最近工作中我都是基于注解实现 AOP 功能，常用的开启 AOP 的注解是 @EnableAspectJAutoProxy，我们就从它入手。
上面的动图的流程的步骤就是：@EnableAspectJAutoProxy --> AspectJAutoProxyRegistrar -->AopConfigUtils .registerAspectJAnnotationAutoProxyCreatorIfNecessary -->AnnotationAwareAspectJAutoProxyCreator.class
“AnnotationAwareAspectJAutoProxyCreator 查看其中文注释（如下），确定它就是 AOP 的核心类！-- 温安适 20191020
org.springframework.aop
.framework.autoproxy.AbstractAdvisorAutoProxyCreator
@SuppressWarnings("serial")
public class AnnotationAwareAspectJAutoProxyCreator
extends AspectJAwareAdvisorAutoProxyCreator {
//...省略实现
}注解切面
虽然找到了核心类，但是并没有找到核心方法！下面我们尝试画类图确定核心方法。
AnnotationAwareAspectJAutoProxyCreator 的部分类图。
AnnotationAwareAspectJAutoProxyCreator 从类图看到了 AnnotationAwareAspectJAutoProxyCreator 实现了 BeanPostProcessor，而 AOP 功能应该在创建完 Bean 之后执行，猜测 AnnotationAwareAspectJAutoProxyCreator 实现 BeanPostProcessor 的 postProcessAfterInitialization（实例化 bean 后处理）是核心方法。查看 AnnotationAwareAspectJAutoProxyCreator 实现的 postProcessAfterInitialization 方法，实际该方法在其父类 AbstractAutoProxyCreator 中。
//AbstractAutoProxyCreator中的postProcessAfterInitialization实现
@Override
public Object postProcessAfterInitialization(Object bean, String beanName)
throws BeansException {
if (bean != null) {
Object cacheKey = getCacheKey(bean.getClass(), beanName);
if (!this.earlyProxyReferences.contains(cacheKey)) {
return wrapIfNecessary(bean, beanName, cacheKey);
}
}
return bean;
}
发现发现疑似方法 wrapIfNecessary，查看其源码如下，发现 createProxy 方法。确定找对了地方。
protected Object wrapIfNecessary
(Object bean, String beanName, Object cacheKey) {
if (beanName != null && 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;
}
// 创建代理
Object\[\] specificInterceptors =
getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
if (specificInterceptors != DO\_NOT\_PROXY) {
this.advisedBeans.put(cacheKey, Boolean.TRUE);
Object proxy = createProxy(
bean.getClass(), beanName,
specificInterceptors, new SingletonTargetSource(bean));
this.proxyTypes.put(cacheKey, proxy.getClass());
return proxy;
}
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
即 AnnotationAwareAspectJAutoProxyCreator 实现 BeanPostProcessor 的 postProcessAfterInitialization 方法，在该方法中由 wrapIfNecessary 实现了 AOP 的功能。wrapIfNecessary 中有 2 个和核心方法
查看源码如下，默认实现在 AbstractAdvisorAutoProxyCreator 中。
@Override
@Nullable
protected Object\[\] getAdvicesAndAdvisorsForBean(
Class<?> beanClass, String beanName,
@Nullable TargetSource targetSource) {
List<Advisor> advisors = findEligibleAdvisors(beanClass, beanName);
if (advisors.isEmpty()) {
return DO\_NOT\_PROXY;
}
return advisors.toArray();
}
查阅 findEligibleAdvisors 方法，就干了 3 件事
protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
//找所有增强器
List<Advisor> candidateAdvisors = findCandidateAdvisors();
//找所有匹配的增强器
List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
extendAdvisors(eligibleAdvisors);
if (!eligibleAdvisors.isEmpty()) {
//排序
eligibleAdvisors = sortAdvisors(eligibleAdvisors);
}
return eligibleAdvisors;
}
AnnotationAwareAspectJAutoProxyCreator 重写了 findCandidateAdvisors，下面我们看看具体实现了什么
@Override
protected List<Advisor> findCandidateAdvisors() {
// Add all the Spring advisors found according to superclass rules.
List<Advisor> advisors = super.findCandidateAdvisors();
// Build Advisors for all AspectJ aspects in the bean factory.
if (this.aspectJAdvisorsBuilder != null) {
//@Aspect注解的类在这里除了
advisors.addAll(this.aspectJAdvisorsBuilder.buildAspectJAdvisors());
}
return advisors;
}
从该方法我们可以看到处理 @Aspect 注解的 bean 的方法是：this.aspectJAdvisorsBuilder.buildAspectJAdvisors()。这个方法如下：
public List<Advisor> buildAspectJAdvisors() {
List<String> aspectNames = this.aspectBeanNames;
if (aspectNames == null) {
synchronized (this) {
aspectNames = this.aspectBeanNames;
if (aspectNames == null) {
List<Advisor> advisors = new ArrayList<>();
aspectNames = new ArrayList<>();
//找到所有BeanName
String\[\] beanNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
this.beanFactory, Object.class, true, false);
for (String beanName : beanNames) {
if (!isEligibleBean(beanName)) {
continue;
}
// 必须注意，bean会提前暴露，并被Spring容器缓存，但是这时还不能织入。
Class<?> beanType = this.beanFactory.getType(beanName);
if (beanType == null) {
continue;
}
if (this.advisorFactory.isAspect(beanType)) {
//找到所有被@Aspect注解的类
aspectNames.add(beanName);
AspectMetadata amd = new AspectMetadata(beanType, beanName);
if (amd.getAjType().getPerClause().getKind() == PerClauseKind.SINGLETON) {
MetadataAwareAspectInstanceFactory factory =
new BeanFactoryAspectInstanceFactory(this.beanFactory, beanName);
//解析封装为Advisor返回
List<Advisor> classAdvisors = this.advisorFactory.getAdvisors(factory);
if (this.beanFactory.isSingleton(beanName)) {
this.advisorsCache.put(beanName, classAdvisors);
}
else {
this.aspectFactoryCache.put(beanName, factory);
}
advisors.addAll(classAdvisors);
}
else {
// Per target or per this.
if (this.beanFactory.isSingleton(beanName)) {
throw new IllegalArgumentException("Bean with name ‘" + beanName +
"‘ is a singleton, but aspect instantiation model is not singleton");
}
MetadataAwareAspectInstanceFactory factory =
new PrototypeAspectInstanceFactory(this.beanFactory, beanName);
this.aspectFactoryCache.put(beanName, factory);
advisors.addAll(this.advisorFactory.getAdvisors(factory));
}
}
}
this.aspectBeanNames = aspectNames;
return advisors;
}
}
}
if (aspectNames.isEmpty()) {
return Collections.emptyList();
}
List<Advisor> advisors = new ArrayList<>();
for (String aspectName : aspectNames) {
List<Advisor> cachedAdvisors = this.advisorsCache.get(aspectName);
if (cachedAdvisors != null) {
advisors.addAll(cachedAdvisors);
}
else {
MetadataAwareAspectInstanceFactory factory = this.aspectFactoryCache.get(aspectName);
advisors.addAll(this.advisorFactory.getAdvisors(factory));
}
}
return advisors;
}
这个方法可以概括为：
众所周知，创建代理的常用的 2 种方式是：JDK 创建和 CGLIB，下面我们就看看这 2 中创建代理的例子。
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
public class JDKProxyMain {
public static void main(String\[\] args) {
JDKProxyTestInterface target = new JDKProxyTestInterfaceImpl();
// 根据目标对象创建代理对象
JDKProxyTestInterface proxy =
(JDKProxyTestInterface) Proxy
.newProxyInstance(target.getClass().getClassLoader(),
target.getClass().getInterfaces(),
new JDKProxyTestInvocationHandler(target));
// 调用代理对象方法
proxy.testProxy();
}
interface JDKProxyTestInterface {
void testProxy();
}
static class JDKProxyTestInterfaceImpl
implements JDKProxyTestInterface {
@Override
public void testProxy() {
System.out.println("testProxy");
}
}
static class JDKProxyTestInvocationHandler
implements InvocationHandler {
private Object target;
public JDKProxyTestInvocationHandler(Object target){
this.target=target;
}
@Override
public Object invoke(Object proxy, Method method,
Object\[\] args) throws Throwable {
System.out.println("执行前");
Object result= method.invoke(this.target,args);
System.out.println("执行后");
return result;
}
}
import org.springframework.cglib.proxy.Enhancer;
import org.springframework.cglib.proxy.MethodInterceptor;
import org.springframework.cglib.proxy.MethodProxy;
import java.lang.reflect.Method;
public class CglibProxyTest {
static class CglibProxyService {
public CglibProxyService(){
}
void sayHello(){
System.out.println(" hello !");
}
}
static class CglibProxyInterceptor implements MethodInterceptor{
@Override
public Object intercept(Object sub, Method method,
Object\[\] objects, MethodProxy methodProxy)
throws Throwable {
System.out.println("before hello");
Object object = methodProxy.invokeSuper(sub, objects);
System.out.println("after hello");
return object;
}
}
public static void main(String\[\] args) {
// 通过CGLIB动态代理获取代理对象的过程
Enhancer enhancer = new Enhancer();
// 设置enhancer对象的父类
enhancer.setSuperclass(CglibProxyService.class);
// 设置enhancer的回调对象
enhancer.setCallback(new CglibProxyInterceptor());
// 创建代理对象
CglibProxyService proxy= (CglibProxyService)enhancer.create();
System.out.println(CglibProxyService.class);
System.out.println(proxy.getClass());
// 通过代理对象调用目标方法
proxy.sayHello();
}
}
Spring 的选择选择如何代理时在 DefaultAopProxyFactory 中。
public class DefaultAopProxyFactory implements AopProxyFactory,
Serializable {
@Override
public AopProxy createAopProxy(AdvisedSupport config)
throws AopConfigException {
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);
}
}
//...
}
“//exposeProxy=true AopContext 可以访问，proxyTargetClass=true CGLIB 生成代理 @EnableAspectJAutoProxy(exposeProxy=true,proxyTargetClass=true)
总结下 Spring 如何选择创建代理的方式：
Spring 如何实现 AOP？，您可以这样说：
Spring 如何实现 AOP，请不要再说 cglib 了！
原文：https://www.cnblogs.com/89757m/p/13710736.html