如今大型的電子商務系統,在數據庫層面大都採用讀寫分離技術,就是一個Master數據庫,多個Slave數據庫。Master庫負責數據更新和實時數據查詢,Slave庫固然負責非實時數據查詢。由於在實際的應用中,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),而讀取數據一般耗時比較長,佔用數據庫服務器的CPU較多,從而影響用戶體驗。咱們一般的作法就是把查詢從主庫中抽取出來,採用多個從庫,使用負載均衡,減輕每一個從庫的查詢壓力。javascript
採用讀寫分離技術的目標:有效減輕Master庫的壓力,又能夠把用戶查詢數據的請求分發到不一樣的Slave庫,從而保證系統的健壯性。咱們看下采用讀寫分離的背景。html
隨着網站的業務不斷擴展,數據不斷增長,用戶愈來愈多,數據庫的壓力也就愈來愈大,採用傳統的方式,好比:數據庫或者SQL的優化基本已達不到要求,這個時候能夠採用讀寫分離的策 略來改變現狀。java
具體到開發中,如何方便的實現讀寫分離呢?目前經常使用的有兩種方式:mysql
1 第一種方式是咱們最經常使用的方式,就是定義2個數據庫鏈接,一個是MasterDataSource,另外一個是SlaveDataSource。更新數據時咱們讀取MasterDataSource,查詢數據時咱們讀取SlaveDataSource。這種方式很簡單,我就不贅述了。spring
2 第二種方式動態數據源切換,就是在程序運行時,把數據源動態織入到程序中,從而選擇讀取主庫仍是從庫。主要使用的技術是:annotation,Spring AOP ,反射。下面會詳細的介紹實現方式。sql
在介紹實現方式以前,咱們先準備一些必要的知識,spring 的AbstractRoutingDataSource 類數據庫
AbstractRoutingDataSource這個類 是spring2.0之後增長的,咱們先來看下AbstractRoutingDataSource的定義:express
Java代碼 服務器

- public abstract class AbstractRoutingDataSource extends AbstractDataSource implements InitializingBean {}
Java代碼 session

- public abstract class AbstractRoutingDataSource extends AbstractDataSource implements InitializingBean {
-
- private Map<Object, Object> targetDataSources;
-
- private Object defaultTargetDataSource;
-
- private DataSourceLookup dataSourceLookup = new JndiDataSourceLookup();
-
- private Map<Object, DataSource> resolvedDataSources;
-
- private DataSource resolvedDefaultDataSource;
AbstractRoutingDataSource繼承了AbstractDataSource ,而AbstractDataSource 又是DataSource 的子類。
DataSource 是javax.sql 的數據源接口,定義以下:
Java代碼

- public interface DataSource extends CommonDataSource,Wrapper {
-
- Connection getConnection() throws SQLException;
-
- Connection getConnection(String username, String password)
- throws SQLException;
- }
DataSource 接口定義了2個方法,都是獲取數據庫鏈接。咱們在看下AbstractRoutingDataSource 如何實現了DataSource接口:
Java代碼

- public Connection getConnection() throws SQLException {
- return determineTargetDataSource().getConnection();
- }
-
- public Connection getConnection(String username, String password) throws SQLException {
- return determineTargetDataSource().getConnection(username, password);
- }
很顯然就是調用本身的determineTargetDataSource() 方法獲取到connection。determineTargetDataSource方法定義以下:
Java代碼

- 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;
- }
咱們最關心的仍是下面2句話:
Object lookupKey = determineCurrentLookupKey();
DataSource dataSource = this.resolvedDataSources.get(lookupKey);
determineCurrentLookupKey方法返回lookupKey,resolvedDataSources方法就是根據lookupKey從Map中得到數據源。resolvedDataSources 和determineCurrentLookupKey定義以下:
private Map<Object, DataSource> resolvedDataSources;
protected abstract Object determineCurrentLookupKey()
看到以上定義,咱們是否是有點思路了,resolvedDataSources是Map類型,咱們能夠把MasterDataSource和SlaveDataSource存到Map中,以下:
key value
master MasterDataSource
slave SlaveDataSource
咱們在寫一個類DynamicDataSource 繼承AbstractRoutingDataSource,實現其determineCurrentLookupKey() 方法,該方法返回Map的key,master或slave。
好了,說了這麼多,有點煩了,下面咱們看下怎麼實現。
上面已經提到了咱們要使用的技術,咱們先看下annotation的定義:
Java代碼

- @Retention(RetentionPolicy.RUNTIME)
- @Target(ElementType.METHOD)
- public @interface DataSource {
- String value();
- }
咱們還須要實現spring的抽象類AbstractRoutingDataSource,就是實現determineCurrentLookupKey方法:
Java代碼

- public class DynamicDataSource extends AbstractRoutingDataSource {
-
- @Override
- protected Object determineCurrentLookupKey() {
- // TODO Auto-generated method stub
- return DynamicDataSourceHolder.getDataSouce();
- }
-
- }
-
-
- 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();
- }
- }
從DynamicDataSource 的定義看出,他返回的是DynamicDataSourceHolder.getDataSouce()值,咱們須要在程序運行時調用DynamicDataSourceHolder.putDataSource()方法,對其賦值。下面是咱們實現的核心部分,也就是AOP部分,DataSourceAspect定義以下:
Java代碼

- 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
- }
- }
- }
爲了方便測試,我定義了2個數據庫,shop模擬Master庫,test模擬Slave庫,shop和test的表結構一致,但數據不一樣,數據庫配置以下:
Xml代碼

- <bean id="masterdataSource"
- class="org.springframework.jdbc.datasource.DriverManagerDataSource">
- <property name="driverClassName" value="com.mysql.jdbc.Driver" />
- <property name="url" value="jdbc:mysql://127.0.0.1:3306/shop" />
- <property name="username" value="root" />
- <property name="password" value="yangyanping0615" />
- </bean>
-
- <bean id="slavedataSource"
- class="org.springframework.jdbc.datasource.DriverManagerDataSource">
- <property name="driverClassName" value="com.mysql.jdbc.Driver" />
- <property name="url" value="jdbc:mysql://127.0.0.1:3306/test" />
- <property name="username" value="root" />
- <property name="password" value="yangyanping0615" />
- </bean>
-
- <beans:bean id="dataSource" class="com.air.shop.common.db.DynamicDataSource">
- <property name="targetDataSources">
- <map key-type="java.lang.String">
- <!-- write -->
- <entry key="master" value-ref="masterdataSource"/>
- <!-- read -->
- <entry key="slave" value-ref="slavedataSource"/>
- </map>
-
- </property>
- <property name="defaultTargetDataSource" ref="masterdataSource"/>
- </beans:bean>
-
- <bean id="transactionManager"
- class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
- <property name="dataSource" ref="dataSource" />
- </bean>
-
-
- <!-- 配置SqlSessionFactoryBean -->
- <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
- <property name="dataSource" ref="dataSource" />
- <property name="configLocation" value="classpath:config/mybatis-config.xml" />
- </bean>
在spring的配置中增長aop配置
Xml代碼

- <!-- 配置數據庫註解aop -->
- <aop:aspectj-autoproxy></aop:aspectj-autoproxy>
- <beans:bean id="manyDataSourceAspect" class="com.air.shop.proxy.DataSourceAspect" />
- <aop:config>
- <aop:aspect id="c" ref="manyDataSourceAspect">
- <aop:pointcut id="tx" expression="execution(* com.air.shop.mapper.*.*(..))"/>
- <aop:before pointcut-ref="tx" method="before"/>
- </aop:aspect>
- </aop:config>
- <!-- 配置數據庫註解aop -->
下面是MyBatis的UserMapper的定義,爲了方便測試,登陸讀取的是Master庫,用戶列表讀取Slave庫:
Java代碼

- public interface UserMapper {
- @DataSource("master")
- public void add(User user);
-
- @DataSource("master")
- public void update(User user);
-
- @DataSource("master")
- public void delete(int id);
-
- @DataSource("slave")
- public User loadbyid(int id);
-
- @DataSource("master")
- public User loadbyname(String name);
-
- @DataSource("slave")
- public List<User> list();
- }
好了,運行咱們的Eclipse看看效果,輸入用戶名admin 登陸看看效果


從圖中能夠看出,登陸的用戶和用戶列表的數據是不一樣的,也驗證了咱們的實現,登陸讀取Master庫,用戶列表讀取Slave庫。
例子來源:
http://www.cnblogs.com/surge/p/3582248.html
2、配置動態數據源
Xml代碼

- <bean id="dataSource" class="org.springframework.jndi.JndiObjectFactoryBean">
- <property name="jndiName">
- <value>java:/datasources/visesbdb</value>
- </property>
- </bean>
-
- <!-- config dynamicDataSource -->
- <bean id="dynamicDataSource" class="com.vispractice.soa.lightesb.common.datasource.MutiDataSourceBean">
- <property name="targetDataSources">
- <map key-type="java.lang.String">
- <entry value-ref="dataSource" key="dataSource"></entry>
- </map>
- </property>
- <property name="defaultTargetDataSource" ref="dataSource"></property>
- </bean>
-
- <bean class="org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor"/>
-
- <!-- Hibernate SessionFactory -->
- <bean id="sessionFactory" class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean">
- <property name="dataSource" ref="dynamicDataSource"/>
- <property name="packagesToScan">
- <list>
- <value>com.vispractice.soa.lightesb.bean</value>
- </list>
- </property>
- <property name="hibernateProperties">
- <props>
- <prop key="connection.useUnicode">true</prop>
- <prop key="connection.characterEncoding">UTF-8</prop>
- <prop key="hibernate.dialect">${hibernate.dialect}</prop>
- <prop key="hibernate.hbm2ddl.auto">${hibernate.hbm2ddl.auto}</prop>
- <prop key="hibernate.show_sql">${hibernate.show_sql}</prop>
- <prop key="hibernate.format_sql">${hibernate.format_sql}</prop>
- <prop key="hibernate.cache.use_second_level_cache">${hibernate.cache.use_second_level_cache}</prop>
- <prop key="hibernate.cache.use_query_cache">${hibernate.cache.use_query_cache}</prop>
- </props>
- </property>
- </bean>
-
- <!-- Transaction manager for a single Hibernate SessionFactory (alternative to JTA) -->
- <bean id="transactionManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager">
- <property name="sessionFactory" ref="sessionFactory"/>
- </bean>
Java代碼

- /**
- * 在applicationContext中配置本地數據源做爲默認數據源
- * 讀取project-datasource-jndi.properties中的jndi名稱獲取其餘節點的數據源
- * 該文件放在D:\jboss-5.1.0.GA\server\default\conf\props 目錄下
- *
- */
- public class MutiDataSourceBean extends AbstractRoutingDataSource implements ApplicationContextAware {
-
- private static final Logger logger = LoggerFactory.getLogger(MutiDataSourceBean.class);
-
- private static ApplicationContext ctx;
-
- private Map<Object,Object> tds = new HashMap<Object,Object>();
-
- @Override
- public void setApplicationContext(ApplicationContext applicationContext)
- throws BeansException {
- ctx = applicationContext;
- }
-
- @Override
- protected Object determineCurrentLookupKey() {
- return DataSourceContextHolder.getDataSourceType();
- }
-
- //重寫InitializingBean類中方法
- @Override
- public void afterPropertiesSet() {
- logger.info("Init MutiDataSource start...");
- try {
- initailizeMutiDataSource();
- } catch (Exception e) {
- logger.error("Init MutiDataSource error...", e);
- }
- logger.info("Init MutiDataSource end...");
- super.afterPropertiesSet();
- }
-
- /**
- * 讀取配置文件中的jndi名稱,獲取數據源
- * @throws Exception
- */
- private void initailizeMutiDataSource() throws Exception {
- // 讀取數據源配置文件
- ResourceBundle lw = ResourceBundle.getBundle("props.project-datasource-jndi");
-
- // 初始化jndi context
- Context jndiCtx = new InitialContext();
-
- DefaultListableBeanFactory dlbf = (DefaultListableBeanFactory) ctx.getAutowireCapableBeanFactory();
-
- // 獲取配置的數據源
- for(String key : lw.keySet()){
- Object ds = jndiCtx.lookup(lw.getString(key));
- // 將數據源交給spring管理
- dlbf.registerSingleton(key, ds);
-
- tds.put(key, ds);
- }
- super.setTargetDataSources(tds);
- }
-
- @Override
- public void setTargetDataSources(Map<Object, Object> targetDataSources) {
- tds = targetDataSources;
- super.setTargetDataSources(targetDataSources);
- }
-
- }
Java代碼

- /**
- * 經過ThreadLocal來存儲當前所使用數據源對應的key
- *
- */
- public class DataSourceContextHolder {
-
- private static final ThreadLocal<String> contextHolder = new ThreadLocal<String>();
-
- public static void setDataSourceType(String dataSourceType) {
- contextHolder.set(dataSourceType);
- }
-
- public static String getDataSourceType() {
- return contextHolder.get();
- }
-
- public static void clearDataSourceType() {
- contextHolder.remove();
- }
- }
查詢前設置值:
Java代碼

- MutiDataSourceUtil.determineTargetDataSourceByInstanceUUID(EsbServiceInstanceV.getInstanceUUID());
- Map<String,Object> result = esbServiceMonitorDao.findEsbServiceInstanceVPagedList(pageQueryParameter, EsbServiceInstanceV);
- // reset datasource
- DataSourceContextHolder.clearDataSourceType();
Java代碼

- public class MutiDataSourceUtil {
-
- /**
- * 經過實例UUID切換到對應的數據源
- *
- * @param instanceUUID
- */
- public static void determineTargetDataSourceByInstanceUUID(String instanceUUID) {
- if(StringUtils.isNotBlank(instanceUUID) && StringUtils.contains(instanceUUID, '-')){
- DataSourceContextHolder.setDataSourceType(StringUtils.substringBefore(instanceUUID, "-"));
- }
- }
-
- }
lightesb-datasource-jndi.properties:
Xml代碼

- N1=java:/datasources/visesbdb
- N2=java:/datasources/n2visesbdb
實例號如:
N1-AB2DFE3C48BA43D699529868B20152CC