正文
系列目录
引子
本节我们将会从上一节的”简单样例“入手：Spring Boot+Atomikos(TM)+Mybatis(ORM)+Mysql(DB)，深入源码，看看这个分布式事务是怎么定义、执行的。
先来回忆一下第二节讲的JTA规范，如下图。Atomikos是什么角色？起到什么作用？
角色：
Atomikos根本上是一个事务管理器(TM)也就是JTA模型的核心，上图扇形的中心位置。
作用：
TM调用 【Resource Manager资源管理器】 的XAResource接口来实现事务操作。
TM依赖 【Application Server应用服务器】 的TransactionManager接口当然如果服务器不支持事务管理，自然也就只能使用第三方包，例如Atomikos。
TM依赖 【Application应用程序】 设置事务边界、属性，application调用UserTransaction接口控制事务开始、提交、回滚。
一、bean定义
1.1 JtaTransactionManager
org.springframework.transaction.jta.JtaTransactionManager类是spring提供的分布式事务管理器。
JtaTransactionManager类图如下：
实现了接口如下：
- PlatformTransactionManager ：获取事务，提交事务，回滚事务
- TransactionFactory：创建事务
- InitializingBean：初始化bean
JtaTransactionManager实现了InitializingBean接口的afterPropertiesSet()方法，处于bean生命周期的容器初始化->实例化期->初始化中期，如下图：
下面我们看一下JtaTransactionManager在bean初始化中期InitializingBean接口的afterPropertiesSet()做了什么：
1 /**
2 * Initialize the UserTransaction as well as the TransactionManager handle.
3 * @see #initUserTransactionAndTransactionManager()
4 */
5 @Override
6 public void afterPropertiesSet() throws TransactionSystemException {
7 initUserTransactionAndTransactionManager();
8 checkUserTransactionAndTransactionManager();
9 initTransactionSynchronizationRegistry();
10 }
-
1.initUserTransactionAndTransactionManager：初始化UserTransaction和TransactionManager接口。主要是如果没有定义的话，可以支持JNDI。
-
2.checkUserTransactionAndTransactionManager：校验2个接口是否存在。UserTransaction必须定义，TransactionManager可以不定义。
源码如下：
对应控制台打印：
o.s.t.jta.JtaTransactionManager : Using JTA UserTransaction: com.atomikos.icatch.jta.UserTransactionImp@614aeccc o.s.t.jta.JtaTransactionManager : Using JTA TransactionManager: com.atomikos.icatch.jta.UserTransactionManager@5116ac09
- 3.initTransactionSynchronizationRegistry：初始化事务同步注册，这个不使用JNDI的话没啥用。
上一节分布式事务（三）简单样例中我们配置了JtaTransactionManagerConfig类，如下：
1 package study.config.datasource;
2
3 import com.atomikos.icatch.jta.UserTransactionImp;
4 import com.atomikos.icatch.jta.UserTransactionManager;
5 import org.springframework.context.annotation.Bean;
6 import org.springframework.context.annotation.Configuration;
7 import org.springframework.transaction.jta.JtaTransactionManager;
8
9 import javax.transaction.UserTransaction;
10
11 /**
12 * 事务管理器配置类
13 *
14 * @author denny
15 */
16 @Configuration
17 public class JtaTransactionManagerConfig {
18
19 @Bean(name = "atomikosTransactionManager")
20 public JtaTransactionManager regTransactionManager() {
21 UserTransactionManager userTransactionManager = new UserTransactionManager();
22 UserTransaction userTransaction = new UserTransactionImp();
23 return new JtaTransactionManager(userTransaction, userTransactionManager);
24 }
25 }
如上图，我们定义了一个name = "atomikosTransactionManager"的bean,具体类型为JtaTransactionManager。其中构造了2个实现类UserTransactionImp（javax.transaction.UserTransaction接口）、UserTransactionManager（javax.transaction.TransactionManager接口）。并用这2个实现类构造了一个JtaTransactionManager。
1.UserTransaction接口
提供给用户操控事务的：开启，提交，回滚等等。源码如下：
2 TransactionManager接口
源码如下：
相比UserTransaction，TransactionManager接口多了接口的挂起、恢复、获取事务3个接口。这3个方法明显是留给系统自己调用的。
1.2 AtomikosDataSourceBean
Spring 为Atomikos定制了一个org.springframework.boot.jta.atomikos.AtomikosDataSourceBean，提供了bean生命周期的一些接口：
- BeanNameAware：设置bean名称
- InitializingBean：初始化bean
- DisposableBean:销毁bean
我们只需要定义这个bean即可轻松使得spring来维护。
com.atomikos.jdbc.AtomikosDataSourceBean类图如下:
其中核心接口：
DataSource接口：getConnection获取数据库连接
ConnectionPoolProperties接口：用于载入连接池的属性
二、源码剖析
2.1 自动配置类
老套路哈，spring boot就这么点花花肠子，既然使用@Transactional这种注解的方式，那么我们就从springboot 容器启动时的自动配置载入（spring boot容器启动详解）开始看。在/META-INF/spring.factories中配置文件中查找，如下图：
载入2个关于事务的自动配置类：
org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,
org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,
由于本文是分布式事务，故2个配置文件都生效了，我们先看JtaAutoConfiguration
2.2 JtaAutoConfiguration
1 /**
2 * {@link EnableAutoConfiguration Auto-configuration} for JTA.
3 *
4 * @author Josh Long
5 * @author Phillip Webb
6 * @since 1.2.0
7 */
8 @ConditionalOnClass(javax.transaction.Transaction.class)
9 @ConditionalOnProperty(prefix = "spring.jta", value = "enabled", matchIfMissing = true)
10 @AutoConfigureBefore({ XADataSourceAutoConfiguration.class,
11 ActiveMQAutoConfiguration.class, ArtemisAutoConfiguration.class,
12 HibernateJpaAutoConfiguration.class })
13 @Import({ JndiJtaConfiguration.class, BitronixJtaConfiguration.class,
14 AtomikosJtaConfiguration.class, NarayanaJtaConfiguration.class })
15 @EnableConfigurationProperties(JtaProperties.class)
16 public class JtaAutoConfiguration {
17
18 }
如上，JtaAutoConfiguration这个类竟然是个空壳，只有一堆注解，挑几个重要的讲一讲：
1.@ConditionalOnClass(javax.transaction.Transaction.class)：代表类路径下存在javax.transaction.Transaction.class这个类，那么JtaAutoConfiguration生效。
2.@ConditionalOnProperty(prefix = "spring.jta", value = "enabled", matchIfMissing = true)，自动开启spring.jta.enabled=true.
3.@Import({ JndiJtaConfiguration.class, BitronixJtaConfiguration.class, AtomikosJtaConfiguration.class, NarayanaJtaConfiguration.class }),又是spring套路哈，用来导入类。这里导入了4个配置类，可见支持4种第三方事务管理器。AtomikosJtaConfiguration.class自然就是Atomikos了。
AtomikosJtaConfiguration.class这个配置类
1 @Configuration
2 @EnableConfigurationProperties({ AtomikosProperties.class, JtaProperties.class })
3 @ConditionalOnClass({ JtaTransactionManager.class, UserTransactionManager.class })
4 @ConditionalOnMissingBean(PlatformTransactionManager.class)
5 class AtomikosJtaConfiguration {
6
7 private final JtaProperties jtaProperties;
8
9 private final TransactionManagerCustomizers transactionManagerCustomizers;
10
11 AtomikosJtaConfiguration(JtaProperties jtaProperties,
12 ObjectProvider<TransactionManagerCustomizers> transactionManagerCustomizers) {
13 this.jtaProperties = jtaProperties;
14 this.transactionManagerCustomizers = transactionManagerCustomizers
15 .getIfAvailable();
16 }
17
18 @Bean(initMethod = "init", destroyMethod = "shutdownForce")
19 @ConditionalOnMissingBean(UserTransactionService.class)
20 public UserTransactionServiceImp userTransactionService(
21 AtomikosProperties atomikosProperties) {
22 Properties properties = new Properties();
23 if (StringUtils.hasText(this.jtaProperties.getTransactionManagerId())) {
24 properties.setProperty("com.atomikos.icatch.tm_unique_name",
25 this.jtaProperties.getTransactionManagerId());
26 }
27 properties.setProperty("com.atomikos.icatch.log_base_dir", getLogBaseDir());
28 properties.putAll(atomikosProperties.asProperties());
29 return new UserTransactionServiceImp(properties);
30 }
31
32 private String getLogBaseDir() {
33 if (StringUtils.hasLength(this.jtaProperties.getLogDir())) {
34 return this.jtaProperties.getLogDir();
35 }
36 File home = new ApplicationHome().getDir();
37 return new File(home, "transaction-logs").getAbsolutePath();
38 }
39
40 @Bean(initMethod = "init", destroyMethod = "close")
41 @ConditionalOnMissingBean
42 public UserTransactionManager atomikosTransactionManager(
43 UserTransactionService userTransactionService) throws Exception {
44 UserTransactionManager manager = new UserTransactionManager();
45 manager.setStartupTransactionService(false);
46 manager.setForceShutdown(true);
47 return manager;
48 }
49
50 @Bean
51 @ConditionalOnMissingBean(XADataSourceWrapper.class)
52 public AtomikosXADataSourceWrapper xaDataSourceWrapper() {
53 return new AtomikosXADataSourceWrapper();
54 }
55
56 @Bean
57 @ConditionalOnMissingBean
58 public static AtomikosDependsOnBeanFactoryPostProcessor atomikosDependsOnBeanFactoryPostProcessor() {
59 return new AtomikosDependsOnBeanFactoryPostProcessor();
60 }
61
62 @Bean
63 public JtaTransactionManager transactionManager(UserTransaction userTransaction,
64 TransactionManager transactionManager) {
65 JtaTransactionManager jtaTransactionManager = new JtaTransactionManager(
66 userTransaction, transactionManager);
67 if (this.transactionManagerCustomizers != null) {
68 this.transactionManagerCustomizers.customize(jtaTransactionManager);
69 }
70 return jtaTransactionManager;
71 }
72
73 @Configuration
74 @ConditionalOnClass(Message.class)
75 static class AtomikosJtaJmsConfiguration {
76
77 @Bean
78 @ConditionalOnMissingBean(XAConnectionFactoryWrapper.class)
79 public AtomikosXAConnectionFactoryWrapper xaConnectionFactoryWrapper() {
80 return new AtomikosXAConnectionFactoryWrapper();
81 }
82
83 }
84
85 }
2.3 TransactionAutoConfiguration
这里和本地事务分析过程一致，就不再重复，飞机票spring事务详解（三）源码详解，一直看到第二节结束.这里只截个图：
最终源码调用具体事务管理器的PlatformTransactionManager接口的3个方法：
1 public interface PlatformTransactionManager {
2 // 获取事务状态
3 TransactionStatus getTransaction(TransactionDefinition definition) throws TransactionException;
4 // 事务提交
5 void commit(TransactionStatus status) throws TransactionException;
6 // 事务回滚
7 void rollback(TransactionStatus status) throws TransactionException;
8 }
三、核心源码
核心实现类图：
如上提所示，PlatformTransactionManager顶级接口定义了最核心的事务管理方法，下面一层是AbstractPlatformTransactionManager抽象类，实现了PlatformTransactionManager接口的方法并定义了一些抽象方法，供子类拓展。最下面一层是2个经典事务管理器：
1.DataSourceTransactionmanager: 即本地单资源事务管理器。
2.JtaTransactionManager: 即多资源事务管理器（又叫做分布式事务管理器），其实现了JTA规范，使用XA协议进行两阶段提交。
我们这里自然是JTA分布式环境，我们只需要从JtaTransactionManager这个实现类入手即可。
3.1 getTransaction获取事务
AbstractPlatformTransactionManager实现了getTransaction()方法如下：
1 @Override
2 public final TransactionStatus getTransaction(TransactionDefinition definition) throws TransactionException {
3 Object transaction = doGetTransaction();
4
5 // Cache debug flag to avoid repeated checks.
6 boolean debugEnabled = logger.isDebugEnabled();
7
8 if (definition == null) {
9 // Use defaults if no transaction definition given.
10 definition = new DefaultTransactionDefinition();
11 }
12 // 如果当前已经存在事务
13 if (isExistingTransaction(transaction)) {
14 // 根据不同传播机制不同处理
15 return handleExistingTransaction(definition, transaction, debugEnabled);
16 }
17
18 // 超时不能小于默认值
19 if (definition.getTimeout() < TransactionDefinition.TIMEOUT_DEFAULT) {
20 throw new InvalidTimeoutException("Invalid transaction timeout", definition.getTimeout());
21 }
22
23 // 当前不存在事务，传播机制=MANDATORY（支持当前事务，没事务报错），报错
24 if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_MANDATORY) {
25 throw new IllegalTransactionStateException(
26 "No existing transaction found for transaction marked with propagation 'mandatory'");
27 }// 当前不存在事务，传播机制=REQUIRED/REQUIRED_NEW/NESTED,这三种情况，需要新开启事务，且加上事务同步
28 else if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRED ||
29 definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW ||
30 definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) {
31 SuspendedResourcesHolder suspendedResources = suspend(null);
32 if (debugEnabled) {
33 logger.debug("Creating new transaction with name [" + definition.getName() + "]: " + definition);
34 }
35 try {// 是否需要新开启同步// 开启// 开启
36 boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
37 DefaultTransactionStatus status = newTransactionStatus(
38 definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
39 doBegin(transaction, definition);// 开启新事务
40 prepareSynchronization(status, definition);//预备同步
41 return status;
42 }
43 catch (RuntimeException ex) {
44 resume(null, suspendedResources);
45 throw ex;
46 }
47 catch (Error err) {
48 resume(null, suspendedResources);
49 throw err;
50 }
51 }
52 else {
53 // 当前不存在事务当前不存在事务，且传播机制=PROPAGATION_SUPPORTS/PROPAGATION_NOT_SUPPORTED/PROPAGATION_NEVER，这三种情况，创建“空”事务:没有实际事务，但可能是同步。警告：定义了隔离级别，但并没有真实的事务初始化，隔离级别被忽略有隔离级别但是并没有定义实际的事务初始化，有隔离级别但是并没有定义实际的事务初始化，
54 if (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT && logger.isWarnEnabled()) {
55 logger.warn("Custom isolation level specified but no actual transaction initiated; " +
56 "isolation level will effectively be ignored: " + definition);
57 }
58 boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS);
59 return prepareTransactionStatus(definition, null, true, newSynchronization, debugEnabled, null);
60 }
61 }
上图核心步骤就是：
- 1.doGetTransaction()：获取事务
- 2.doBegin：准备工作
3.1.1 JtaTransactionManager的doGetTransaction()
其实也就是把UserTransaction封装成一个JtaTransactionObject返回。
1 @Override
2 protected Object doGetTransaction() {
3 UserTransaction ut = getUserTransaction();
4 if (ut == null) {
5 throw new CannotCreateTransactionException("No JTA UserTransaction available - " +
6 "programmatic PlatformTransactionManager.getTransaction usage not supported");
7 }
8 if (!this.cacheUserTransaction) {
9 ut = lookupUserTransaction(
10 this.userTransactionName != null ? this.userTransactionName : DEFAULT_USER_TRANSACTION_NAME);
11 }
12 return doGetJtaTransaction(ut);
13 }
14
15 /**
16 * Get a JTA transaction object for the given current UserTransaction.
17 * <p>Subclasses can override this to provide a JtaTransactionObject
18 * subclass, for example holding some additional JTA handle needed.
19 * @param ut the UserTransaction handle to use for the current transaction
20 * @return the JtaTransactionObject holding the UserTransaction
21 */
22 protected JtaTransactionObject doGetJtaTransaction(UserTransaction ut) {
23 return new JtaTransactionObject(ut);
24 }
3.1.2 JtaTransactionManager.doBegin
1 @Override
2 protected void doBegin(Object transaction, TransactionDefinition definition) {
3 JtaTransactionObject txObject = (JtaTransactionObject) transaction;
4 try {
5 doJtaBegin(txObject, definition);
6 }
7 catch (NotSupportedException ex) {
8 // assume nested transaction not supported
9 throw new NestedTransactionNotSupportedException(
10 "JTA implementation does not support nested transactions", ex);
11 }
12 catch (UnsupportedOperationException ex) {
13 // assume nested transaction not supported
14 throw new NestedTransactionNotSupportedException(
15 "JTA implementation does not support nested transactions", ex);
16 }
17 catch (SystemException ex) {
18 throw new CannotCreateTransactionException("JTA failure on begin", ex);
19 }
20 }
调用JtaTransactionManager.doJtaBegin：
1 protected void doJtaBegin(JtaTransactionObject txObject, TransactionDefinition definition)
2 throws NotSupportedException, SystemException {
3
4 applyIsolationLevel(txObject, definition.getIsolationLevel());
5 int timeout = determineTimeout(definition);
6 applyTimeout(txObject, timeout);
7 txObject.getUserTransaction().begin();
8 }
UserTransactionImp.begin->TransactionManagerImp.begin
1 public void begin ( int timeout ) throws NotSupportedException,
2 SystemException
3 {
4 CompositeTransaction ct = null;
5 ResumePreviousTransactionSubTxAwareParticipant resumeParticipant = null;
6
7 ct = compositeTransactionManager.getCompositeTransaction();
8 if ( ct != null && ct.getProperty ( JTA_PROPERTY_NAME ) == null ) {
9 LOGGER.logWarning ( "JTA: temporarily suspending incompatible transaction: " + ct.getTid() +
10 " (will be resumed after JTA transaction ends)" );
11 ct = compositeTransactionManager.suspend();
12 resumeParticipant = new ResumePreviousTransactionSubTxAwareParticipant ( ct );
13 }
14
15 try {
16 ct = compositeTransactionManager.createCompositeTransaction ( ( ( long ) timeout ) * 1000 );
17 if ( resumeParticipant != null ) ct.addSubTxAwareParticipant ( resumeParticipant );
18 if ( ct.isRoot () && getDefaultSerial () )
19 ct.getTransactionControl ().setSerial ();
20 ct.setProperty ( JTA_PROPERTY_NAME , "true" );
21 } catch ( SysException se ) {
22 String msg = "Error in begin()";
23 LOGGER.logWarning( msg , se );
24 throw new ExtendedSystemException ( msg , se
25 .getErrors () );
26 }
27 recreateCompositeTransactionAsJtaTransaction(ct);
28 }
createCompositeTransaction创建混合事务
1 public CompositeTransaction createCompositeTransaction ( long timeout ) throws SysException
2 {
3 Stack errors = new Stack();
4 CompositeTransaction ct = null , ret = null;
5 // 获取当前线程绑定的事务
6 ct = getCurrentTx ();
// 当前线程不存在事务
7 if ( ct == null ) {
// 创建组合事务
8 ret = service_.createCompositeTransaction ( timeout );
9 if(LOGGER.isInfoEnabled()){
10 LOGGER.logInfo("createCompositeTransaction ( " + timeout + " ): "
11 + "created new ROOT transaction with id " + ret.getTid ());
12 }
// 当前线程存在事务
13 } else {
14 if(LOGGER.isInfoEnabled()) LOGGER.logInfo("createCompositeTransaction ( " + timeout + " )");
// 创建子事务
15 ret = ct.getTransactionControl ().createSubTransaction ();
16
17 }
18 Thread thread = Thread.currentThread ();
// 绑定当前线程和事务的2个映射map
19 setThreadMappings ( ret, thread );
20
21 return ret;
22 }
如果当前线程不存在事务，创建组合事务。如果当前线程存在事务，创建子事务。
调用TransactionServiceImp的createCompositeTransaction创建混合事务
1 public CompositeTransaction createCompositeTransaction ( long timeout ) throws SysException
2 {
3 if ( !initialized_ ) throw new IllegalStateException ( "Not initialized" );
4
5 if ( maxNumberOfActiveTransactions_ >= 0 &&
6 tidToTransactionMap_.size () >= maxNumberOfActiveTransactions_ ) {
7 throw new IllegalStateException ( "Max number of active transactions reached:" + maxNumberOfActiveTransactions_ );
8 }
9
10 String tid = tidmgr_.get ();
11 Stack lineage = new Stack ();
12 //创建协调者
15 CoordinatorImp cc = createCC ( null, tid, true, false, timeout );
// 创建组合事务
16 CompositeTransaction ct = createCT ( tid, cc, lineage, false );
17 return ct;
18 }
3.2 commit 提交事务
事务提交流程图如下：
AbstractPlatformTransactionManager的commit源码如下：
1 @Override
2 public final void commit(TransactionStatus status) throws TransactionException {
3 if (status.isCompleted()) {// 如果事务已完结，报错无法再次提交
4 throw new IllegalTransactionStateException(
5 "Transaction is already completed - do not call commit or rollback more than once per transaction");
6 }
7
8 DefaultTransactionStatus defStatus = (DefaultTransactionStatus) status;
9 if (defStatus.isLocalRollbackOnly()) {// 如果事务明确标记为回滚，
10 if (defStatus.isDebug()) {
11 logger.debug("Transactional code has requested rollback");
12 }
13 processRollback(defStatus);//执行回滚
14 return;
15 }//如果不需要全局回滚时提交 且 全局回滚
16 if (!shouldCommitOnGlobalRollbackOnly() && defStatus.isGlobalRollbackOnly()) {
17 if (defStatus.isDebug()) {
18 logger.debug("Global transaction is marked as rollback-only but transactional code requested commit");
19 }//执行回滚
20 processRollback(defStatus);
21 // 仅在最外层事务边界（新事务）或显式地请求时抛出“未期望的回滚异常”
23 if (status.isNewTransaction() || isFailEarlyOnGlobalRollbackOnly()) {
24 throw new UnexpectedRollbackException(
25 "Transaction rolled back because it has been marked as rollback-only");
26 }
27 return;
28 }
29 // 执行提交事务
30 processCommit(defStatus);
31 }
如上图，各种判断：
- 1.如果事务明确标记为本地回滚，-》执行回滚
- 2.如果不需要全局回滚时提交 且 全局回滚-》执行回滚
- 3.提交事务，核心方法processCommit()
processCommit如下：
1 private void processCommit(DefaultTransactionStatus status) throws TransactionException {
2 try {
3 boolean beforeCompletionInvoked = false;
4 try {//3个前置操作
5 prepareForCommit(status);
6 triggerBeforeCommit(status);
7 triggerBeforeCompletion(status);
8 beforeCompletionInvoked = true;//3个前置操作已调用
9 boolean globalRollbackOnly = false;//新事务 或 全局回滚失败
10 if (status.isNewTransaction() || isFailEarlyOnGlobalRollbackOnly()) {
11 globalRollbackOnly = status.isGlobalRollbackOnly();
12 }//1.有保存点，即嵌套事务
13 if (status.hasSavepoint()) {
14 if (status.isDebug()) {
15 logger.debug("Releasing transaction savepoint");
16 }//释放保存点
17 status.releaseHeldSavepoint();
18 }//2.新事务
19 else if (status.isNewTransaction()) {
20 if (status.isDebug()) {
21 logger.debug("Initiating transaction commit");
22 }//调用事务处理器提交事务
23 doCommit(status);
24 }
25 // 3.非新事务，且全局回滚失败，但是提交时没有得到异常，抛出异常
27 if (globalRollbackOnly) {
28 throw new UnexpectedRollbackException(
29 "Transaction silently rolled back because it has been marked as rollback-only");
30 }
31 }
32 catch (UnexpectedRollbackException ex) {
33 // 触发完成后事务同步，状态为回滚
34 triggerAfterCompletion(status, TransactionSynchronization.STATUS_ROLLED_BACK);
35 throw ex;
36 }// 事务异常
37 catch (TransactionException ex) {
38 // 提交失败回滚
39 if (isRollbackOnCommitFailure()) {
40 doRollbackOnCommitException(status, ex);
41 }// 触发完成后回调，事务同步状态为未知
42 else {
43 triggerAfterCompletion(status, TransactionSynchronization.STATUS_UNKNOWN);
44 }
45 throw ex;
46 }// 运行时异常
47 catch (RuntimeException ex) {
// 如果3个前置步骤未完成，调用前置的最后一步操作
48 if (!beforeCompletionInvoked) {
49 triggerBeforeCompletion(status);
50 }// 提交异常回滚
51 doRollbackOnCommitException(status, ex);
52 throw ex;
53 }// 其它异常
54 catch (Error err) {
// 如果3个前置步骤未完成，调用前置的最后一步操作
55 if (!beforeCompletionInvoked) {
56 triggerBeforeCompletion(status);
57 }// 提交异常回滚
58 doRollbackOnCommitException(status, err);
59 throw err;
60 }
61
62 // Trigger afterCommit callbacks, with an exception thrown there
63 // propagated to callers but the transaction still considered as committed.
64 try {
65 triggerAfterCommit(status);
66 }
67 finally {
68 triggerAfterCompletion(status, TransactionSynchronization.STATUS_COMMITTED);
69 }
70
71 }
72 finally {
73 cleanupAfterCompletion(status);
74 }
75 }
如上图，commit事务时，有6个核心操作，分别是3个前置操作，3个后置操作，如下：
1.prepareForCommit(status);源码是空的，没有拓展目前。
2.triggerBeforeCommit(status); 提交前触发操作
1 protected final void triggerBeforeCommit(DefaultTransactionStatus status) {
2 if (status.isNewSynchronization()) {
3 if (status.isDebug()) {
4 logger.trace("Triggering beforeCommit synchronization");
5 }
6 TransactionSynchronizationUtils.triggerBeforeCommit(status.isReadOnly());
7 }
8 }
triggerBeforeCommit源码如下：
1 public static void triggerBeforeCommit(boolean readOnly) {
2 for (TransactionSynchronization synchronization : TransactionSynchronizationManager.getSynchronizations()) {
3 synchronization.beforeCommit(readOnly);
4 }
5 }
如上图，TransactionSynchronizationManager类定义了多个ThreadLocal（线程本地变量），其中一个用以保存当前线程的事务同步：
private static final ThreadLocal<Set<TransactionSynchronization>> synchronizations = new NamedThreadLocal<Set<TransactionSynchronization>>("Transaction synchronizations");
遍历事务同步器，把每个事务同步器都执行“提交前”操作，比如咱们用的jdbc事务，那么最终就是SqlSessionUtils.beforeCommit()->this.holder.getSqlSession().commit();提交会话。
3.triggerBeforeCompletion(status);完成前触发操作，如果是jdbc事务，那么最终就是
SqlSessionUtils.beforeCompletion->
TransactionSynchronizationManager.unbindResource(sessionFactory); 解绑当前线程的会话工厂
this.holder.getSqlSession().close();关闭会话。
4.triggerAfterCommit(status);提交事务后触发操作。TransactionSynchronizationUtils.triggerAfterCommit();->TransactionSynchronizationUtils.invokeAfterCommit，如下：
1 public static void invokeAfterCommit(List<TransactionSynchronization> synchronizations) {
2 if (synchronizations != null) {
3 for (TransactionSynchronization synchronization : synchronizations) {
4 synchronization.afterCommit();
5 }
6 }
7 }
好吧，一顿找，最后在TransactionSynchronizationAdapter中复写过，并且是空的....SqlSessionSynchronization继承了TransactionSynchronizationAdapter但是没有复写这个方法。
5. triggerAfterCompletion(status, TransactionSynchronization.STATUS_COMMITTED);
TransactionSynchronizationUtils.TransactionSynchronizationUtils.invokeAfterCompletion,如下：
1 public static void invokeAfterCompletion(List<TransactionSynchronization> synchronizations, int completionStatus) {
2 if (synchronizations != null) {
3 for (TransactionSynchronization synchronization : synchronizations) {
4 try {
5 synchronization.afterCompletion(completionStatus);
6 }
7 catch (Throwable tsex) {
8 logger.error("TransactionSynchronization.afterCompletion threw exception", tsex);
9 }
10 }
11 }
12 }
afterCompletion：对于JDBC事务来说，最终：
1）如果会话任然活着，关闭会话，
2）重置各种属性：SQL会话同步器（SqlSessionSynchronization）的SQL会话持有者（SqlSessionHolder）的referenceCount引用计数、synchronizedWithTransaction同步事务、rollbackOnly只回滚、deadline超时时间点。
6.cleanupAfterCompletion(status);
1）设置事务状态为已完成。
2) 如果是新的事务同步，解绑当前线程绑定的数据库资源，重置数据库连接
3）如果存在挂起的事务（嵌套事务），唤醒挂起的老事务的各种资源：数据库资源、同步器。
1 private void cleanupAfterCompletion(DefaultTransactionStatus status) {
2 status.setCompleted();//设置事务状态完成
//如果是新的同步，清空当前线程绑定的除了资源外的全部线程本地变量：包括事务同步器、事务名称、只读属性、隔离级别、真实的事务激活状态
3 if (status.isNewSynchronization()) {
4 TransactionSynchronizationManager.clear();
5 }//如果是新的事务同步
6 if (status.isNewTransaction()) {
7 doCleanupAfterCompletion(status.getTransaction());
8 }//如果存在挂起的资源
9 if (status.getSuspendedResources() != null) {
10 if (status.isDebug()) {
11 logger.debug("Resuming suspended transaction after completion of inner transaction");
12 }//唤醒挂起的事务和资源（重新绑定之前挂起的数据库资源，唤醒同步器，注册同步器到TransactionSynchronizationManager）
13 resume(status.getTransaction(), (SuspendedResourcesHolder) status.getSuspendedResources());
14 }
15 }
对于DataSourceTransactionManager，doCleanupAfterCompletion源码如下：
1 protected void doCleanupAfterCompletion(Object transaction) {
2 DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
3
4 // 如果是最新的连接持有者，解绑当前线程绑定的<数据库资源，ConnectionHolder>
5 if (txObject.isNewConnectionHolder()) {
6 TransactionSynchronizationManager.unbindResource(this.dataSource);
7 }
8
9 // 重置数据库连接（隔离级别、只读）
10 Connection con = txObject.getConnectionHolder().getConnection();
11 try {
12 if (txObject.isMustRestoreAutoCommit()) {
13 con.setAutoCommit(true);
14 }
15 DataSourceUtils.resetConnectionAfterTransaction(con, txObject.getPreviousIsolationLevel());
16 }
17 catch (Throwable ex) {
18 logger.debug("Could not reset JDBC Connection after transaction", ex);
19 }
20
21 if (txObject.isNewConnectionHolder()) {
22 if (logger.isDebugEnabled()) {
23 logger.debug("Releasing JDBC Connection [" + con + "] after transaction");
24 }// 资源引用计数-1，关闭数据库连接
25 DataSourceUtils.releaseConnection(con, this.dataSource);
26 }
27 // 重置连接持有者的全部属性
28 txObject.getConnectionHolder().clear();
29 }
上面这6个方法是AbstractPlatformTransactionManager做的事，本地事务和分布式事务都会执行。
doCommit就是调用事务管理器来实现事务提交。分布式事务环境下调用的是：JtaTransactionManager.doCommit()。
3.2.1 JtaTransactionManager.doCommit
1 @Override
2 protected void doCommit(DefaultTransactionStatus status) {
3 JtaTransactionObject txObject = (JtaTransactionObject) status.getTransaction();
4 try {
5 int jtaStatus = txObject.getUserTransaction().getStatus();
6 if (jtaStatus == Status.STATUS_NO_TRANSACTION) {
7 // 事务状态=已完结，非事务状态。一般不会触发
10 throw new UnexpectedRollbackException("JTA transaction already completed - probably rolled back");
11 }
12 if (jtaStatus == Status.STATUS_ROLLEDBACK) {
13 // 回滚
16 try {
17 txObject.getUserTransaction().rollback();
18 }
19 catch (IllegalStateException ex) {
20 if (logger.isDebugEnabled()) {
21 logger.debug("Rollback failure with transaction already marked as rolled back: " + ex);
22 }
23 }
24 throw new UnexpectedRollbackException("JTA transaction already rolled back (probably due to a timeout)");
25 }//核心操作：提交事务
26 txObject.getUserTransaction().commit();
27 }
28 catch (RollbackException ex) {
29 throw new UnexpectedRollbackException(
30 "JTA transaction unexpectedly rolled back (maybe due to a timeout)", ex);
31 }
32 catch (HeuristicMixedException ex) {
33 throw new HeuristicCompletionException(HeuristicCompletionException.STATE_MIXED, ex);
34 }
35 catch (HeuristicRollbackException ex) {
36 throw new HeuristicCompletionException(HeuristicCompletionException.STATE_ROLLED_BACK, ex);
37 }
38 catch (IllegalStateException ex) {
39 throw new TransactionSystemException("Unexpected internal transaction state", ex);
40 }
41 catch (SystemException ex) {
42 throw new TransactionSystemException("JTA failure on commit", ex);
43 }
44 }
txObject.getUserTransaction().commit()-->调用UserTransactionImp的commit()
1 public void commit () throws javax.transaction.RollbackException,
2 javax.transaction.HeuristicMixedException,
3 javax.transaction.HeuristicRollbackException,
4 javax.transaction.SystemException, java.lang.IllegalStateException,
5 java.lang.SecurityException
6 {
7 checkSetup ();
8 txmgr_.commit ();
9 }
TransactionManager的commit
1 public void commit () throws javax.transaction.RollbackException,
2 javax.transaction.HeuristicMixedException,
3 javax.transaction.HeuristicRollbackException,
4 javax.transaction.SystemException, java.lang.IllegalStateException,
5 java.lang.SecurityException
6 {
7 Transaction tx = getTransaction();
8 if ( tx == null ) raiseNoTransaction();
9 tx.commit();
10 }
最终调用的是TransactionImp的commit()
1 public void commit() throws javax.transaction.RollbackException,
2 javax.transaction.HeuristicMixedException,
3 javax.transaction.HeuristicRollbackException,
4 javax.transaction.SystemException, java.lang.SecurityException
5 {
6 try {
7 ct_.commit();
8 } catch ( HeurHazardException hh ) {
9 rethrowAsJtaHeuristicMixedException ( hh.getMessage () , hh );
10 } catch ( HeurRollbackException hr ) {
11 rethrowAsJtaHeuristicRollbackException ( hr.getMessage () , hr );
12 } catch ( HeurMixedException hm ) {
13 rethrowAsJtaHeuristicMixedException ( hm.getMessage () , hm );
14 } catch ( SysException se ) {
15 LOGGER.logWarning ( se.getMessage() , se );
16 throw new ExtendedSystemException ( se.getMessage (), se
17 .getErrors () );
18 } catch ( com.atomikos.icatch.RollbackException rb ) {
19 //see case 29708: all statements have been closed
20 String msg = rb.getMessage ();
21 Throwable cause = rb.getCause();
22 if (cause == null) cause = rb;
23 rethrowAsJtaRollbackException (msg , cause);
24 }
25 }
这里就是调用CompositeTransaction接口的实现类CompositeTransactionImp的commit()
1 public void commit () throws HeurRollbackException, HeurMixedException,
2 HeurHazardException, SysException, SecurityException,
3 RollbackException
4 {
5 getTerminator().commit();
6 }
调用“组合命令行实现类”CompositeTerminatorImp的commit()
1 public void commit () throws HeurRollbackException, HeurMixedException,
2 HeurHazardException, SysException, java.lang.SecurityException,
3 RollbackException
4 {
5 Stack errors = new Stack ();
6 // 1.标记事务状态
7 transaction_.doCommit ();
8 setSiblingInfoForIncoming1pcRequestFromRemoteClient();
9
10 if ( transaction_.isRoot () ) {
11 try {//2.提交事务，核心操作
12 coordinator_.terminate ( true );
13 }
14
15 catch ( RollbackException rb ) {
16 throw rb;
17 } catch ( HeurHazardException hh ) {
18 throw hh;
19 } catch ( HeurRollbackException hr ) {
20 throw hr;
21 } catch ( HeurMixedException hm ) {
22 throw hm;
23 } catch ( SysException se ) {
24 throw se;
25 } catch ( Exception e ) {
26 errors.push ( e );
27 throw new SysException (
28 "Unexpected error: " + e.getMessage (), errors );
29 }
30 }
31
32 }
如上，1.调用“组合事务实现类”CompositeTransactionImp的doCommit()这里只做标记为非活动，没有提交事务。
2.调用CoordinatorImp的terminate()终结事务。
1 protected void terminate ( boolean commit ) throws HeurRollbackException,
2 HeurMixedException, SysException, java.lang.SecurityException,
3 HeurCommitException, HeurHazardException, RollbackException,
4 IllegalStateException
5
6 {
7 synchronized ( fsm_ ) {
8 if ( commit ) {// 如果只有一个参与者，直接一阶段提交
9 if ( participants_.size () <= 1 ) {
10 commit ( true );
11 } else {//二阶段提交：prepare阶段
12 int prepareResult = prepare ();
13 // 二阶段提交：commit阶段。非只读事务，才需要提交事务，
14 if ( prepareResult != Participant.READ_ONLY )
15 commit ( false );
16 }
17 } else {
18 rollback ();
19 }
20 }
21 }
如上图是源码的优化精华：
1.根据参与者判断，如果只有一个参与者，直接优化成一阶段提交。
2.prepare完后，commit阶段如果是只读事务，不用commit。
咱们是分布式事务，插入2个库，肯定是两阶段提交。
CoordinatorImp的commit
1 public HeuristicMessage[] commit ( boolean onePhase )
2 throws HeurRollbackException, HeurMixedException,
3 HeurHazardException, java.lang.IllegalStateException,
4 RollbackException, SysException
5 {
6 HeuristicMessage[] ret = null;
7 synchronized ( fsm_ ) {
8 ret = stateHandler_.commit(onePhase);
9 }
10 return ret;
11 }
追踪到IndoubtStateHandler的commit，这个操作加了同步锁。具体实现如下：
1 protected HeuristicMessage[] commit ( boolean onePhase )
2 throws HeurRollbackException, HeurMixedException,
3 HeurHazardException, java.lang.IllegalStateException,
4 RollbackException, SysException
5 {
6
7 return commitWithAfterCompletionNotification ( new CommitCallback() {
8 public HeuristicMessage[] doCommit()
9 throws HeurRollbackException, HeurMixedException,
10 HeurHazardException, IllegalStateException,
11 RollbackException, SysException {
12 return commitFromWithinCallback ( false, false );
13 }
14 });
15
16 }
如上，核心接口就是CommitCallback的doCommit方法，方法体就是commitFromWithinCallback。
1 protected HeuristicMessage[] commitFromWithinCallback ( boolean heuristic ,
2 boolean onePhase ) throws HeurRollbackException,
3 HeurMixedException, HeurHazardException,
4 java.lang.IllegalStateException, RollbackException, SysException
5 {
6 Stack<Exception> errors = new Stack<Exception> ();
7 CoordinatorStateHandler nextStateHandler = null;
8
9 try {
10
11 Vector<Participant> participants = coordinator_.getParticipants();
12 int count = (participants.size () - readOnlyTable_.size ());
13 TerminationResult commitresult = new TerminationResult ( count );
14
15 // cf bug 64546: avoid committed_ being null upon recovery!
16 committed_ = new Boolean ( true );
17 // for replaying completion: commit decision was reached
18 // otherwise, replay requests might only see TERMINATED!
19
20 try {
21 coordinator_.setState ( TxState.COMMITTING );
22 } catch ( RuntimeException error ) {
23 //See case 23334
24 String msg = "Error in committing: " + error.getMessage() + " - rolling back instead";
25 LOGGER.logWarning ( msg , error );
26 try {
27 rollbackFromWithinCallback(getCoordinator().isRecoverableWhileActive().booleanValue(),false);
28 throw new RollbackException ( msg , error );
29 } catch ( HeurCommitException e ) {
30 LOGGER.logWarning ( "Illegal heuristic commit during rollback:" + e );
31 throw new HeurMixedException ( e.getHeuristicMessages() );
32 }
33 }
34
35
36 // start messages
37 Enumeration<Participant> enumm = participants.elements ();
38 while ( enumm.hasMoreElements () ) {
39 Participant p = enumm.nextElement ();
40 if ( !readOnlyTable_.containsKey ( p ) ) {
41 CommitMessage cm = new CommitMessage ( p, commitresult,
42 onePhase );
43
44 // if onephase: set cascadelist anyway, because if the
45 // participant is a REMOTE one, then it might have
46 // multiple participants that are not visible here!
47
48 if ( onePhase && cascadeList_ != null ) { // null for OTS
49 Integer sibnum = (Integer) cascadeList_.get ( p );
50 if ( sibnum != null ) // null for local participant!
51 p.setGlobalSiblingCount ( sibnum.intValue () );
52 p.setCascadeList ( cascadeList_ );
53 }
54 propagator_.submitPropagationMessage ( cm );
55 }
56 } // while
57
58 commitresult.waitForReplies ();
59 int res = commitresult.getResult ();
60
61 if ( res != TerminationResult.ALL_OK ) {
62
63 if ( res == TerminationResult.HEUR_MIXED ) {
64 Hashtable<Participant,TxState> hazards = commitresult.getPossiblyIndoubts ();
65 Hashtable heuristics = commitresult
66 .getHeuristicParticipants ();
67 addToHeuristicMap ( heuristics );
68 enumm = participants.elements ();
69 while ( enumm.hasMoreElements () ) {
70 Participant p = (Participant) enumm.nextElement ();
71 if ( !heuristics.containsKey ( p ) )
72 addToHeuristicMap ( p, TxState.TERMINATED );
73 }
74 nextStateHandler = new HeurMixedStateHandler ( this,
75 hazards );
76
77 coordinator_.setStateHandler ( nextStateHandler );
78 throw new HeurMixedException ( getHeuristicMessages () );
79 }
80
81 else if ( res == TerminationResult.ROLLBACK ) {
82 // 1PC and rolled back before commit arrived.
83 nextStateHandler = new TerminatedStateHandler ( this );
84 coordinator_.setStateHandler ( nextStateHandler );
85 throw new RollbackException ( "Rolled back already." );
86 } else if ( res == TerminationResult.HEUR_ROLLBACK ) {
87 nextStateHandler = new HeurAbortedStateHandler ( this );
88 coordinator_.setStateHandler ( nextStateHandler );
89 // Here, we do NOT need to add extra information, since ALL
90 // participants agreed to rollback.
91 // Therefore, we need not worry about who aborted and who committed.
92 throw new HeurRollbackException ( getHeuristicMessages () );
93
94 }
95
96 else if ( res == TerminationResult.HEUR_HAZARD ) {
97 Hashtable hazards = commitresult.getPossiblyIndoubts ();
98 Hashtable heuristics = commitresult
99 .getHeuristicParticipants ();
100 addToHeuristicMap ( heuristics );
101 enumm = participants.elements ();
102 while ( enumm.hasMoreElements () ) {
103 Participant p = (Participant) enumm.nextElement ();
104 if ( !heuristics.containsKey ( p ) )
105 addToHeuristicMap ( p, TxState.TERMINATED );
106 }
107 nextStateHandler = new HeurHazardStateHandler ( this,
108 hazards );
109 coordinator_.setStateHandler ( nextStateHandler );
110 throw new HeurHazardException ( getHeuristicMessages () );
111 }
112
113 } else {
114 // all OK
115 if ( heuristic ) {
116 nextStateHandler = new HeurCommittedStateHandler ( this );
117 // again, here we do NOT need to preserve extra per-participant
118 // state mappings, since ALL participants were heur. committed.
119 } else
120 nextStateHandler = new TerminatedStateHandler ( this );
121
122 coordinator_.setStateHandler ( nextStateHandler );
123 }
124 } catch ( RuntimeException runerr ) {
125 errors.push ( runerr );
126 throw new SysException ( "Error in commit: " + runerr.getMessage (), errors );
127 }
128
129 catch ( InterruptedException intr ) {
130 // cf bug 67457
131 InterruptedExceptionHelper.handleInterruptedException ( intr );
132 errors.push ( intr );
133 throw new SysException ( "Error in commit" + intr.getMessage (), errors );
134 }
135
136 return getHeuristicMessages ();
137
138 }
如上，构造了一个CommitMessage，调用传播者Propagator的submitPropagationMessage()提交传播消息。-》CommitMessage的send()方法-》Participant的commit().
-》XAResourceTransaction的commit提交XA资源-》XAResource的commit ( xid_, onePhase );饶了一大圈终于到了最最核心的代码了....我们这里XAResource接口的实现类是MysqlXAConnection。
1 public void commit(Xid xid, boolean onePhase) throws XAException {
2 StringBuilder commandBuf = new StringBuilder(MAX_COMMAND_LENGTH);
3 commandBuf.append("XA COMMIT ");
4 appendXid(commandBuf, xid);
5
6 if (onePhase) {
7 commandBuf.append(" ONE PHASE");
8 }
9
10 try {
11 dispatchCommand(commandBuf.toString());
12 } finally {
13 this.underlyingConnection.setInGlobalTx(false);
14 }
15 }
dispatchCommand调度命令如下：
1 private ResultSet dispatchCommand(String command) throws XAException {
2 Statement stmt = null;
3
4 try {
5 if (this.logXaCommands) {
6 this.log.logDebug("Executing XA statement: " + command);
7 }
8
9 // TODO: Cache this for lifetime of XAConnection这里还规划要做缓存 - -！
10 stmt = this.underlyingConnection.createStatement();
11 // 核心执行事务提交
12 stmt.execute(command);
13
14 ResultSet rs = stmt.getResultSet();
15
16 return rs;
17 } catch (SQLException sqlEx) {
18 throw mapXAExceptionFromSQLException(sqlEx);
19 } finally {
20 if (stmt != null) {
21 try {
22 stmt.close();
23 } catch (SQLException sqlEx) {
24 }
25 }
26 }
27 }
如上就是一个经典的使用jdbc执行sql语句的过程：
1.使用com.mysql.jdbc.Connection创建Statement。
2.Statement执行sql命令.
3.得到结果。
3.3 rollback回滚事务
AbstractPlatformTransactionManager中rollback源码如下：
1 public final void rollback(TransactionStatus status) throws TransactionException {
2 if (status.isCompleted()) {
3 throw new IllegalTransactionStateException(
4 "Transaction is already completed - do not call commit or rollback more than once per transaction");
5 }
6
7 DefaultTransactionStatus defStatus = (DefaultTransactionStatus) status;
8 processRollback(defStatus);
9 }
processRollback源码如下：
1 private void processRollback(DefaultTransactionStatus status) {
2 try {
3 try {// 解绑当前线程绑定的会话工厂，并关闭会话
4 triggerBeforeCompletion(status);
5 if (status.hasSavepoint()) {// 1.如果有保存点，即嵌套式事务
6 if (status.isDebug()) {
7 logger.debug("Rolling back transaction to savepoint");
8 }//回滚到保存点
9 status.rollbackToHeldSavepoint();
10 }//2.如果就是一个简单事务
11 else if (status.isNewTransaction()) {
12 if (status.isDebug()) {
13 logger.debug("Initiating transaction rollback");
14 }//回滚核心方法
15 doRollback(status);
16 }//3.当前存在事务且没有保存点，即加入当前事务的
17 else if (status.hasTransaction()) {//如果已经标记为回滚 或 当加入事务失败时全局回滚（默认true）
18 if (status.isLocalRollbackOnly() || isGlobalRollbackOnParticipationFailure()) {
19 if (status.isDebug()) {//debug时会打印：加入事务失败-标记已存在事务为回滚
20 logger.debug("Participating transaction failed - marking existing transaction as rollback-only");
21 }//设置当前connectionHolder：当加入一个已存在事务时回滚
22 doSetRollbackOnly(status);
23 }
24 else {
25 if (status.isDebug()) {
26 logger.debug("Participating transaction failed - letting transaction originator decide on rollback");
27 }
28 }
29 }
30 else {
31 logger.debug("Should roll back transaction but cannot - no transaction available");
32 }
33 }
34 catch (RuntimeException ex) {//关闭会话，重置SqlSessionHolder属性
35 triggerAfterCompletion(status, TransactionSynchronization.STATUS_UNKNOWN);
36 throw ex;
37 }
38 catch (Error err) {
39 triggerAfterCompletion(status, TransactionSynchronization.STATUS_UNKNOWN);
40 throw err;
41 }
42 triggerAfterCompletion(status, TransactionSynchronization.STATUS_ROLLED_BACK);
43 }
44 finally {、、解绑当前线程
45 cleanupAfterCompletion(status);
46 }
47 }
核心操作是doRollback,分布式环境下调用的是JtaTransactionManager的doRollback。
1 @Override
2 protected void doRollback(DefaultTransactionStatus status) {
3 JtaTransactionObject txObject = (JtaTransactionObject) status.getTransaction();
4 try {
5 int jtaStatus = txObject.getUserTransaction().getStatus();
6 if (jtaStatus != Status.STATUS_NO_TRANSACTION) {
7 try {
8 txObject.getUserTransaction().rollback();
9 }
10 catch (IllegalStateException ex) {
11 if (jtaStatus == Status.STATUS_ROLLEDBACK) {
12 // Only really happens on JBoss 4.2 in case of an early timeout...
13 if (logger.isDebugEnabled()) {
14 logger.debug("Rollback failure with transaction already marked as rolled back: " + ex);
15 }
16 }
17 else {
18 throw new TransactionSystemException("Unexpected internal transaction state", ex);
19 }
20 }
21 }
22 }
23 catch (SystemException ex) {
24 throw new TransactionSystemException("JTA failure on rollback", ex);
25 }
26 }
调用的UserTransactionImp的rollback
1 public void rollback () throws IllegalStateException, SystemException,
2 SecurityException
3 {
4 checkSetup ();
5 txmgr_.rollback ();
6 }
TransactionManagerImp的rollback
1 public void rollback () throws IllegalStateException, SystemException,
2 SecurityException
3 {
4 Transaction tx = getTransaction();
5 if ( tx == null ) raiseNoTransaction();
6 tx.rollback();
7
8 }
TransactionImp的rollback
1 public void rollback() throws IllegalStateException, SystemException
2 {
3 try {
4 ct_.rollback();
5 } catch ( SysException se ) {
6 LOGGER.logWarning ( se.getMessage() , se );
7 throw new ExtendedSystemException ( se.getMessage (), se
8 .getErrors () );
9 }
10
11 }
CompositeTransactionImp的rollback
1 public void rollback () throws IllegalStateException, SysException
2 {
3 getTerminator().rollback();
4 }
CompositeTerminatorImp的rollback
1 public void rollback () throws IllegalStateException, SysException
2 {
3 Stack errors = new Stack ();
4
5 transaction_.doRollback ();
6
7 if ( transaction_.isRoot () )
8 try {
9 coordinator_.terminate ( false );
10 } catch ( Exception e ) {
11 errors.push ( e );
12 throw new SysException ( "Unexpected error in rollback: " + e.getMessage (), errors );
13 }
14 }
一直追踪到
RollbackMessage.send
1 protected Object send () throws PropagationException
2 {
3 Participant part = getParticipant ();
4 HeuristicMessage[] msgs = null;
5 try {
6 msgs = part.rollback ();
7
8 } catch ( HeurCommitException heurc ) {
9 throw new PropagationException ( heurc, false );
10 } catch ( HeurMixedException heurm ) {
11 throw new PropagationException ( heurm, false );
12 }
13
14 catch ( Exception e ) {
15 // only retry if might be indoubt. Otherwise ignore.
16 if ( indoubt_ ) {
17 // here, participant might be indoubt!
18 // fill in exact heuristic msgs by using buffered effect of proxies
19 HeurHazardException heurh = new HeurHazardException ( part.getHeuristicMessages () );
20 throw new PropagationException ( heurh, true );
21 }
22 }
23 return msgs;
24 }
XAResourceTransaction.rollback->MysqlXAConnection.rollback
1 public void rollback(Xid xid) throws XAException {
2 StringBuilder commandBuf = new StringBuilder(MAX_COMMAND_LENGTH);
3 commandBuf.append("XA ROLLBACK ");
4 appendXid(commandBuf, xid);
5
6 try {
7 dispatchCommand(commandBuf.toString());
8 } finally {
9 this.underlyingConnection.setInGlobalTx(false);
10 }
11 }
dispatchCommand执行sql
1 private ResultSet dispatchCommand(String command) throws XAException {
2 Statement stmt = null;
3
4 try {
5 if (this.logXaCommands) {
6 this.log.logDebug("Executing XA statement: " + command);
7 }
8
9 // TODO: Cache this for lifetime of XAConnection
10 stmt = this.underlyingConnection.createStatement();
11
12 stmt.execute(command);
13
14 ResultSet rs = stmt.getResultSet();
15
16 return rs;
17 } catch (SQLException sqlEx) {
18 throw mapXAExceptionFromSQLException(sqlEx);
19 } finally {
20 if (stmt != null) {
21 try {
22 stmt.close();
23 } catch (SQLException sqlEx) {
24 }
25 }
26 }
27 }
debug得到command：XA ROLLBACK 0x3139322e3136382e36302e31312e746d30303030313030303437,0x3139322e3136382e36302e31312e746d31,0x41544f4d
至此，回滚完毕。
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