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。
最简单的办法其实就是建两个包，把之前数据源那一套配置copy一份，指向另外的包，但是这样扩展很有限，所有采用下面的办法。
参考了两篇文章如下：
http://blog.csdn.net/zl3450341/article/details/20150687
http://www.blogjava.net/hoojo/archive/2013/10/22/405488.html
这两篇文章都对原理进行了分析，下面只写自己的实现过程其他不再叙述。
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/sincetimes/slg/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/sincetimes/slg/dao/*.xml"/>
</bean>
两个SqlSessionFactory使用同一个SqlSessionTemplate配置：
<bean id="MasterAndSlaveSqlSessionTemplate" class="com.sincetimes.slg.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>
配置Mybatis自动扫描dao
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<property name="basePackage" value="com.sincetimes.slg.dao" />
<property name="sqlSessionTemplateBeanName" value="MasterAndSlaveSqlSessionTemplate" />
</bean>
自己重写了SqlSessionTemplate代码如下：
package com.sincetimes.slg.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.sincetimes.slg.framework.util.SqlSessionContentHolder; /**
*
* TODO 重写SqlSessionTemplate
* @author ccg
* @version 1.0
* Created 2017年4月21日 下午3:15:15
*/
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.sincetimes.slg.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：
package com.sincetimes.slg.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.sincetimes.slg.framework.util.SqlSessionContentHolder; @Aspect
public class DynamicDataSourceAspect { @Pointcut("execution( * com.sincetimes.slg.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);
}
} }