ProxyFactoryBean 如何实现AOP proxy都有可能转为Advised接口
1、ProxyFactoryBean 把proxy的创建交给AopProxy去做。
public class ProxyFactoryBean extends AdvisedSupport
implements FactoryBean, BeanFactoryAware, AdvisedSupportListener {
public Object getObject() throws BeansException {
//invoke AopProxy 去 创建proxy
return this.singleton ? getSingletonInstance() : newPrototypeInstance();
}
//inherited from ProxyConfig
public void setAopProxyFactory(AopProxyFactory apf) {
this.aopProxyFactory = apf;
}
//inherited from ProxyConfig
public AopProxyFactory getAopProxyFactory() {
return this.aopProxyFactory;
}
}
2.、那么AopProxy又如何获取？答案是从AopProxyFactory获得。这个AopProxyFactory已在ProxyFactoryBean掌控范围内，如上述代码所示。AopProxyFactory interface如下所示：
public interface AopProxyFactory {
AopProxy createAopProxy(AdvisedSupport advisedSupport) throws AopConfigException;
}
3、AopProxy是如何introduce Advised interface的？那要先从AopProxyFactory的implementation说起。
AopProxyFactory的实现类目前只有DefaultAopProxyFactory。这个类的核心方法如下：
public AopProxy createAopProxy(AdvisedSupport advisedSupport) throws AopConfigException {
if (advisedSupport.isOptimize() || advisedSupport.isProxyTargetClass() ||
advisedSupport.getProxiedInterfaces().length == 0) {
if (!cglibAvailable) {
throw new AopConfigException(
"Cannot proxy target class because CGLIB2 is not available. " +
"Add CGLIB to the class path or specify proxy interfaces.");
}
return CglibProxyFactory.createCglibProxy(advisedSupport);
}
else {
return new JdkDynamicAopProxy(advisedSupport);
}
}
这个方法主要是依赖CglibProxyFactory 类和JdkDynamicAopProxy类。这两个类是如何代理所有的接口的呢？
这两个类都是重要接口AopProxy的实现类，这个接口的核心方法是
public Object getProxy(ClassLoader classLoader)。
其中JdkDynamicAopProxy实现该方法用到的获取需要代理的接口的代码如下：
public Object getProxy(ClassLoader classLoader) {
if (logger.isDebugEnabled()) {
Class targetClass = this.advised.getTargetSource().getTargetClass();
logger.debug("Creating JDK dynamic proxy" +
(targetClass != null ? " for [" + targetClass.getName() + "]" : ""));
}
Class[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised);
return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
}
而CglibProxyFactory的getProxy(ClassLoader classLoader)方法如下：
public Object getProxy(ClassLoader classLoader) {
……
Enhancer enhancer = new Enhancer();
……
enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
……
}
从上面可以看出，这两个AopProxy实现方案在获取接口时都是通过AopProxyUtils.completeProxiedInterfaces(this.advised)获取的。该方法如下：
/**
* Get complete set of interfaces to proxy. This will always add the Advised interface
* unless the AdvisedSupport's "opaque" flag is true.
* @return the complete set of interfaces to proxy
*/
public static Class[] completeProxiedInterfaces(AdvisedSupport advised) {
// Won't include Advised, which may be necessary.
Class[] specifiedInterfaces = advised.getProxiedInterfaces();
Class[] proxiedInterfaces = specifiedInterfaces;
if (!advised.isOpaque() && !advised.isInterfaceProxied(Advised.class)) {
// We need to add the Advised interface.
proxiedInterfaces = new Class[specifiedInterfaces.length + 1];
proxiedInterfaces[0] = Advised.class;
System.arraycopy(specifiedInterfaces, 0, proxiedInterfaces, 1, specifiedInterfaces.length);
}
return proxiedInterfaces;
}
从这可以看出，是在这强制加了对Advised interface的实现。前提是是否允许代理该interafce，这由isOpaque方法确定，该方法Return whether proxies created by this configuration should be prevented from being cast to Advised.
4. 顺便提一下，Advised interface的具体实现又是怎样的，在哪呢？
4.1 在JdkDynamicAopProxy里，
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
……
if (Advised.class == method.getDeclaringClass()) {
// service invocations on ProxyConfig with the proxy config
return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args);
}
……
}
注意第一个参数是this.advised，其实就是ProxyFactoryBean本身，注意在我发表的其天的Spring文章里也曾提到，ProxyFactoryBean extends AdvisedSupport，
而AdisedSupport extends ProxyConfig implements Advised，也就是说Advised的默认实现就是AdisedSupport。
4.2 在Cglib2AopProxy里（如果不熟Cglib，建议先看看其天有关的Cglib资料），
public Object getProxy(ClassLoader classLoader) {
……
Enhancer enhancer = new Enhancer();
……
enhancer.setCallbackFilter(new ProxyCallbackFilter(this.advised));
……
Callback[] callbacks = getCallbacks(rootClass);
……
……
……
}
private Callback[] getCallbacks(Class rootClass) throws Exception {
……
Callback[] mainCallbacks = new Callback[]{
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)
};
……
}
private class ProxyCallbackFilter implements CallbackFilter {
public int accept(Method method) {
if (method.getDeclaringClass() == Advised.class) {
if (logger.isDebugEnabled()) {
logger.debug("Method " + method + " is declared on Advised - using DISPATCH_ADVISED");
}
return DISPATCH_ADVISED;// DISPATCH_ADVISED 值为4.
}
……
}
}
private final transient AdvisedDispatcher advisedDispatcher = new AdvisedDispatcher();
/**
* Dispatcher for any methods declared on the Advised class.
*/
private class AdvisedDispatcher implements Dispatcher, Serializable {
public Object loadObject() throws Exception {
return advised;
}
}
注意Dispatcher extends Callback interface 。
public class ProxyFactoryBean extends AdvisedSupport
implements FactoryBean, BeanFactoryAware, AdvisedSupportListener {
public Object getObject() throws BeansException {
//invoke AopProxy 去 创建proxy
return this.singleton ? getSingletonInstance() : newPrototypeInstance();
}
//inherited from ProxyConfig
public void setAopProxyFactory(AopProxyFactory apf) {
this.aopProxyFactory = apf;
}
//inherited from ProxyConfig
public AopProxyFactory getAopProxyFactory() {
return this.aopProxyFactory;
}
}
2.、那么AopProxy又如何获取？答案是从AopProxyFactory获得。这个AopProxyFactory已在ProxyFactoryBean掌控范围内，如上述代码所示。AopProxyFactory interface如下所示：
public interface AopProxyFactory {
AopProxy createAopProxy(AdvisedSupport advisedSupport) throws AopConfigException;
}
3、AopProxy是如何introduce Advised interface的？那要先从AopProxyFactory的implementation说起。
AopProxyFactory的实现类目前只有DefaultAopProxyFactory。这个类的核心方法如下：
public AopProxy createAopProxy(AdvisedSupport advisedSupport) throws AopConfigException {
if (advisedSupport.isOptimize() || advisedSupport.isProxyTargetClass() ||
advisedSupport.getProxiedInterfaces().length == 0) {
if (!cglibAvailable) {
throw new AopConfigException(
"Cannot proxy target class because CGLIB2 is not available. " +
"Add CGLIB to the class path or specify proxy interfaces.");
}
return CglibProxyFactory.createCglibProxy(advisedSupport);
}
else {
return new JdkDynamicAopProxy(advisedSupport);
}
}
这个方法主要是依赖CglibProxyFactory 类和JdkDynamicAopProxy类。这两个类是如何代理所有的接口的呢？
这两个类都是重要接口AopProxy的实现类，这个接口的核心方法是
public Object getProxy(ClassLoader classLoader)。
其中JdkDynamicAopProxy实现该方法用到的获取需要代理的接口的代码如下：
public Object getProxy(ClassLoader classLoader) {
if (logger.isDebugEnabled()) {
Class targetClass = this.advised.getTargetSource().getTargetClass();
logger.debug("Creating JDK dynamic proxy" +
(targetClass != null ? " for [" + targetClass.getName() + "]" : ""));
}
Class[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised);
return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
}
而CglibProxyFactory的getProxy(ClassLoader classLoader)方法如下：
public Object getProxy(ClassLoader classLoader) {
……
Enhancer enhancer = new Enhancer();
……
enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
……
}
从上面可以看出，这两个AopProxy实现方案在获取接口时都是通过AopProxyUtils.completeProxiedInterfaces(this.advised)获取的。该方法如下：
/**
* Get complete set of interfaces to proxy. This will always add the Advised interface
* unless the AdvisedSupport's "opaque" flag is true.
* @return the complete set of interfaces to proxy
*/
public static Class[] completeProxiedInterfaces(AdvisedSupport advised) {
// Won't include Advised, which may be necessary.
Class[] specifiedInterfaces = advised.getProxiedInterfaces();
Class[] proxiedInterfaces = specifiedInterfaces;
if (!advised.isOpaque() && !advised.isInterfaceProxied(Advised.class)) {
// We need to add the Advised interface.
proxiedInterfaces = new Class[specifiedInterfaces.length + 1];
proxiedInterfaces[0] = Advised.class;
System.arraycopy(specifiedInterfaces, 0, proxiedInterfaces, 1, specifiedInterfaces.length);
}
return proxiedInterfaces;
}
从这可以看出，是在这强制加了对Advised interface的实现。前提是是否允许代理该interafce，这由isOpaque方法确定，该方法Return whether proxies created by this configuration should be prevented from being cast to Advised.
4. 顺便提一下，Advised interface的具体实现又是怎样的，在哪呢？
4.1 在JdkDynamicAopProxy里，
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
……
if (Advised.class == method.getDeclaringClass()) {
// service invocations on ProxyConfig with the proxy config
return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args);
}
……
}
注意第一个参数是this.advised，其实就是ProxyFactoryBean本身，注意在我发表的其天的Spring文章里也曾提到，ProxyFactoryBean extends AdvisedSupport，
而AdisedSupport extends ProxyConfig implements Advised，也就是说Advised的默认实现就是AdisedSupport。
4.2 在Cglib2AopProxy里（如果不熟Cglib，建议先看看其天有关的Cglib资料），
public Object getProxy(ClassLoader classLoader) {
……
Enhancer enhancer = new Enhancer();
……
enhancer.setCallbackFilter(new ProxyCallbackFilter(this.advised));
……
Callback[] callbacks = getCallbacks(rootClass);
……
……
……
}
private Callback[] getCallbacks(Class rootClass) throws Exception {
……
Callback[] mainCallbacks = new Callback[]{
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)
};
……
}
private class ProxyCallbackFilter implements CallbackFilter {
public int accept(Method method) {
if (method.getDeclaringClass() == Advised.class) {
if (logger.isDebugEnabled()) {
logger.debug("Method " + method + " is declared on Advised - using DISPATCH_ADVISED");
}
return DISPATCH_ADVISED;// DISPATCH_ADVISED 值为4.
}
……
}
}
private final transient AdvisedDispatcher advisedDispatcher = new AdvisedDispatcher();
/**
* Dispatcher for any methods declared on the Advised class.
*/
private class AdvisedDispatcher implements Dispatcher, Serializable {
public Object loadObject() throws Exception {
return advised;
}
}
注意Dispatcher extends Callback interface 。