Spring + Mybatis 读写分离
项目背景：项目开发中数据库使用了读写分离，所有查询语句走从库，除此之外走主库。
实现思路是：
第一步，实现动态切换数据源：配置两个DataSource，配置两个SqlSessionFactory指向两个不同的DataSource，两个SqlSessionFactory都用一个SqlSessionTemplate，同时重写Mybatis提供的SqlSessionTemplate类，最后配置Mybatis自动扫描。
第二步，利用aop切面，拦截dao层所有方法，因为dao层方法命名的特点，比如所有查询sql都是select开头，或者get开头等等，拦截这些方法，并把当前数据源切换至从库。
spring中配置如下：
主库数据源配置：
<bean id="masterDataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource" destroy-method="close"> <property name="driverClass" value="${master_mysql_jdbc_driver}" /> <property name="jdbcUrl" value="${master_mysql_jdbc_url}" /> <property name="user" value="${master_mysql_jdbc_user}" /> <property name="password" value="${master_mysql_jdbc_password}" /> </bean>
从库数据源配置：
<bean id="masterDataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource" destroy-method="close"> <property name="driverClass" value="${slave_mysql_jdbc_driver}" /> <property name="jdbcUrl" value="${slave_mysql_jdbc_url}" /> <property name="user" value="${slave_mysql_jdbc_user}" /> <property name="password" value="${slave_mysql_jdbc_password}" /> </bean>
主库SqlSessionFactory配置：
<bean id="masterSqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"> <property name="dataSource" ref="masterDataSource" /> <property name="mapperLocations" value="classpath:com/bhrk/dao/*.xml"/> </bean>
从库SqlSessionFactory配置：
<bean id="slaveSqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"> <property name="dataSource" ref="slaveDataSource" /> <property name="mapperLocations" value="classpath:com/bhrk/dao/*.xml"/> </bean>
两个SqlSessionFactory使用同一个SqlSessionTemplate配置：
<bean id="DynamicSqlSessionTemplate" class="com.bhrk.framework.core.DynamicSqlSessionTemplate"> <constructor-arg index="0" ref="masterSqlSessionFactory" /> <property name="targetSqlSessionFactorys"> <map> <entry value-ref="masterSqlSessionFactory" key="master"/> <entry value-ref="slaveSqlSessionFactory" key="slave"/> </map> </property> </bean>
重写SqlSessionTemplate代码如下：
package com.bhrk.framework.core; import static java.lang.reflect.Proxy.newProxyInstance; import static org.apache.ibatis.reflection.ExceptionUtil.unwrapThrowable; import static org.mybatis.spring.SqlSessionUtils.closeSqlSession; import static org.mybatis.spring.SqlSessionUtils.getSqlSession; import static org.mybatis.spring.SqlSessionUtils.isSqlSessionTransactional; import java.lang.reflect.InvocationHandler; import java.lang.reflect.Method; import java.sql.Connection; import java.util.List; import java.util.Map; import org.apache.ibatis.exceptions.PersistenceException; import org.apache.ibatis.executor.BatchResult; import org.apache.ibatis.session.Configuration; import org.apache.ibatis.session.ExecutorType; import org.apache.ibatis.session.ResultHandler; import org.apache.ibatis.session.RowBounds; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.mybatis.spring.MyBatisExceptionTranslator; import org.mybatis.spring.SqlSessionTemplate; import org.springframework.dao.support.PersistenceExceptionTranslator; import org.springframework.util.Assert; import com.bhrk.framework.util.SqlSessionContentHolder; /** * * TODO 重写SqlSessionTemplate * @author bhrk * @version 1.0 * Created 2017年11月21日 下午1:15:15 */ public class DynamicSqlSessionTemplate extends SqlSessionTemplate { private final SqlSessionFactory sqlSessionFactory; private final ExecutorType executorType; private final SqlSession sqlSessionProxy; private final PersistenceExceptionTranslator exceptionTranslator; private Map<Object, SqlSessionFactory> targetSqlSessionFactorys; private SqlSessionFactory defaultTargetSqlSessionFactory; public void setTargetSqlSessionFactorys(Map<Object, SqlSessionFactory> targetSqlSessionFactorys) { this.targetSqlSessionFactorys = targetSqlSessionFactorys; } public Map<Object, SqlSessionFactory> getTargetSqlSessionFactorys(){ return targetSqlSessionFactorys; } public void setDefaultTargetSqlSessionFactory(SqlSessionFactory defaultTargetSqlSessionFactory) { this.defaultTargetSqlSessionFactory = defaultTargetSqlSessionFactory; } public DynamicSqlSessionTemplate(SqlSessionFactory sqlSessionFactory) { this(sqlSessionFactory, sqlSessionFactory.getConfiguration().getDefaultExecutorType()); } public DynamicSqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType) { this(sqlSessionFactory, executorType, new MyBatisExceptionTranslator(sqlSessionFactory.getConfiguration() .getEnvironment().getDataSource(), true)); } public DynamicSqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) { super(sqlSessionFactory, executorType, exceptionTranslator); this.sqlSessionFactory = sqlSessionFactory; this.executorType = executorType; this.exceptionTranslator = exceptionTranslator; this.sqlSessionProxy = (SqlSession) newProxyInstance( SqlSessionFactory.class.getClassLoader(), new Class[] { SqlSession.class }, new SqlSessionInterceptor()); this.defaultTargetSqlSessionFactory = sqlSessionFactory; } @Override public SqlSessionFactory getSqlSessionFactory() { SqlSessionFactory targetSqlSessionFactory = targetSqlSessionFactorys.get(SqlSessionContentHolder.getContextType()); if (targetSqlSessionFactory != null) { return targetSqlSessionFactory; } else if (defaultTargetSqlSessionFactory != null) { return defaultTargetSqlSessionFactory; } else { Assert.notNull(targetSqlSessionFactorys, "Property 'targetSqlSessionFactorys' or 'defaultTargetSqlSessionFactory' are required"); Assert.notNull(defaultTargetSqlSessionFactory, "Property 'defaultTargetSqlSessionFactory' or 'targetSqlSessionFactorys' are required"); } return this.sqlSessionFactory; } @Override public Configuration getConfiguration() { return this.getSqlSessionFactory().getConfiguration(); } public ExecutorType getExecutorType() { return this.executorType; } public PersistenceExceptionTranslator getPersistenceExceptionTranslator() { return this.exceptionTranslator; } /** * {@inheritDoc} */ public <T> T selectOne(String statement) { return this.sqlSessionProxy.<T> selectOne(statement); } /** * {@inheritDoc} */ public <T> T selectOne(String statement, Object parameter) { return this.sqlSessionProxy.<T> selectOne(statement, parameter); } /** * {@inheritDoc} */ public <K, V> Map<K, V> selectMap(String statement, String mapKey) { return this.sqlSessionProxy.<K, V> selectMap(statement, mapKey); } /** * {@inheritDoc} */ public <K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey) { return this.sqlSessionProxy.<K, V> selectMap(statement, parameter, mapKey); } /** * {@inheritDoc} */ public <K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey, RowBounds rowBounds) { return this.sqlSessionProxy.<K, V> selectMap(statement, parameter, mapKey, rowBounds); } /** * {@inheritDoc} */ public <E> List<E> selectList(String statement) { return this.sqlSessionProxy.<E> selectList(statement); } /** * {@inheritDoc} */ public <E> List<E> selectList(String statement, Object parameter) { return this.sqlSessionProxy.<E> selectList(statement, parameter); } /** * {@inheritDoc} */ public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) { return this.sqlSessionProxy.<E> selectList(statement, parameter, rowBounds); } /** * {@inheritDoc} */ public void select(String statement, ResultHandler handler) { this.sqlSessionProxy.select(statement, handler); } /** * {@inheritDoc} */ public void select(String statement, Object parameter, ResultHandler handler) { this.sqlSessionProxy.select(statement, parameter, handler); } /** * {@inheritDoc} */ public void select(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler) { this.sqlSessionProxy.select(statement, parameter, rowBounds, handler); } /** * {@inheritDoc} */ public int insert(String statement) { return this.sqlSessionProxy.insert(statement); } /** * {@inheritDoc} */ public int insert(String statement, Object parameter) { return this.sqlSessionProxy.insert(statement, parameter); } /** * {@inheritDoc} */ public int update(String statement) { return this.sqlSessionProxy.update(statement); } /** * {@inheritDoc} */ public int update(String statement, Object parameter) { return this.sqlSessionProxy.update(statement, parameter); } /** * {@inheritDoc} */ public int delete(String statement) { return this.sqlSessionProxy.delete(statement); } /** * {@inheritDoc} */ public int delete(String statement, Object parameter) { return this.sqlSessionProxy.delete(statement, parameter); } /** * {@inheritDoc} */ public <T> T getMapper(Class<T> type) { return getConfiguration().getMapper(type, this); } /** * {@inheritDoc} */ public void commit() { throw new UnsupportedOperationException("Manual commit is not allowed over a Spring managed SqlSession"); } /** * {@inheritDoc} */ public void commit(boolean force) { throw new UnsupportedOperationException("Manual commit is not allowed over a Spring managed SqlSession"); } /** * {@inheritDoc} */ public void rollback() { throw new UnsupportedOperationException("Manual rollback is not allowed over a Spring managed SqlSession"); } /** * {@inheritDoc} */ public void rollback(boolean force) { throw new UnsupportedOperationException("Manual rollback is not allowed over a Spring managed SqlSession"); } /** * {@inheritDoc} */ public void close() { throw new UnsupportedOperationException("Manual close is not allowed over a Spring managed SqlSession"); } /** * {@inheritDoc} */ public void clearCache() { this.sqlSessionProxy.clearCache(); } /** * {@inheritDoc} */ public Connection getConnection() { return this.sqlSessionProxy.getConnection(); } /** * {@inheritDoc} * @since 1.0.2 */ public List<BatchResult> flushStatements() { return this.sqlSessionProxy.flushStatements(); } /** * Proxy needed to route MyBatis method calls to the proper SqlSession got from Spring's Transaction Manager It also * unwraps exceptions thrown by {@code Method#invoke(Object, Object...)} to pass a {@code PersistenceException} to * the {@code PersistenceExceptionTranslator}. */ private class SqlSessionInterceptor implements InvocationHandler { public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { final SqlSession sqlSession = getSqlSession( DynamicSqlSessionTemplate.this.getSqlSessionFactory(), DynamicSqlSessionTemplate.this.executorType, DynamicSqlSessionTemplate.this.exceptionTranslator); try { Object result = method.invoke(sqlSession, args); if (!isSqlSessionTransactional(sqlSession, DynamicSqlSessionTemplate.this.getSqlSessionFactory())) { // force commit even on non-dirty sessions because some databases require // a commit/rollback before calling close() sqlSession.commit(true); } return result; } catch (Throwable t) { Throwable unwrapped = unwrapThrowable(t); if (DynamicSqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) { Throwable translated = DynamicSqlSessionTemplate.this.exceptionTranslator .translateExceptionIfPossible((PersistenceException) unwrapped); if (translated != null) { unwrapped = translated; } } throw unwrapped; } finally { closeSqlSession(sqlSession, DynamicSqlSessionTemplate.this.getSqlSessionFactory()); } } } }
SqlSessionContentHolder类代码如下：
package com.bhrk.framework.util; public abstract class SqlSessionContentHolder { public final static String SESSION_FACTORY_MASTER = "master"; public final static String SESSION_FACTORY_SLAVE = "slave"; private static final ThreadLocal<String> contextHolder = new ThreadLocal<String>(); public static void setContextType(String contextType) { contextHolder.set(contextType); } public static String getContextType() { return contextHolder.get(); } public static void clearContextType() { contextHolder.remove(); } }
最后就是写切面去对dao所有方法进行处理了，代码很简单如下：
<h1 style="color:red">一定要引入Aspect相关的包</h1>
package com.bhrk.framework.core; import org.aspectj.lang.JoinPoint; import org.aspectj.lang.annotation.Aspect; import org.aspectj.lang.annotation.Before; import org.aspectj.lang.annotation.Pointcut; import com.bhrk.framework.util.SqlSessionContentHolder; @Aspect public class DynamicDataSourceAspect { @Pointcut("execution( * com.bhrk.dao.*.*(..))") public void pointCut(){ } @Before("pointCut()") public void before(JoinPoint jp){ String methodName = jp.getSignature().getName(); //dao方法查询走从库 if(methodName.startsWith("query") || methodName.startsWith("get") || methodName.startsWith("count") || methodName.startsWith("list")){ SqlSessionContentHolder.setContextType(SqlSessionContentHolder.SESSION_FACTORY_SLAVE); }else{ SqlSessionContentHolder.setContextType(SqlSessionContentHolder.SESSION_FACTORY_MASTER); } } }
