mysql+spring+mybatis实现数据库读写分离的代码配置

来源：jb51　　时间：2019/3/12 8:37:46　　对本文有异议

场景：一个读数据源一个读写数据源。

原理：借助spring的【org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource】这个抽象类实现，看名字可以了解到是一个路由数据源的东西，这个类中有一个方法

/** 
 * Determine the current lookup key. This will typically be 
 * implemented to check a thread-bound transaction context. 
 * <p>Allows for arbitrary keys. The returned key needs 
 * to match the stored lookup key type, as resolved by the 
 * {@link #resolveSpecifiedLookupKey} method. 
 */ 
protected abstract Object determineCurrentLookupKey();

每次去连数据库的时候，spring会调用这个方法去找对应的数据源。返回值即对应的数据源的LookUpKey.那么这个LookUpKey在哪定义的呢？看下面的dataBase.xml的配置

<!--数据源 读写 --> 
<bean id="dataSourceRW" class="org.logicalcobwebs.proxool.ProxoolDataSource"> 
  <property name="alias" value="ihotelRW"></property> 
  <property name="delegateProperties"> 
    <value>user=${jdbc.username},password=${jdbc.password} 
    </value> 
  </property> 
  <property name="user" value="${jdbc.username}" /> 
  <property name="password" value="${jdbc.password}" /> 
  <property name="driver" value="${jdbc.driverClassName}" /> 
  <property name="driverUrl" value="${jdbc.url}" /> 
  <property name="maximumConnectionCount" value="${jdbc.maximumConnectionCount}"></property> 
  <property name="maximumActiveTime" value="${jdbc.maximumActiveTime}"></property> 
  <property name="maximumConnectionLifetime" value="${jdbc.maximumConnectionLifetime}"></property> 
  <property name="prototypeCount" value="${jdbc.prototypeCount}"></property> 
  <property name="houseKeepingSleepTime" value="${jdbc.houseKeepingSleepTime}"></property> 
  <property name="simultaneousBuildThrottle" value="${jdbc.simultaneousBuildThrottle}"></property> 
  <property name="houseKeepingTestSql" value="${jdbc.houseKeepingTestSql}"></property> 
  <property name="verbose" value="${jdbc.verbose}"></property> 
  <property name="statistics" value="${jdbc.statistics}"></property> 
  <property name="statisticsLogLevel" value="${jdbc.statisticsLogLevel}"></property> 
</bean> 
  <!--数据源 读--> 
  <bean id="dataSourceR" class="org.logicalcobwebs.proxool.ProxoolDataSource"> 
    <property name="alias" value="ihotelR"></property> 
    <property name="delegateProperties"> 
      <value>user=${jdbc.r.username},password=${jdbc.r.password} 
      </value> 
    </property> 
    <property name="user" value="${jdbc.r.username}" /> 
    <property name="password" value="${jdbc.r.password}" /> 
    <property name="driver" value="${jdbc.r.driverClassName}" /> 
    <property name="driverUrl" value="${jdbc.r.url}" /> 
    <property name="maximumConnectionCount" value="${jdbc.maximumConnectionCount}"></property> 
    <property name="maximumActiveTime" value="${jdbc.maximumActiveTime}"></property> 
    <property name="maximumConnectionLifetime" value="${jdbc.maximumConnectionLifetime}"></property> 
    <property name="prototypeCount" value="${jdbc.prototypeCount}"></property> 
    <property name="houseKeepingSleepTime" value="${jdbc.houseKeepingSleepTime}"></property> 
    <property name="simultaneousBuildThrottle" value="${jdbc.simultaneousBuildThrottle}"></property> 
    <property name="houseKeepingTestSql" value="${jdbc.houseKeepingTestSql}"></property> 
    <property name="verbose" value="${jdbc.verbose}"></property> 
    <property name="statistics" value="${jdbc.statistics}"></property> 
    <property name="statisticsLogLevel" value="${jdbc.statisticsLogLevel}"></property> 
  </bean> 
  <!-- 动态数据源 --> 
  <bean id="dynamicDataSource" class="com.dao.datasource.DynamicDataSource"> 
    <!-- 通过key-value关联数据源 --> 
    <property name="targetDataSources"> 
      <map> 
        <entry value-ref="dataSourceRW" key="dataSourceKeyRW"></entry> 
        <entry value-ref="dataSourceR" key="dataSourceKeyR"></entry> 
      </map> 
    </property> 
    <property name="defaultTargetDataSource" ref="dataSourceRW" />   
  </bean> 
<!--mybatis与Spring整合 开始 --> 
<bean id="sqlSessionFactory" name="sqlSessionFactory" 
  class="org.mybatis.spring.SqlSessionFactoryBean"> 
  <property name="configLocation" value="classpath:conf/core/sqlMapConfig.xml" /> 
  <property name="dataSource" ref="dynamicDataSource" /> 
</bean>

动态数据源dynamicDataSource中的dataSourceKeyRW、dataSourceKeyR就是

protected abstract Object determineCurrentLookupKey();

这个方法要返回的值。那么如何设置，让这个方法的返回值是根据我们的需要返回dataSourceKeyRW、dataSourceKeyR呢？由于这个方法没有入参，并且是spring自动调用的，因此考虑使用静态变量存储dataSource的key，在调用sql语句前设置静态变量的值，然后在这个方法中得到静态变量的值，返回。又考虑到多线程，同时可能会有很多请求，为避免线程之间相互干扰，考虑使用threadLocal。

先看存储dataSourceKey的容器类。

public class DBContextHolder { 
  /** 
   * 线程threadlocal 
   */ 
  private static ThreadLocal<String> contextHolder = new ThreadLocal<>(); 
  private String DB_TYPE_RW = "dataSourceKeyRW"; 
  private String DB_TYPE_R = "dataSourceKeyR"; 
  public String getDbType() { 
    String db = contextHolder.get(); 
    if (db == null) { 
      db = DB_TYPE_RW;// 默认是读写库 
    } 
    return db; 
  } 
  /** 
   * 设置本线程的dbtype 
   * @param str 
   * @see [相关类/方法](可选) 
   * @since [产品/模块版本](可选) 
   */ 
  public void setDbType(String str) { 
    contextHolder.set(str); 
  } 
  /** 
   * clearDBType 
   * @Title: clearDBType 
   * @Description: 清理连接类型 
   */ 
  public static void clearDBType() { 
    contextHolder.remove(); 
  } 
}

动态数据源的实现类。

public class DynamicDataSource extends AbstractRoutingDataSource { 
  /* 
   * (non-Javadoc) 
   * @see javax.sql.CommonDataSource#getParentLogger() 
   */ 
  @Override 
  public Logger getParentLogger() throws SQLFeatureNotSupportedException { 
    // TODO Auto-generated method stub 
    return null; 
  } 
  /** 
   * override determineCurrentLookupKey 
   * <p> 
   * Title: determineCurrentLookupKey 
   * </p> 
   * <p> 
   * Description: 自动查找datasource 
   * </p> 
   * @return 
   */ 
  @Override 
  protected Object determineCurrentLookupKey() { 
    return DBContextHolder.getDbType(); 
  } 
}

在DAO层中设置数据库类型。

/** 
   * 添加邮件 
   * @param sms 
   * @return 
   */ 
  public boolean insertEmail(Email email) { 
    //根据具体需要设置不同的数据库 
    DBContextHolder.setDbType(DBContextHolder.DB_TYPE_RW); 
    //DBContextHolder.setDbType(DBContextHolder.DB_TYPE_R); 
    int result = this.getSqlSession().insert(STATEMENT + ".addEntity", 
        email); 
    return result == 1; 
  }