java实现mysql数据库读写分离之定义多数据源方式

Posted 2020-10-01 java一生

 

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：

 1 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：
 2 
 3 public abstract class AbstractRoutingDataSource extends AbstractDataSource implements InitializingBean  {}
 4 
 5 public interface DataSource  extends CommonDataSource,Wrapper {
 6 
 7   /**
 8    * <p>Attempts to establish a connection with the data source that
 9    * this <code>DataSource</code> object represents.
10    *
11    * @return  a connection to the data source
12    * @exception SQLException if a database access error occurs
13    */
14   Connection getConnection() throws SQLException;
15 
16   /**
17    * <p>Attempts to establish a connection with the data source that
18    * this <code>DataSource</code> object represents.
19    *
20    * @param username the database user on whose behalf the connection is
21    *  being made
22    * @param password the user‘s password
23    * @return  a connection to the data source
24    * @exception SQLException if a database access error occurs
25    * @since 1.4
26    */
27   Connection getConnection(String username, String password)
28     throws SQLException;
29 
30 }
31 
32 
33 public Connection getConnection() throws SQLException {
34         return determineTargetDataSource().getConnection();
35     }
36 
37     public Connection getConnection(String username, String password) throws SQLException {
38         return determineTargetDataSource().getConnection(username, password);
39     }
40 
41 protected DataSource determineTargetDataSource() {
42         Assert.notNull(this.resolvedDataSources, "DataSource router not initialized");
43         Object lookupKey = determineCurrentLookupKey();
44         DataSource dataSource = this.resolvedDataSources.get(lookupKey);
45         if (dataSource == null && (this.lenientFallback || lookupKey == null)) {
46             dataSource = this.resolvedDefaultDataSource;
47         }
48         if (dataSource == null) {
49             throw new IllegalStateException("Cannot determine target DataSource for lookup key [" + lookupKey + "]");
50         }
51         return dataSource;
52     }

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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>  

View Code

 

第二步：

1 public class DynamicDataSource extends AbstractRoutingDataSource {
2 
3     @Override
4     protected Object determineCurrentLookupKey() {
5      
6         return DynamicDataSourceHolder.getDataSouce();
7     }
8 
9 }

创建动态数据源类继承AbstractRoutingDataSource

第三步：

 1 public class DynamicDataSourceHolder {
 2     public static final ThreadLocal<String> holder = new ThreadLocal<String>();
 3 
 4     public static void putDataSource(String name) {
 5         holder.set(name);
 6     }
 7 
 8     public static String getDataSouce() {
 9         return holder.get();
10     }
11 }

设置及获取每个线程访问的哪个数据源

第四步：

 1 @Service("userService")  
 2 @Transactional
 3 public class UserServiceImpl implements UserService{
 4 
 5     @Autowired
 6     private UserMapper userDao;public void add(User user) {
 7         
 8         DynamicDataSourceHolder.putDataSource("masterdataSource");
 9         userDao.add(user);
10     }
11 
12     public void update(User user) {
13         
14         DynamicDataSourceHolder.putDataSource("masterdataSource");
15         userDao.updates(user);
16     
17         
18     }
19 
20     @Transactional(propagation = Propagation.NOT_SUPPORTED)
21     public List<User> query() {
22         
23         DynamicDataSourceHolder.putDataSource("slavedataSource");
24         List<User> user = userDao.query();
25         return user;
26         
27     }
28 
29     
30     
31     
32 }

对service实现层加入设置数据源代码

 

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