一、事务状态：org.springframework.transaction.TransactionStatus
isNewTransaction 是否是新事务
hasSavepoint 是否有保存点
setRollbackOnly 设置回滚
isRollbackOnly 是否回滚
flush 刷新
isCompleted 是否完成
二、传播行为
1.传播行为分类
类别 | 简称 | 无事务 | 已有事务 |
PROPAGATION_REQUIRED | Required（必须-默认） | 创建一个新的事务 | 使用该事务 |
PROPAGATION_SUPPORTS | Supports（支持） | 以非事务执行 | 使用该事务 |
PROPAGATION_MANDATORY | Mandatory（强制） | 抛异常 | 使用该事务 |
PROPAGATION_REQUIRES_NEW | requires_new（必须新的） | 创建一个新的事务 | 原事务挂起，创建一个新的事务 |
PROPAGATION_NOT_SUPPORTED | not_supported（不支持） | 以非事务执行 | 原事务挂起，以非事务执行 |
PROPAGATION_NEVER | Never（从不） | 以非事务执行 | 抛异常 |
PROPAGATION_NESTED | Nested（嵌套） | 创建一个新事务 | 在嵌套事务内执行 |
2.传播行为源码分析
（1）获取事务org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(TransactionDefinition definition)
//---------------------------------------------------------------------
// Implementation of PlatformTransactionManager
//---------------------------------------------------------------------
/**
* This implementation handles propagation behavior. Delegates to
* <code>doGetTransaction</code>, <code>isExistingTransaction</code>
* and <code>doBegin</code>.
* @see #doGetTransaction
* @see #isExistingTransaction
* @see #doBegin
*/
public final TransactionStatus getTransaction(TransactionDefinition definition) throws TransactionException {
Object transaction = doGetTransaction();
// Cache debug flag to avoid repeated checks.
boolean debugEnabled = logger.isDebugEnabled();
if (definition == null) {
// Use defaults if no transaction definition given.
definition = new DefaultTransactionDefinition();
}
// 判断是否存在事务
if (isExistingTransaction(transaction)) {
// 如果有事务，根据传播行为处理
// 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());
}
// 下面是不存在事务情况下，根据传播行为处理
// 如果配置的是mandatory强制，抛异常
// 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'");
}
// 如果是required必须、requires_new必须新的和nested嵌套时，创建一个新的事物
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);
doBegin(transaction, definition);
prepareSynchronization(status, definition);
return status;
}
catch (RuntimeException ex) {
resume(null, suspendedResources);
throw ex;
}
catch (Error err) {
resume(null, suspendedResources);
throw err;
}
}
else {
// Create "empty" transaction: no actual transaction, but potentially synchronization.
boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS);
return prepareTransactionStatus(definition, null, true, newSynchronization, debugEnabled, null);
}
}
（2）已有事务时处理org.springframework.transaction.support.AbstractPlatformTransactionManager.TransactionStatus handleExistingTransaction(TransactionDefinition definition, Object transaction, boolean debugEnabled)
/**
* Create a TransactionStatus for an existing transaction.
*/
private TransactionStatus handleExistingTransaction(
TransactionDefinition definition, Object transaction, boolean debugEnabled)
throws TransactionException {
// 下面是对已有事务，根据传播行为处理
// 如果配置的是never从不，抛异常
if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NEVER) {
throw new IllegalTransactionStateException(
"Existing transaction found for transaction marked with propagation 'never'");
}
// 如果配置的是not_support不支持，原事务挂起，以非事务执行
if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NOT_SUPPORTED) {
if (debugEnabled) {
logger.debug("Suspending current transaction");
}
Object suspendedResources = suspend(transaction);
boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS);
return prepareTransactionStatus(
definition, null, false, newSynchronization, debugEnabled, suspendedResources);
}
// 如果配置的是requires_new，原事务挂起，创建一个新事务执行
if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW) {
if (debugEnabled) {
logger.debug("Suspending current transaction, creating new transaction with name [" +
definition.getName() + "]");
}
SuspendedResourcesHolder suspendedResources = suspend(transaction);
try {
boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
DefaultTransactionStatus status = newTransactionStatus(
definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
doBegin(transaction, definition);
prepareSynchronization(status, definition);
return status;
}
catch (RuntimeException beginEx) {
resumeAfterBeginException(transaction, suspendedResources, beginEx);
throw beginEx;
}
catch (Error beginErr) {
resumeAfterBeginException(transaction, suspendedResources, beginErr);
throw beginErr;
}
}
// 如果配置是nested嵌套，在嵌套事务中执行
if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) {
if (!isNestedTransactionAllowed()) {
throw new NestedTransactionNotSupportedException(
"Transaction manager does not allow nested transactions by default - " +
"specify 'nestedTransactionAllowed' property with value 'true'");
}
if (debugEnabled) {
logger.debug("Creating nested transaction with name [" + definition.getName() + "]");
}
if (useSavepointForNestedTransaction()) {
// Create savepoint within existing Spring-managed transaction,
// through the SavepointManager API implemented by TransactionStatus.
// Usually uses JDBC 3.0 savepoints. Never activates Spring synchronization.
DefaultTransactionStatus status =
prepareTransactionStatus(definition, transaction, false, false, debugEnabled, null);
status.createAndHoldSavepoint();
return status;
}
else {
// Nested transaction through nested begin and commit/rollback calls.
// Usually only for JTA: Spring synchronization might get activated here
// in case of a pre-existing JTA transaction.
boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
DefaultTransactionStatus status = newTransactionStatus(
definition, transaction, true, newSynchronization, debugEnabled, null);
doBegin(transaction, definition);
prepareSynchronization(status, definition);
return status;
}
}
// Assumably PROPAGATION_SUPPORTS or PROPAGATION_REQUIRED.
if (debugEnabled) {
logger.debug("Participating in existing transaction");
}
if (isValidateExistingTransaction()) {
if (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT) {
Integer currentIsolationLevel = TransactionSynchronizationManager.getCurrentTransactionIsolationLevel();
if (currentIsolationLevel == null || currentIsolationLevel != definition.getIsolationLevel()) {
Constants isoConstants = DefaultTransactionDefinition.constants;
throw new IllegalTransactionStateException("Participating transaction with definition [" +
definition + "] specifies isolation level which is incompatible with existing transaction: " +
(currentIsolationLevel != null ?
isoConstants.toCode(currentIsolationLevel, DefaultTransactionDefinition.PREFIX_ISOLATION) :
"(unknown)"));
}
}
if (!definition.isReadOnly()) {
if (TransactionSynchronizationManager.isCurrentTransactionReadOnly()) {
throw new IllegalTransactionStateException("Participating transaction with definition [" +
definition + "] is not marked as read-only but existing transaction is");
}
}
}
boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
return prepareTransactionStatus(definition, transaction, false, newSynchronization, debugEnabled, null);
}
三、 Spring隔离级别：
（1）、ISOLATION_DEFAULT：使用后端数据库默认的隔离级别
（2）、ISOLATION_READ_UNCOMMITTED：最低的隔离级别，允许读取尚未提交的数据变更，可能会导致脏读、幻读或不可重复读
（3）、ISOLATION_READ_COMMITTED：允许读取并发事务已经提交的数据，可以阻止脏读，但是幻读或不可重复读仍有可能发生
（4）、ISOLATION_REPEATABLE_READ：对同一字段的多次读取结果都是一致的，除非数据是被本身事务自己所修改，可以阻止脏读和不可重复读，但幻读仍有可能发生
（5）、ISOLATION_SERIALIZABLE：最高的隔离级别，完全服从ACID的隔离级别，确保阻止脏读、不可重复读以及幻读，也是最慢的事务隔离级别，因为它通常是通过完全锁定事务相关的数据库表来实现的
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