本篇文章主要带大家简单分析一下AOP的代理对象，至于AOP是什么，如何配置等基础性知识，不在这里讨论。在这之前我们需要了解springframework的三个核心接口与getBean方法
一、FactoryBean&BeanFactory&ObjectFactory
这三个接口都为Springframework的核心接口，虽然这三个名字很像，但是意义却千差万别。面试的时候也常问它们之间的区别。BeanFactory本身就是一个bean的工厂，同时也是我们的IOC容器，而FactoryBean是一个特殊的Bean,我们可以来看看这个接口：
/*
* Copyright 2002-2016 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.beans.factory;
import org.springframework.lang.Nullable;
/**
* Interface to be implemented by objects used within a {@link BeanFactory} which
* are themselves factories for individual objects. If a bean implements this
* interface, it is used as a factory for an object to expose, not directly as a
* bean instance that will be exposed itself.
*
* <p><b>NB: A bean that implements this interface cannot be used as a normal bean.</b>
* A FactoryBean is defined in a bean style, but the object exposed for bean
* references ({@link #getObject()}) is always the object that it creates.
*
* <p>FactoryBeans can support singletons and prototypes, and can either create
* objects lazily on demand or eagerly on startup. The {@link SmartFactoryBean}
* interface allows for exposing more fine-grained behavioral metadata.
*
* <p>This interface is heavily used within the framework itself, for example for
* the AOP {@link org.springframework.aop.framework.ProxyFactoryBean} or the
* {@link org.springframework.jndi.JndiObjectFactoryBean}. It can be used for
* custom components as well; however, this is only common for infrastructure code.
*
* <p><b>{@code FactoryBean} is a programmatic contract. Implementations are not
* supposed to rely on annotation-driven injection or other reflective facilities.</b>
* {@link #getObjectType()} {@link #getObject()} invocations may arrive early in
* the bootstrap process, even ahead of any post-processor setup. If you need access
* other beans, implement {@link BeanFactoryAware} and obtain them programmatically.
*
* <p>Finally, FactoryBean objects participate in the containing BeanFactory's
* synchronization of bean creation. There is usually no need for internal
* synchronization other than for purposes of lazy initialization within the
* FactoryBean itself (or the like).
*
* @author Rod Johnson
* @author Juergen Hoeller
* @since 08.03.2003
* @see org.springframework.beans.factory.BeanFactory
* @see org.springframework.aop.framework.ProxyFactoryBean
* @see org.springframework.jndi.JndiObjectFactoryBean
*/
public interface FactoryBean<T> {
/**
* Return an instance (possibly shared or independent) of the object
* managed by this factory.
* <p>As with a {@link BeanFactory}, this allows support for both the
* Singleton and Prototype design pattern.
* <p>If this FactoryBean is not fully initialized yet at the time of
* the call (for example because it is involved in a circular reference),
* throw a corresponding {@link FactoryBeanNotInitializedException}.
* <p>As of Spring 2.0, FactoryBeans are allowed to return {@code null}
* objects. The factory will consider this as normal value to be used; it
* will not throw a FactoryBeanNotInitializedException in this case anymore.
* FactoryBean implementations are encouraged to throw
* FactoryBeanNotInitializedException themselves now, as appropriate.
* @return an instance of the bean (can be {@code null})
* @throws Exception in case of creation errors
* @see FactoryBeanNotInitializedException
*/
@Nullable
T getObject() throws Exception;
/**
* Return the type of object that this FactoryBean creates,
* or {@code null} if not known in advance.
* <p>This allows one to check for specific types of beans without
* instantiating objects, for example on autowiring.
* <p>In the case of implementations that are creating a singleton object,
* this method should try to avoid singleton creation as far as possible;
* it should rather estimate the type in advance.
* For prototypes, returning a meaningful type here is advisable too.
* <p>This method can be called <i>before</i> this FactoryBean has
* been fully initialized. It must not rely on state created during
* initialization; of course, it can still use such state if available.
* <p><b>NOTE:</b> Autowiring will simply ignore FactoryBeans that return
* {@code null} here. Therefore it is highly recommended to implement
* this method properly, using the current state of the FactoryBean.
* @return the type of object that this FactoryBean creates,
* or {@code null} if not known at the time of the call
* @see ListableBeanFactory#getBeansOfType
*/
@Nullable
Class<?> getObjectType();
/**
* Is the object managed by this factory a singleton? That is,
* will {@link #getObject()} always return the same object
* (a reference that can be cached)?
* <p><b>NOTE:</b> If a FactoryBean indicates to hold a singleton object,
* the object returned from {@code getObject()} might get cached
* by the owning BeanFactory. Hence, do not return {@code true}
* unless the FactoryBean always exposes the same reference.
* <p>The singleton status of the FactoryBean itself will generally
* be provided by the owning BeanFactory; usually, it has to be
* defined as singleton there.
* <p><b>NOTE:</b> This method returning {@code false} does not
* necessarily indicate that returned objects are independent instances.
* An implementation of the extended {@link SmartFactoryBean} interface
* may explicitly indicate independent instances through its
* {@link SmartFactoryBean#isPrototype()} method. Plain {@link FactoryBean}
* implementations which do not implement this extended interface are
* simply assumed to always return independent instances if the
* {@code isSingleton()} implementation returns {@code false}.
* <p>The default implementation returns {@code true}, since a
* {@code FactoryBean} typically manages a singleton instance.
* @return whether the exposed object is a singleton
* @see #getObject()
* @see SmartFactoryBean#isPrototype()
*/
default boolean isSingleton() {
return true;
}
}
这里面有三个方法，分别为：getObject，getObjectType，isSingleton。根据文档解释，它只是一个生产对象的工厂，被Spring管理 。这个工厂负责提供我们需要的对象。当需要特殊的方式创建Bean时，则考虑实现该接口。我举个例子来说明：
package org.hzgj.spring.study;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.stereotype.Component;
@Component
public class WaterFactoryBean implements FactoryBean<Water> {
@Override
public Water getObject() throws Exception {
Water water=new Water();
water.setCapacity(20);
return water;
}
@Override
public Class<?> getObjectType() {
return Water.class;
}
@Override
public boolean isSingleton() {
return true;
}
}
//.....
package org.hzgj.spring.study;
@Deprecated
public class Water {
private int capacity;
public int getCapacity() {
return capacity;
}
public void setCapacity(int capacity) {
this.capacity = capacity;
}
public void test() {
System.out.println("test");
}
@Deprecated
public void test1() {
System.out.println("test1");
}
}
//.....
ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring-config.xml");
Water water = applicationContext.getBean(Water.class);
water.test1();
// ....能够成功获取到对象
在上面例子里，我们本身是要获得Water对象，那么此时Water对象实际上是通过FactoryBean创建的，因此我们在获取对象时添加我们自己的逻辑。
下面我们根据源代码来追溯一下getBean与BeanFactory关联，具体可以参考一下AbstractBeanFactory的doGetBean方法，那么在这里简单的说明一下执行过程：
1) 如果是单例对象的Bean会去缓存中获取
我们先看一下getSinglelone方法：
/** Cache of singleton objects: bean name --> bean instance */
private final Map<String, Object> singletonObjects = new ConcurrentHashMap<String, Object>(256);
/** Cache of singleton factories: bean name --> ObjectFactory */
private final Map<String, ObjectFactory<?>> singletonFactories = new HashMap<String, ObjectFactory<?>>(16);
/** Cache of early singleton objects: bean name --> bean instance */
private final Map<String, Object> earlySingletonObjects = new HashMap<String, Object>(16);
/**
* Return the (raw) singleton object registered under the given name.
* <p>Checks already instantiated singletons and also allows for an early
* reference to a currently created singleton (resolving a circular reference).
* @param beanName the name of the bean to look for
* @param allowEarlyReference whether early references should be created or not
* @return the registered singleton object, or {@code null} if none found
*/
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
Object singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
synchronized (this.singletonObjects) {
singletonObject = this.earlySingletonObjects.get(beanName);
if (singletonObject == null && allowEarlyReference) {
ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
if (singletonFactory != null) {
singletonObject = singletonFactory.getObject();
this.earlySingletonObjects.put(beanName, singletonObject);
this.singletonFactories.remove(beanName);
}
}
}
}
return (singletonObject != NULL_OBJECT ? singletonObject : null);
}
在这里我们获取单例对象时一定和ObjectFactory有关系
2）从它的parentBeanFactory中获取
// Check if bean definition exists in this factory.
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
String nameToLookup = originalBeanName(name);
if (args != null) {
// Delegation to parent with explicit args.
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else {
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
}
3）处理bean的dependsOn
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
// Guarantee initialization of beans that the current bean depends on.
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
for (String dep : dependsOn) {
if (isDependent(beanName, dep)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
}
registerDependentBean(dep, beanName);
getBean(dep);
}
}
4）根据bean的scope类型来获取对应的bean
// Create bean instance.
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
@Override
public Object getObject() throws BeansException {
try {
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
// Explicitly remove instance from singleton cache: It might have been put there
// eagerly by the creation process, to allow for circular reference resolution.
// Also remove any beans that received a temporary reference to the bean.
destroySingleton(beanName);
throw ex;
}
}
});
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
else if (mbd.isPrototype()) {
// It's a prototype -> create a new instance.
Object prototypeInstance = null;
try {
beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
else {
String scopeName = mbd.getScope();
final Scope scope = this.scopes.get(scopeName);
if (scope == null) {
throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
}
try {
Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
@Override
public Object getObject() throws BeansException {
beforePrototypeCreation(beanName);
try {
return createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
}
});
bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
}
catch (IllegalStateException ex) {
throw new BeanCreationException(beanName,
"Scope '" + scopeName + "' is not active for the current thread; consider " +
"defining a scoped proxy for this bean if you intend to refer to it from a singleton",
ex);
}
}
}
catch (BeansException ex) {
cleanupAfterBeanCreationFailure(beanName);
throw ex;
}
}
5) 根据需要做类型转换
// Check if required type matches the type of the actual bean instance.
if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
try {
return getTypeConverter().convertIfNecessary(bean, requiredType);
}
catch (TypeMismatchException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Failed to convert bean '" + name + "' to required type '" +
ClassUtils.getQualifiedName(requiredType) + "'", ex);
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
}
6）getObjectForBeanInstance
通过源代码我们可以发觉 getObjectForBeanInstance方法调用频率异常之高，那么我们就来看一看，它到底是做什么的：
/**
* Get the object for the given bean instance, either the bean
* instance itself or its created object in case of a FactoryBean.
* @param beanInstance the shared bean instance
* @param name name that may include factory dereference prefix
* @param beanName the canonical bean name
* @param mbd the merged bean definition
* @return the object to expose for the bean
*/
protected Object getObjectForBeanInstance(
Object beanInstance, String name, String beanName, RootBeanDefinition mbd) {
// Don't let calling code try to dereference the factory if the bean isn't a factory.
if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {
throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());
}
// Now we have the bean instance, which may be a normal bean or a FactoryBean.
// If it's a FactoryBean, we use it to create a bean instance, unless the
// caller actually wants a reference to the factory.
if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {
return beanInstance;
}
Object object = null;
if (mbd == null) {
object = getCachedObjectForFactoryBean(beanName);
}
if (object == null) {
// Return bean instance from factory.
FactoryBean<?> factory = (FactoryBean<?>) beanInstance;
// Caches object obtained from FactoryBean if it is a singleton.
if (mbd == null && containsBeanDefinition(beanName)) {
mbd = getMergedLocalBeanDefinition(beanName);
}
boolean synthetic = (mbd != null && mbd.isSynthetic());
object = getObjectFromFactoryBean(factory, beanName, !synthetic);
}
return object;
}
这段代码最主要是看看是否需要从FactoryBean获取对象的。
最后我们在聊聊ObjectFactory：
public interface ObjectFactory<T> {
/**
* Return an instance (possibly shared or independent)
* of the object managed by this factory.
* @return an instance of the bean (should never be {@code null})
* @throws BeansException in case of creation errors
*/
T getObject() throws BeansException;
}
该接口和FactoryBean很像，根据文档说明其getObject方法的返回值不建议为null，另外我们可以发现Bean为singlone时会大量的使用ObjectFactory处理，代码示例：
package org.hzgj.spring.study;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.ObjectFactory;
import org.springframework.stereotype.Component;
@Component
public class WaterFactory implements ObjectFactory {
@Override
public Object getObject() throws BeansException {
return new Water();
}
}
//这样子无法获取water，它只单纯是个工厂
ObjectFactory更像是一个在BeanFactory通过Bean名称关联的对象，只不过它在运行时确定getObject()方法返回的对象内容，再者它不具备BeanFactory能够制定Bean的类型
二、AOP的核心探究
2.1、核心接口初探
为什么刚开始要说FactoryBean,因为它的文档注释已经提醒我们去参考ProxyFactoryBean了，ProxyFactoryBean是生成目标对象的代理的核心，那么我们在此先看一下类图：
我们可以得知ProxyFactoryBean实现了FactoryBean。
关于AOP的几个重要的核心接口和类如下：
ProxyConfig:
/*
* Copyright 2002-2012 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.aop.framework;
import java.io.Serializable;
import org.springframework.util.Assert;
/**
* Convenience superclass for configuration used in creating proxies,
* to ensure that all proxy creators have consistent properties.
*
* @author Rod Johnson
* @author Juergen Hoeller
* @see AdvisedSupport
*/
public class ProxyConfig implements Serializable {
/** use serialVersionUID from Spring 1.2 for interoperability */
private static final long serialVersionUID = -8409359707199703185L;
private boolean proxyTargetClass = false;
private boolean optimize = false;
boolean opaque = false;
boolean exposeProxy = false;
private boolean frozen = false;
/**
* Set whether to proxy the target class directly, instead of just proxying
* specific interfaces. Default is "false".
* <p>Set this to "true" to force proxying for the TargetSource's exposed
* target class. If that target class is an interface, a JDK proxy will be
* created for the given interface. If that target class is any other class,
* a CGLIB proxy will be created for the given class.
* <p>Note: Depending on the configuration of the concrete proxy factory,
* the proxy-target-class behavior will also be applied if no interfaces
* have been specified (and no interface autodetection is activated).
* @see org.springframework.aop.TargetSource#getTargetClass()
*/
public void setProxyTargetClass(boolean proxyTargetClass) {
this.proxyTargetClass = proxyTargetClass;
}
/**
* Return whether to proxy the target class directly as well as any interfaces.
*/
public boolean isProxyTargetClass() {
return this.proxyTargetClass;
}
/**
* Set whether proxies should perform aggressive optimizations.
* The exact meaning of "aggressive optimizations" will differ
* between proxies, but there is usually some tradeoff.
* Default is "false".
* <p>For example, optimization will usually mean that advice changes won't
* take effect after a proxy has been created. For this reason, optimization
* is disabled by default. An optimize value of "true" may be ignored
* if other settings preclude optimization: for example, if "exposeProxy"
* is set to "true" and that's not compatible with the optimization.
*/
public void setOptimize(boolean optimize) {
this.optimize = optimize;
}
/**
* Return whether proxies should perform aggressive optimizations.
*/
public boolean isOptimize() {
return this.optimize;
}
/**
* Set whether proxies created by this configuration should be prevented
* from being cast to {@link Advised} to query proxy status.
* <p>Default is "false", meaning that any AOP proxy can be cast to
* {@link Advised}.
*/
public void setOpaque(boolean opaque) {
this.opaque = opaque;
}
/**
* Return whether proxies created by this configuration should be
* prevented from being cast to {@link Advised}.
*/
public boolean isOpaque() {
return this.opaque;
}
/**
* Set whether the proxy should be exposed by the AOP framework as a
* ThreadLocal for retrieval via the AopContext class. This is useful
* if an advised object needs to call another advised method on itself.
* (If it uses {@code this}, the invocation will not be advised).
* <p>Default is "false", in order to avoid unnecessary extra interception.
* This means that no guarantees are provided that AopContext access will
* work consistently within any method of the advised object.
*/
public void setExposeProxy(boolean exposeProxy) {
this.exposeProxy = exposeProxy;
}
/**
* Return whether the AOP proxy will expose the AOP proxy for
* each invocation.
*/
public boolean isExposeProxy() {
return this.exposeProxy;
}
/**
* Set whether this config should be frozen.
* <p>When a config is frozen, no advice changes can be made. This is
* useful for optimization, and useful when we don't want callers to
* be able to manipulate configuration after casting to Advised.
*/
public void setFrozen(boolean frozen) {
this.frozen = frozen;
}
/**
* Return whether the config is frozen, and no advice changes can be made.
*/
public boolean isFrozen() {
return this.frozen;
}
/**
* Copy configuration from the other config object.
* @param other object to copy configuration from
*/
public void copyFrom(ProxyConfig other) {
Assert.notNull(other, "Other ProxyConfig object must not be null");
this.proxyTargetClass = other.proxyTargetClass;
this.optimize = other.optimize;
this.exposeProxy = other.exposeProxy;
this.frozen = other.frozen;
this.opaque = other.opaque;
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append("proxyTargetClass=").append(this.proxyTargetClass).append("; ");
sb.append("optimize=").append(this.optimize).append("; ");
sb.append("opaque=").append(this.opaque).append("; ");
sb.append("exposeProxy=").append(this.exposeProxy).append("; ");
sb.append("frozen=").append(this.frozen);
return sb.toString();
}
}
该类定义代理类最基本的代理配置
Advised:
/*
* Copyright 2002-2015 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.aop.framework;
import org.aopalliance.aop.Advice;
import org.springframework.aop.Advisor;
import org.springframework.aop.TargetClassAware;
import org.springframework.aop.TargetSource;
/**
* Interface to be implemented by classes that hold the configuration
* of a factory of AOP proxies. This configuration includes the
* Interceptors and other advice, Advisors, and the proxied interfaces.
*
* <p>Any AOP proxy obtained from Spring can be cast to this interface to
* allow manipulation of its AOP advice.
*
* @author Rod Johnson
* @author Juergen Hoeller
* @since 13.03.2003
* @see org.springframework.aop.framework.AdvisedSupport
*/
public interface Advised extends TargetClassAware {
/**
* Return whether the Advised configuration is frozen,
* in which case no advice changes can be made.
*/
boolean isFrozen();
/**
* Are we proxying the full target class instead of specified interfaces?
*/
boolean isProxyTargetClass();
/**
* Return the interfaces proxied by the AOP proxy.
* <p>Will not include the target class, which may also be proxied.
*/
Class<?>[] getProxiedInterfaces();
/**
* Determine whether the given interface is proxied.
* @param intf the interface to check
*/
boolean isInterfaceProxied(Class<?> intf);
/**
* Change the {@code TargetSource} used by this {@code Advised} object.
* <p>Only works if the configuration isn't {@linkplain #isFrozen frozen}.
* @param targetSource new TargetSource to use
*/
void setTargetSource(TargetSource targetSource);
/**
* Return the {@code TargetSource} used by this {@code Advised} object.
*/
TargetSource getTargetSource();
/**
* Set whether the proxy should be exposed by the AOP framework as a
* {@link ThreadLocal} for retrieval via the {@link AopContext} class.
* <p>It can be necessary to expose the proxy if an advised object needs
* to invoke a method on itself with advice applied. Otherwise, if an
* advised object invokes a method on {@code this}, no advice will be applied.
* <p>Default is {@code false}, for optimal performance.
*/
void setExposeProxy(boolean exposeProxy);
/**
* Return whether the factory should expose the proxy as a {@link ThreadLocal}.
* <p>It can be necessary to expose the proxy if an advised object needs
* to invoke a method on itself with advice applied. Otherwise, if an
* advised object invokes a method on {@code this}, no advice will be applied.
* <p>Getting the proxy is analogous to an EJB calling {@code getEJBObject()}.
* @see AopContext
*/
boolean isExposeProxy();
/**
* Set whether this proxy configuration is pre-filtered so that it only
* contains applicable advisors (matching this proxy's target class).
* <p>Default is "false". Set this to "true" if the advisors have been
* pre-filtered already, meaning that the ClassFilter check can be skipped
* when building the actual advisor chain for proxy invocations.
* @see org.springframework.aop.ClassFilter
*/
void setPreFiltered(boolean preFiltered);
/**
* Return whether this proxy configuration is pre-filtered so that it only
* contains applicable advisors (matching this proxy's target class).
*/
boolean isPreFiltered();
/**
* Return the advisors applying to this proxy.
* @return a list of Advisors applying to this proxy (never {@code null})
*/
Advisor[] getAdvisors();
/**
* Add an advisor at the end of the advisor chain.
* <p>The Advisor may be an {@link org.springframework.aop.IntroductionAdvisor},
* in which new interfaces will be available when a proxy is next obtained
* from the relevant factory.
* @param advisor the advisor to add to the end of the chain
* @throws AopConfigException in case of invalid advice
*/
void addAdvisor(Advisor advisor) throws AopConfigException;
/**
* Add an Advisor at the specified position in the chain.
* @param advisor the advisor to add at the specified position in the chain
* @param pos position in chain (0 is head). Must be valid.
* @throws AopConfigException in case of invalid advice
*/
void addAdvisor(int pos, Advisor advisor) throws AopConfigException;
/**
* Remove the given advisor.
* @param advisor the advisor to remove
* @return {@code true} if the advisor was removed; {@code false}
* if the advisor was not found and hence could not be removed
*/
boolean removeAdvisor(Advisor advisor);
/**
* Remove the advisor at the given index.
* @param index index of advisor to remove
* @throws AopConfigException if the index is invalid
*/
void removeAdvisor(int index) throws AopConfigException;
/**
* Return the index (from 0) of the given advisor,
* or -1 if no such advisor applies to this proxy.
* <p>The return value of this method can be used to index into the advisors array.
* @param advisor the advisor to search for
* @return index from 0 of this advisor, or -1 if there's no such advisor
*/
int indexOf(Advisor advisor);
/**
* Replace the given advisor.
* <p><b>Note:</b> If the advisor is an {@link org.springframework.aop.IntroductionAdvisor}
* and the replacement is not or implements different interfaces, the proxy will need
* to be re-obtained or the old interfaces won't be supported and the new interface
* won't be implemented.
* @param a the advisor to replace
* @param b the advisor to replace it with
* @return whether it was replaced. If the advisor wasn't found in the
* list of advisors, this method returns {@code false} and does nothing.
* @throws AopConfigException in case of invalid advice
*/
boolean replaceAdvisor(Advisor a, Advisor b) throws AopConfigException;
/**
* Add the given AOP Alliance advice to the tail of the advice (interceptor) chain.
* <p>This will be wrapped in a DefaultPointcutAdvisor with a pointcut that always
* applies, and returned from the {@code getAdvisors()} method in this wrapped form.
* <p>Note that the given advice will apply to all invocations on the proxy,
* even to the {@code toString()} method! Use appropriate advice implementations
* or specify appropriate pointcuts to apply to a narrower set of methods.
* @param advice advice to add to the tail of the chain
* @throws AopConfigException in case of invalid advice
* @see #addAdvice(int, Advice)
* @see org.springframework.aop.support.DefaultPointcutAdvisor
*/
void addAdvice(Advice advice) throws AopConfigException;
/**
* Add the given AOP Alliance Advice at the specified position in the advice chain.
* <p>This will be wrapped in a {@link org.springframework.aop.support.DefaultPointcutAdvisor}
* with a pointcut that always applies, and returned from the {@link #getAdvisors()}
* method in this wrapped form.
* <p>Note: The given advice will apply to all invocations on the proxy,
* even to the {@code toString()} method! Use appropriate advice implementations
* or specify appropriate pointcuts to apply to a narrower set of methods.
* @param pos index from 0 (head)
* @param advice advice to add at the specified position in the advice chain
* @throws AopConfigException in case of invalid advice
*/
void addAdvice(int pos, Advice advice) throws AopConfigException;
/**
* Remove the Advisor containing the given advice.
* @param advice the advice to remove
* @return {@code true} of the advice was found and removed;
* {@code false} if there was no such advice
*/
boolean removeAdvice(Advice advice);
/**
* Return the index (from 0) of the given AOP Alliance Advice,
* or -1 if no such advice is an advice for this proxy.
* <p>The return value of this method can be used to index into
* the advisors array.
* @param advice AOP Alliance advice to search for
* @return index from 0 of this advice, or -1 if there's no such advice
*/
int indexOf(Advice advice);
/**
* As {@code toString()} will normally be delegated to the target,
* this returns the equivalent for the AOP proxy.
* @return a string description of the proxy configuration
*/
String toProxyConfigString();
}
该接口主要定义了代理类的工厂基本的行为，比如说添加Advisor，添加Advise，删除与替换Adivsor等
Adivise:
通知接口，该接口没有方法定义，其常见的子接口有BeforeAdvise,AfterAdvise,MethodInterceptor等
PointCut:
切点接口，该接口定义如下：
/*
* Copyright 2002-2012 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.aop;
/**
* Core Spring pointcut abstraction.
*
* <p>A pointcut is composed of a {@link ClassFilter} and a {@link MethodMatcher}.
* Both these basic terms and a Pointcut itself can be combined to build up combinations
* (e.g. through {@link org.springframework.aop.support.ComposablePointcut}).
*
* @author Rod Johnson
* @see ClassFilter
* @see MethodMatcher
* @see org.springframework.aop.support.Pointcuts
* @see org.springframework.aop.support.ClassFilters
* @see org.springframework.aop.support.MethodMatchers
*/
public interface Pointcut {
/**
* Return the ClassFilter for this pointcut.
* @return the ClassFilter (never {@code null})
*/
ClassFilter getClassFilter();
/**
* Return the MethodMatcher for this pointcut.
* @return the MethodMatcher (never {@code null})
*/
MethodMatcher getMethodMatcher();
/**
* Canonical Pointcut instance that always matches.
*/
Pointcut TRUE = TruePointcut.INSTANCE;
}
Pointcut由ClassFilter和MethodMatcher构成。它通过ClassFilter定位到某些特定类上，通过MethodMatcher定位到某些特定方法上，这样Pointcut就拥有了描述某些类的某些特定方法的能力。
Advisor:
代表一般切面，它仅包含一个Advice，我们说过，因为Advice包含了横切代码和连接点的信息，所以Advior本身就是一个简单的切面，只不过它代表的横切的连接点是所有目标类的所有方法，因为这个横切面太宽泛，所以一般不会直接使用。
2.2、源码分析
我们先来看看ProxyFactoryBean的相关方法
getObject方法：
/**
* Return a proxy. Invoked when clients obtain beans from this factory bean.
* Create an instance of the AOP proxy to be returned by this factory.
* The instance will be cached for a singleton, and create on each call to
* {@code getObject()} for a proxy.
* @return a fresh AOP proxy reflecting the current state of this factory
*/
@Override
public Object getObject() throws BeansException {
initializeAdvisorChain();
if (isSingleton()) {
return getSingletonInstance();
}
else {
if (this.targetName == null) {
logger.warn("Using non-singleton proxies with singleton targets is often undesirable. " +
"Enable prototype proxies by setting the 'targetName' property.");
}
return newPrototypeInstance();
}
}
这里面我们关注一下getSingletonInstance方法：
/**
* 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;
}
在这里我们关在关注一下getProxy(AopProxy aopProxy)方法,AopProxy是一个接口：
/*
* Copyright 2002-2012 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.aop.framework;
/**
* Delegate interface for a configured AOP proxy, allowing for the creation
* of actual proxy objects.
*
* <p>Out-of-the-box implementations are available for JDK dynamic proxies
* and for CGLIB proxies, as applied by {@link DefaultAopProxyFactory}.
*
* @author Rod Johnson
* @author Juergen Hoeller
* @see DefaultAopProxyFactory
*/
public interface AopProxy {
/**
* Create a new proxy object.
* <p>Uses the AopProxy's default class loader (if necessary for proxy creation):
* usually, the thread context class loader.
* @return the new proxy object (never {@code null})
* @see Thread#getContextClassLoader()
*/
Object getProxy();
/**
* Create a new proxy object.
* <p>Uses the given class loader (if necessary for proxy creation).
* {@code null} will simply be passed down and thus lead to the low-level
* proxy facility's default, which is usually different from the default chosen
* by the AopProxy implementation's {@link #getProxy()} method.
* @param classLoader the class loader to create the proxy with
* (or {@code null} for the low-level proxy facility's default)
* @return the new proxy object (never {@code null})
*/
Object getProxy(ClassLoader classLoader);
}
该接口有如下实现类：JdkDynamicAopProxy , CglibAopProxy , ObjenesisCglibAopProxy。
那么在这里我们看一下JdkDynamicAopProxy的源码，我只贴出其中一个关键部分：
@Override
public Object getProxy(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);
}
那么我们可以看出：JDK的动态代理是AOP的实现方式之一
三、基于AOP的核心类与接口实现代理
1、先定义基本的JavaBean:
package org.hzgj.spring.study;
@Aop
public class Water {
private int capacity;
public int getCapacity() {
return capacity;
}
public void setCapacity(int capacity) {
this.capacity = capacity;
}
public void test() {
System.out.println("test");
}
@Aop
public void test1() {
System.out.println("test1");
}
}
2、自定义注解
package org.hzgj.spring.study;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD,ElementType.TYPE})
public @interface Aop {
}
3、定义JavaBean的代理
package org.hzgj.spring.study;
import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
import org.springframework.aop.framework.AbstractSingletonProxyFactoryBean;
import org.springframework.aop.support.DefaultPointcutAdvisor;
import org.springframework.aop.support.annotation.AnnotationMatchingPointcut;
import org.springframework.stereotype.Component;
/**
*
*/
@Component
public class WaterProxyFactoryBean extends AbstractSingletonProxyFactoryBean {
public WaterProxyFactoryBean() {
super.setTarget(new Water());
}
@Override
protected Object createMainInterceptor() {
AnnotationMatchingPointcut pointcut = new AnnotationMatchingPointcut(Aop.class, Aop.class);
DefaultPointcutAdvisor advisor = new DefaultPointcutAdvisor(pointcut, (MethodInterceptor) invocation -> {
System.out.println(1);
return invocation.proceed();
});
return advisor;
}
}
该类继承AbstractSingletonProxyFactoryBean,然后需要重写createMainInterceptor，我在这里定义了一个DefaultPointcutAdvisor与扫描注解的PointCut，至此切点，通知，代理都有了，那么AOP最基本的条件也就具备了
4、主程序
package org.hzgj.spring.study;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Main {
public static void main(String[] args) {
ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring-config.xml");
Water water = applicationContext.getBean(Water.class);
water.test1();
}
}
运行成功时会得到如下结果：
