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首页 > 软件编程 > java > spring REQUIRED_NESTED原理

spring的事务传播属性REQUIRED_NESTED原理

作者:morris131

这篇文章主要介绍了spring的事务传播属性REQUIRED_NESTED原理,在spring中,要想使用事务中的回滚点,可以使用传播属性NESTED,需要的朋友可以参考下

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。

到此这篇关于spring的事务传播属性REQUIRED_NESTED原理的文章就介绍到这了,更多相关spring REQUIRED_NESTED原理内容请搜索脚本之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持脚本之家!

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