手动配置Spring AOP的源码分析
这里写自定义目录标题
- ProxyFactoryBean模式
-
- 目标对象拦截器链的初始化
- 获取拦截目标对象
ProxyFactoryBean模式
在Spring中实现aop功能有两种方式，一种是手动配置的方式，另一种是自动配置。
手动配置的实现主要有以下几个类完成：
使用ProxyFactoryBean时，需要设置targetName（代理对象），以及作用在代理对象上的拦截器interceptorNames属性，如果使用注解的方式编程，示例代码如下：
@Configuration
public class MainConfig1 {
//注册目标对象
@Bean
public Service1 service1() {
return new Service1();
}
//注册一个前置通知
@Bean
public MethodBeforeAdvice beforeAdvice() {
MethodBeforeAdvice advice = new MethodBeforeAdvice() {
@Override
public void before(Method method, Object[] args, @Nullable Object target) throws Throwable {
System.out.println("准备调用：" + method);
}
};
return advice;
}
//注册一个后置通知
@Bean
public MethodInterceptor costTimeInterceptor() {
MethodInterceptor methodInterceptor = new MethodInterceptor() {
@Override
public Object invoke(MethodInvocation invocation) throws Throwable {
long starTime = System.nanoTime();
Object result = invocation.proceed();
long endTime = System.nanoTime();
System.out.println(invocation.getMethod() + ",耗时(纳秒)：" + (endTime - starTime));
return result;
}
};
return methodInterceptor;
}
//注册ProxyFactoryBean
@Bean
public ProxyFactoryBean service1Proxy() {
//1.创建ProxyFactoryBean
ProxyFactoryBean proxyFactoryBean = new ProxyFactoryBean();
//2.设置目标对象的bean名称
proxyFactoryBean.setTargetName("service1");
//3.设置拦截器的bean名称列表，此处2个（advice1和advice2)
proxyFactoryBean.setInterceptorNames("beforeAdvice", "costTimeInterceptor");
return proxyFactoryBean;
}
}
其中service1是目标bean，设置在它上面的拦截器有beforeAdvice和costTimeInterceptor两个通知。
ProxyFactoryBean是对一个目标类进行AOP的。ProxyFactoryBean这个类是一个FactoryBean，也就是我们生成对象的时候，是调用其getObject方法获得实际的bean的。获得的bean就是目标bean的代理ProxyBean对象。getObject方法源码如下：
@Override
@Nullable
public Object getObject() throws BeansException {
initializeAdvisorChain();
if (isSingleton()) {
return getSingletonInstance();
}
else {
if (this.targetName == null) {
logger.info("Using non-singleton proxies with singleton targets is often undesirable. " +
"Enable prototype proxies by setting the 'targetName' property.");
}
return newPrototypeInstance();
}
}
initializeAdvisorChain()方法进行拦截器链的初始化。
目标对象拦截器链的初始化
这个过程是将配置中的拦截器提取出来的过程，有两种方式：
1.通过通知名称通配符（*）匹配拦截器（通知）
2.通过具体的通知器名称获取拦截器（通知）
上述测试代码未使用通配符，所以进入的是通过完全名称的方式获取通知的。
获取通知的过程就是将通知的名字传给beanFactory，调用它的getBean方法获取bean，为什么ProxyFactoryBean能有beanFactory的引用，因为其实现了BeanFactoryAware接口，当spring创建完ProxyFactoryBean的实例后，会调用后处理器方法设置spring容器到proxyFactoryBean对象的引用中。
private synchronized void initializeAdvisorChain() throws AopConfigException, BeansException {
if (this.advisorChainInitialized) {
return;
}
if (!ObjectUtils.isEmpty(this.interceptorNames)) {
if (this.beanFactory == null) {
throw new IllegalStateException("No BeanFactory available anymore (probably due to serialization) " +
"- cannot resolve interceptor names " + Arrays.asList(this.interceptorNames));
}
// Globals can't be last unless we specified a targetSource using the property...
if (this.interceptorNames[this.interceptorNames.length - 1].endsWith(GLOBAL_SUFFIX) &&
this.targetName == null && this.targetSource == EMPTY_TARGET_SOURCE) {
throw new AopConfigException("Target required after globals");
}
// Materialize interceptor chain from bean names.
for (String name : this.interceptorNames) {
if (name.endsWith(GLOBAL_SUFFIX)) {
if (!(this.beanFactory instanceof ListableBeanFactory)) {
throw new AopConfigException(
"Can only use global advisors or interceptors with a ListableBeanFactory");
}
addGlobalAdvisors((ListableBeanFactory) this.beanFactory,
name.substring(0, name.length() - GLOBAL_SUFFIX.length()));
}
else {
// If we get here, we need to add a named interceptor.
// We must check if it's a singleton or prototype.
Object advice;
if (this.singleton || this.beanFactory.isSingleton(name)) {
// Add the real Advisor/Advice to the chain. 通过beanFactory获取bean
advice = this.beanFactory.getBean(name);
}
else {
// It's a prototype Advice or Advisor: replace with a prototype.
// Avoid unnecessary creation of prototype bean just for advisor chain initialization.
advice = new PrototypePlaceholderAdvisor(name);
}
addAdvisorOnChainCreation(advice);
}
}
}
this.advisorChainInitialized = true;
}
addAdvisorOnChainCreation方法经过一些转换后，会把通知设置到拦截器链中。
获取拦截目标对象
根据目标类是单例还是多例确定初始化方法，获得bean
下面分析获取单例代理对象的过程：
/**
* Return the singleton instance of this class's proxy object,
* lazily creating it if it hasn't been created already.
* @return the shared singleton proxy
*/
private synchronized Object getSingletonInstance() {
if (this.singletonInstance == null) {
this.targetSource = freshTargetSource();
if (this.autodetectInterfaces && getProxiedInterfaces().length == 0 && !isProxyTargetClass()) {
// Rely on AOP infrastructure to tell us what interfaces to proxy.
Class<?> targetClass = getTargetClass();
if (targetClass == null) {
throw new FactoryBeanNotInitializedException("Cannot determine target class for proxy");
}
setInterfaces(ClassUtils.getAllInterfacesForClass(targetClass, this.proxyClassLoader));
}
// Initialize the shared singleton instance.
super.setFrozen(this.freezeProxy);
this.singletonInstance = getProxy(createAopProxy());
}
return this.singletonInstance;
}
freshTargetSource()主要是创建被代理的目标实例，而不是创建代理对象，接着为对象设置实现的接口，最主要的代码是this.singletonInstance = getProxy(createAopProxy());
首先进入createAopProxy方法，这个方法在ProxyFactoryBean的父类ProxyCreateSupport中：
/**
* Subclasses should call this to get a new AOP proxy. They should not
* create an AOP proxy with {@code this} as an argument.
*/
protected final synchronized AopProxy createAopProxy() {
if (!this.active) {
activate();
}
return getAopProxyFactory().createAopProxy(this);
}
上述getAopProxyFactory()获取的是在构造函数中实例化的默认AopProxyFactory：
public ProxyCreatorSupport() {
this.aopProxyFactory = new DefaultAopProxyFactory();
}
进入DefaultAopProxyFactory的createAopProxy方法，
public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {
@Override
public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
if (!NativeDetector.inNativeImage() &&
(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);
}
}
...
上述方法根据目标类是否实现了接口来确定代理类是使用java代理还是Cglib代理类。我们先分析一下Jdk动态代理。这个JdkDynamicAopProxy类封装了对目标对象的方法调用拦截：
/**
* Construct a new JdkDynamicAopProxy for the given AOP configuration.
* @param config the AOP configuration as AdvisedSupport object
* @throws AopConfigException if the config is invalid. We try to throw an informative
* exception in this case, rather than let a mysterious failure happen later.
*/
public JdkDynamicAopProxy(AdvisedSupport config) throws AopConfigException {
Assert.notNull(config, "AdvisedSupport must not be null");
if (config.getAdvisorCount() == 0 && config.getTargetSource() == AdvisedSupport.EMPTY_TARGET_SOURCE) {
throw new AopConfigException("No advisors and no TargetSource specified");
}
this.advised = config;
this.proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
findDefinedEqualsAndHashCodeMethods(this.proxiedInterfaces);
}
Jdk动态代理的构造函数以配置类（就是当前ProxyFactoryBean对象）作为参数。因为需要获取要拦截的目标对象和通知器，所以要传入这个参数。
获取到代理后回到ProxyFactoryBean的getSingletonInstance方法，在该方法中会调用JdkDynamicProxy的getProxy方法：
protected Object getProxy(AopProxy aopProxy) {
return aopProxy.getProxy(this.proxyClassLoader);
}
触发了在JdkDynamicProxy方法中，获取代理的方法如下：
@Override
public Object getProxy(@Nullable ClassLoader classLoader) {
if (logger.isTraceEnabled()) {
logger.trace("Creating JDK dynamic proxy: " + this.advised.getTargetSource());
}
return Proxy.newProxyInstance(classLoader, this.proxiedInterfaces, this);
}
在上面的方法中，用JDK动态代理设置回调对象为JdkDynamicProxy，所以当客户端调用目标对象的方法时会触发对JdkDynamicProxy的invoke方法回调，从而将对应的通知织入被代理的目标对象方法：
/**
* Implementation of {@code InvocationHandler.invoke}.
* Callers will see exactly the exception thrown by the target,
* unless a hook method throws an exception.
*/
@Override
@Nullable
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
Object oldProxy = null;
boolean setProxyContext = false;
TargetSource targetSource = this.advised.targetSource;
Object target = null;
try {
if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
// The target does not implement the equals(Object) method itself.
return equals(args[0]);
}
else if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
// The target does not implement the hashCode() method itself.
return hashCode();
}
else if (method.getDeclaringClass() == DecoratingProxy.class) {
// There is only getDecoratedClass() declared -> dispatch to proxy config.
return AopProxyUtils.ultimateTargetClass(this.advised);
}
else if (!this.advised.opaque && method.getDeclaringClass().isInterface() &&
method.getDeclaringClass().isAssignableFrom(Advised.class)) {
// Service invocations on ProxyConfig with the proxy config...
return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args);
}
Object retVal;
if (this.advised.exposeProxy) {
// Make invocation available if necessary.
oldProxy = AopContext.setCurrentProxy(proxy);
setProxyContext = true;
}
// Get as late as possible to minimize the time we "own" the target,
// in case it comes from a pool.
target = targetSource.getTarget();
Class<?> targetClass = (target != null ? target.getClass() : null);
// Get the interception chain for this method.
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
// Check whether we have any advice. If we don't, we can fallback on direct
// reflective invocation of the target, and avoid creating a MethodInvocation.
if (chain.isEmpty()) {
// We can skip creating a MethodInvocation: just invoke the target directly
// Note that the final invoker must be an InvokerInterceptor so we know it does
// nothing but a reflective operation on the target, and no hot swapping or fancy proxying.
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
}
else {
// We need to create a method invocation...
MethodInvocation invocation =
new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
// Proceed to the joinpoint through the interceptor chain.
retVal = invocation.proceed();
}
// Massage return value if necessary.
Class<?> returnType = method.getReturnType();
if (retVal != null && retVal == target &&
returnType != Object.class && returnType.isInstance(proxy) &&
!RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
// Special case: it returned "this" and the return type of the method
// is type-compatible. Note that we can't help if the target sets
// a reference to itself in another returned object.
retVal = proxy;
}
else if (retVal == null && returnType != Void.TYPE && returnType.isPrimitive()) {
throw new AopInvocationException(
"Null return value from advice does not match primitive return type for: " + method);
}
return retVal;
}
finally {
if (target != null && !targetSource.isStatic()) {
// Must have come from TargetSource.
targetSource.releaseTarget(target);
}
if (setProxyContext) {
// Restore old proxy.
AopContext.setCurrentProxy(oldProxy);
}
}
}
到这里基本清楚了当被代理对象是实现了接口的时候，动态代理的创建过程。如果是使用CgLib代理，则生成的代理对象对目标对象方法的拦截设置是在CglibAopProxy中完成的:
@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 (rootClass.getName().contains(ClassUtils.CGLIB_CLASS_SEPARATOR)) {
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...
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 ClassLoaderAwareGeneratorStrategy(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.
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);
}
}
从上面的逻辑可以看出，CglibAopProxy的代理对象生成通过设置增强器的属性, 设置拦截器，实现对目标对象方法调用的拦截。以一个拦截器的实现为例：
private static class DynamicAdvisedInterceptor implements MethodInterceptor, Serializable {
private final AdvisedSupport advised;
public DynamicAdvisedInterceptor(AdvisedSupport advised) {
this.advised = advised;
}
@Override
@Nullable
public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
Object oldProxy = null;
boolean setProxyContext = false;
Object target = null;
TargetSource targetSource = this.advised.getTargetSource();
try {
if (this.advised.exposeProxy) {
// Make invocation available if necessary.
oldProxy = AopContext.setCurrentProxy(proxy);
setProxyContext = true;
}
// Get as late as possible to minimize the time we "own" the target, in case it comes from a pool...
target = targetSource.getTarget();
Class<?> targetClass = (target != null ? target.getClass() : null);
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
Object retVal;
// Check whether we only have one InvokerInterceptor: that is,
// no real advice, but just reflective invocation of the target.
if (chain.isEmpty() && Modifier.isPublic(method.getModifiers())) {
// We can skip creating a MethodInvocation: just invoke the target directly.
// Note that the final invoker must be an InvokerInterceptor, so we know
// it does nothing but a reflective operation on the target, and no hot
// swapping or fancy proxying.
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = methodProxy.invoke(target, argsToUse);
}
else {
// We need to create a method invocation...
retVal = new CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed();
}
retVal = processReturnType(proxy, target, method, retVal);
return retVal;
}
finally {
if (target != null && !targetSource.isStatic()) {
targetSource.releaseTarget(target);
}
if (setProxyContext) {
// Restore old proxy.
AopContext.setCurrentProxy(oldProxy);
}
}
}
@Override
public boolean equals(@Nullable Object other) {
return (this == other ||
(other instanceof DynamicAdvisedInterceptor &&
this.advised.equals(((DynamicAdvisedInterceptor) other).advised)));
}
/**
* CGLIB uses this to drive proxy creation.
*/
@Override
public int hashCode() {
return this.advised.hashCode();
}
}
DynamicAdvisedInterceptor会作为目标对象拦截器中的一个，在getCallbacks中获取到，设置到目标对象方法调用拦截器链中，其intercept方法：
retVal = new CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed();
接下来就要分析，通知器的调用机制，也就是说，当目标对象被调用时，如何适配不同的通知器（advisor）对织入代码的前后顺序，执行顺序进行控制。