1.美图
2.概述
寻找代理，请参考以前的文章
3.前文概要
/**
* Wrap the given bean if necessary, i.e. if it is eligible for being proxied.
* @param bean the raw bean instance
* @param beanName the name of the bean
* @param cacheKey the cache key for metadata access
* @return a proxy wrapping the bean, or the raw bean instance as-is
*
* 如果需要则包装该bean,例如该bean可以被代理
*/
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
// 1、如果已经处理过或者不需要创建代理，则返回
if (StringUtils.hasLength(beanName) && 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.
// 2、创建代理
// 2.1 根据指定的bean获取所有的适合该bean的增强
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
if (specificInterceptors != DO_NOT_PROXY) {
// 2.2 为指定bean创建代理
this.advisedBeans.put(cacheKey, Boolean.TRUE);
Object proxy = createProxy(
bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
this.proxyTypes.put(cacheKey, proxy.getClass());
return proxy;
}
// 3、缓存
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
这里第二步骤主要是创建代理
4.创建代理
/**
* 为给定的bean创建代理
*
* Create an AOP proxy for the given bean.
* @param beanClass the class of the bean
* @param beanName the name of the bean
* @param specificInterceptors the set of interceptors that is
* specific to this bean (may be empty, but not null)
* @param targetSource the TargetSource for the proxy,
* already pre-configured to access the bean
* @return the AOP proxy for the bean
* @see #buildAdvisors
*/
protected Object createProxy(Class<?> beanClass, @Nullable String beanName,
@Nullable Object[] specificInterceptors, TargetSource targetSource) {
// 1、当前beanFactory是ConfigurableListableBeanFactory类型，则尝试暴露当前bean的target class
if (this.beanFactory instanceof ConfigurableListableBeanFactory) {
AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory) this.beanFactory, beanName, beanClass);
}
// 2、创建ProxyFactory并配置
ProxyFactory proxyFactory = new ProxyFactory();
proxyFactory.copyFrom(this);
// 是否直接代理目标类以及接口
if (!proxyFactory.isProxyTargetClass()) {
// 确定给定bean是否应该用它的目标类而不是接口进行代理
if (shouldProxyTargetClass(beanClass, beanName)) {
proxyFactory.setProxyTargetClass(true);
}
// 检查给定bean类上的接口，如果合适的话，将它们应用到ProxyFactory。即添加代理接口
else {
evaluateProxyInterfaces(beanClass, proxyFactory);
}
}
// 3、确定给定bean的advisors，包括特定的拦截器和公共拦截器，是否适配Advisor接口。
Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
// 设置增强
proxyFactory.addAdvisors(advisors);
// 设置代理目标
proxyFactory.setTargetSource(targetSource);
// 定制proxyFactory（空的模板方法，可在子类中自己定制）
customizeProxyFactory(proxyFactory);
// 锁定proxyFactory
proxyFactory.setFrozen(this.freezeProxy);
if (advisorsPreFiltered()) {
proxyFactory.setPreFiltered(true);
}
// 4、创建代理
return proxyFactory.getProxy(getProxyClassLoader());
}
4.1 创建代理的具体过程
public Object getProxy(@Nullable ClassLoader classLoader) {
return createAopProxy().getProxy(classLoader);
}
/**
* Subclasses should call this to get a new AOP proxy. They should <b>not</b>
* create an AOP proxy with {@code this} as an argument.
*/
protected final synchronized AopProxy createAopProxy() {
if (!this.active) {
activate();
}
return getAopProxyFactory().createAopProxy(this);
}
从上面的代码可以看到，创建代理的具体工作委托给了AopProxyFactory的createAopProxy方法。
public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {
@Override
public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
// 1、判断是否需要创建CGLIB动态代理
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.");
}
// todo 这里有疑问 即
// targetClass.isInterface()
// Proxy.isProxyClass(targetClass)
// 什么情况下会生效
if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
// 创建jdk动态代理
return new JdkDynamicAopProxy(config);
}
// 创建CGLIB动态代理
return new ObjenesisCglibAopProxy(config);
}
// 2、默认创建JDK动态代理
else {
return new JdkDynamicAopProxy(config);
}
}
这里我们终于看到了判断CGLIB和JDK动态代理的判断条件，这也是面试会碰到的一个常见的问题。
判断是否需要创建CGLIB动态代理
config.isOptimize()：判断通过CGLIB创建的代理是否使用了优化策略
该条件取值于ProxyConfig类的optimize属性。此属性标记是否对代理进行优化。启动优化通常意味着在代理对象被创建后，增强的修改将不会生效，因此默认值为false。如果exposeProxy设置为true，即使optimize为true也会被忽略。config.isProxyTargetClass()：是否配置了proxy-target-class为true
该条件取值于ProxyConfig类的proxyTargetClass属性。此属性标记是否直接对目标类进行代理，而不是通过接口产生代理。hasNoUserSuppliedProxyInterfaces(config)：是否存在代理接口
满足以上三者条件的任何一个，则会考虑开启CGLIB动态代理，但是在该if条件里还有另外一层判断 targetClass.isInterface() || Proxy.isProxyClass(targetClass),即如果目标类本身就是一个接口，或者目标类是由Proxy.newProxyInstance()或Proxy.getProxyClass()生成时，则依然采用jdk动态代理。
4.2 获取CGLIB动态代理
@Override
public Object getProxy(@Nullable ClassLoader classLoader) {
if (logger.isTraceEnabled()) {
logger.trace("Creating CGLIB proxy: " + this.advised.getTargetSource());
}
try {
Class<?> rootClass = this.advised.getTargetClass();
Assert.state(rootClass != null, "Target class must be available for creating a CGLIB proxy");
Class<?> proxySuperClass = rootClass;
if (ClassUtils.isCglibProxyClass(rootClass)) {
proxySuperClass = rootClass.getSuperclass();
Class<?>[] additionalInterfaces = rootClass.getInterfaces();
for (Class<?> additionalInterface : additionalInterfaces) {
this.advised.addInterface(additionalInterface);
}
}
// Validate the class, writing log messages as necessary.
validateClassIfNecessary(proxySuperClass, classLoader);
// Configure CGLIB Enhancer...
// 新建并配置Enhancer
Enhancer enhancer = createEnhancer();
if (classLoader != null) {
enhancer.setClassLoader(classLoader);
if (classLoader instanceof SmartClassLoader &&
((SmartClassLoader) classLoader).isClassReloadable(proxySuperClass)) {
enhancer.setUseCache(false);
}
}
enhancer.setSuperclass(proxySuperClass);
enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
enhancer.setStrategy(new ClassLoaderAwareUndeclaredThrowableStrategy(classLoader));
Callback[] callbacks = getCallbacks(rootClass);
Class<?>[] types = new Class<?>[callbacks.length];
for (int x = 0; x < types.length; x++) {
types[x] = callbacks[x].getClass();
}
// fixedInterceptorMap only populated at this point, after getCallbacks call above
enhancer.setCallbackFilter(new ProxyCallbackFilter(
this.advised.getConfigurationOnlyCopy(), this.fixedInterceptorMap, this.fixedInterceptorOffset));
enhancer.setCallbackTypes(types);
// Generate the proxy class and create a proxy instance.
// 生成代理类并创建代理实例
return createProxyClassAndInstance(enhancer, callbacks);
}
catch (CodeGenerationException | IllegalArgumentException ex) {
throw new AopConfigException("Could not generate CGLIB subclass of " + this.advised.getTargetClass() +
": Common causes of this problem include using a final class or a non-visible class",
ex);
}
catch (Throwable ex) {
// TargetSource.getTarget() failed
throw new AopConfigException("Unexpected AOP exception", ex);
}
}
紧接着看 Spring ： Spring Aop CGLIB动态代理调用过程
4.3 获取JDK动态代理
@Override
public Object getProxy(@Nullable ClassLoader classLoader) {
if (logger.isTraceEnabled()) {
logger.trace("Creating JDK dynamic proxy: " + this.advised.getTargetSource());
}
// 确定用于给定AOP配置的代理的完整接口集。
Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
// 判断被代理接口有没有重写equals和hashCode方法
findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
// 为接口创建代理
return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
}
