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.*;
/**
* 传统JDBC中回滚点的使用
*/
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)
@Override
public 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)
@Override
public 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_DEFAULT DEBUG 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 transaction DEBUG 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 update DEBUG JdbcTemplate:609 - Executing prepared SQL statement [insert into t_good(good_name, price) values(?,?)] DEBUG DataSourceTransactionManager:767 - Releasing transaction savepoint DEBUG DataSourceTransactionManager:477 - Creating nested transaction with name [com.morris.spring.service.AreaServiceImpl.addArea] DEBUG DataSourceTransactionManager:870 - Rolling back transaction to savepoint DEBUG DataSourceTransactionManager:877 - Initiating transaction rollback DEBUG 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 transaction java.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=true
if (status.isDebug()) {
logger.debug("Initiating transaction rollback");
}
// 事务的回滚
/**
* @see org.springframework.jdbc.datasource.DataSourceTransactionManager#doRollback(org.springframework.transaction.support.DefaultTransactionStatus)
*/
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。