这篇文章主要介绍了spring的事务传播属性REQUIRED_NESTED的原理介绍，具有一定借鉴价值，需要的朋友可以参考下。下面就和我一起来看看吧。
传统事务中回滚点的使用
package com.morris.spring.demo.jdbc;import java.sql.*;public class TraditionSavePointDemo {public static void main(String[] args) throws SQLException {String url = "jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&allowMultiQueries=true&characterEncoding=UTF-8&useFastDateParsing=false&zeroDateTimeBehavior=convertToNull";String username = "user";String password = "user";Connection connection = DriverManager.getConnection(url, username, password);connection.setAutoCommit(false); // 不自动提交Savepoint one = connection.setSavepoint("one");Savepoint two = null;try {Statement statement = connection.createStatement();statement.execute("insert into t_good(good_name, price) values('iphone14', 9999)");statement.close();two = connection.setSavepoint("two");} catch (Exception e) {e.printStackTrace();connection.rollback(one); // 回滚事务}try {Statement statement = connection.createStatement();statement.execute("insert into t_good(good_name, price) values('iphone15', 9999)");statement.close();boolean flag = true;if(flag) {throw new RuntimeException("xxxx");}} catch (Exception e) {e.printStackTrace();connection.rollback(two); // 回滚事务}connection.commit();}}在一个事务中可以指定回滚事务到某一个阶段，实现精确控制事务。
事务的传播属性NESTED
在spring中，要想使用事务中的回滚点，可以使用传播属性NESTED。
com.morris.spring.service.TransactionService#addGoodAndArea
@Transactional(propagation = Propagation.REQUIRED)public void addGoodAndArea() {System.out.println("------addGoodAndArea-------");goodService.addGood();areaService.addArea(0);}com.morris.spring.service.AreaServiceImpl#addArea
@Transactional(propagation = Propagation.NESTED)@Overridepublic boolean addArea(int i) {int y = 1000000 / i;Area area = new Area();area.setAreaCode(y);area.setAreaName("shenzhen");return areaDao.insert(area);}com.morris.spring.service.GoodServiceImpl#addGood
@Transactional(propagation = Propagation.NESTED)@Overridepublic boolean addGood() {Good good = new Good();good.setGoodName("iphone");good.setPrice(BigDecimal.valueOf(99999));return goodDao.insert(good);}运行结果如下：
DEBUG DataSourceTransactionManager:384 - Creating new transaction with name [com.morris.spring.service.TransactionService.addGoodAndArea]: PROPAGATION_REQUIRED,ISOLATION_DEFAULTDEBUG DriverManagerDataSource:144 - Creating new JDBC DriverManager Connection to [jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&allowMultiQueries=true&characterEncoding=UTF-8&useFastDateParsing=false&zeroDateTimeBehavior=convertToNull]DEBUG DataSourceTransactionManager:267 - Acquired Connection [com.mysql.cj.jdbc.ConnectionImpl@8ef162] for JDBC transactionDEBUG DataSourceTransactionManager:285 - Switching JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@8ef162] to manual commit------addGoodAndArea-------DEBUG DataSourceTransactionManager:477 - Creating nested transaction with name [com.morris.spring.service.GoodServiceImpl.addGood]DEBUG JdbcTemplate:860 - Executing prepared SQL updateDEBUG JdbcTemplate:609 - Executing prepared SQL statement [insert into t_good(good_name, price) values(?,?)]DEBUG DataSourceTransactionManager:767 - Releasing transaction savepointDEBUG DataSourceTransactionManager:477 - Creating nested transaction with name [com.morris.spring.service.AreaServiceImpl.addArea]DEBUG DataSourceTransactionManager:870 - Rolling back transaction to savepointDEBUG DataSourceTransactionManager:877 - Initiating transaction rollbackDEBUG DataSourceTransactionManager:347 - Rolling back JDBC transaction on Connection [com.mysql.cj.jdbc.ConnectionImpl@8ef162]DEBUG DataSourceTransactionManager:392 - Releasing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@8ef162] after transactionjava.lang.ArithmeticException: / by zero... ...发现整个事务都已经回滚了，按照回滚点的逻辑，addArea()方法抛出异常，不是应该只回滚到addArea()前吗，也就是addGood()应该被提交，这是为什么呢？
如果我们将addArea()方法try catch起来，就能得到我们想要的结果，addGood()被提交，而addArea()回滚，这又是为什么呢？我们带着这几个问题来分析源码。
addAreaAndGood()开启事务
addAreaAndGood()开启事务，最外层方法使用传播属性PROPAGATION_REQUIRED、PROPAGATION_REQUIRES_NEW、PROPAGATION_NESTED效果都一样，都是开启一个新的事务。
org.springframework.transaction.support.AbstractPlatformTransactionManager#getTransaction
else if (def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRED ||def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW ||def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) {// 第一次进来SuspendedResourcesHolder suspendedResources = suspend(null);if (debugEnabled) {logger.debug("Creating new transaction with name [" + def.getName() + "]: " + def);}try {// 开启新事务return startTransaction(def, transaction, debugEnabled, suspendedResources);}catch (RuntimeException | Error ex) {resume(null, suspendedResources);throw ex;}}addGood()获得事务并创建回滚点
addGood()从ThreadLocal中获得addAreaAndGood()创建的事务，然后发现自己的传播属性为PROPAGATION_NESTED，就创建了一个回滚点。
org.springframework.transaction.support.AbstractPlatformTransactionManager#handleExistingTransaction
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);// 创建回滚点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.return startTransaction(definition, transaction, debugEnabled, null);}}addGood()提交事务时释放回滚点
addGood()并不会真正的提交事务，因为事务并不是addGood()创建的，只是在提交时会将之前创建的回滚点释放。
org.springframework.transaction.support.AbstractPlatformTransactionManager#processCommit
if (status.hasSavepoint()) {// NESTED的提交if (status.isDebug()) {logger.debug("Releasing transaction savepoint");}unexpectedRollback = status.isGlobalRollbackOnly();// 只是释放回滚点status.releaseHeldSavepoint();}addArea()获得事务并创建回滚点
流程与addGood()一致。
addArea()回滚事务释放回滚点
addArea()发生异常，会执行回滚事务的逻辑，并没有真正的回滚事务，因为事务并不是addArea()创建的，，只是将之前创建的回滚点释放。 org.springframework.transaction.support.AbstractPlatformTransactionManager#processRollback
if (status.hasSavepoint()) {// 用于NESTED传播机制，发生异常// 回滚至回滚点if (status.isDebug()) {logger.debug("Rolling back transaction to savepoint");}status.rollbackToHeldSavepoint();}addAreaAndGood()回滚这个事务
addArea()发生异常后继续往外抛，addAreaAndGood()也会捕获到异常，然后执行回滚逻辑，这样整个事务都回滚了。 org.springframework.transaction.support.AbstractPlatformTransactionManager#processRollback
else if (status.isNewTransaction()) {// 只有最外层的事务newTransaction=trueif (status.isDebug()) {logger.debug("Initiating transaction rollback");}// 事务的回滚doRollback(status);}为什么将addArea()方法try catch起来，整个事务就不会回滚了呢？
因为将addArea()方法try catch起来后，addAreaAndGood()就会执行提交事务的逻辑，这样addGood()就被提交了。
以上就是spring的事务传播属性REQUIRED_NESTED的原理介绍的详细内容了，看完之后是否有所收获呢？如果想了解更多相关内容，欢迎来编程网行业资讯！
