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spring的事务传播属性REQUIRED_NESTED的原理介绍

作者：有用网 阅读量：793 发布时间：2023-06-29
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本文地址： https://www.cnuseful.com/detail?id=60

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。

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