Spring + Mybatis 项目实现动态切换数据源实例详解

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：

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">2 <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);
 }
 }
}

以上所述是小编给大家介绍的spring + mybatis 项目实现动态切换数据源实例详解，希望对大家有所帮助