Spring + Mybatis 项目实现动态切换数据源

Posted 2020-09-12 FlyHeLanMan

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：

1 <bean id="masterDataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource" destroy-method="close">
2     <property name="driverClass" value="${master_mysql_jdbc_driver}" />
3     <property name="jdbcUrl" value="${master_mysql_jdbc_url}" />
4     <property name="user" value="${master_mysql_jdbc_user}" />
5     <property name="password" value="${master_mysql_jdbc_password}" />
6 </bean>

从库数据源配置：

1 <bean id="masterDataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource" destroy-method="close">
2     <property name="driverClass" value="${slave_mysql_jdbc_driver}" />
3     <property name="jdbcUrl" value="${slave_mysql_jdbc_url}" />
4     <property name="user" value="${slave_mysql_jdbc_user}" />
5     <property name="password" value="${slave_mysql_jdbc_password}" />
6 </bean>

主库SqlSessionFactory配置：

1 <bean id="masterSqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
2     <property name="dataSource" ref="masterDataSource" />
3     <property name="mapperLocations"  value="classpath:com/sincetimes/slg/dao/*.xml"/>
4 </bean>

从库SqlSessionFactory配置：

1 <bean id="slaveSqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
2     <property name="dataSource" ref="slaveDataSource" />
3     <property name="mapperLocations"  value="classpath:com/sincetimes/slg/dao/*.xml"/>
4 </bean>

两个SqlSessionFactory使用同一个SqlSessionTemplate配置：

1 <bean id="MasterAndSlaveSqlSessionTemplate" class="com.sincetimes.slg.framework.core.DynamicSqlSessionTemplate">
2     <constructor-arg index="0" ref="masterSqlSessionFactory" />
3     <property name="targetSqlSessionFactorys">
4         <map>  
5             <entry value-ref="masterSqlSessionFactory" key="master"/>  
6             <entry value-ref="slaveSqlSessionFactory" key="slave"/>  
7         </map>  
8     </property>
9 </bean>

配置Mybatis自动扫描dao

1 <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
2     <property name="basePackage" value="com.sincetimes.slg.dao" />
3     <property name="sqlSessionTemplateBeanName" value="MasterAndSlaveSqlSessionTemplate" />
4 </bean>

自己重写了SqlSessionTemplate代码如下：

  1 package com.sincetimes.slg.framework.core;
  2 
  3 import static java.lang.reflect.Proxy.newProxyInstance;
  4 import static org.apache.ibatis.reflection.ExceptionUtil.unwrapThrowable;
  5 import static org.mybatis.spring.SqlSessionUtils.closeSqlSession;
  6 import static org.mybatis.spring.SqlSessionUtils.getSqlSession;
  7 import static org.mybatis.spring.SqlSessionUtils.isSqlSessionTransactional;
  8  
  9 import java.lang.reflect.InvocationHandler;
 10 import java.lang.reflect.Method;
 11 import java.sql.Connection;
 12 import java.util.List;
 13 import java.util.Map;
 14 
 15 import org.apache.ibatis.exceptions.PersistenceException;
 16 import org.apache.ibatis.executor.BatchResult;
 17 import org.apache.ibatis.session.Configuration;
 18 import org.apache.ibatis.session.ExecutorType;
 19 import org.apache.ibatis.session.ResultHandler;
 20 import org.apache.ibatis.session.RowBounds;
 21 import org.apache.ibatis.session.SqlSession;
 22 import org.apache.ibatis.session.SqlSessionFactory;
 23 import org.mybatis.spring.MyBatisExceptionTranslator;
 24 import org.mybatis.spring.SqlSessionTemplate;
 25 import org.springframework.dao.support.PersistenceExceptionTranslator;
 26 import org.springframework.util.Assert;
 27 
 28 import com.sincetimes.slg.framework.util.SqlSessionContentHolder;
 29 
 30 
 31 /**
 32  * 
 33  * TODO         重写SqlSessionTemplate
 34  * @author      ccg
 35  * @version        1.0
 36  * Created        2017年4月21日 下午3:15:15
 37  */
 38 public class DynamicSqlSessionTemplate extends SqlSessionTemplate {
 39  
 40     private final SqlSessionFactory sqlSessionFactory;
 41     private final ExecutorType executorType;
 42     private final SqlSession sqlSessionProxy;
 43     private final PersistenceExceptionTranslator exceptionTranslator;
 44  
 45     private Map<Object, SqlSessionFactory> targetSqlSessionFactorys;
 46     private SqlSessionFactory defaultTargetSqlSessionFactory;
 47  
 48     public void setTargetSqlSessionFactorys(Map<Object, SqlSessionFactory> targetSqlSessionFactorys) {
 49         this.targetSqlSessionFactorys = targetSqlSessionFactorys;
 50     }
 51     
 52     public Map<Object, SqlSessionFactory> getTargetSqlSessionFactorys(){
 53         return targetSqlSessionFactorys;
 54     }
 55  
 56     public void setDefaultTargetSqlSessionFactory(SqlSessionFactory defaultTargetSqlSessionFactory) {
 57         this.defaultTargetSqlSessionFactory = defaultTargetSqlSessionFactory;
 58     }
 59  
 60     public DynamicSqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
 61         this(sqlSessionFactory, sqlSessionFactory.getConfiguration().getDefaultExecutorType());
 62     }
 63  
 64     public DynamicSqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType) {
 65         this(sqlSessionFactory, executorType, new MyBatisExceptionTranslator(sqlSessionFactory.getConfiguration()
 66                 .getEnvironment().getDataSource(), true));
 67     }
 68  
 69     public DynamicSqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType,
 70             PersistenceExceptionTranslator exceptionTranslator) {
 71  
 72         super(sqlSessionFactory, executorType, exceptionTranslator);
 73  
 74         this.sqlSessionFactory = sqlSessionFactory;
 75         this.executorType = executorType;
 76         this.exceptionTranslator = exceptionTranslator;
 77         
 78         this.sqlSessionProxy = (SqlSession) newProxyInstance(
 79                 SqlSessionFactory.class.getClassLoader(),
 80                 new Class[] { SqlSession.class }, 
 81                 new SqlSessionInterceptor());
 82  
 83         this.defaultTargetSqlSessionFactory = sqlSessionFactory;
 84     }
 85  
 86     @Override
 87     public SqlSessionFactory getSqlSessionFactory() {
 88  
 89         SqlSessionFactory targetSqlSessionFactory = targetSqlSessionFactorys.get(SqlSessionContentHolder.getContextType());
 90         if (targetSqlSessionFactory != null) {
 91             return targetSqlSessionFactory;
 92         } else if (defaultTargetSqlSessionFactory != null) {
 93             return defaultTargetSqlSessionFactory;
 94         } else {
 95             Assert.notNull(targetSqlSessionFactorys, "Property ‘targetSqlSessionFactorys‘ or ‘defaultTargetSqlSessionFactory‘ are required");
 96             Assert.notNull(defaultTargetSqlSessionFactory, "Property ‘defaultTargetSqlSessionFactory‘ or ‘targetSqlSessionFactorys‘ are required");
 97         }
 98         return this.sqlSessionFactory;
 99     }
100  
101     @Override
102     public Configuration getConfiguration() {
103         return this.getSqlSessionFactory().getConfiguration();
104     }
105  
106     public ExecutorType getExecutorType() {
107         return this.executorType;
108     }
109  
110     public PersistenceExceptionTranslator getPersistenceExceptionTranslator() {
111         return this.exceptionTranslator;
112     }
113  
114     /**
115      * {@inheritDoc}
116      */
117     public <T> T selectOne(String statement) {
118         return this.sqlSessionProxy.<T> selectOne(statement);
119     }
120  
121     /**
122      * {@inheritDoc}
123      */
124     public <T> T selectOne(String statement, Object parameter) {
125         return this.sqlSessionProxy.<T> selectOne(statement, parameter);
126     }
127  
128     /**
129      * {@inheritDoc}
130      */
131     public <K, V> Map<K, V> selectMap(String statement, String mapKey) {
132         return this.sqlSessionProxy.<K, V> selectMap(statement, mapKey);
133     }
134  
135     /**
136      * {@inheritDoc}
137      */
138     public <K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey) {
139         return this.sqlSessionProxy.<K, V> selectMap(statement, parameter, mapKey);
140     }
141  
142     /**
143      * {@inheritDoc}
144      */
145     public <K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey, RowBounds rowBounds) {
146         return this.sqlSessionProxy.<K, V> selectMap(statement, parameter, mapKey, rowBounds);
147     }
148  
149     /**
150      * {@inheritDoc}
151      */
152     public <E> List<E> selectList(String statement) {
153         return this.sqlSessionProxy.<E> selectList(statement);
154     }
155  
156     /**
157      * {@inheritDoc}
158      */
159     public <E> List<E> selectList(String statement, Object parameter) {
160         return this.sqlSessionProxy.<E> selectList(statement, parameter);
161     }
162  
163     /**
164      * {@inheritDoc}
165      */
166     public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
167         return this.sqlSessionProxy.<E> selectList(statement, parameter, rowBounds);
168     }
169  
170     /**
171      * {@inheritDoc}
172      */
173     public void select(String statement, ResultHandler handler) {
174         this.sqlSessionProxy.select(statement, handler);
175     }
176  
177     /**
178      * {@inheritDoc}
179      */
180     public void select(String statement, Object parameter, ResultHandler handler) {
181         this.sqlSessionProxy.select(statement, parameter, handler);
182     }
183  
184     /**
185      * {@inheritDoc}
186      */
187     public void select(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler) {
188         this.sqlSessionProxy.select(statement, parameter, rowBounds, handler);
189     }
190  
191     /**
192      * {@inheritDoc}
193      */
194     public int insert(String statement) {
195         return this.sqlSessionProxy.insert(statement);
196     }
197  
198     /**
199      * {@inheritDoc}
200      */
201     public int insert(String statement, Object parameter) {
202         return this.sqlSessionProxy.insert(statement, parameter);
203     }
204  
205     /**
206      * {@inheritDoc}
207      */
208     public int update(String statement) {
209         return this.sqlSessionProxy.update(statement);
210     }
211  
212     /**
213      * {@inheritDoc}
214      */
215     public int update(String statement, Object parameter) {
216         return this.sqlSessionProxy.update(statement, parameter);
217     }
218  
219     /**
220      * {@inheritDoc}
221      */
222     public int delete(String statement) {
223         return this.sqlSessionProxy.delete(statement);
224     }
225  
226     /**
227      * {@inheritDoc}
228      */
229     public int delete(String statement, Object parameter) {
230         return this.sqlSessionProxy.delete(statement, parameter);
231     }
232  
233     /**
234      * {@inheritDoc}
235      */
236     public <T> T getMapper(Class<T> type) {
237         return getConfiguration().getMapper(type, this);
238     }
239  
240     /**
241      * {@inheritDoc}
242      */
243     public void commit() {
244         throw new UnsupportedOperationException("Manual commit is not allowed over a Spring managed SqlSession");
245     }
246  
247     /**
248      * {@inheritDoc}
249      */
250     public void commit(boolean force) {
251         throw new UnsupportedOperationException("Manual commit is not allowed over a Spring managed SqlSession");
252     }
253  
254     /**
255      * {@inheritDoc}
256      */
257     public void rollback() {
258         throw new UnsupportedOperationException("Manual rollback is not allowed over a Spring managed SqlSession");
259     }
260  
261     /**
262      * {@inheritDoc}
263      */
264     public void rollback(boolean force) {
265         throw new UnsupportedOperationException("Manual rollback is not allowed over a Spring managed SqlSession");
266     }
267  
268     /**
269      * {@inheritDoc}
270      */
271     public void close() {
272         throw new UnsupportedOperationException("Manual close is not allowed over a Spring managed SqlSession");
273     }
274  
275     /**
276      * {@inheritDoc}
277      */
278     public void clearCache() {
279         this.sqlSessionProxy.clearCache();
280     }
281  
282     /**
283      * {@inheritDoc}
284      */
285     public Connection getConnection() {
286         return this.sqlSessionProxy.getConnection();
287     }
288  
289     /**
290      * {@inheritDoc}
291      * @since 1.0.2
292      */
293     public List<BatchResult> flushStatements() {
294         return this.sqlSessionProxy.flushStatements();
295     }
296  
297     /**
298      * Proxy needed to route MyBatis method calls to the proper SqlSession got from Spring‘s Transaction Manager It also
299      * unwraps exceptions thrown by {@code Method#invoke(Object, Object...)} to pass a {@code PersistenceException} to
300      * the {@code PersistenceExceptionTranslator}.
301      */
302     private class SqlSessionInterceptor implements InvocationHandler {
303         public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
304             final SqlSession sqlSession = getSqlSession(
305                     DynamicSqlSessionTemplate.this.getSqlSessionFactory(),
306                     DynamicSqlSessionTemplate.this.executorType, 
307                     DynamicSqlSessionTemplate.this.exceptionTranslator);
308             try {
309                 Object result = method.invoke(sqlSession, args);
310                 if (!isSqlSessionTransactional(sqlSession, DynamicSqlSessionTemplate.this.getSqlSessionFactory())) {
311                     // force commit even on non-dirty sessions because some databases require
312                     // a commit/rollback before calling close()
313                     sqlSession.commit(true);
314                 }
315                 return result;
316             } catch (Throwable t) {
317                 Throwable unwrapped = unwrapThrowable(t);
318                 if (DynamicSqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {
319                     Throwable translated = DynamicSqlSessionTemplate.this.exceptionTranslator
320                         .translateExceptionIfPossible((PersistenceException) unwrapped);
321                     if (translated != null) {
322                         unwrapped = translated;
323                     }
324                 }
325                 throw unwrapped;
326             } finally {
327                 closeSqlSession(sqlSession, DynamicSqlSessionTemplate.this.getSqlSessionFactory());
328             }
329         }
330     }
331  
332 }

SqlSessionContentHolder类代码如下：

 1 package com.sincetimes.slg.framework.util;
 2 
 3 public abstract class SqlSessionContentHolder {
 4 
 5     public final static String SESSION_FACTORY_MASTER = "master";
 6     public final static String SESSION_FACTORY_SLAVE = "slave";
 7     
 8     private static final ThreadLocal<String> contextHolder = new ThreadLocal<String>();  
 9     
10     public static void setContextType(String contextType) {  
11         contextHolder.set(contextType);  
12     }  
13       
14     public static String getContextType() {  
15         return contextHolder.get();  
16     }  
17       
18     public static void clearContextType() {  
19         contextHolder.remove();  
20     } 
21 }

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：

 1 package com.sincetimes.slg.framework.core;
 2 
 3 import org.aspectj.lang.JoinPoint;
 4 import org.aspectj.lang.annotation.Aspect;
 5 import org.aspectj.lang.annotation.Before;
 6 import org.aspectj.lang.annotation.Pointcut;
 7 
 8 import com.sincetimes.slg.framework.util.SqlSessionContentHolder;
 9 
10 @Aspect
11 public class DynamicDataSourceAspect {
12 
13     @Pointcut("execution( * com.sincetimes.slg.dao.*.*(..))")
14     public void pointCut(){
15         
16     }
17     @Before("pointCut()")
18     public void before(JoinPoint jp){
19         String methodName = jp.getSignature().getName();  
20         //dao方法查询走从库
21         if(methodName.startsWith("query") || methodName.startsWith("get") || methodName.startsWith("count") || methodName.startsWith("list")){
22             SqlSessionContentHolder.setContextType(SqlSessionContentHolder.SESSION_FACTORY_SLAVE);
23         }else{
24             SqlSessionContentHolder.setContextType(SqlSessionContentHolder.SESSION_FACTORY_MASTER);
25         }
26     }
27     
28 }