版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/huanshirenjian/article/details/89681654
1.开启事务配置
开启事务管理器分为三步：
- 注册事务管理器
@Bean
public PlatformTransactionManager platformTransactionManager() throws PropertyVetoException{
return new DataSourceTransactionManager(dataSource());
}
- 开启事务管理
用@EnableTransactionManagement注解 - 在需要事务管理的方法上加上@Transactional
2.源码分析
看到@EnableTransactionManagement是不是感觉有点熟悉，在分析AOP源码时，开启AOP使用@EnableAspectJAutoProxy。所以@EnableTransactionManagement注解中肯定是向IOC容器中注册了bean。
//向容器注册了TransactionManagementConfigurationSelector
@Import(TransactionManagementConfigurationSelector.class)
public @interface EnableTransactionManagement {
/**
* Indicate whether subclass-based (CGLIB) proxies are to be created ({@code true}) as
* opposed to standard Java interface-based proxies ({@code false}). The default is
* {@code false}. <strong>Applicable only if {@link #mode()} is set to
* {@link AdviceMode#PROXY}</strong>.
* <p>Note that setting this attribute to {@code true} will affect <em>all</em>
* Spring-managed beans requiring proxying, not just those marked with
* {@code @Transactional}. For example, other beans marked with Spring's
* {@code @Async} annotation will be upgraded to subclass proxying at the same
* time. This approach has no negative impact in practice unless one is explicitly
* expecting one type of proxy vs another, e.g. in tests.
*/
boolean proxyTargetClass() default false;
/**
* Indicate how transactional advice should be applied.
* <p><b>The default is {@link AdviceMode#PROXY}.</b>
* Please note that proxy mode allows for interception of calls through the proxy
* only. Local calls within the same class cannot get intercepted that way; an
* {@link Transactional} annotation on such a method within a local call will be
* ignored since Spring's interceptor does not even kick in for such a runtime
* scenario. For a more advanced mode of interception, consider switching this to
* {@link AdviceMode#ASPECTJ}.
*/
AdviceMode mode() default AdviceMode.PROXY;
/**
* Indicate the ordering of the execution of the transaction advisor
* when multiple advices are applied at a specific joinpoint.
* <p>The default is {@link Ordered#LOWEST_PRECEDENCE}.
*/
int order() default Ordered.LOWEST_PRECEDENCE;
}
TransactionManagementConfigurationSelector实现了ImportSelector，也是用来向容器注册bean。
protected String[] selectImports(AdviceMode adviceMode) {
switch (adviceMode) {
case PROXY:
//如果是PROXY模式，向容器注册AutoProxyRegistrar和ProxyTransactionManagementConfiguration
return new String[] {AutoProxyRegistrar.class.getName(),
ProxyTransactionManagementConfiguration.class.getName()};
case ASPECTJ:
//如果使用ASPECTJ，向容器注册AspectJTransactionManagementConfiguration
return new String[] {determineTransactionAspectClass()};
default:
return null;
}
}
默认的模式是PROXY。这里我们分析下AutoProxyRegistrar和ProxyTransactionManagementConfiguration两个类。
2.1AutoProxyRegistrar
AutoProxyRegistrar又实现了ImportBeanDefinitionRegistrar接口，这个同样是向容器注册bean的。
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
boolean candidateFound = false;
Set<String> annTypes = importingClassMetadata.getAnnotationTypes();
for (String annType : annTypes) {
AnnotationAttributes candidate = AnnotationConfigUtils.attributesFor(importingClassMetadata, annType);
if (candidate == null) {
continue;
}
Object mode = candidate.get("mode");
Object proxyTargetClass = candidate.get("proxyTargetClass");
if (mode != null && proxyTargetClass != null && AdviceMode.class == mode.getClass() &&
Boolean.class == proxyTargetClass.getClass()) {
candidateFound = true;
if (mode == AdviceMode.PROXY) {
//默认模式是PROXY
AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);
if ((Boolean) proxyTargetClass) {
AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
return;
}
}
}
}
if (!candidateFound && logger.isInfoEnabled()) {
String name = getClass().getSimpleName();
logger.info(String.format("%s was imported but no annotations were found " +
"having both 'mode' and 'proxyTargetClass' attributes of type " +
"AdviceMode and boolean respectively. This means that auto proxy " +
"creator registration and configuration may not have occurred as " +
"intended, and components may not be proxied as expected. Check to " +
"ensure that %s has been @Import'ed on the same class where these " +
"annotations are declared; otherwise remove the import of %s " +
"altogether.", name, name, name));
}
}
registerAutoProxyCreatorIfNecessary方法
public static BeanDefinition registerAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry) {
return registerAutoProxyCreatorIfNecessary(registry, null);
}
public static BeanDefinition registerAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry,
@Nullable Object source) {
return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);
}
最后向容器注册了InfrastructureAdvisorAutoProxyCreator,这个类就是AOP的创建代理对象的核心类。如果你看过我AOP的文章可能有点疑惑，我们再分析AOP源码的时候，发现启动AOP注册的是AnnotationAwareAspectJAutoProxyCreator。其实这两个类只是不同的实现，本质上还是使用动态代理封装对象。
InfrastructureAdvisorAutoProxyCreator继承自AbstractAdvisorAutoProxyCreator类。AnnotationAwareAspectJAutoProxyCreator类继承AspectJAwareAdvisorAutoProxyCreator类，而AspectJAwareAdvisorAutoProxyCreator同样继承自AbstractAdvisorAutoProxyCreator类。到这里可以知道事务管理本质上也是使用了AOP，对方法进行拦截，对对象进行封装。对AOP不明白的可以看我分析AOP的文章。这里出现了很多向IOC注册bean的类，这个我在之前的文章也说过，有兴趣的可以看下。
2.2ProxyTransactionManagementConfiguration
public class ProxyTransactionManagementConfiguration extends AbstractTransactionManagementConfiguration {
@Bean(name = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
//事务增强器(Advisor)
public BeanFactoryTransactionAttributeSourceAdvisor transactionAdvisor() {
BeanFactoryTransactionAttributeSourceAdvisor advisor = new BeanFactoryTransactionAttributeSourceAdvisor();
advisor.setTransactionAttributeSource(transactionAttributeSource());
advisor.setAdvice(transactionInterceptor());
if (this.enableTx != null) {
advisor.setOrder(this.enableTx.<Integer>getNumber("order"));
}
return advisor;
}
@Bean
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
//@Transactional注解的解析类；负责解析事务方法上@Transactional中的各个参数配置
public TransactionAttributeSource transactionAttributeSource() {
return new AnnotationTransactionAttributeSource();
}
@Bean
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
//拦截器，实际是一个MethodInterceptor
// 在目标方法执行的时候；执行拦截器链；
public TransactionInterceptor transactionInterceptor() {
TransactionInterceptor interceptor = new TransactionInterceptor();
interceptor.setTransactionAttributeSource(transactionAttributeSource());
if (this.txManager != null) {
interceptor.setTransactionManager(this.txManager);
}
return interceptor;
}
}
2.3 事务动态代理
既然事务也是AOP动态代理，前一篇我们也分析了AOP源码，这里我们直接看下核心部分。
前面AOP的时候有个canApply方法判断增强器是否需要在当前类增强，我们直接从这里开始分析。
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();
if (methodMatcher == MethodMatcher.TRUE) {
// No need to iterate the methods if we're matching any method anyway...
return true;
}
IntroductionAwareMethodMatcher introductionAwareMethodMatcher = null;
if (methodMatcher instanceof IntroductionAwareMethodMatcher) {
introductionAwareMethodMatcher = (IntroductionAwareMethodMatcher) methodMatcher;
}
Set<Class<?>> classes = new LinkedHashSet<>();
if (!Proxy.isProxyClass(targetClass)) {
classes.add(ClassUtils.getUserClass(targetClass));
}
classes.addAll(ClassUtils.getAllInterfacesForClassAsSet(targetClass));
for (Class<?> clazz : classes) {
Method[] methods = ReflectionUtils.getAllDeclaredMethods(clazz);
for (Method method : methods) {
if (introductionAwareMethodMatcher != null ?
introductionAwareMethodMatcher.matches(method, targetClass, hasIntroductions) :
methodMatcher.matches(method, targetClass)) {//判断方法是否需要增强
return true;
}
}
}
return false;
}
是不是很熟悉，我们直接看判断方法是否需要增强的部分。这里的methodMatcher.matches(method, targetClass)调用的是TransactionAttributeSourcePointcut类的matches方法。
（1）matches方法
public boolean matches(Method method, @Nullable Class<?> targetClass) {
if (targetClass != null && TransactionalProxy.class.isAssignableFrom(targetClass)) {
return false;
}
TransactionAttributeSource tas = getTransactionAttributeSource();
return (tas == null || tas.getTransactionAttribute(method, targetClass) != null);
}
（2）getTransactionAttribute方法
public TransactionAttribute getTransactionAttribute(Method method, @Nullable Class<?> targetClass) {
if (method.getDeclaringClass() == Object.class) {
return null;
}
// First, see if we have a cached value.
Object cacheKey = getCacheKey(method, targetClass);
TransactionAttribute 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 cached;
}
}
else {
// We need to work it out.
//方法匹配的判断
TransactionAttribute txAttr = computeTransactionAttribute(method, targetClass);
// Put it in the cache.
if (txAttr == null) {
this.attributeCache.put(cacheKey, NULL_TRANSACTION_ATTRIBUTE);
}
else {
String methodIdentification = ClassUtils.getQualifiedMethodName(method, targetClass);
if (txAttr instanceof DefaultTransactionAttribute) {
((DefaultTransactionAttribute) txAttr).setDescriptor(methodIdentification);
}
if (logger.isTraceEnabled()) {
logger.trace("Adding transactional method '" + methodIdentification + "' with attribute: " + txAttr);
}
this.attributeCache.put(cacheKey, txAttr);
}
return txAttr;
}
}
（3）computeTransactionAttribute方法
protected TransactionAttribute computeTransactionAttribute(Method method, @Nullable Class<?> targetClass) {
// Don't allow no-public methods as required.
if (allowPublicMethodsOnly() && !Modifier.isPublic(method.getModifiers())) {
return null;
}
// 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 = AopUtils.getMostSpecificMethod(method, targetClass);
// First try is the method in the target class.
TransactionAttribute txAttr = findTransactionAttribute(specificMethod);
if (txAttr != null) {
return txAttr;
}
// Second try is the transaction attribute on the target class.
txAttr = findTransactionAttribute(specificMethod.getDeclaringClass());
if (txAttr != null && ClassUtils.isUserLevelMethod(method)) {
return txAttr;
}
if (specificMethod != method) {
// Fallback is to look at the original method.
txAttr = findTransactionAttribute(method);
if (txAttr != null) {
return txAttr;
}
// Last fallback is the class of the original method.
txAttr = findTransactionAttribute(method.getDeclaringClass());
if (txAttr != null && ClassUtils.isUserLevelMethod(method)) {
return txAttr;
}
}
return null;
}
（4）findTransactionAttribute
protected TransactionAttribute findTransactionAttribute(Method method) {
return determineTransactionAttribute(method);
}
继续往下看
（5）determineTransactionAttribute
protected TransactionAttribute determineTransactionAttribute(AnnotatedElement ae) {
for (TransactionAnnotationParser annotationParser : this.annotationParsers) {
TransactionAttribute attr = annotationParser.parseTransactionAnnotation(ae);
if (attr != null) {
return attr;
}
}
return null;
}
我们看下parseTransactionAnnotation，这个是解析事务的方法
（6）parseTransactionAnnotation
这个方法调用的是SpringTransactionAnnotationParser的方法。
public TransactionAttribute parseTransactionAnnotation(AnnotatedElement ae) {
AnnotationAttributes attributes = AnnotatedElementUtils.findMergedAnnotationAttributes(
ae, Transactional.class, false, false);
if (attributes != null) {
return parseTransactionAnnotation(attributes);
}
else {
return null;
}
}
我们可以看到接续判断是否包含@Transactional属性。
（7）parseTransactionAnnotation
这个方法就是用来解析属性的。
protected TransactionAttribute parseTransactionAnnotation(AnnotationAttributes attributes) {
RuleBasedTransactionAttribute rbta = new RuleBasedTransactionAttribute();
Propagation propagation = attributes.getEnum("propagation");
rbta.setPropagationBehavior(propagation.value());
Isolation isolation = attributes.getEnum("isolation");
rbta.setIsolationLevel(isolation.value());
rbta.setTimeout(attributes.getNumber("timeout").intValue());
rbta.setReadOnly(attributes.getBoolean("readOnly"));
rbta.setQualifier(attributes.getString("value"));
ArrayList<RollbackRuleAttribute> rollBackRules = new ArrayList<>();
Class<?>[] rbf = attributes.getClassArray("rollbackFor");
for (Class<?> rbRule : rbf) {
RollbackRuleAttribute rule = new RollbackRuleAttribute(rbRule);
rollBackRules.add(rule);
}
String[] rbfc = attributes.getStringArray("rollbackForClassName");
for (String rbRule : rbfc) {
RollbackRuleAttribute rule = new RollbackRuleAttribute(rbRule);
rollBackRules.add(rule);
}
Class<?>[] nrbf = attributes.getClassArray("noRollbackFor");
for (Class<?> rbRule : nrbf) {
NoRollbackRuleAttribute rule = new NoRollbackRuleAttribute(rbRule);
rollBackRules.add(rule);
}
String[] nrbfc = attributes.getStringArray("noRollbackForClassName");
for (String rbRule : nrbfc) {
NoRollbackRuleAttribute rule = new NoRollbackRuleAttribute(rbRule);
rollBackRules.add(rule);
}
rbta.getRollbackRules().addAll(rollBackRules);
return rbta;
}
2.4 事务的拦截
前面AOP的封装和需要拦截的增强器也分析了，这里分析下方法调用的逻辑，和AOP类似，最后方法调用肯定是用了拦截器，这里就是在前面看到的TransactionInterceptor的invoke方法。
public Object invoke(final 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);
}
（1）invokeWithinTransaction
这里调用的是TransactionAspectSupport类的invokeWithinTransaction方法。
protected Object invokeWithinTransaction(Method method, @Nullable Class<?> targetClass,
final InvocationCallback invocation) throws Throwable {
// If the transaction attribute is null, the method is non-transactional.
TransactionAttributeSource tas = getTransactionAttributeSource();
final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
final PlatformTransactionManager tm = determineTransactionManager(txAttr);
final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);
if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {
// Standard transaction demarcation with getTransaction and commit/rollback calls.
//开启事务
TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);
Object retVal;
try {
// This is an around advice: Invoke the next interceptor in the chain.
// This will normally result in a target object being invoked.
retVal = invocation.proceedWithInvocation();
} catch (Throwable ex) {
// target invocation exception
//开启抛出异常后，回滚事务
completeTransactionAfterThrowing(txInfo, ex);
throw ex;
} finally {
cleanupTransactionInfo(txInfo);
}
if (vavrPresent && VavrDelegate.isVavrTry(retVal)) {
// Set rollback-only in case of Vavr failure matching our rollback rules...
TransactionStatus status = txInfo.getTransactionStatus();
if (status != null && txAttr != null) {
retVal = VavrDelegate.evaluateTryFailure(retVal, txAttr, status);
}
}
//提交事务
commitTransactionAfterReturning(txInfo);
return retVal;
} 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 {
//执行被拦截的方法
Object retVal = invocation.proceedWithInvocation();
if (vavrPresent && VavrDelegate.isVavrTry(retVal)) {
// Set rollback-only in case of Vavr failure matching our rollback rules...
retVal = VavrDelegate.evaluateTryFailure(retVal, txAttr, status);
}
return retVal;
} 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;
}
}
}
（2）createTransactionIfNecessary
protected TransactionInfo createTransactionIfNecessary(@Nullable PlatformTransactionManager tm,
@Nullable TransactionAttribute txAttr, final String joinpointIdentification) {
// If no name specified, apply method identification as transaction name.
if (txAttr != null && txAttr.getName() == null) {
txAttr = new DelegatingTransactionAttribute(txAttr) {
@Override
public String getName() {
return joinpointIdentification;
}
};
}
TransactionStatus status = null;
if (txAttr != null) {
if (tm != null) {
//开启事务
status = tm.getTransaction(txAttr);
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Skipping transactional joinpoint [" + joinpointIdentification +
"] because no transaction manager has been configured");
}
}
}
return prepareTransactionInfo(tm, txAttr, joinpointIdentification, status);
}
（3）getTransaction
这里调用的是AbstractPlatformTransactionManager类的方法。
public final TransactionStatus getTransaction(@Nullable TransactionDefinition definition) throws TransactionException {
Object transaction = doGetTransaction();//子类实现
// Cache debug flag to avoid repeated checks.
boolean debugEnabled = logger.isDebugEnabled();
if (definition == null) {
// Use defaults if no transaction definition given.
definition = new DefaultTransactionDefinition();
}
if (isExistingTransaction(transaction)) {
// Existing transaction found -> check propagation behavior to find out how to behave.
return handleExistingTransaction(definition, transaction, debugEnabled);
}
// Check definition settings for new transaction.
if (definition.getTimeout() < TransactionDefinition.TIMEOUT_DEFAULT) {
throw new InvalidTimeoutException("Invalid transaction timeout", definition.getTimeout());
}
// No existing transaction found -> check propagation behavior to find out how to proceed.
if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_MANDATORY) {
throw new IllegalTransactionStateException(
"No existing transaction found for transaction marked with propagation 'mandatory'");
}
else if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRED ||
definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW ||
definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) {
SuspendedResourcesHolder suspendedResources = suspend(null);
if (debugEnabled) {
logger.debug("Creating new transaction with name [" + definition.getName() + "]: " + definition);
}
try {
boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
DefaultTransactionStatus status = newTransactionStatus(
definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
//开启事务
doBegin(transaction, definition);
prepareSynchronization(status, definition);
return status;
}
catch (RuntimeException | Error ex) {
resume(null, suspendedResources);
throw ex;
}
}
else {
// Create "empty" transaction: no actual transaction, but potentially synchronization.
if (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT && logger.isWarnEnabled()) {
logger.warn("Custom isolation level specified but no actual transaction initiated; " +
"isolation level will effectively be ignored: " + definition);
}
boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS);
return prepareTransactionStatus(definition, null, true, newSynchronization, debugEnabled, null);
}
}
（4）doGetTransaction、doBegin
这个方法是需要子类实现的，我们在前面定义的事务管理器是DataSourceTransactionManager。看下doGetTransaction和doBegin方法。
protected Object doGetTransaction() {
//获得事务
DataSourceTransactionObject txObject = new DataSourceTransactionObject();
txObject.setSavepointAllowed(isNestedTransactionAllowed());
ConnectionHolder conHolder =
(ConnectionHolder) TransactionSynchronizationManager.getResource(obtainDataSource());
txObject.setConnectionHolder(conHolder, false);
return txObject;
}
protected void doBegin(Object transaction, TransactionDefinition definition) {
DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
Connection con = null;
try {
if (!txObject.hasConnectionHolder() ||
txObject.getConnectionHolder().isSynchronizedWithTransaction()) {
Connection newCon = obtainDataSource().getConnection();
if (logger.isDebugEnabled()) {
logger.debug("Acquired Connection [" + newCon + "] for JDBC transaction");
}
txObject.setConnectionHolder(new ConnectionHolder(newCon), true);
}
txObject.getConnectionHolder().setSynchronizedWithTransaction(true);
con = txObject.getConnectionHolder().getConnection();
Integer previousIsolationLevel = DataSourceUtils.prepareConnectionForTransaction(con, definition);
txObject.setPreviousIsolationLevel(previousIsolationLevel);
// Switch to manual commit if necessary. This is very expensive in some JDBC drivers,
// so we don't want to do it unnecessarily (for example if we've explicitly
// configured the connection pool to set it already).
if (con.getAutoCommit()) {
txObject.setMustRestoreAutoCommit(true);
if (logger.isDebugEnabled()) {
logger.debug("Switching JDBC Connection [" + con + "] to manual commit");
}
//设置自动提交
con.setAutoCommit(false);
}
prepareTransactionalConnection(con, definition);
txObject.getConnectionHolder().setTransactionActive(true);
int timeout = determineTimeout(definition);
if (timeout != TransactionDefinition.TIMEOUT_DEFAULT) {
txObject.getConnectionHolder().setTimeoutInSeconds(timeout);
}
// Bind the connection holder to the thread.
if (txObject.isNewConnectionHolder()) {
TransactionSynchronizationManager.bindResource(obtainDataSource(), txObject.getConnectionHolder());
}
}
catch (Throwable ex) {
if (txObject.isNewConnectionHolder()) {
DataSourceUtils.releaseConnection(con, obtainDataSource());
txObject.setConnectionHolder(null, false);
}
throw new CannotCreateTransactionException("Could not open JDBC Connection for transaction", ex);
}
}
（5）completeTransactionAfterThrowing
我们会过来再看下抛出异常的回滚方法。
protected void completeTransactionAfterThrowing(@Nullable TransactionInfo txInfo, Throwable ex) {
if (txInfo != null && txInfo.getTransactionStatus() != null) {
if (logger.isTraceEnabled()) {
logger.trace("Completing transaction for [" + txInfo.getJoinpointIdentification() +
"] after exception: " + ex);
}
if (txInfo.transactionAttribute != null && txInfo.transactionAttribute.rollbackOn(ex)) {
try {
//事务回滚
txInfo.getTransactionManager().rollback(txInfo.getTransactionStatus());
} catch (TransactionSystemException ex2) {
logger.error("Application exception overridden by rollback exception", ex);
ex2.initApplicationException(ex);
throw ex2;
} catch (RuntimeException | Error ex2) {
logger.error("Application exception overridden by rollback exception", ex);
throw ex2;
}
} else {
// We don't roll back on this exception.
// Will still roll back if TransactionStatus.isRollbackOnly() is true.
try {
txInfo.getTransactionManager().commit(txInfo.getTransactionStatus());
} catch (TransactionSystemException ex2) {
logger.error("Application exception overridden by commit exception", ex);
ex2.initApplicationException(ex);
throw ex2;
} catch (RuntimeException | Error ex2) {
logger.error("Application exception overridden by commit exception", ex);
throw ex2;
}
}
}
}
这里的回滚调用的也是我们定义事务管理器的方法。
protected void doRollback(DefaultTransactionStatus status) {
DataSourceTransactionObject txObject = (DataSourceTransactionObject) status.getTransaction();
Connection con = txObject.getConnectionHolder().getConnection();
if (status.isDebug()) {
logger.debug("Rolling back JDBC transaction on Connection [" + con + "]");
}
try {
//事务回滚
con.rollback();
}
catch (SQLException ex) {
throw new TransactionSystemException("Could not roll back JDBC transaction", ex);
}
}
（6）commitTransactionAfterReturning
再看下事务提交方法。
protected void commitTransactionAfterReturning(@Nullable TransactionInfo txInfo) {
if (txInfo != null && txInfo.getTransactionStatus() != null) {
if (logger.isTraceEnabled()) {
logger.trace("Completing transaction for [" + txInfo.getJoinpointIdentification() + "]");
}
//事务提交
txInfo.getTransactionManager().commit(txInfo.getTransactionStatus());
}
}
这里的回滚提交的也是我们定义事务管理器的方法。
protected void doCommit(DefaultTransactionStatus status) {
DataSourceTransactionObject txObject = (DataSourceTransactionObject) status.getTransaction();
Connection con = txObject.getConnectionHolder().getConnection();
if (status.isDebug()) {
logger.debug("Committing JDBC transaction on Connection [" + con + "]");
}
try {
//事务提交
con.commit();
}
catch (SQLException ex) {
throw new TransactionSystemException("Could not commit JDBC transaction", ex);
}
}
至此事务分析结束。
总结：
其实spring中的事务也是AOP动态代理，利用增强器对方法进行增强。事务的提交、回滚都是调用的我们定义的事务管理器。
这里把所有和AOP拦截的代码去掉，和我们自己进行简单的事务控制一样。分为以下几步：
- 获得事务GetTransaction
- 开启事务doBegin
- 事务提交commit
- 如果方法抛出异常，事务回滚rollback