java實現mysql數據庫讀寫分離之定義多數據源方式
阿新 • • 發佈：2017-08-05
修改 protect frame auto ret 更新數據 logs cannot initial 
該示例是基於spring提供的AbstractRoutingDataSource，實現了一個動態數據源的功能，在spring配置中定義多個數據庫分為主、從數據庫，實現效果為當進行保存和修改記錄時則對主表操作，查詢則對從表進行操作，從而實現對數據庫表的讀寫分離。這樣做有利於提高網站的性能，特別是在數據庫這一層。因為在實際的應用中，數據庫都是讀多寫少（讀取數據的頻率高，更新數據的頻率相對較少），而讀取數據通常耗時比較長，占用數據庫服務器的CPU較多，從而影響用戶體驗。我們通常的做法就是把查詢從主庫中抽取出來，采用多個從庫，使用負載均衡，減輕每個從庫的查詢壓力。該示例並未對數據庫同步進行說明，只對讀寫操作的分離實現：
在進行操作之前，先簡單說一下AbstractRoutingDataSource相關的東西：
1 AbstractRoutingDataSource繼承了AbstractDataSource ，而AbstractDataSource 又是DataSource 的子類。DataSource 是javax.sql 的數據源接口，定義如下： 2 3 public abstract class AbstractRoutingDataSource extends AbstractDataSource implements InitializingBean {} 4 5 publicView Codeinterface 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 occurs13 */ 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 }
從上面的代碼中不難看出，獲取數據源首先是通過對determineCurrentLookupKey（）的調用獲取resolvedDataSources對應key的值，故執行創建一個動態數據源類繼承AbstractRoutingDataSource，復寫determineCurrentLookupKey（）去自定義設置和獲取resolvedDataSources的key就可以實現了
具體步驟如下：
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> <!-- 註解式事務管理，[email protected] --> <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 }創建動態數據源類繼承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 }設置及獲取每個線程訪問的哪個數據源
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 }對service實現層加入設置數據源代碼
上述為實現讀寫分離的關鍵部分，只是為了簡單的做一個示例，完成上面操作以後，可自行的對數據庫進行新增和查詢操作，查看效果
java實現mysql數據庫讀寫分離之定義多數據源方式