声明：本编文章是自己在查看Spring提取@Transactional注解的源码过程中随手记下的笔记，只做了大概流程的记录，未做详细分析，如有错误还请谅解。
1、事务切面匹配处理类
AopUtils#canApply(Pointcut, Class , boolean)
方法中会调用到 TransactionAttributeSourcePointcut#matches 方法
public static boolean canApply(Pointcut pc, Class<?> targetClass, boolean hasIntroductions) {
Assert.notNull(pc, "Pointcut must not be null");
if (!pc.getClassFilter().matches(targetClass)) {
return false;
}
MethodMatcher methodMatcher = pc.getMethodMatcher();
IntroductionAwareMethodMatcher introductionAwareMethodMatcher = null;
if (methodMatcher instanceof IntroductionAwareMethodMatcher) {
introductionAwareMethodMatcher = (IntroductionAwareMethodMatcher) methodMatcher;
}
Set<Class> classes = new HashSet<Class>(ClassUtils.getAllInterfacesForClassAsSet(targetClass));
classes.add(targetClass);
for (Class<?> clazz : classes) {
Method[] methods = clazz.getMethods();
for (Method method : methods) {
//methodMatcher.matches(method, targetClass) 方法会匹配对应的处理类，在Transaction提取的过程中会匹配到：TransactionAttributeSourcePointcut
if ((introductionAwareMethodMatcher != null &&
introductionAwareMethodMatcher.matches(method, targetClass, hasIntroductions)) ||
methodMatcher.matches(method, targetClass)) {
return true;
}
}
}
return false;
}
2、事务切点匹配
TransactionAttributeSourcePointcut#matches
在阅读TransactionAttributeSourcePointcut内的源代码的时候，我们发现该类是一个抽象，但是他确没有实现的子类！！！那么这个类到底在哪被引用了呢？
abstract class TransactionAttributeSourcePointcut extends StaticMethodMatcherPointcut implements Serializable {
public boolean matches(Method method, Class targetClass) {
// 该处调用了 getTransactionAttributeSource() 的抽象方法，但是却没有子类实现这个方法，这是怎么一回事呢？
TransactionAttributeSource tas = getTransactionAttributeSource();
return (tas == null || tas.getTransactionAttribute(method, targetClass) != null);
}
@Override
public boolean equals(Object other) {
if (this == other) {
return true;
}
if (!(other instanceof TransactionAttributeSourcePointcut)) {
return false;
}
TransactionAttributeSourcePointcut otherPc = (TransactionAttributeSourcePointcut) other;
return ObjectUtils.nullSafeEquals(getTransactionAttributeSource(), otherPc.getTransactionAttributeSource());
}
@Override
public int hashCode() {
return TransactionAttributeSourcePointcut.class.hashCode();
}
@Override
public String toString() {
return getClass().getName() + ": " + getTransactionAttributeSource();
}
/**
* Obtain the underlying TransactionAttributeSource (may be {@code null}).
* To be implemented by subclasses.
*/
protected abstract TransactionAttributeSource getTransactionAttributeSource();
}
3、TransactionAttributeSourcePointcut 抽象类的应用
我们怀着上面的疑问全局搜索 TransactionAttributeSourcePointcut 可以在 BeanFactoryTransactionAttributeSourceAdvisor 里面找到如下的代码：
public class BeanFactoryTransactionAttributeSourceAdvisor extends AbstractBeanFactoryPointcutAdvisor {
private TransactionAttributeSource transactionAttributeSource;
// 此处利用了匿名内部类的方式实例化了 TransactionAttributeSourcePointcut 对象，在此我们找到了上面问题的答案。
private final TransactionAttributeSourcePointcut pointcut = new TransactionAttributeSourcePointcut() {
@Override
protected TransactionAttributeSource getTransactionAttributeSource() {
return transactionAttributeSource;
}
};
/**
* Set the transaction attribute source which is used to find transaction
* attributes. This should usually be identical to the source reference
* set on the transaction interceptor itself.
* @see TransactionInterceptor#setTransactionAttributeSource
*/
public void setTransactionAttributeSource(TransactionAttributeSource transactionAttributeSource) {
this.transactionAttributeSource = transactionAttributeSource;
}
/**
* Set the {@link ClassFilter} to use for this pointcut.
* Default is {@link ClassFilter#TRUE}.
*/
public void setClassFilter(ClassFilter classFilter) {
this.pointcut.setClassFilter(classFilter);
}
public Pointcut getPointcut() {
return this.pointcut;
}
}
3、TransactionAttributeSource 属性的 Bean 定义过程
其实，在实例化 BeanFactoryTransactionAttributeSourceAdvisor 时，Spring 已经为我们的 BeanFactoryTransactionAttributeSourceAdvisor 设置了 TransactionAttributeSource 属性，可以进入 AnnotationDrivenBeanDefinitionParser.AopAutoProxyConfigurer#configureAutoProxyCreator 方法中看源代码：
private static class AopAutoProxyConfigurer {
public static void configureAutoProxyCreator(Element element, ParserContext parserContext) {
AopNamespaceUtils.registerAutoProxyCreatorIfNecessary(parserContext, element);
String txAdvisorBeanName = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME;
if (!parserContext.getRegistry().containsBeanDefinition(txAdvisorBeanName)) {
Object eleSource = parserContext.extractSource(element);
// 注解事务 transactionAttributeSource Spring 定义的Bean为： AnnotationTransactionAttributeSource 实例
// Create the TransactionAttributeSource definition.
RootBeanDefinition sourceDef = new RootBeanDefinition(AnnotationTransactionAttributeSource.class);
sourceDef.setSource(eleSource);
sourceDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
String sourceName = parserContext.getReaderContext().registerWithGeneratedName(sourceDef);
// Create the TransactionInterceptor definition.
RootBeanDefinition interceptorDef = new RootBeanDefinition(TransactionInterceptor.class);
interceptorDef.setSource(eleSource);
interceptorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
registerTransactionManager(element, interceptorDef);
interceptorDef.getPropertyValues().add("transactionAttributeSource", new RuntimeBeanReference(sourceName));
String interceptorName = parserContext.getReaderContext().registerWithGeneratedName(interceptorDef);
// create BeanFactoryTransactionAttributeSourceAdvisor Bean 的定义
// Create the TransactionAttributeSourceAdvisor definition.
RootBeanDefinition advisorDef = new RootBeanDefinition(BeanFactoryTransactionAttributeSourceAdvisor.class);
advisorDef.setSource(eleSource);
advisorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
// 设置 transactionAttributeSource 属性
advisorDef.getPropertyValues().add("transactionAttributeSource", new RuntimeBeanReference(sourceName));
advisorDef.getPropertyValues().add("adviceBeanName", interceptorName);
if (element.hasAttribute("order")) {
advisorDef.getPropertyValues().add("order", element.getAttribute("order"));
}
parserContext.getRegistry().registerBeanDefinition(txAdvisorBeanName, advisorDef);
CompositeComponentDefinition compositeDef = new CompositeComponentDefinition(element.getTagName(), eleSource);
compositeDef.addNestedComponent(new BeanComponentDefinition(sourceDef, sourceName));
compositeDef.addNestedComponent(new BeanComponentDefinition(interceptorDef, interceptorName));
compositeDef.addNestedComponent(new BeanComponentDefinition(advisorDef, txAdvisorBeanName));
parserContext.registerComponent(compositeDef);
}
}
}
4、TransactionAttributeSource#getTransactionAttribute 方法的调用过程
通过以上的分析，我们可以确定
TransactionAttributeSourcePointcut#getTransactionAttributeSource 返回的是：AnnotationTransactionAttributeSource 实例，AnnotationTransactionAttributeSource继承自：AbstractFallbackTransactionAttributeSource, 故此TransactionAttributeSourcePointcut#matches 最终会调用到 AbstractFallbackTransactionAttributeSource#getTransactionAttribute 方法
abstract class TransactionAttributeSourcePointcut extends StaticMethodMatcherPointcut implements Serializable {
public boolean matches(Method method, Class targetClass) {
TransactionAttributeSource tas = getTransactionAttributeSource();
// 最终会调用到 AbstractFallbackTransactionAttributeSource#getTransactionAttribute 方法
return (tas == null || tas.getTransactionAttribute(method, targetClass) != null);
}
// 省略其他代码 ……………………
}
再看 AbstractFallbackTransactionAttributeSource#getTransactionAttribute 方法
// 获取事务属性
public TransactionAttribute getTransactionAttribute(Method method, Class<?> targetClass) {
// First, see if we have a cached value.
Object cacheKey = getCacheKey(method, targetClass);
Object cached = this.attributeCache.get(cacheKey);
if (cached != null) {
// Value will either be canonical value indicating there is no transaction attribute,
// or an actual transaction attribute.
if (cached == NULL_TRANSACTION_ATTRIBUTE) {
return null;
}
else {
return (TransactionAttribute) cached;
}
}
else {
// We need to work it out. 根据 method、targetClass 推算事务属性，TransactionAttribute
TransactionAttribute txAtt = computeTransactionAttribute(method, targetClass);
// Put it in the cache.
if (txAtt == null) {
this.attributeCache.put(cacheKey, NULL_TRANSACTION_ATTRIBUTE);
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Adding transactional method '" + method.getName() + "' with attribute: " + txAtt);
}
this.attributeCache.put(cacheKey, txAtt);
}
return txAtt;
}
}
5、事务属性的推算过程：
// 推算事务属性，TransactionAttribute
private TransactionAttribute computeTransactionAttribute(Method method, Class<?> targetClass) {
// Don't allow no-public methods as required.
if (allowPublicMethodsOnly() && !Modifier.isPublic(method.getModifiers())) {
return null;
}
// Ignore CGLIB subclasses - introspect the actual user class.
Class<?> userClass = ClassUtils.getUserClass(targetClass);
// The method may be on an interface, but we need attributes from the target class.
// If the target class is null, the method will be unchanged.
Method specificMethod = ClassUtils.getMostSpecificMethod(method, userClass);
// If we are dealing with method with generic parameters, find the original method.
specificMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);
// 通过上面的分析，findTransactionAttribute 该方法最终会调用到：AnnotationTransactionAttributeSource#findTransactionAttribute(java.lang.Class<?>)
// First try is the method in the target class. 方式1： 从目标类的方法上找 Transaction注解
TransactionAttribute txAtt = findTransactionAttribute(specificMethod);
if (txAtt != null) {
return txAtt;
}
// Second try is the transaction attribute on the target class. 方式2： 从目标类上找 Transaction注解
txAtt = findTransactionAttribute(specificMethod.getDeclaringClass());
if (txAtt != null) {
return txAtt;
}
if (specificMethod != method) {// 以上两种方式如果还没有找到 TransactionAttribute 属性，那就要从目标类的接口开始找
// Fallback is to look at the original method. 方式3：接口的方法上找 Transaction注解
txAtt = findTransactionAttribute(method);
if (txAtt != null) {
return txAtt;
}
// Last fallback is the class of the original method. 方式4：接口的类上找 Transaction注解
return findTransactionAttribute(method.getDeclaringClass());
}
return null;
}
６、事务注解属性的解析
AnnotationTransactionAttributeSource#findTransactionAttribute(java.lang.Class
7、获取事务注解
public class SpringTransactionAnnotationParser implements TransactionAnnotationParser, Serializable {
public TransactionAttribute parseTransactionAnnotation(AnnotatedElement ae) {
//获取 Transactional 注解
Transactional ann = AnnotationUtils.getAnnotation(ae, Transactional.class);
if (ann != null) {
//从 @Transactional 注解上获取事务属性值，并包装成 TransactionAttribute 返回
return parseTransactionAnnotation(ann);
}
else {
return null;
}
}
public TransactionAttribute parseTransactionAnnotation(Transactional ann) {
RuleBasedTransactionAttribute rbta = new RuleBasedTransactionAttribute();
rbta.setPropagationBehavior(ann.propagation().value());
rbta.setIsolationLevel(ann.isolation().value());
rbta.setTimeout(ann.timeout());
rbta.setReadOnly(ann.readOnly());
rbta.setQualifier(ann.value());
ArrayList<RollbackRuleAttribute> rollBackRules = new ArrayList<RollbackRuleAttribute>();
Class[] rbf = ann.rollbackFor();
for (Class rbRule : rbf) {
RollbackRuleAttribute rule = new RollbackRuleAttribute(rbRule);
rollBackRules.add(rule);
}
String[] rbfc = ann.rollbackForClassName();
for (String rbRule : rbfc) {
RollbackRuleAttribute rule = new RollbackRuleAttribute(rbRule);
rollBackRules.add(rule);
}
Class[] nrbf = ann.noRollbackFor();
for (Class rbRule : nrbf) {
NoRollbackRuleAttribute rule = new NoRollbackRuleAttribute(rbRule);
rollBackRules.add(rule);
}
String[] nrbfc = ann.noRollbackForClassName();
for (String rbRule : nrbfc) {
NoRollbackRuleAttribute rule = new NoRollbackRuleAttribute(rbRule);
rollBackRules.add(rule);
}
rbta.getRollbackRules().addAll(rollBackRules);
return rbta;
}
@Override
public boolean equals(Object other) {
return (this == other || other instanceof SpringTransactionAnnotationParser);
}
@Override
public int hashCode() {
return SpringTransactionAnnotationParser.class.hashCode();
}
}
