问题来源

　以前一直有个疑惑，为什么我创建的controller中注入的service类有时候是代理类，有时候是普通javabean，当时能力不够，现在已经有了点经验就大胆跟了跟源码，看看到底咋回事。

首先看看问题现象：

a1:service是代理类，并且是CGLIB类型代理

a2:service是代理类，并且是jdk 动态代理

b:serivce不是代理类，而是普通类　

问题分析

　我对service类进行了以下的测试：(前提开启事务注解<tx:annotation-driven/>)

　　1）service方法添加@Transactional注解或者加入其它的aop拦截配置，没有实现任何接口。对应问题现状 a1

　　2）service方法添加@Transactional注解或者加入其它的aop拦截配置，实现了接口。对应问题现状a2

　　3）serice方法没有添加@Transactional注解或者其它的aop拦截配置。对应问题现状b

　看来出现这种问题的原因就是spring的问题，因为这个类是它创建的，这就需要我们来看下spring创建bean的代码，由于spring太庞大了

我们只看最关键的部分，在创建bean是都会调用getBean()方法，

 @SuppressWarnings("unchecked")
    protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
            @Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
　　　　　　return createBean(beanName, mbd, args);
    }

经过不断的流转会进入AbstractAutowireCapableBeanFactory的createBean方法

@Override
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {try {
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
if (logger.isDebugEnabled()) {
logger.debug("Finished creating instance of bean '" + beanName + "'");
}
return beanInstance;
}
catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
// A previously detected exception with proper bean creation context already,
// or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.
throw ex;
}

}

然后调用doCreateBean方法

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
if (instanceWrapper == null) {　　　　　　　
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
final Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}// Initialize the bean instance.
Object exposedObject = bean;
try {
populateBean(beanName, mbd, instanceWrapper);
exposedObject = initializeBean(beanName, exposedObject, mbd);
}
catch (Throwable ex) {
if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
throw (BeanCreationException) ex;
}
else {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
}
}return exposedObject;
}

然后进入核心的createBeanInstance方法,省去了不相关方法

protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {// No special handling: simply use no-arg constructor.
        return instantiateBean(beanName, mbd);
    }

然后调用instantiateBean进行bea的实例化

protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) {
try {
Object beanInstance;
final BeanFactory parent = this;
if (System.getSecurityManager() != null) {
beanInstance = AccessController.doPrivileged((PrivilegedAction<Object>) () ->
getInstantiationStrategy().instantiate(mbd, beanName, parent),
getAccessControlContext());
}
else {
beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);
}
BeanWrapper bw = new BeanWrapperImpl(beanInstance);
initBeanWrapper(bw);
return bw;
}
catch (Throwable ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex);
}
}

实例化时会调用SimpleInstantiationStrategy的instantiate方法

@Override
public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {
// Don't override the class with CGLIB if no overrides.
if (!bd.hasMethodOverrides()) {
Constructor<?> constructorToUse;
synchronized (bd.constructorArgumentLock) {
constructorToUse = (Constructor<?>) bd.resolvedConstructorOrFactoryMethod;
if (constructorToUse == null) {
final Class<?> clazz = bd.getBeanClass();
if (clazz.isInterface()) {
throw new BeanInstantiationException(clazz, "Specified class is an interface");
}
try {
if (System.getSecurityManager() != null) {
constructorToUse = AccessController.doPrivileged(
(PrivilegedExceptionAction<Constructor<?>>) clazz::getDeclaredConstructor);
}
else {
constructorToUse = clazz.getDeclaredConstructor();
}
bd.resolvedConstructorOrFactoryMethod = constructorToUse;
}
catch (Throwable ex) {
throw new BeanInstantiationException(clazz, "No default constructor found", ex);
}
}
}
return BeanUtils.instantiateClass(constructorToUse);
}
else {
// Must generate CGLIB subclass.
return instantiateWithMethodInjection(bd, beanName, owner);
}
}

该方法就是真正的实例化bean，根据不同情况通过CGLIB的方式

instantiateWithMethodInjection(bd, beanName, owner)

或者java的反射方式

BeanUtils.instantiateClass(constructorToUse)

实例化一个bean，这是时候都是一个纯洁无瑕的javabean，那每个bean的额外加工，例如为某个bean添加事务支持，

添加aop配置，还有就是将springmvc的controller进行url和handler的映射，等等这些都是在spring的扩展点完成的，回到

上面的doCreateBean方法

执行完实例化bean后执行

populateBean(beanName, mbd, instanceWrapper);

initializeBean(beanName, exposedObject, mbd);

其中的populateBean是为了给生成的bean装配属性，这不是我们这次讨论的重点，关键是initializebean方法

protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareMethods(beanName, bean);
return null;
}, getAccessControlContext());
}
else {
invokeAwareMethods(beanName, bean);
}

Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}

try {
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}

return wrappedBean;
}

这个方法就是对生成的bean进行一些扩展处理，主要是这个方法就，会调用我们自定义的扩展点

applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);

public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
throws BeansException {

Object result = existingBean;
for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
Object current = beanProcessor.postProcessAfterInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}

可以看到这里是获取所有的beanProcessor，调用postProcessAfterInitialization方法，我们要关注是的一个叫InfrastructureAdvisorAutoProxyCreator的扩展类。

/**
* Auto-proxy creator that considers infrastructure Advisor beans only,
* ignoring any application-defined Advisors.
*
* @author Juergen Hoeller
* @since 2.0.7
*/
@SuppressWarnings("serial")
public class InfrastructureAdvisorAutoProxyCreator extends AbstractAdvisorAutoProxyCreator {}

看下这个类的注释可以发现这个类是为配置了aop配置（包括注解和xml配置两种方式）的类，生成代理类。核心方法是下面这个方法wrapIfNecessary方法。

protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
if (beanName != null && this.targetSourcedBeans.contains(beanName)) {
return bean;
}
if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
return bean;
}
if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}

// Create proxy if we have advice.
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
if (specificInterceptors != DO_NOT_PROXY) {
this.advisedBeans.put(cacheKey, Boolean.TRUE);
Object proxy = createProxy(bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
this.proxyTypes.put(cacheKey, proxy.getClass());
return proxy;
}

this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}

下面解析下这个函数

首先看下getAdvicesAndAdvisorsForBean这个方法：名字很明显用来获取当前bean的advisor和adices的，这些都是生成代理类时需要的信息。

protected Object[] getAdvicesAndAdvisorsForBean(Class<?> beanClass, String beanName, TargetSource targetSource) {
List<Advisor> advisors = findEligibleAdvisors(beanClass, beanName);
if (advisors.isEmpty()) {
return DO_NOT_PROXY;
}
return advisors.toArray();
}

然后调用findEligibleAdvisors，获取配置的advisor信息

protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
List<Advisor> candidateAdvisors = findCandidateAdvisors();
List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
extendAdvisors(eligibleAdvisors);
if (!eligibleAdvisors.isEmpty()) {
eligibleAdvisors = sortAdvisors(eligibleAdvisors);
}
return eligibleAdvisors;
}

来看下findCandidateAdvisors方法,最终调BeanFactoryAdvisorRetrievalHelper.findAdvisorBeans

public List<Advisor> findAdvisorBeans() {
// Determine list of advisor bean names, if not cached already.
String[] advisorNames = null;
synchronized (this) {
advisorNames = this.cachedAdvisorBeanNames;
if (advisorNames == null) {
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the auto-proxy creator apply to them!
advisorNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
this.beanFactory, Advisor.class, true, false);
this.cachedAdvisorBeanNames = advisorNames;
}
}
if (advisorNames.length == 0) {
return new LinkedList<>();
}

List<Advisor> advisors = new LinkedList<>();
for (String name : advisorNames) {
if (isEligibleBean(name)) {
if (this.beanFactory.isCurrentlyInCreation(name)) {

}
else {
try {
advisors.add(this.beanFactory.getBean(name, Advisor.class));
}
catch (BeanCreationException ex) {
throw ex;
}
}
}
}
return advisors;
}

1）首先获取spring管理的Advisor类型的类名称。

2）通过beanFactory获取该bean对应的实体类，并装入advisors。

生成的这个advisor可是相当复杂，这里我们以事务advisor为例说明

可以看到这个advisor包含了advice（aop中的通知），pointcut(aop中的切入点)，

advice是TransactionInterceptor，这个通知是用来管理spring的事务的可以看到包含事务的管理器等管理事务的属性，具体的方法见TransactionAspectSupport.invokeWithinTransaction
pointcut是TransactionAttributeSourcePointcut。

public boolean matches(Method method, @Nullable Class<?> targetClass) {
if (targetClass != null && TransactionalProxy.class.isAssignableFrom(targetClass)) {
return false;
}
TransactionAttributeSource tas = getTransactionAttributeSource();
return (tas == null || tas.getTransactionAttribute(method, targetClass) != null);
}

这个是pointcut的核心方法，用来匹配某个类是否符合事务管理的aop拦截要求。
ok，回到之前的wrapIfNecessary方法

protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
if (beanName != null && this.targetSourcedBeans.contains(beanName)) {
return bean;
}
if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
return bean;
}
if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}

// Create proxy if we have advice.
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
if (specificInterceptors != DO_NOT_PROXY) {
this.advisedBeans.put(cacheKey, Boolean.TRUE);
Object proxy = createProxy(bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
this.proxyTypes.put(cacheKey, proxy.getClass());
return proxy;
}

this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}

我们之前分析道getAdvicesAndAdvisorsForBean方法，可以看到如果得到的结果是DO_NOT_PROXY，就会将这个bean直接返回，

如果不是DO_NOT_PROXY,（其实DO_NOT_PROXY就是null，但是使用DO_NOT_PROXY会使得代码逻辑更加清晰），就会执行

createProxy方法，创建一个代理类，然后返回一个代理类，ok，现在我们就清楚了问题分析中的第3）和第 1） 2）区别，那就是

service类是否配置了相关的aop拦截配置，无论是注解还是xml形式，目前我们还不清楚第1）和第2）的区别，就是为什么有时候

生成jdk代理，有时候生成cglib代理，这就需要继续向下看creatProxy方法了，最终会进入一个DefaultAopProxyFactory的createAopProxy

方法：

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() || Proxy.isProxyClass(targetClass)) {
return new JdkDynamicAopProxy(config);
}
return new ObjenesisCglibAopProxy(config);
}
else {
return new JdkDynamicAopProxy(config);
}
}