10.1SqlSession的使用范圍10.2原始DAO開發(fā)方法10.3Mapper接口開發(fā)方法10.1SqlSession的使用范圍10.1.1SqlSessionFactoryBuilderSqlSessionFactoryBuilder用于創(chuàng)建SqlSessionFacoty，一旦SqlSessionFacoty創(chuàng)建完成就不需要SqlSessionFactoryBuilder了。此處可將SqlSessionFactoryBuilder當(dāng)成一個(gè)工具類使用，其最佳使用范圍是方法范圍即方法體內(nèi)局部變量。10.1.2SqlSessionFactorySqlSessionFactory是一個(gè)接口，接口中定義了openSession的不同重載方法，SqlSessionFactory的最佳使用范圍是整個(gè)應(yīng)用運(yùn)行期間，一旦創(chuàng)建后可以重復(fù)使用，通常以單例模式管理SqlSessionFactory。10.1.3SqlSessionSqlSession是一個(gè)面向用戶的接口，定義了數(shù)據(jù)庫(kù)操作，默認(rèn)使用DefaultSqlSession實(shí)現(xiàn)類。執(zhí)行過(guò)程如下：①加載數(shù)據(jù)源等配置信息。Environmentenvironment=configuration.getEnvironment();②創(chuàng)建數(shù)據(jù)庫(kù)鏈接。③創(chuàng)建事務(wù)對(duì)象。④創(chuàng)建Executor，SqlSession所有操作都是通過(guò)Executor完成。MyBatis源碼如下：if(ExecutorType.BATCH==executorType){executor=newBatchExecutor(this,transaction);}elseif(ExecutorType.REUSE==executorType){executor=newReuseExecutor(this,transaction);}else{executor=newSimpleExecutor(this,transaction);}if(cacheEnabled){executor=newCachingExecutor(executor,autoCommit);}⑤SqlSession的實(shí)現(xiàn)類即DefaultSqlSession，此對(duì)象中對(duì)操作數(shù)據(jù)庫(kù)實(shí)質(zhì)上用的是Executor。結(jié)論：每個(gè)線程都應(yīng)該有它自己的SqlSession實(shí)例。SqlSession的實(shí)例不能共享使用，它也是線程不安全的。因此最佳的范圍是請(qǐng)求或方法范圍。絕對(duì)不能將SqlSession實(shí)例的引用放在一個(gè)類的靜態(tài)字段或?qū)嵗侄沃?。打開一個(gè)SqlSession；使用完畢就要關(guān)閉它。通常把這個(gè)關(guān)閉操作放到finally塊中以確保每次都能執(zhí)行關(guān)閉。如下：SqlSessionsession=sqlSessionFactory.openSession();try{//dowork}finally{session.close();}10.2原始DAO開發(fā)方法10.2.1映射文件<?xmlversion="1.0"encoding="UTF-8"?><!DOCTYPEmapperPUBLIC"-////DTDMapper3.0//EN""/dtd/mybatis-3-mapper.dtd"><mappernamespace="test"><!--根據(jù)id獲取用戶信息--><selectid="findUserById"parameterType="int"resultType="cn.itcast.mybatis.po.User">select*fromuserwhereid=#{id}</select><!--添加用戶--><insertid="insertUser"parameterType="cn.itcast.mybatis.po.User"><selectKeykeyProperty="id"order="AFTER"resultType="java.lang.Integer">selectLAST_INSERT_ID()</selectKey>insertintouser(username,birthday,sex,address)values(#{username},#{birthday},#{sex},#{address})</insert></mapper>10.2.2DAO接口PublicinterfaceUserDao{publicUsergetUserById(intid)throwsException;publicvoidinsertUser(Useruser)throwsException;}PublicclassUserDaoImplimplementsUserDao{//注入SqlSessionFactorypublicUserDaoImpl(SqlSessionFactorysqlSessionFactory){this.setSqlSessionFactory(sqlSessionFactory);}

privateSqlSessionFactorysqlSessionFactory;@OverridepublicUsergetUserById(intid)throwsException{SqlSessionsession=sqlSessionFactory.openSession();Useruser=null;try{//通過(guò)SqlSession調(diào)用selectOne方法獲取一條結(jié)果集//參數(shù)1：指定定義的statement的id，參數(shù)2：指定向statement中傳遞的參數(shù)

user=session.selectOne("test.findUserById",1);System.out.println(user);}finally{session.close();}returnuser;}@OverridePublicvoidinsertUser(Useruser)throwsException{SqlSessionsqlSession=sqlSessionFactory.openSession();try{sqlSession.insert("insertUser",user);

sqlSmit();}finally{session.close();}}}10.3Mapper接口開發(fā)方法10.3.1實(shí)現(xiàn)原理Mapper接口開發(fā)方法只需要程序員編寫Mapper接口(相當(dāng)于DAO接口)，由Mybatis框架根據(jù)接口定義創(chuàng)建接口的動(dòng)態(tài)代理對(duì)象，代理對(duì)象的方法體同上邊DAO接口實(shí)現(xiàn)類方法。Mapper接口開發(fā)需要遵循以下規(guī)范：(1)Mapper.xml文件中的namespace與mapper接口的類路徑相同。(2)Mapper接口方法名和Mapper.xml中定義的每個(gè)statement的id相同。(3)Mapper接口方法的輸入?yún)?shù)類型和mapper.xml中定義的每個(gè)sql的parameterType的類型相同。(4)Mapper接口方法的輸出參數(shù)類型和mapper.xml中定義的每個(gè)sql的resultType的類型相同。10.3.2Mapper.xml(映射文件)定義Mapper映射文件UserMapper.xml(內(nèi)容同Users.xml)，需要將namespace的值修改為UserMapper接口路徑。將UserMapper.xml放在classpath的mapper目錄下。<?xmlversion="1.0"encoding="UTF-8"?><!DOCTYPEmapperPUBLIC"-////DTDMapper3.0//EN""/dtd/mybatis-3-mapper.dtd"><mappernamespace="cn.itcast.mybatis.mapper.UserMapper"><!--根據(jù)id獲取用戶信息--><selectid="findUserById"parameterType="int"resultType="cn.itcast.mybatis.po.User">select*fromuserwhereid=#{id}</select><!--自定義條件查詢用戶列表--><selectid="findUserByUsername"parameterType="java.lang.String"resultType="cn.itcast.mybatis.po.User">select*fromuserwhereusernamelike'%${value}%'</select><!--添加用戶--><insertid="insertUser"parameterType="cn.itcast.mybatis.po.User"><selectKeykeyProperty="id"order="AFTER"resultType="java.lang.Integer">selectLAST_INSERT_ID()</selectKey>insertintouser(username,birthday,sex,address)values(#{username},#{birthday},#{sex},#{address})</insert></mapper>10.3.3Mapper.java(接口)/***用戶管理Mapper*/PublicinterfaceUserMapper{//根據(jù)用戶id查詢用戶信息publicUserfindUserById(intid)throwsException;//查詢用戶列表publicList<User>findUserByUsername(Stringusername)throwsException;//添加用戶信息publicvoidinsertUser(Useruser)throwsException;}接口定義有如下特點(diǎn)：(1)Mapper接口方法名和Mapper.xml中定義的statement的id相同。(2)Mapper接口方法的輸入?yún)?shù)類型和mapper.xml中定義的statement的parameterType的類型相同。(3)Mapper接口方法的輸出參數(shù)類型和mapper.xml中定義的statement的resultType的類型相同。10.3.4加載UserMapper.xml文件修改SqlMapConfig.xml文件：<!--加載映射文件--><mappers><mapperresource="mapper/UserMapper.xml"/></mappers>10.3.5測(cè)試PublicclassUserMapperTestextendsTestCase{privateSqlSessionFactorysqlSessionFactory;protectedvoidsetUp()throwsException{//MyBatis配置文件Stringresource="sqlMapConfig.xml";

InputStreaminputStream=Resources.getResourceAsStream(resource);//使用SqlSessionFactoryBuilder創(chuàng)建sessionFactorysqlSessionFactory=newSqlSessionFactoryBuilder().build(inputStream);}PublicvoidtestFindUserById()throwsException{//獲取sessionSqlSessionsession=sqlSessionFactory.openSession();//獲取Mapper接口的代理對(duì)象UserMapperuserMapper=session.getMapper(UserMapper.class);//調(diào)用代理對(duì)象方法Useruser=userMapper.findUserById(1);System.out.println(user);

//關(guān)閉sessionsession.close();}@TestpublicvoidtestFindUserByUsername()throwsException{SqlSessionsqlSession=sqlSessionFactory.openSession();UserMapperuserM