1.引
上一节已经分析了基于@Transactional注解的声明式事物事物标签提取，接下来我们就接下来我们就要分析Spring事物的实现过程了，因为这里会涉及到事物传播特性、事物嵌套调用等等很多复杂的内容，所以第一个分析，还是以最简单的形式去分析，及单个service下的单个方法调用。业务方法摘要如下，在业务方法上配置了Transactional注解，并将事物传播特性定义为REQUIRED。在分析完这个最简单的例子之后，再去分析比较复杂的事物调用过程。。。
@Override
@Transactional(propagation = Propagation.REQUIRED, rollbackFor = Exception.class)
public void delete() throws RuntimeException {
System.out.println("==调用AccountService的delete方法\n");
jdbcTemplate.update(insert_sql);
throw new RuntimeException("==AccountService的delete方法手动抛出异常");
}
2.拦截器链调用回顾
拦截器链调用入口：
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 {
// 1、处理equals方法，如果接口中没有定义equals而在实现类中覆盖了equals方法，那么该equals方法不会被增强
if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
// The target does not implement the equals(Object) method itself.
return equals(args[0]);
}
// 2、处理hashCode方法，如果接口中没有定义hashCode而在实现类中覆盖了hashCode方法，那么该hashCode方法不会被增强
else if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
// The target does not implement the hashCode() method itself.
return hashCode();
}
// 3、如果目标对象是DecoratingProxy类型，则返回目标对象的最终对象类型
// DecoratingProxy接口只有一个getDecoratedClass方法，用于返回目标对象的最终对象类型
else if (method.getDeclaringClass() == DecoratingProxy.class) {
// There is only getDecoratedClass() declared -> dispatch to proxy config.
return AopProxyUtils.ultimateTargetClass(this.advised);
}
// 4、如果目标对象是Advice类型，则直接使用反射进行调用
// opaque-->标记是否需要阻止通过该配置创建的代理对象转换为Advised类型，默认值为false，表示代理对象可以被转换为Advised类型
// method.getDeclaringClass().isInterface()-->目标对象是接口
// method.getDeclaringClass().isAssignableFrom(Advised.class)-->
// 是用来判断一个类Class1和另一个类Class2是否相同或者Class1类是不是Class2的父类。例如：Class1.isAssignableFrom(Class2)
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;
// 5、解决目标对象内部自我调用无法实施切面增强，在这里暴露代理
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.
// 6、获取当前方法的拦截器链，并执行调用
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
// 检测是否拦截器链是否为空，如果拦截器链为空，那么直接通过反射调用目标对象的方法，避免创建MethodInvocation
// 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.
// 通过反射直接调用目标对象的方法
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
}
else {
// 创建MethodInvocation对象并调用proceed方法，拦截器链被封装到了invocation中
// We need to create a method invocation...
invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
// Proceed to the joinpoint through the interceptor chain.
// 调用拦截器链
retVal = invocation.proceed();
}
// 7、返回结果
// Massage return value if necessary.
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);
}
}
}
真正执行拦截器链调用
public Object proceed() throws Throwable {
// We start with an index of -1 and increment early.
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
return invokeJoinpoint();
}
Object interceptorOrInterceptionAdvice = this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
// 动态匹配增强
if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
// Evaluate dynamic method matcher here: static part will already have
// been evaluated and found to match.
InterceptorAndDynamicMethodMatcher dm = (InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
Class<?> targetClass = (this.targetClass != null ? this.targetClass : this.method.getDeclaringClass());
// 匹配成功则执行
if (dm.methodMatcher.matches(this.method, targetClass, this.arguments)) {
return dm.interceptor.invoke(this);
}
// 匹配失败则跳过并执行下一个拦截器
else {
// Dynamic matching failed.
// Skip this interceptor and invoke the next in the chain.
return proceed();
}
}
// 静态增强
else {
// It's an interceptor, so we just invoke it: The pointcut will have
// been evaluated statically before this object was constructed.
// System.out.println(interceptorOrInterceptionAdvice.getClass());
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}
以上的代码之前都已经分析过，像其中的拦截器链获取等，就不再详细分析了，当代码执行到这里的proceed方法里，如果我们没有配置其他的AOP增强，那么第一个被执行的拦截器就是TransactionInterceptor（事物拦截器）
3.TransactionInterceptor实现事物管理过程简析
public Object invoke(MethodInvocation invocation) throws Throwable {
// Work out the target class: may be {@code null}.
// The TransactionAttributeSource should be passed the target class
// as well as the method, which may be from an interface.
Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);
// Adapt to TransactionAspectSupport's invokeWithinTransaction...
return invokeWithinTransaction(invocation.getMethod(), targetClass, invocation::proceed);
}
protected Object invokeWithinTransaction(Method method,
@Nullable Class<?> targetClass,
final InvocationCallback invocation) throws Throwable {
// 1.准备工作
// If the transaction attribute is null, the method is non-transactional.
TransactionAttributeSource tas = getTransactionAttributeSource();
// 获取事物属性
final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
// 获取事物管理器
final PlatformTransactionManager tm = determineTransactionManager(txAttr);
// 获取目标类全限定类名+连接点方法名 例如:com.lyc.cn.v2.day09.AccountServiceImpl.save
final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);
// 2.处理声明式事物
if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {
// Standard transaction demarcation with getTransaction and commit/rollback calls.
// 2.2 创建事物
TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);
System.out.println("==创建了名为:["+joinpointIdentification+"]的事物");
Object retVal = null;
try {
// This is an around advice: Invoke the next interceptor in the chain.
// This will normally result in a target object being invoked.
// 2.3 继续调用方法拦截器链,这里一般将会调用目标类的方法,如:com.lyc.cn.v2.day09.AccountServiceImpl.save方法
retVal = invocation.proceedWithInvocation();
} catch (Throwable ex) {
// target invocation exception
// 2.4 如果目标类方法抛出异常,则在此处理,例如:事物回滚
completeTransactionAfterThrowing(txInfo, ex);
throw ex;
} finally {
// 2.5 清除上一步创建的事物信息
cleanupTransactionInfo(txInfo);
}
// 2.6 调用成功完成后执行，但不是在异常被处理后执行。如果我们不创建事务，就什么也不做。
commitTransactionAfterReturning(txInfo);
return retVal;
}
// 3.处理编程式事物
else {
final ThrowableHolder throwableHolder = new ThrowableHolder();
// It's a CallbackPreferringPlatformTransactionManager: pass a TransactionCallback in.
try {
Object result = ((CallbackPreferringPlatformTransactionManager) tm).execute(txAttr, status -> {
TransactionInfo txInfo = prepareTransactionInfo(tm, txAttr, joinpointIdentification, status);
try {
return invocation.proceedWithInvocation();
} catch (Throwable ex) {
if (txAttr.rollbackOn(ex)) {
// A RuntimeException: will lead to a rollback.
if (ex instanceof RuntimeException) {
throw (RuntimeException) ex;
} else {
throw new ThrowableHolderException(ex);
}
} else {
// A normal return value: will lead to a commit.
throwableHolder.throwable = ex;
return null;
}
} finally {
cleanupTransactionInfo(txInfo);
}
});
// Check result state: It might indicate a Throwable to rethrow.
if (throwableHolder.throwable != null) {
throw throwableHolder.throwable;
}
return result;
} catch (ThrowableHolderException ex) {
throw ex.getCause();
} catch (TransactionSystemException ex2) {
if (throwableHolder.throwable != null) {
logger.error("Application exception overridden by commit exception", throwableHolder.throwable);
ex2.initApplicationException(throwableHolder.throwable);
}
throw ex2;
} catch (Throwable ex2) {
if (throwableHolder.throwable != null) {
logger.error("Application exception overridden by commit exception", throwableHolder.throwable);
}
throw ex2;
}
}
}
这里对声明式事物和编程式事物分别做了不同的处理，我们主要看声明式事物的实现过程，第一步的准备工作比较简单，第二步是整个事物的核心所在。
- 创建事物
- 继续调用方法拦截器链,这里一般将会调用目标类的方法,如:com.lyc.cn.v2.day09.AccountServiceImpl.save方法
- 如果目标类方法抛出异常,则在此处理,例如:事物回滚
- 清除上一步创建的事物信息
- 调用成功完成后执行commitTransactionAfterReturning方法，但不是在异常被处理后执行。如果我们不创建事务，就什么也不做。
分析到这里，我们也仅仅是得到了Spring事物管理的一些步骤，继续分析，接下来就是Spring创建事物的过程了。这一部分的内容太多了，还是分篇幅介绍吧。。。
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