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在一個Spring Boot項目中，連接多個數(shù)據(jù)源還是比較常見的。之前也介紹了如何在幾種常用框架的場景下配置多數(shù)據(jù)源，具體可見：

Spring Boot 2.x基礎(chǔ)教程：JdbcTemplate的多數(shù)據(jù)源配置
Spring Boot 2.x基礎(chǔ)教程：Spring Data JPA的多數(shù)據(jù)源配置
Spring Boot 2.x基礎(chǔ)教程：MyBatis的多數(shù)據(jù)源配置

當(dāng)我們采用多數(shù)據(jù)源的時候，同時也會出現(xiàn)一個這樣的特殊場景：我們希望對A數(shù)據(jù)源的更新和B數(shù)據(jù)源的更新具備事務(wù)性。這樣的例子很常見，比如：在訂單庫中創(chuàng)建一條訂單記錄，同時還需要在商品庫中扣減商品庫存。如果庫存扣減失敗，那么我們希望訂單創(chuàng)建也能夠回滾。

如果這兩條數(shù)據(jù)在一個數(shù)據(jù)庫中，那么通過之前介紹的事務(wù)管理就能輕松解決了。但是，當(dāng)這兩個操作位于不同的數(shù)據(jù)庫中，那么就無法實現(xiàn)了。

本文就來介紹一種解決這類問題的方法：JTA事務(wù)。

什么是JTA

JTA，全稱：Java Transaction API。JTA事務(wù)比JDBC事務(wù)更強(qiáng)大。一個JTA事務(wù)可以有多個參與者，而一個JDBC事務(wù)則被限定在一個單一的數(shù)據(jù)庫連接。所以，當(dāng)我們在同時操作多個數(shù)據(jù)庫的時候，使用JTA事務(wù)就可以彌補(bǔ)JDBC事務(wù)的不足。

在Spring Boot 2.x中，整合了這兩個JTA的實現(xiàn)：

Atomikos：可以通過引入spring-boot-starter-jta-atomikos依賴來使用
Bitronix：可以通過引入spring-boot-starter-jta-bitronix依賴來使用

由于Bitronix自Spring Boot 2.3.0開始不推薦使用，所以在下面的動手環(huán)節(jié)中，我們將使用Atomikos作為例子來介紹JTA的使用。

動手試試

下面我們就來實操一下，如何在Spring Boot中使用JTA來實現(xiàn)多數(shù)據(jù)源下的事務(wù)管理。

準(zhǔn)備工作

這里我們將使用最基礎(chǔ)的JdbcTemplate來實現(xiàn)數(shù)據(jù)訪問，所以如果你還不會使用JdbcTemplate配置多數(shù)據(jù)源，建議先看一下JdbcTemplate的多數(shù)據(jù)源配置。
場景設(shè)定：

假設(shè)我們有兩個庫，分別為：test1和test2
這兩個庫中都有一張User表，我們希望這兩張表中的數(shù)據(jù)是一致的
假設(shè)這兩張表中都已經(jīng)有一條數(shù)據(jù)：name=aaa，age=30；因為這兩張表中數(shù)據(jù)是一致的，所以要update的時候，就必須兩個庫中的User表更新時候，要么都成功，要么都失敗。

操作詳細(xì)

在pom.xml中加入JTA的實現(xiàn)Atomikos的Starter

<dependency>
????<groupId>org.springframework.bootgroupId>
????<artifactId>spring-boot-starter-jta-atomikosartifactId>
dependency>

在application.properties配置文件中配置兩個test1和test2數(shù)據(jù)源

spring.jta.enabled=true

spring.jta.atomikos.datasource.primary.xa-properties.url=jdbc:mysql://localhost:3306/test1
spring.jta.atomikos.datasource.primary.xa-properties.user=root
spring.jta.atomikos.datasource.primary.xa-properties.password=12345678
spring.jta.atomikos.datasource.primary.xa-data-source-class-name=com.mysql.cj.jdbc.MysqlXADataSource
spring.jta.atomikos.datasource.primary.unique-resource-name=test1
spring.jta.atomikos.datasource.primary.max-pool-size=25
spring.jta.atomikos.datasource.primary.min-pool-size=3
spring.jta.atomikos.datasource.primary.max-lifetime=20000
spring.jta.atomikos.datasource.primary.borrow-connection-timeout=10000

spring.jta.atomikos.datasource.secondary.xa-properties.url=jdbc:mysql://localhost:3306/test2
spring.jta.atomikos.datasource.secondary.xa-properties.user=root
spring.jta.atomikos.datasource.secondary.xa-properties.password=12345678
spring.jta.atomikos.datasource.secondary.xa-data-source-class-name=com.mysql.cj.jdbc.MysqlXADataSource
spring.jta.atomikos.datasource.secondary.unique-resource-name=test2
spring.jta.atomikos.datasource.secondary.max-pool-size=25
spring.jta.atomikos.datasource.secondary.min-pool-size=3
spring.jta.atomikos.datasource.secondary.max-lifetime=20000
spring.jta.atomikos.datasource.secondary.borrow-connection-timeout=10000

創(chuàng)建多數(shù)據(jù)源配置類

@Configuration
public?class?DataSourceConfiguration?{

????@Primary
????@Bean
????@ConfigurationProperties(prefix?=?"spring.jta.atomikos.datasource.primary")
????public?DataSource?primaryDataSource()?{
????????return?new?AtomikosDataSourceBean();
????}

????@Bean
????@ConfigurationProperties(prefix?=?"spring.jta.atomikos.datasource.secondary")
????public?DataSource?secondaryDataSource()?{
????????return?new?AtomikosDataSourceBean();
????}

????@Bean
????public?JdbcTemplate?primaryJdbcTemplate(@Qualifier("primaryDataSource")?DataSource?primaryDataSource)?{
????????return?new?JdbcTemplate(primaryDataSource);
????}

????@Bean
????public?JdbcTemplate?secondaryJdbcTemplate(@Qualifier("secondaryDataSource")?DataSource?secondaryDataSource)?{
????????return?new?JdbcTemplate(secondaryDataSource);
????}

}

注意，這里除了家在的配置不同之外，DataSource也采用了AtomikosDataSourceBean注意與之前配置多數(shù)據(jù)源使用的配置和實現(xiàn)類的區(qū)別。

創(chuàng)建一個Service實現(xiàn)，模擬兩種不同的情況。

@Service
public?class?TestService?{

????private?JdbcTemplate?primaryJdbcTemplate;
????private?JdbcTemplate?secondaryJdbcTemplate;

????public?TestService(JdbcTemplate?primaryJdbcTemplate,?JdbcTemplate?secondaryJdbcTemplate)?{
????????this.primaryJdbcTemplate?=?primaryJdbcTemplate;
????????this.secondaryJdbcTemplate?=?secondaryJdbcTemplate;
????}

????@Transactional
????public?void?tx()?{
????????//?修改test1庫中的數(shù)據(jù)
????????primaryJdbcTemplate.update("update?user?set?age?=???where?name?=??",?30,?"aaa");
????????//?修改test2庫中的數(shù)據(jù)
????????secondaryJdbcTemplate.update("update?user?set?age?=???where?name?=??",?30,?"aaa");
????}

????@Transactional
????public?void?tx2()?{
????????//?修改test1庫中的數(shù)據(jù)
????????primaryJdbcTemplate.update("update?user?set?age?=???where?name?=??",?40,?"aaa");
????????//?模擬：修改test2庫之前拋出異常
????????throw?new?RuntimeException();
????}

}

這里tx函數(shù)，是兩句update操作，一般都會成功；而tx2函數(shù)中，我們?nèi)藶榈闹圃炝艘粋€異常，這個異常是在test1庫中的數(shù)據(jù)更新后才產(chǎn)生的，這樣就可以測試一下test1更新成功，之后是否還能在JTA的幫助下實現(xiàn)回滾。

創(chuàng)建測試類，編寫測試用例

@SpringBootTest(classes?=?Chapter312Application.class)
public?class?Chapter312ApplicationTests?{

????@Autowired
????protected?JdbcTemplate?primaryJdbcTemplate;
????@Autowired
????protected?JdbcTemplate?secondaryJdbcTemplate;

????@Autowired
????private?TestService?testService;

????@Test
????public?void?test1()?throws?Exception?{
????????//?正確更新的情況
????????testService.tx();
????????Assertions.assertEquals(30,?primaryJdbcTemplate.queryForObject("select?age?from?user?where?name=?",?Integer.class,?"aaa"));
????????Assertions.assertEquals(30,?secondaryJdbcTemplate.queryForObject("select?age?from?user?where?name=?",?Integer.class,?"aaa"));
????}

????@Test
????public?void?test2()?throws?Exception?{
????????//?更新失敗的情況
????????try?{
????????????testService.tx2();
????????}?catch?(Exception?e)?{
????????????e.printStackTrace();
????????}?finally?{
????????????//?部分更新失敗，test1中的更新應(yīng)該回滾
????????????Assertions.assertEquals(30,?primaryJdbcTemplate.queryForObject("select?age?from?user?where?name=?",?Integer.class,?"aaa"));
????????????Assertions.assertEquals(30,?secondaryJdbcTemplate.queryForObject("select?age?from?user?where?name=?",?Integer.class,?"aaa"));
????????}
????}

}

這里有兩個測試用例：

test1：因為沒有故意制造的異常，不出意外兩個庫的update都會成功，所以根據(jù)name=aaa去把兩個數(shù)據(jù)查出來，看age是否都被更新到了30。
test2：tx2函數(shù)會把test1中name=aaa的用戶age更新為40，然后拋出異常，JTA事務(wù)生效的話，會把a(bǔ)ge回滾回30，所以這里的檢查也是兩個庫的aaa用戶的age應(yīng)該都為30，這樣就意味著JTA事務(wù)生效，保證了test1和test2兩個庫中的User表數(shù)據(jù)更新一致，沒有制造出臟數(shù)據(jù)。

測試驗證

將上面編寫的單元測試運(yùn)行起來:

觀察一下啟動階段的日志，可以看到這些Atomikos初始化日志輸出：

2021-02-02?19:00:36.145??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.default_max_wait_time_on_shutdown?=?9223372036854775807
2021-02-02?19:00:36.145??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.allow_subtransactions?=?true
2021-02-02?19:00:36.145??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.recovery_delay?=?10000
2021-02-02?19:00:36.145??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.automatic_resource_registration?=?true
2021-02-02?19:00:36.145??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.oltp_max_retries?=?5
2021-02-02?19:00:36.145??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.client_demarcation?=?false
2021-02-02?19:00:36.145??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.threaded_2pc?=?false
2021-02-02?19:00:36.145??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.serial_jta_transactions?=?true
2021-02-02?19:00:36.145??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.log_base_dir?=?/Users/didi/Documents/GitHub/SpringBoot-Learning/2.x/chapter3-12/transaction-logs
2021-02-02?19:00:36.145??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.rmi_export_class?=?none
2021-02-02?19:00:36.145??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.max_actives?=?50
2021-02-02?19:00:36.145??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.checkpoint_interval?=?500
2021-02-02?19:00:36.145??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.enable_logging?=?true
2021-02-02?19:00:36.145??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.log_base_name?=?tmlog
2021-02-02?19:00:36.146??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.max_timeout?=?300000
2021-02-02?19:00:36.146??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.trust_client_tm?=?false
2021-02-02?19:00:36.146??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?java.naming.factory.initial?=?com.sun.jndi.rmi.registry.RegistryContextFactory
2021-02-02?19:00:36.146??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.tm_unique_name?=?127.0.0.1.tm
2021-02-02?19:00:36.146??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.forget_orphaned_log_entries_delay?=?86400000
2021-02-02?19:00:36.146??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.oltp_retry_interval?=?10000
2021-02-02?19:00:36.146??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?java.naming.provider.url?=?rmi://localhost:1099
2021-02-02?19:00:36.146??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.force_shutdown_on_vm_exit?=?false
2021-02-02?19:00:36.146??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?USING:?com.atomikos.icatch.default_jta_timeout?=?10000
2021-02-02?19:00:36.147??INFO?8868?---?[???????????main]?c.a.icatch.provider.imp.AssemblerImp?????:?Using?default?(local)?logging?and?recovery...
2021-02-02?19:00:36.184??INFO?8868?---?[???????????main]?c.a.d.xa.XATransactionalResource?????????:?test1:?refreshed?XAResource
2021-02-02?19:00:36.203??INFO?8868?---?[???????????main]?c.a.d.xa.XATransactionalResource?????????:?test2:?refreshed?XAResource

同時，我們在transaction-logs目錄下，還能找到關(guān)于事務(wù)的日志信息：

{"id":"127.0.0.1.tm161226409083100001","wasCommitted":true,"participants":[{"uri":"127.0.0.1.tm1","state":"COMMITTING","expires":1612264100801,"resourceName":"test1"},{"uri":"127.0.0.1.tm2","state":"COMMITTING","expires":1612264100801,"resourceName":"test2"}]}
{"id":"127.0.0.1.tm161226409083100001","wasCommitted":true,"participants":[{"uri":"127.0.0.1.tm1","state":"TERMINATED","expires":1612264100804,"resourceName":"test1"},{"uri":"127.0.0.1.tm2","state":"TERMINATED","expires":1612264100804,"resourceName":"test2"}]}
{"id":"127.0.0.1.tm161226409092800002","wasCommitted":false,"participants":[{"uri":"127.0.0.1.tm3","state":"TERMINATED","expires":1612264100832,"resourceName":"test1"}]}