　　之前试过使用Spring动态切换数据库,通过继承AbstractRoutingDataSource重写determineCurrentLookupKey()方法，来决定使用那个数据库。在开启事务之前，通过改变lookupKey来达到切换数据源目的。但是这种方法多个数据库之前没办法做事务管理，或许对于主从（读写）数据库会好用一些，而对于需要一个操作中更新多个数据库的情况，使用Atomikos或许会更好一些。

　　本文采用spring4+hibernate4+Atomikos进行事务管理。

依赖dependency

　　Atomikos要使用的库使用maven导入，spring和hibernate的依赖就不一一列出，需要额外添加的dependency如下：

　　　　<dependency>

            <groupId>com.atomikos</groupId>

            <artifactId>atomikos-util</artifactId>

            <version>3.9.3</version>

        </dependency>

        <dependency>

            <groupId>com.atomikos</groupId>

            <artifactId>transactions-jdbc</artifactId>

            <version>3.9.3</version>

        </dependency>

        <dependency>

            <groupId>com.atomikos</groupId>

            <artifactId>transactions-jta</artifactId>

            <version>3.9.3</version>

        </dependency>

        <dependency>

            <groupId>com.atomikos</groupId>

            <artifactId>transactions</artifactId>

            <version>3.9.3</version>

        </dependency>

        <dependency>

            <groupId>com.atomikos</groupId>

            <artifactId>transactions-api</artifactId>

            <version>3.9.3</version>

        </dependency>

        <dependency>

            <groupId>javax.transaction</groupId>

            <artifactId>jta</artifactId>

            <version>1.1</version>

        </dependency>

使用的数据库驱动依赖如下：

        <!-- 加入mysql驱动依赖包 -->

        <dependency>

            <groupId>mysql</groupId>

            <artifactId>mysql-connector-java</artifactId>

            <version>5.1.34</version>

        </dependency>

        <!-- sql server数据库驱动 -->

        <dependency>

            <groupId>net.sourceforge.jtds</groupId>

            <artifactId>jtds</artifactId>

            <version>1.3.1</version>

        </dependency>

        <!-- 加入druid数据源依赖包 -->

        <dependency>

            <groupId>com.alibaba</groupId>

            <artifactId>druid</artifactId>

            <version>1.0.26</version>

        </dependency>

有点需要注意的是，druid的版本应该跟上mysql的版本，不然可能找不到MySQL的XADataSource。

配置configuration

配置数据源xml代码：

　　<bean id="mysql" class="com.alibaba.druid.pool.xa.DruidXADataSource" init-method="init" destroy-method="close">

        <property name="url" value="${jdbc_url}" />

        <property name="username" value="${jdbc_username}" />

        <property name="password" value="${jdbc_password}" />

        <!-- 初始化连接大小 -->

        <property name="initialSize" value="0" />

        <!-- 连接池最大使用连接数量 -->

        <property name="maxActive" value="20" />

        <!-- 连接池最小空闲 -->

        <property name="minIdle" value="0" />

        <!-- 获取连接最大等待时间 -->

        <property name="maxWait" value="60000" />

        <!-- <property name="poolPreparedStatements" value="true" />

        <property name="maxPoolPreparedStatementPerConnectionSize" value="33" /> -->

        <property name="validationQuery" value="SELECT 1" />

        <property name="testOnBorrow" value="false" />

        <property name="testOnReturn" value="false" />

        <property name="testWhileIdle" value="true" />

        <!-- 配置间隔多久才进行一次检测，检测需要关闭的空闲连接，单位是毫秒 -->

        <property name="timeBetweenEvictionRunsMillis" value="60000" />

        <!-- 配置一个连接在池中最小生存的时间，单位是毫秒 -->

        <property name="minEvictableIdleTimeMillis" value="25200000" />

        <!-- 打开removeAbandoned功能 -->

        <property name="removeAbandoned" value="true" />

        <!-- 1800秒，也就是30分钟 -->

        <property name="removeAbandonedTimeout" value="1800" />

        <!-- 关闭abanded连接时输出错误日志 -->

        <property name="logAbandoned" value="true" />

        <!-- 监控数据库 -->

        <!-- <property name="filters" value="mergeStat" /> -->

        <!-- <property name="filters" value="stat" /> -->

        <!--<property name="filters" value="config" />

          <property name="connectionProperties" value="config.decrypt=true" />-->

    </bean>

    <bean id="mysqlDataSource" class="com.atomikos.jdbc.AtomikosDataSourceBean"

          init-method="init" destroy-method="close">

        <!-- Set unique name for this DataSource -->

        <property name="uniqueResourceName">

            <value>mysql</value>

        </property>

        <!-- Set XADatasource class name-->

        <property name="xaDataSource" ref="mysql"/>

        <!-- set properties for datasource connection pool -->

        <property name="poolSize" value="3" />

        <!-- 管理 Connection 被占用的时间 -->

        <!-- 如果不设置这个值，Atomikos使用默认的300秒(即5分钟)，那么在处理大批量数据读取的时候，一旦超过5分钟，就会抛出类似 Resultset is close 的错误 -->

        <property name="reapTimeout"><value>20000</value></property>

    </bean>

配置SessionFactory的xml代码：

<bean id="noticesSessionFactory"

          class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">

        <property name="dataSource" ref="mysqlDataSource" />

        <property name="jtaTransactionManager" ref="springTransactionManager"></property>

        <property name="packagesToScan">

            <list>

                <value>com.test.model</value>

            </list>

        </property>

        <property name="hibernateProperties">

            <props>

                <!-- 慎重(推荐禁止) 固定为update -->

                <prop key="hibernate.hbm2ddl.auto">${hibernate.hbm2ddl.auto}</prop>

                <prop key="hibernate.dialect">org.hibernate.dialect.MySQLDialect</prop>

                <prop key="hibernate.autoReconnect">true</prop>

                <prop key="hibernate.show_sql">${hibernate.show_sql}</prop>

                <prop key="hibernate.format_sql">${hibernate.format_sql}</prop>

                <prop key="hibernate.use_sql_comments">${hibernate.use_sql_comments}</prop>

                <prop key="hibernate.jdbc.batch_size">${hibernate.batch_size}</prop>

            </props>

        </property>

    </bean>

如果要使用getCurrentSession()的话，要注意加上：

<property name="jtaTransactionManager" ref="springTransactionManager"></property>

添加多个数据库的话，只需要把上面的xml再写一遍。

下面配置atomikos的事务管理器xml代码：

<!-- atomikos事务管理器 -->

    <bean id="atomikosTransactionManager" class="com.atomikos.icatch.jta.UserTransactionManager"

          init-method="init" destroy-method="close">

        <property name="forceShutdown">

            <value>true</value>

        </property>

    </bean>

    <bean id="atomikosUserTransaction" class="com.atomikos.icatch.jta.UserTransactionImp">

        <property name="transactionTimeout" value="300" />

    </bean>

spring的事务管理器xml代码：

<!-- spring 事务管理器 -->

    <bean id="springTransactionManager"

          class="org.springframework.transaction.jta.JtaTransactionManager">

        <property name="transactionManager" ref="atomikosTransactionManager"/>

        <property name="userTransaction" ref="atomikosUserTransaction" />

        <property name="allowCustomIsolationLevels" value="true"/>

    </bean>

    <!-- 注解方式配置事物-->

   <tx:annotation-driven transaction-manager="springTransactionManager" />

添加transactions.properties文件：

# SAMPLE PROPERTIES FILE FOR THE TRANSACTION SERVICE

# THIS FILE ILLUSTRATES THE DIFFERENT SETTINGS FOR THE TRANSACTION MANAGER

# UNCOMMENT THE ASSIGNMENTS TO OVERRIDE DEFAULT VALUES;

# Required: factory implementation class of the transaction core.

# NOTE: there is no default for this, so it MUST be specified!

#

com.atomikos.icatch.service=com.atomikos.icatch.standalone.UserTransactionServiceFactory

# Set base name of file where messages are output

# (also known as the 'console file').

#

# com.atomikos.icatch.console_file_name = tm.out

# Size limit (in bytes) for the console file;

# negative means unlimited.

#

# com.atomikos.icatch.console_file_limit=-1

# For size-limited console files, this option

# specifies a number of rotating files to

# maintain.

#

# com.atomikos.icatch.console_file_count=1

# Set the number of log writes between checkpoints

#

# com.atomikos.icatch.checkpoint_interval=500

# Set output directory where console file and other files are to be put

# make sure this directory exists!

#

# com.atomikos.icatch.output_dir = ./

# Set directory of log files; make sure this directory exists!

#

# com.atomikos.icatch.log_base_dir = ./

# Set base name of log file

# this name will be  used as the first part of

# the system-generated log file name

#

# com.atomikos.icatch.log_base_name = tmlog

# Set the max number of active local transactions

# or -1 for unlimited.

#

# com.atomikos.icatch.max_actives = 50

# Set the default timeout (in milliseconds) for local transactions

#

# com.atomikos.icatch.default_jta_timeout = 10000

# Set the max timeout (in milliseconds) for local transactions

#

# com.atomikos.icatch.max_timeout = 300000

# The globally unique name of this transaction manager process

# override this value with a globally unique name

#

# com.atomikos.icatch.tm_unique_name = tm

# Do we want to use parallel subtransactions? JTA's default

# is NO for J2EE compatibility

#

#com.atomikos.icatch.serial_jta_transactions=false

# If you want to do explicit resource registration then

# you need to set this value to false.

#

# com.atomikos.icatch.automatic_resource_registration=true  

# Set this to WARN, INFO or DEBUG to control the granularity

# of output to the console file.

#

# com.atomikos.icatch.console_log_level=WARN

# Do you want transaction logging to be enabled or not?

# If set to false, then no logging overhead will be done

# at the risk of losing data after restart or crash.

#

# com.atomikos.icatch.enable_logging=true

# Should two-phase commit be done in (multi-)threaded mode or not?

# Set this to false if you want commits to be ordered according

# to the order in which resources are added to the transaction.

#

# NOTE: threads are reused on JDK 1.5 or higher.

# For JDK 1.4, thread reuse is enabled as soon as the

# concurrent backport is in the classpath - see

# http://mirrors.ibiblio.org/pub/mirrors/maven2/backport-util-concurrent/backport-util-concurrent/

#

# com.atomikos.icatch.threaded_2pc=false

# Should shutdown of the VM trigger shutdown of the transaction core too?

#

# com.atomikos.icatch.force_shutdown_on_vm_exit=false

好了，Atomikos算是配置完成，我们可以写代码测试一下。测试的代码这里就不写出了。

性能优化

尽管这个软件有着很大的优势，但是想要更好的发挥其作用，可以按以下的方法优化：

　　l 更高的内存，意味着更高的吞吐量（每秒的事务数目）。

　　l 使连接池尽可能的大。

　　l 一旦你不需要的连接请马上关闭它们。不要把你的应用程序放在缓存里，让内部连接池为你做这些，这将促使更高效的连接使用。

　　l 不要让活动的事务闲置：终止所有情况下的事务，尤其是在异常报错情况下的事务。这将减少数据库的锁定时间，并且最大效率的处理启用的使用。

总结

　　这么长的配置文件要小心点写，我的粗心结果就是datasource乱套了，导致花了不少时间排错。当然还有各种乱七八糟的糟心问题，这些问题会在后面的文章中列出来，大家可以注意避免。最后用上Atomikos的分布式事务，没有了各种的脏数据，舒心了不少。

秒客网

Atomikos实现多数据源的事物管理

依赖dependency

配置configuration

性能优化

总结

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