Spring源码-AOP(八)-创建代理
2017-09-12 本文已影响172人
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前言
上一篇结束了增强器的获取，接下来我们看下代理是如何创建的。
通过时序图可以看出该模块主要是由AbstractAutoProxyCreator和ProxyFactory来完成的相应功能，下面进行详细分析。
初始化操作
接上一章wrapIfNecessary()方法，我们看下createProxy（）这个方法的内部实现
【AbstractAutoProxyCreator】
············
Object proxy = createProxy(
bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
············
}
接下来我们看createProxy()的具体实现
protected Object createProxy(Class<?> beanClass, @Nullable String beanName,
@Nullable Object[] specificInterceptors, TargetSource targetSource) {
if (this.beanFactory instanceof ConfigurableListableBeanFactory) {
AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory) this.beanFactory, beanName, beanClass);
}
ProxyFactory proxyFactory = new ProxyFactory();
//获取当前类中的属性
proxyFactory.copyFrom(this);
/**
*决定对给定的bean是否使用targetClass，而不是他的接口代理
*检查proxyTargetClass设置以及presserveTargetClass属性
*/
if (!proxyFactory.isProxyTargetClass()) {
if (shouldProxyTargetClass(beanClass, beanName)) {
proxyFactory.setProxyTargetClass(true);
}
else {
//添加代理接口
evaluateProxyInterfaces(beanClass, proxyFactory);
}
}
Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
for (Advisor advisor : advisors) {
//添加增强器
proxyFactory.addAdvisor(advisor);
}
//设置要被代理的类
proxyFactory.setTargetSource(targetSource);
//定制代理
customizeProxyFactory(proxyFactory);
/**
* 用来控制代理工厂被配置之后，是否允许修改通知
* 缺省值为false()
*/
proxyFactory.setFrozen(this.freezeProxy);
if (advisorsPreFiltered()) {
proxyFactory.setPreFiltered(true);
}
return proxyFactory.getProxy(getProxyClassLoader());
}
对于代理类的创建及处理，spring委托给了ProxyFactory去处理，而在函数中主要是对ProxyFactory的初始化操作，包括如下
- 1、获取当前类中的属性
- 2、添加代理接口。
- 3、封装Advisor并加入到proxyFactory中
- 4、设置要代理的类
- 5、当然在Spring中还未子类提供了定制的函数customizeProxyFactory,子类可以在此函数中对proxyFactory的进一步封装。
- 6、进行获取代理操作
封装逻辑
其中，封装Advisor并加入到ProxyFactory中以及创建代理是两个相对繁琐的过程，可以通过ProxyFactory提供的addAdvisor方法直接将增强器置入代理创建工厂中，但是将拦截器封装为增强器还是需要一定的逻辑的。接下来我们看看buildAdvisors()的具体实现
【AbstractAutoProxyCreator】
protected Advisor[] buildAdvisors(@Nullable String beanName, @Nullable Object[] specificInterceptors) {
// Handle prototypes correctly...
//解析出来所以的interceptorName
Advisor[] commonInterceptors = resolveInterceptorNames();
List<Object> allInterceptors = new ArrayList<>();
if (specificInterceptors != null) {
//加入拦截器
allInterceptors.addAll(Arrays.asList(specificInterceptors));
if (commonInterceptors.length > 0) {
if (this.applyCommonInterceptorsFirst) {
allInterceptors.addAll(0, Arrays.asList(commonInterceptors));
}
else {
allInterceptors.addAll(Arrays.asList(commonInterceptors));
}
}
}
if (logger.isDebugEnabled()) {
int nrOfCommonInterceptors = commonInterceptors.length;
int nrOfSpecificInterceptors = (specificInterceptors != null ? specificInterceptors.length : 0);
logger.debug("Creating implicit proxy for bean '" + beanName + "' with " + nrOfCommonInterceptors +
" common interceptors and " + nrOfSpecificInterceptors + " specific interceptors");
}
Advisor[] advisors = new Advisor[allInterceptors.size()];
for (int i = 0; i < allInterceptors.size(); i++) {
//拦截器进行封装转化为Advisor
advisors[i] = this.advisorAdapterRegistry.wrap(allInterceptors.get(i));
}
return advisors;
}
【DefaultAdvisorAdapterRegistry】
public Advisor wrap(Object adviceObject) throws UnknownAdviceTypeException {
//如果要封装的对象本身就是Advisor类型的那么无需再做过多的处理
if (adviceObject instanceof Advisor) {
return (Advisor) adviceObject;
}
//因为此封装的方法只对Advisor与Advice两种类型的数据有效，如果不是将不能进行封装
if (!(adviceObject instanceof Advice)) {
throw new UnknownAdviceTypeException(adviceObject);
}
Advice advice = (Advice) adviceObject;
if (advice instanceof MethodInterceptor) {
// So well-known it doesn't even need an adapter.
//如果是MethodInterceptor类型则使用DefaultPointcutAdvisor封装
return new DefaultPointcutAdvisor(advice);
}
//如果存在Advisor的适配器那么也同样需要进行封装。
for (AdvisorAdapter adapter : this.adapters) {
// Check that it is supported.
if (adapter.supportsAdvice(advice)) {
return new DefaultPointcutAdvisor(advice);
}
}
throw new UnknownAdviceTypeException(advice);
}
由于Spring中涉及过多的拦截器、通知器、增强方法等方式来对逻辑进行增强，所以非常有必要统一封装成Advisor来进行代理的创建，完成了增强的封装过程，那么解析最重要的移步就是代理的创建与获取了。
【ProxyFactory】
public Object getProxy(@Nullable ClassLoader classLoader) {
return createAopProxy().getProxy(classLoader);
}
创建代理
【ProxyCreatorSupport】
protected final synchronized AopProxy createAopProxy() {
if (!this.active) {
activate();
}
//创建代理
return getAopProxyFactory().createAopProxy(this);
}
该方法封装在AopProxyFactory 接口中，由实现类DefaultAopFactory完成相应实现
【DefaultAopFactory】
public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
//此处判断是JDKProxy的实现还是CGLIB的实现
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);
}
}
到此已经完成了代理的创建。这里最终的实现是由JDKProxy或者CGLIB代理实现。这里需要注意三个判断条件
- 1、optimize:用了控制通过CGLIB创建的代理是否使用激进的优化策略。除非完全了解AOP。否则不统计。目前这个属性也仅仅用于CGLIB。
- 2、proxyTargetClass:这个属性为true时，目标本身被代理而不是目标类的接口，如果这个属性为true，CGLIB代理将被创建，设置方式<aop：aspectj-autoproxy proxy-target-class="true"/>
- 3、hasNoUserSuppliedProxyInterfaces：是否存在代理接口。
创建代理的方法
根据之前的分析得知，SpringAop动态生成代理有两种方式：JDK和CGLIB。
- 1、目标对象实现了接口，默认采用JDK动态代理实现，也可强制使用CGLIB。
- 2、若没有实现接口，必须采用CGLIB，Spring会自动在JDK动态代理和CGLIB之间转换。而且，jdk动态接口只能对实现了接口类生产代理，而不能针对类。CGLIB是针对类实现代理的，覆盖其中的方法，是继承实现，所以该类或方法最后不要声明诚final。
这里需要注意：
AopProxy才是生产代理的主要位置，而前面看到的ProxyFactory在AopProxy代理对象和IOC容器配置之间仅仅是一个桥梁作用。AopProxy代理对象可以由JDK或者CGLIB生产，如下图
JDK动态代理
在JDK代理的使用中，其实现类是JdkDynamicAopProxy，而JdkDynamicAopProxy类最为核心的是InvocationHandler接口。而在JdkDynamicAopProxy的方法中最为重要的有以下三个
- 构造函数
- invoke
- getProxy()
构造函数
【JdkDynamicAopProxy】
public JdkDynamicAopProxy(AdvisedSupport config) throws AopConfigException {
Assert.notNull(config, "AdvisedSupport must not be null");
if (config.getAdvisors().length == 0 && config.getTargetSource() == AdvisedSupport.EMPTY_TARGET_SOURCE) {
throw new AopConfigException("No advisors and no TargetSource specified");
}
this.advised = config;
}
从源码可以看出构造函数主要用于值的传递
【JdkDynamicAopProxy】
public Object getProxy(@Nullable ClassLoader classLoader) {
if (logger.isDebugEnabled()) {
logger.debug("Creating JDK dynamic proxy: target source is " + this.advised.getTargetSource());
}
Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
}
该方法主要用于获取生成的代理对象，是必不可少的方法
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
MethodInvocation invocation;
Object oldProxy = null;
boolean setProxyContext = false;
TargetSource targetSource = this.advised.targetSource;
Object target = null;
try {
//equals方法的处理
if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
// The target does not implement the equals(Object) method itself.
return equals(args[0]);
}
//hash方法的处理
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;
/**
* 有时候目标对象内部的自我调用将无法实施切面中的增强
* 则需要通过属性暴露代理
*/
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.
//获取当前方法的拦截器
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.
//如果没有发现任何拦截器那么直接调入切点方法
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
}
else {
// We need to create a method invocation...
//将拦截器封装在ReflectiveMethodInvocation
//以便于使用期processd进行链接表拦截器
invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
// Proceed to the joinpoint through the interceptor chain.
//执行拦截器链
retVal = invocation.proceed();
}
// Massage return value if necessary.
//返回结果
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);
}
}
}
上面函数主要工作是创建了一个拦截器链，并使用ReflectiveMethodInvocation类进行了链的封装，而在ReflectiveMethodInvocation类的proceed方法中实现了拦截器的逐一调用，接下来看看proceed方法怎么实现？
【ReflectiveMethodInvocation】
public Object proceed() throws Throwable {
// We start with an index of -1 and increment early.
//执行完所有增强后执行切点方法
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
return invokeJoinpoint();
}
//获取下一个要执行的拦截器
Object interceptorOrInterceptionAdvice =
this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
// Evaluate dynamic method matcher here: static part will already have
// been evaluated and found to match.
//动态匹配
InterceptorAndDynamicMethodMatcher dm =
(InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
if (dm.methodMatcher.matches(this.method, this.targetClass, this.arguments)) {
return dm.interceptor.invoke(this);
}
else {
// Dynamic matching failed.
// Skip this interceptor and invoke the next in the chain.
//不匹配则不执行拦截器
return proceed();
}
}
else {
// It's an interceptor, so we just invoke it: The pointcut will have
// been evaluated statically before this object was constructed.
//将this作为参数传递保证当前实例中调用连的执行
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}
在proceed方法中，ReflectiveMethodInvocation主要职责是维护了一个链接调用的计数器，记录着当前调用链接的位置，以便链可以有序的执行，那么在这个翻翻中并没有之前维护的各种增强的顺序，而是将工作委托给各个增强器，使各个增强器在内部进行逻辑实现
CGLIB代理
字节码生成代理：
CGLIB是一个强大的高性能的代码生成包。SpringAOP中完成CGLIB是通过委托给CglibAopProxy实现的，这个类的入口是getProxy。
public Object getProxy(@Nullable ClassLoader classLoader) {
if (logger.isDebugEnabled()) {
logger.debug("Creating CGLIB proxy: target source is " + 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.
//验证class
validateClassIfNecessary(proxySuperClass, classLoader);
// Configure CGLIB Enhancer...
//创建及配置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));
//设置拦截器
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.
//生成代理类以及创建代理
return createProxyClassAndInstance(enhancer, callbacks);
}
catch (CodeGenerationException | IllegalArgumentException ex) {
throw new AopConfigException("Could not generate CGLIB subclass of class [" +
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);
}
}
CGLIB的实现最重要的就是EnHancer。以上函数完整的阐述了Spring中的Enhancer过程，这块是通过getCallBacks方法设置拦截器链的。接下来我们看看getCallBacks方法。
getCallbacks
private Callback[] getCallbacks(Class<?> rootClass) throws Exception {
// Parameters used for optimization choices...
//属性的处理
boolean exposeProxy = this.advised.isExposeProxy();
boolean isFrozen = this.advised.isFrozen();
boolean isStatic = this.advised.getTargetSource().isStatic();
// Choose an "aop" interceptor (used for AOP calls).
//将拦截器封装在DYnamicAdvisedInterceptor中
Callback aopInterceptor = new DynamicAdvisedInterceptor(this.advised);
// Choose a "straight to target" interceptor. (used for calls that are
// unadvised but can return this). May be required to expose the proxy.
Callback targetInterceptor;
if (exposeProxy) {
targetInterceptor = isStatic ?
new StaticUnadvisedExposedInterceptor(this.advised.getTargetSource().getTarget()) :
new DynamicUnadvisedExposedInterceptor(this.advised.getTargetSource());
}
else {
targetInterceptor = isStatic ?
new StaticUnadvisedInterceptor(this.advised.getTargetSource().getTarget()) :
new DynamicUnadvisedInterceptor(this.advised.getTargetSource());
}
// Choose a "direct to target" dispatcher (used for
// unadvised calls to static targets that cannot return this).
Callback targetDispatcher = isStatic ?
new StaticDispatcher(this.advised.getTargetSource().getTarget()) : new SerializableNoOp();
Callback[] mainCallbacks = new Callback[] {
//将拦截器加入callback中
aopInterceptor, // for normal advice
targetInterceptor, // invoke target without considering advice, if optimized
new SerializableNoOp(), // no override for methods mapped to this
targetDispatcher, this.advisedDispatcher,
new EqualsInterceptor(this.advised),
new HashCodeInterceptor(this.advised)
};
Callback[] callbacks;
// If the target is a static one and the advice chain is frozen,
// then we can make some optimizations by sending the AOP calls
// direct to the target using the fixed chain for that method.
if (isStatic && isFrozen) {
Method[] methods = rootClass.getMethods();
Callback[] fixedCallbacks = new Callback[methods.length];
this.fixedInterceptorMap = new HashMap<>(methods.length);
// TODO: small memory optimization here (can skip creation for methods with no advice)
for (int x = 0; x < methods.length; x++) {
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(methods[x], rootClass);
fixedCallbacks[x] = new FixedChainStaticTargetInterceptor(
chain, this.advised.getTargetSource().getTarget(), this.advised.getTargetClass());
this.fixedInterceptorMap.put(methods[x].toString(), x);
}
// Now copy both the callbacks from mainCallbacks
// and fixedCallbacks into the callbacks array.
callbacks = new Callback[mainCallbacks.length + fixedCallbacks.length];
System.arraycopy(mainCallbacks, 0, callbacks, 0, mainCallbacks.length);
System.arraycopy(fixedCallbacks, 0, callbacks, mainCallbacks.length, fixedCallbacks.length);
this.fixedInterceptorOffset = mainCallbacks.length;
}
else {
callbacks = mainCallbacks;
}
return callbacks;
}
至此，AOP的源码分析完成，下一篇我们会整体梳理下相关流程。
