
14. ????????????????throw?new?BeanCreationException(mbd.getResourceDescription(),?beanName,?"Initialization?of?bean?failed",?ex);??
15. ????????????}??
16. ????????}??

其中createBeanInstance中最简单的生成期是

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1. //?No?special?handling:?simply?use?no-arg?constructor.??
2. ????????return?instantiateBean(beanName,?mbd);??

它的核心代码：

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1. if?(System.getSecurityManager()?!=?null)?{??
2. ????????????????beanInstance?=?AccessController.doPrivileged(new?PrivilegedAction<Object>()?{??
3. ????????????????????public?Object?run()?{??
4. ????????????????????????return?getInstantiationStrategy().instantiate(mbd,?beanName,?parent);??
5. ????????????????????}??
6. ????????????????},?getAccessControlContext());??
7. ????????????}??
8. ????????????else?{??
9. ????????????????beanInstance?=?getInstantiationStrategy().instantiate(mbd,?beanName,?parent);??
10. ????????????}??

这里使用了策略模式，将实际的算法放到策略接口中去

?

一般最简单的实现的策略模式就是：

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1. /**?
2. ?*?Default?object?instantiation?strategy?for?use?in?BeanFactories.?
3. ?*?Uses?CGLIB?to?generate?subclasses?dynamically?if?methods?need?to?be?
4. ?*?overridden?by?the?container,?to?implement?Method?Injection.?
5. ?*?
6. ?*?<p>Using?Method?Injection?features?requires?CGLIB?on?the?classpath.?
7. ?*?However,?the?core?IoC?container?will?still?run?without?CGLIB?being?available.?
8. ?*?
9. ?*?@author?Rod?Johnson?
10. ?*?@author?Juergen?Hoeller?
11. ?*?@since?1.1?
12. ?*/??
13. public?class?CglibSubclassingInstantiationStrategy?extends?SimpleInstantiationStrategy?{??

?

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1. /**?
2. ?????????*?Create?a?new?instance?of?a?dynamically?generated?subclasses?implementing?the?
3. ?????????*?required?lookups.?
4. ?????????*?@param?ctor?constructor?to?use.?If?this?is?<code>null</code>,?use?the?
5. ?????????*?no-arg?constructor?(no?parameterization,?or?Setter?Injection)?
6. ?????????*?@param?args?arguments?to?use?for?the?constructor.?
7. ?????????*?Ignored?if?the?ctor?parameter?is?<code>null</code>.?
8. ?????????*?@return?new?instance?of?the?dynamically?generated?class?
9. ?????????*/??
10. ????????public?Object?instantiate(Constructor?ctor,?Object[]?args)?{??
11. ????????????Enhancer?enhancer?=?new?Enhancer();??
12. ????????????enhancer.setSuperclass(this.beanDefinition.getBeanClass());??
13. ????????????enhancer.setCallbackFilter(new?CallbackFilterImpl());??
14. ????????????enhancer.setCallbacks(new?Callback[]?{??
15. ????????????????????NoOp.INSTANCE,??
16. ????????????????????new?LookupOverrideMethodInterceptor(),??
17. ????????????????????new?ReplaceOverrideMethodInterceptor()??
18. ????????????});??
19. ??
20. ????????????return?(ctor?==?null)?????
21. ????????????????????enhancer.create()?:???
22. ????????????????????enhancer.create(ctor.getParameterTypes(),?args);??
23. ????????}??

真正最终的对象生成器是

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1. net.sf.cglib.proxy.Enhancer;??

?

spring没有用原生态的代理反射，而是用这个开源jar包来实现了动态生成

?

最后spring对对象的实例化，和参数的注入，是以下代码：

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1. /**?
2. ?????*?Populate?the?bean?instance?in?the?given?BeanWrapper?with?the?property?values?
3. ?????*?from?the?bean?definition.?
4. ?????*?@param?beanName?the?name?of?the?bean?
5. ?????*?@param?mbd?the?bean?definition?for?the?bean?
6. ?????*?@param?bw?BeanWrapper?with?bean?instance?
7. ?????*/??
8. ????protected?void?populateBean(String?beanName,?AbstractBeanDefinition?mbd,?BeanWrapper?bw)?{??
9. ????????PropertyValues?pvs?=?mbd.getPropertyValues();??
10. ??
11. ????????if?(bw?==?null)?{??
12. ????????????if?(!pvs.isEmpty())?{??
13. ????????????????throw?new?BeanCreationException(??
14. ????????????????????????mbd.getResourceDescription(),?beanName,?"Cannot?apply?property?values?to?null?instance");??
15. ????????????}??
16. ????????????else?{??
17. ????????????????//?Skip?property?population?phase?for?null?instance.??
18. ????????????????return;??
19. ????????????}??
20. ????????}??
21. ??
22. ????????//?Give?any?InstantiationAwareBeanPostProcessors?the?opportunity?to?modify?the??
23. ????????//?state?of?the?bean?before?properties?are?set.?This?can?be?used,?for?example,??
24. ????????//?to?support?styles?of?field?injection.??
25. ????????boolean?continueWithPropertyPopulation?=?true;??
26. ??
27. ????????if?(!mbd.isSynthetic()?&&?hasInstantiationAwareBeanPostProcessors())?{??
28. ????????????for?(BeanPostProcessor?bp?:?getBeanPostProcessors())?{??
29. ????????????????if?(bp?instanceof?InstantiationAwareBeanPostProcessor)?{??
30. ????????????????????InstantiationAwareBeanPostProcessor?ibp?=?(InstantiationAwareBeanPostProcessor)?bp;??
31. ????????????????????if?(!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(),?beanName))?{??
32. ????????????????????????continueWithPropertyPopulation?=?false;??
33. ????????????????????????break;??
34. ????????????????????}??
35. ????????????????}??
36. ????????????}??
37. ????????}??
38. ??
39. ????????if?(!continueWithPropertyPopulation)?{??
40. ????????????return;??
41. ????????}??
42. ??
43. ????????if?(mbd.getResolvedAutowireMode()?==?RootBeanDefinition.AUTOWIRE_BY_NAME?||??
44. ????????????????mbd.getResolvedAutowireMode()?==?RootBeanDefinition.AUTOWIRE_BY_TYPE)?{??
45. ????????????MutablePropertyValues?newPvs?=?new?MutablePropertyValues(pvs);??
46. ??
47. ????????????//?Add?property?values?based?on?autowire?by?name?if?applicable.??
48. ????????????if?(mbd.getResolvedAutowireMode()?==?RootBeanDefinition.AUTOWIRE_BY_NAME)?{??
49. ????????????????autowireByName(beanName,?mbd,?bw,?newPvs);??
50. ????????????}??
51. ??
52. ????????????//?Add?property?values?based?on?autowire?by?type?if?applicable.??
53. ????????????if?(mbd.getResolvedAutowireMode()?==?RootBeanDefinition.AUTOWIRE_BY_TYPE)?{??
54. ????????????????autowireByType(beanName,?mbd,?bw,?newPvs);??
55. ????????????}??
56. ??
57. ????????????pvs?=?newPvs;??
58. ????????}??
59. ??
60. ????????boolean?hasInstAwareBpps?=?hasInstantiationAwareBeanPostProcessors();??
61. ????????boolean?needsDepCheck?=?(mbd.getDependencyCheck()?!=?RootBeanDefinition.DEPENDENCY_CHECK_NONE);??
62. ??
63. ????????if?(hasInstAwareBpps?||?needsDepCheck)?{??
64. ????????????PropertyDescriptor[]?filteredPds?=?filterPropertyDescriptorsForDependencyCheck(bw);??
65. ????????????if?(hasInstAwareBpps)?{??
66. ????????????????for?(BeanPostProcessor?bp?:?getBeanPostProcessors())?{??
67. ????????????????????if?(bp?instanceof?InstantiationAwareBeanPostProcessor)?{??
68. ????????????????????????InstantiationAwareBeanPostProcessor?ibp?=?(InstantiationAwareBeanPostProcessor)?bp;??
69. ????????????????????????pvs?=?ibp.postProcessPropertyValues(pvs,?filteredPds,?bw.getWrappedInstance(),?beanName);??
70. ????????????????????????if?(pvs?==?null)?{??
71. ????????????????????????????return;??
72. ????????????????????????}??
73. ????????????????????}??
74. ????????????????}??
75. ????????????}??
76. ????????????if?(needsDepCheck)?{??
77. ????????????????checkDependencies(beanName,?mbd,?filteredPds,?pvs);??
78. ????????????}??
79. ????????}??
80. ??
81. ????????applyPropertyValues(beanName,?mbd,?bw,?pvs);??
82. ????}??

?

我真不知道这些代码是怎么写出来的。

怎么能这么牛，有时候看到这些浩如烟海的牛逼的代码，真是觉得自己和人家比起来，技术的道路算是到头了。

这些人真是他妈的天才。

?

?

附：cglib的简单介绍：

http://java.csecs.com/posts/list/1633.html

http://www.blogjava.net/stone2083/archive/2008/03/16/186615.html

http://www.blogjava.net/georgehill/archive/2005/05/24/5126.html

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