java - 在使用 AbstractRoutingDataSource 切换数据源时共享事务

Question

使用 AbstractRoutingDataSource 时如何在数据源之间共享事务切换 Activity 数据源？

到目前为止，在没有事务的情况下，查询会在两个数据库上正确执行，但是当我开始事务时，所有内容都在同一个数据库上执行(即我不能再切换到第二个数据库)。

有什么想法吗？

@Transactional
public void crossDbTransactionTest() {
    // Selects a datasource from my pool of AbstractRoutingDataSources
    DbConnectionContextHolder.setDbConnectionByYear(2012);

    // execute something in the first database
    this.executeSomeJpaQuery("xyz"); 

    // switch to the second database
    DbConnectionContextHolder.setDbConnectionByYear(2011);

    // execute something in the second database
    this.executeSomeJpaQuery("xyz"); // on any errors rollback changes in both databases
}

EDIT1(添加配置文件):

持久性.xml:

<persistence-unit name="primarnaKonekcija" transaction-type="RESOURCE_LOCAL">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <properties>
        <property name="hibernate.dialect" value="org.hibernate.dialect.SQLServerDialect" />
        <property name="hibernate.max_fetch_depth" value="1" />
        <property name="hibernate.transaction.manager_lookup_class"
                              value="org.hibernate.transaction.JBossTransactionManagerLookup" />
    </properties>
</persistence-unit>

spring-jpa.xml:

<!-- Shared DB credentials -->
<context:property-placeholder location="classpath:config.properties" />

<!-- DB connections by year -->
<bean id="parentDataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource" abstract="true">
    <property name="driverClassName" value="${db.driver}" />
    <property name="username" value="${db.user}" />
    <property name="password" value="${db.password}" />
</bean>
<bean id="dataSource" class="myPackage.DbConnectionRoutingDataSource">
    <!-- Placeholder that is replaced in BeanFactoryPostProcessor -->
    <property name="targetDataSources">
        <map key-type="int">
            <entry key="0" value-ref="placeholderDs" />
        </map>
    </property>
    <property name="defaultTargetDataSource" ref="placeholderDs" />
</bean>

<!-- EntityManager configuration -->
<bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
    <property name="persistenceUnitName" value="primarnaKonekcija" />
    <property name="dataSource" ref="dataSource" />
    <property name="jpaVendorAdapter">
        <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
            <property name="databasePlatform" value="org.hibernate.dialect.SQLServerDialect" />
            <property name="showSql" value="true" />
        </bean>
    </property>
</bean>

<tx:annotation-driven />
<tx:jta-transaction-manager />

编辑 2:

尝试将所有内容切换到 JTA 和 JNDI 提供的数据源。

将 transaction-type="RESOURCE_LOCAL"更改为 transaction-type="JTA"也不起作用 - JtaStatusHelper 抛出 NullPointerException，表示 transactionManager 为空。

编辑 3:

将 JBossTransactionManagerLookup 添加到 persistence.xml，现在在事务中切换到第二个数据源时出现“不允许添加多个最后资源”。

编辑 4:

已尝试 setting JBOSS所以我克服了那个错误 - 数据库切换现在可以使用预期的警告:“多个最后资源已添加到当前事务中。这在事务上是不安全的，不应依赖。”。接下来将尝试在 JBOSS 中配置 MSSQL XA 驱动程序。

编辑 5:

在 configuring MSSQL XA 之后，一切都按预期工作，将发布一个答案，其中包含设置所需的步骤。

Answer 1

除非您别无选择，否则我不会推荐这种解决方案。二级缓存不可能与这样的解决方案一起工作，但它是一个(稳定的)解决方案，我被迫使用它来争取时间，直到底层遗留数据库合并为一个。

首先在 JBoss standalone.xml 中将您的数据库连接设置为 XA 数据源。如果使用 MS SQL 服务器，请按照说明如何在 http://msdn.microsoft.com/en-us/library/aa342335.aspx 正确设置 XA。

standalone.xml

<datasources>
    <datasource jndi-name="java:jboss/datasources/ExampleDS" pool-name="ExampleDS" enabled="true" use-java-context="true">
        <connection-url>jdbc:h2:mem:test;DB_CLOSE_DELAY=-1</connection-url>
        <driver>h2</driver>
        <security>
            <user-name>sa</user-name>
            <password>sa</password>
        </security>
    </datasource>
    <xa-datasource jta="true" jndi-name="java:jboss/datasources/MYDB_ONE" pool-name="MYDB_ONE" enabled="true" use-java-context="true" use-ccm="true">
        <xa-datasource-property name="ServerName">
            localhost
        </xa-datasource-property>
        <xa-datasource-property name="DatabaseName">
            MYDB_ONE
        </xa-datasource-property>
        <xa-datasource-property name="SelectMethod">
            cursor
        </xa-datasource-property>
        <xa-datasource-class>com.microsoft.sqlserver.jdbc.SQLServerXADataSource</xa-datasource-class>
        <driver>sqljdbc</driver>
        <xa-pool>
            <is-same-rm-override>false</is-same-rm-override>
        </xa-pool>
        <security>
            <user-name>some_user</user-name>
            <password>some_password</password>
        </security>
        <validation>
            <valid-connection-checker class-name="org.jboss.jca.adapters.jdbc.extensions.mssql.MSSQLValidConnectionChecker"/>
        </validation>
    </xa-datasource>
    <xa-datasource jta="true" jndi-name="java:jboss/datasources/MYDB_TWO" pool-name="MYDB_TWO" enabled="true" use-java-context="true" use-ccm="true">
        <xa-datasource-property name="ServerName">
            localhost
        </xa-datasource-property>
        <xa-datasource-property name="DatabaseName">
            MYDB_TWO
        </xa-datasource-property>
        <xa-datasource-property name="SelectMethod">
            cursor
        </xa-datasource-property>
        <xa-datasource-class>com.microsoft.sqlserver.jdbc.SQLServerXADataSource</xa-datasource-class>
        <driver>sqljdbc</driver>
        <xa-pool>
            <is-same-rm-override>false</is-same-rm-override>
        </xa-pool>
        <security>
            <user-name>some_user</user-name>
            <password>some_password</password>
        </security>
        <validation>
            <valid-connection-checker class-name="org.jboss.jca.adapters.jdbc.extensions.mssql.MSSQLValidConnectionChecker"/>
        </validation>
    </xa-datasource>
    <drivers>
        <driver name="h2" module="com.h2database.h2">
            <xa-datasource-class>org.h2.jdbcx.JdbcDataSource</xa-datasource-class>
        </driver>
        <driver name="sqljdbc" module="com.microsoft.sqlserver.jdbc">
            <driver-class>com.microsoft.sqlserver.jdbc.SQLServerDriver</driver-class>
        </driver>
        <driver name="postgresql" module="org.postgresql">
            <xa-datasource-class>org.postgresql.xa.PGXADataSource</xa-datasource-class>
        </driver>
    </drivers>
</datasources>

然后我设置我的 entityManager bean，它使用我的 AbstractRoutingDataSource 实现作为它的数据源。这是不使用 persistence.xml 文件的 Spring 支持的 JPA 设置；据我所知，这是使用 JBoss 7 时获得实体包自动扫描的唯一方法。

springJpaConfig.xml

<!-- Use @PersistenceContext annotations for injecting entity managers -->
<bean class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor" />

<!-- Set up JTA transaction manager -->
<tx:jta-transaction-manager />

<bean id="entityManagerFactoryMyDB" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
    <property name="persistenceUnitName" value="MyDB" />
    <property name="dataSource" ref="dataSourceMyDB" />
    <property name="packagesToScan" value="my.package.with.jpa.entities" />
    <property name="jpaVendorAdapter">
        <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
            <property name="showSql" value="true" />
        </bean>
    </property>
    <property name="jpaPropertyMap">
        <map>
            <entry key="javax.persistence.transactionType" value="jta" />

            <entry key="hibernate.transaction.jta.platform" value="org.hibernate.service.jta.platform.internal.JBossAppServerJtaPlatform" />
            <entry key="jboss.entity.manager.factory.jndi.name" value="java:app/MyDBEntityManagerFactory" />

            <entry key="hibernate.dialect" value="org.hibernate.dialect.SQLServer2008Dialect" />
        </map>
    </property>
</bean>

<bean id="dataSourceMyDB" class="some.package.AbstractRoutingDataSourceMyDB">
    <property name="lenientFallback" value="false" />
    <property name="defaultTargetDataSource" value="java:jboss/datasources/ExampleDS" />
    <property name="targetDataSources">
        <map key-type="String">
            <!-- This is a placeholder that will be filled in by BeanFactoryPostProcessor -->
        </map>
    </property>
</bean>

<!-- This allows us to modify Spring configuration load the list of datasources -->
<bean class="some.package.DatasourceRegisteringBeanFactoryPostProcessor" />

我在 AbstractRoutingDataSourceMyDB 中使用 ExampleDS 作为默认值，因为您必须提供一个 defaultTargetDataSource，但我总是想手动选择一个有效的数据库，因此如果有人在没有先手动选择连接的情况下尝试访问该数据库，他们将尝试执行他们的查询不存在的 ExampleDS 数据库，这将引发异常(非常 hacky，但它完成了工作)。

在 BeanFactoryPostProcessor 中，我现在需要填写我的数据源列表:

DatasourceRegisteringBeanFactoryPostProcessor.java

package some.package
class DatasourceRegisteringBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        HashMap<String, String> connectionsListMyDB = new HashMap<>();

        // Load your connection list from wherever you need to, you can
        // enumerate them directly from JNDI or some configuration location
        connectionsListMyDB.put("db1", "java:jboss/datasources/MYDB_ONE");
        connectionsListMyDB.put("db2", "java:jboss/datasources/MYDB_TWO");

        if (connectionsList.isEmpty())
            throw new RuntimeException("No JPA connections defined");

        // Configure the dataSource bean properties
        BeanDefinitionRegistry factory = (BeanDefinitionRegistry) beanFactory;
        MutablePropertyValues mpv = factory.getBeanDefinition("dataSourceMyDB").getPropertyValues();

        ManagedMap<String, String> mm = (ManagedMap<String, String>) mpv.getPropertyValue(
                "targetDataSources").getValue();
        mm.clear();
        for (Entry<String, String> e : connectionsListMyDB.entrySet()) {
            mm.put(e.getKey(), e.getValue());
        }
    }
}

这是我对 AbstractRoutingDataSource 的实现，它允许我在运行时切换连接:

AbstractRoutingDataSourceMyDB.java

public class AbstractRoutingDataSourceMyDB extends AbstractRoutingDataSource {
    @Override
    protected Object determineCurrentLookupKey() {
        return getDbConnectionMyDB();
    }

    // ThreadLocal variable so that the connection gets set for the current thread
    // using spring's request scope on the class instead of ThreadLocal would also work here.
    private final ThreadLocal<String> contextHolder = new ThreadLocal<String>();

    public void setDbConnectionMyDB(String myKey) {
        Assert.notNull(myKey, "myKey cannot be null");

        contextHolder.set(myKey);

        String k = contextHolder.get();
    }

    public String getDbConnectionMyDB() {
        return (String) contextHolder.get();
    }

    public void clearDbConnectionMyDB() {
        contextHolder.remove();
    }
}

请注意，在从 DAO 类中更改当前连接之前，您必须调用 entitymanager.flush() 和 clear()，否则该事务范围内的所有未决操作将在事务提交时在新连接上执行。这是因为 Hibernate session 不知道连接曾经发生过更改，据它所知 - 它始终是同一个数据库。

---

所以在您的 DAO 中，您现在可以这样做:

SomeTableDAO.java

@PersistenceContext(unitName = "MyDB")
private EntityManager em;

@Autowired
private AbstractRoutingDataSourceMyDB routingSource;

public void someMethod(int id) {
    em.flush();
    em.clear();
    routingSource.setDbConnectionMyDB("db1");
    em.remove(em.getReference(Something.class, id)); // delete something in db1

    em.flush();
    em.clear();
    routingSource.setDbConnectionMyDB("db2");
    em.remove(em.getReference(Something.class, id)); // delete something else with the same id in db2
}

就这样吧，虽然它不是很漂亮 - 它可以完成 :)