场景：一个读数据源一个读写数据源。
原理：借助spring的【 org.springframework.jdbc.datasource.lookup.abstractroutingdatasource 】这个抽象类实现，看名字可以了解到是一个路由数据源的东西，这个类中有一个方法
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/** * determine the current lookup key. this will typically be * implemented to check a thread-bound transaction context. * <p>allows for arbitrary keys. the returned key needs * to match the stored lookup key type, as resolved by the * {@link #resolvespecifiedlookupkey} method. */ protected abstract object determinecurrentlookupkey(); |
每次去连数据库的时候，spring会调用这个方法去找对应的数据源。返回值即对应的数据源的lookupkey.那么这个lookupkey在哪定义的呢？看下面的 database.xml 的配置
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<!--数据源 读写 --> <bean id= "datasourcerw" class = "org.logicalcobwebs.proxool.proxooldatasource" > <property name= "alias" value= "ihotelrw" ></property> <property name= "delegateproperties" > <value>user=${jdbc.username},password=${jdbc.password} </value> </property> <property name= "user" value= "${jdbc.username}" /> <property name= "password" value= "${jdbc.password}" /> <property name= "driver" value= "${jdbc.driverclassname}" /> <property name= "driverurl" value= "${jdbc.url}" /> <property name= "maximumconnectioncount" value= "${jdbc.maximumconnectioncount}" ></property> <property name= "maximumactivetime" value= "${jdbc.maximumactivetime}" ></property> <property name= "maximumconnectionlifetime" value= "${jdbc.maximumconnectionlifetime}" ></property> <property name= "prototypecount" value= "${jdbc.prototypecount}" ></property> <property name= "housekeepingsleeptime" value= "${jdbc.housekeepingsleeptime}" ></property> <property name= "simultaneousbuildthrottle" value= "${jdbc.simultaneousbuildthrottle}" ></property> <property name= "housekeepingtestsql" value= "${jdbc.housekeepingtestsql}" ></property> <property name= "verbose" value= "${jdbc.verbose}" ></property> <property name= "statistics" value= "${jdbc.statistics}" ></property> <property name= "statisticsloglevel" value= "${jdbc.statisticsloglevel}" ></property> </bean> <!--数据源 读--> <bean id= "datasourcer" class = "org.logicalcobwebs.proxool.proxooldatasource" > <property name= "alias" value= "ihotelr" ></property> <property name= "delegateproperties" > <value>user=${jdbc.r.username},password=${jdbc.r.password} </value> </property> <property name= "user" value= "${jdbc.r.username}" /> <property name= "password" value= "${jdbc.r.password}" /> <property name= "driver" value= "${jdbc.r.driverclassname}" /> <property name= "driverurl" value= "${jdbc.r.url}" /> <property name= "maximumconnectioncount" value= "${jdbc.maximumconnectioncount}" ></property> <property name= "maximumactivetime" value= "${jdbc.maximumactivetime}" ></property> <property name= "maximumconnectionlifetime" value= "${jdbc.maximumconnectionlifetime}" ></property> <property name= "prototypecount" value= "${jdbc.prototypecount}" ></property> <property name= "housekeepingsleeptime" value= "${jdbc.housekeepingsleeptime}" ></property> <property name= "simultaneousbuildthrottle" value= "${jdbc.simultaneousbuildthrottle}" ></property> <property name= "housekeepingtestsql" value= "${jdbc.housekeepingtestsql}" ></property> <property name= "verbose" value= "${jdbc.verbose}" ></property> <property name= "statistics" value= "${jdbc.statistics}" ></property> <property name= "statisticsloglevel" value= "${jdbc.statisticsloglevel}" ></property> </bean> <!-- 动态数据源 --> <bean id= "dynamicdatasource" class = "com.dao.datasource.dynamicdatasource" > <!-- 通过key-value关联数据源 --> <property name= "targetdatasources" > <map> <entry value-ref= "datasourcerw" key= "datasourcekeyrw" ></entry> <entry value-ref= "datasourcer" key= "datasourcekeyr" ></entry> </map> </property> <property name= "defaulttargetdatasource" ref= "datasourcerw" /> </bean> <!--mybatis与spring整合 开始 --> <bean id= "sqlsessionfactory" name= "sqlsessionfactory" class = "org.mybatis.spring.sqlsessionfactorybean" > <property name= "configlocation" value= "classpath:conf/core/sqlmapconfig.xml" /> <property name= "datasource" ref= "dynamicdatasource" /> </bean> |
动态数据源dynamicdatasource中的datasourcekeyrw、datasourcekeyr就是
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protected abstract object determinecurrentlookupkey(); |
这个方法要返回的值。那么如何设置，让这个方法的返回值是根据我们的需要返回datasourcekeyrw、datasourcekeyr呢？由于这个方法没有入参，并且是spring自动调用的，因此考虑使用静态变量存储datasource的key，在调用sql语句前设置静态变量的值，然后在这个方法中得到静态变量的值，返回。又考虑到多线程，同时可能会有很多请求，为避免线程之间相互干扰，考虑使用threadlocal。
先看存储datasourcekey的容器类。
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public class dbcontextholder { /** * 线程threadlocal */ private static threadlocal<string> contextholder = new threadlocal<>(); private string db_type_rw = "datasourcekeyrw" ; private string db_type_r = "datasourcekeyr" ; public string getdbtype() { string db = contextholder.get(); if (db == null ) { db = db_type_rw; // 默认是读写库 } return db; } /** * 设置本线程的dbtype * @param str * @see [相关类/方法](可选) * @since [产品/模块版本](可选) */ public void setdbtype(string str) { contextholder.set(str); } /** * cleardbtype * @title: cleardbtype * @description: 清理连接类型 */ public static void cleardbtype() { contextholder.remove(); } } |
动态数据源的实现类。
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public class dynamicdatasource extends abstractroutingdatasource { /* * (non-javadoc) * @see javax.sql测试数据mondatasource#getparentlogger() */ @override public logger getparentlogger() throws sqlfeaturenotsupportedexception { // todo auto-generated method stub return null; } /** * override determinecurrentlookupkey * <p> * title: determinecurrentlookupkey * </p> * <p> * description: 自动查找datasource * </p> * @return */ @override protected object determinecurrentlookupkey() { return dbcontextholder.getdbtype(); } } |
在dao层中设置数据库类型。
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/** * 添加邮件 * @param sms * @return */ public boolean insertemail(email email) { //根据具体需要设置不同的数据库 dbcontextholder.setdbtype(dbcontextholder.db_type_rw); //dbcontextholder.setdbtype(dbcontextholder.db_type_r); int result = this .getsqlsession().insert(statement + ".addentity" , email); return result == 1 ; } |
在本例中，我们是在dao中指定数据库，我们也可以根据需要在service或者controller中指定db类型，需要记住的是setdbtype是针对线程维度的。要考虑多线程的问题。
总结
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原文链接：https://blog.csdn.net/qq_26562641/article/details/64122643
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