java实现mysql数据库读写分离

 第一中方式：定义2个数据库连接，一个是MasterDataSource,另一个是SlaveDataSource。更新数据时我们读取MasterDataSource，查询数据时我们读取SlaveDataSource

该示例是基于spring提供的AbstractRoutingDataSource，实现了一个动态数据源的功能，在spring配置中定义多个数据库分为主、从数据库，实现效果为当进行保存和修改记录时则对主表操作，查询则对从表进行操作，从而实现对数据库表的读写分离。这样做有利于提高网站的性能，特别是在数据库这一层。因为在实际的应用中，数据库都是读多写少（读取数据的频率高，更新数据的频率相对较少），而读取数据通常耗时比较长，占用数据库服务器的CPU较多，从而影响用户体验。我们通常的做法就是把查询从主库中抽取出来，采用多个从库，使用负载均衡，减轻每个从库的查询压力。该示例并未对数据库同步进行说明，只对读写操作的分离实现：

在进行操作之前，先简单说一下AbstractRoutingDataSource相关的东西：

AbstractRoutingDataSource继承了AbstractDataSource ，而AbstractDataSource 又是DataSource 的子类。DataSource   是javax.sql 的数据源接口，定义如下：

public abstract class AbstractRoutingDataSource extends AbstractDataSource implements InitializingBean  {}

public interface DataSource  extends CommonDataSource,Wrapper {

  /**
   * <p>Attempts to establish a connection with the data source that
   * this <code>DataSource</code> object represents.
   *
   * @return  a connection to the data source
   * @exception SQLException if a database access error occurs
   */
  Connection getConnection() throws SQLException;

  /**
   * <p>Attempts to establish a connection with the data source that
   * this <code>DataSource</code> object represents.
   *
   * @param username the database user on whose behalf the connection is
   *  being made
   * @param password the user's password
   * @return  a connection to the data source
   * @exception SQLException if a database access error occurs
   * @since 1.4
   */
  Connection getConnection(String username, String password)
    throws SQLException;

}


public Connection getConnection() throws SQLException {
        return determineTargetDataSource().getConnection();
    }

    public Connection getConnection(String username, String password) throws SQLException {
        return determineTargetDataSource().getConnection(username, password);
    }

protected DataSource determineTargetDataSource() {
        Assert.notNull(this.resolvedDataSources, "DataSource router not initialized");
        Object lookupKey = determineCurrentLookupKey();
        DataSource dataSource = this.resolvedDataSources.get(lookupKey);
        if (dataSource == null && (this.lenientFallback || lookupKey == null)) {
            dataSource = this.resolvedDefaultDataSource;
        }
        if (dataSource == null) {
            throw new IllegalStateException("Cannot determine target DataSource for lookup key [" + lookupKey + "]");
        }
        return dataSource;
    }

从上面的代码中不难看出，获取数据源首先是通过对determineCurrentLookupKey（）的调用获取resolvedDataSources对应key的值，故执行创建一个动态数据源类继承AbstractRoutingDataSource，复写determineCurrentLookupKey（）去自定义设置和获取resolvedDataSources的key就可以实现了

具体步骤如下：

第一步：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:jdbc="http://www.springframework.org/schema/jdbc" xmlns:tx="http://www.springframework.org/schema/tx"
    xmlns:jpa="http://www.springframework.org/schema/data/jpa"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
        http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.1.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd
        http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc-3.1.xsd
        http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.1.xsd
        http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa.xsd"
    default-lazy-init="true">
    <!-- 引入配置文件 -->  
    <context:component-scan base-package="com.he" />  
     <bean id="masterdataSource"
       class="org.apache.commons.dbcp.BasicDataSource"  
        destroy-method="close">  
        <property name="driverClassName" value="com.mysql.jdbc.Driver" />
        <property name="url" value="jdbc:mysql://localhost:3306/test" />
        <property name="username" value="root" />
        <property name="password" value="111111" />
    </bean>

    <bean id="slavedataSource"
      class="org.apache.commons.dbcp.BasicDataSource"  
        destroy-method="close">  
        <property name="driverClassName" value="com.mysql.jdbc.Driver" />
        <property name="url" value="jdbc:mysql://localhost:3306/test2" />
        <property name="username" value="root" />
        <property name="password" value="111111" />
    </bean>
    
    <bean id="dataSource" class="com.he.mysql.test.DynamicDataSource">
        <property name="targetDataSources">  
              <map key-type="java.lang.String">  
                  <!-- write -->
                 <entry key="masterdataSource" value-ref="masterdataSource"/>  
                 <!-- read -->
                 <entry key="slavedataSource" value-ref="slavedataSource"/>  
              </map>  
              
        </property>  
        <property name="defaultTargetDataSource" ref="masterdataSource"/>  
    </bean>
       
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">  
        <property name="dataSource" ref="dataSource" />  
        <property name="mapperLocations" value="classpath:com/he/dao/*.xml"></property>  
    </bean>  

    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">  
        <property name="basePackage" value="com.he.dao" />  
        <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"></property>  
    </bean>  
    
    <bean id="transactionManager"  
        class="org.springframework.jdbc.datasource.DataSourceTransactionManager">  
        <property name="dataSource" ref="dataSource" />  
    </bean> 
   
    <!-- 注解式事务管理，需要在Service类上标注@Transactional -->
    <tx:annotation-driven transaction-manager="transactionManager" />
     
</beans>  

 

第二步：

public class DynamicDataSource extends AbstractRoutingDataSource {

    @Override
    protected Object determineCurrentLookupKey() {
     
        return DynamicDataSourceHolder.getDataSouce();
    }

}

第三步：

public class DynamicDataSourceHolder {
    public static final ThreadLocal<String> holder = new ThreadLocal<String>();

    public static void putDataSource(String name) {
        holder.set(name);
    }

    public static String getDataSouce() {
        return holder.get();
    }
}

第四步：

@Service("userService")  
@Transactional
public class UserServiceImpl implements UserService{

    @Autowired
    private UserMapper userDao;public void add(User user) {
        
        DynamicDataSourceHolder.putDataSource("masterdataSource");
        userDao.add(user);
    }

    public void update(User user) {
        
        DynamicDataSourceHolder.putDataSource("masterdataSource");
        userDao.updates(user);
    
        
    }

    @Transactional(propagation = Propagation.NOT_SUPPORTED)
    public List<User> query() {
        
        DynamicDataSourceHolder.putDataSource("slavedataSource");
        List<User> user = userDao.query();
        return user;
        
    }

    
    
    
}

 第二种实现方式：基于上述的配置，只需要做部分的更改即可，主要是结合springAOP思想和反射机制去实现

第一步：基于上面的spring配置中加入aop相关配置

<!-- 配置数据库注解aop -->
    <bean id="manyDataSourceAspect" class="com.he.aspect.DataSourceAspect" />
    <aop:config>
        <aop:aspect id="c" ref="manyDataSourceAspect">
            <aop:pointcut id="tx" expression="execution(* com.he.dao.*.*(..))"/>
            <aop:before pointcut-ref="tx" method="before"/>
        </aop:aspect>
    </aop:config>

第二步：构建DataSource和DataSourceAspect

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface DataSource {
    String value();
}

 

import java.lang.reflect.Method;

import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.reflect.MethodSignature;

import com.he.mysql.test.DataSource;
import com.he.mysql.test.DynamicDataSourceHolder;


public class DataSourceAspect {
      public void before(JoinPoint point)
        {
            Object target = point.getTarget();
            String method = point.getSignature().getName();

            Class<?>[] classz = target.getClass().getInterfaces();

            Class<?>[] parameterTypes = ((MethodSignature) point.getSignature())
                    .getMethod().getParameterTypes();
            try {
                Method m = classz[0].getMethod(method, parameterTypes);
                if (m != null && m.isAnnotationPresent(DataSource.class)) {
                    DataSource data = m
                            .getAnnotation(DataSource.class);
                    DynamicDataSourceHolder.putDataSource(data.value());
                    System.out.println(data.value());
                }
                
            } catch (Exception e) {
                // TODO: handle exception
            }
        }

}

 

第三步：将serviceImpl中手动植入的代码移除，在dao层接口加入注解

@Repository
public interface UserMapper {
    @DataSource("masterdataSource")
    public void add(User user);
    @DataSource("masterdataSource")
    public void updates(User user);
    @DataSource("slavedataSource")
    public List<User> query();
}

 

上述为实现读写分离的关键部分，只是为了简单的做一个示例，完成上面操作以后，可自行的对数据库进行新增和查询操作，查看效果