entity層代碼不變，因?yàn)槭莾?yōu)化,所以在dao層新增了一個(gè)通過(guò)id查詢用戶的功能，現(xiàn)在來(lái)演示一下優(yōu)化前后的代碼對(duì)比，希望你們喜歡

entity層代碼不變，dao層中的UserMapper中添加一個(gè)方法

/*** 根據(jù)id查詢用戶*/User findUserById(int id);

在UserMapper.xml映射文件中添加

<select parameterType='int' resultType='com.vg.entity.User'> select * from user where id = #{id}; </select>

在test層中的test中使用沒有優(yōu)化的代碼展示

package com.vg.test;import com.vg.dao.UserMapper;import com.vg.entity.User;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import org.junit.Test;import java.io.InputStream;import java.util.List;/** * 測(cè)試類 */public class TestUserMapper {/** * 測(cè)試方法：查詢所有學(xué)生 * SqlSessionFactoryBuilder => SqlSessionFactory => SqlSession：相當(dāng)于JDBC中的Connection對(duì)象，提供了操作數(shù)據(jù)庫(kù)的CRUD方法 */@Testpublic void testFindAllUsers()throws Exception{// 1. 通過(guò)Resources類，加載sqlMapConfig.xml，得到文件輸入流對(duì)象// Resources類作用：專門讀取src目錄下的資源文件InputStream in = Resources.getResourceAsStream('sqlMapConfig.xml');// 2. 實(shí)例化會(huì)話工廠創(chuàng)建類SqlSessionFactoryBuilderSqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();// 3. 通過(guò)會(huì)話工廠創(chuàng)建類，讀取上面的輸入流，得到會(huì)話工廠SqlSessionFactory類SqlSessionFactory sqlSessionFactory = builder.build(in);// 4. 使用SqlSessionFactory對(duì)象，創(chuàng)建SqlSession對(duì)象// a) 它相當(dāng)于JDBC中的Connection對(duì)象，提供了操作數(shù)據(jù)庫(kù)的CRUD方法// b) 它提供了一個(gè)getMapper()方法，獲取接口的實(shí)現(xiàn)對(duì)象。SqlSession sqlSession = sqlSessionFactory.openSession();// 5. 獲取接口 UserMapper 實(shí)現(xiàn)類對(duì)象（代理對(duì)象）UserMapper userMapper = sqlSession.getMapper(UserMapper.class);System.out.println('userMapper = ' +userMapper);// 6. 執(zhí)行數(shù)據(jù)庫(kù)的查詢操作，輸出用戶信息List<User> userList = userMapper.findAllUsers();for (User user : userList) {System.out.println(user);}// 7. 關(guān)閉會(huì)話，釋放資源。sqlSession.close();}@Testpublic void testFindUserById()throws Exception{// 1. 通過(guò)Resources類，加載sqlMapConfig.xml，得到文件輸入流對(duì)象// Resources類作用：專門讀取src目錄下的資源文件InputStream in = Resources.getResourceAsStream('sqlMapConfig.xml');// 2. 實(shí)例化會(huì)話工廠創(chuàng)建類SqlSessionFactoryBuilderSqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();// 3. 通過(guò)會(huì)話工廠創(chuàng)建類，讀取上面的輸入流，得到會(huì)話工廠SqlSessionFactory類SqlSessionFactory sqlSessionFactory = builder.build(in);// 4. 使用SqlSessionFactory對(duì)象，創(chuàng)建SqlSession對(duì)象// a) 它相當(dāng)于JDBC中的Connection對(duì)象，提供了操作數(shù)據(jù)庫(kù)的CRUD方法// b) 它提供了一個(gè)getMapper()方法，獲取接口的實(shí)現(xiàn)對(duì)象。SqlSession sqlSession = sqlSessionFactory.openSession();// 5. 獲取接口 UserMapper 實(shí)現(xiàn)類對(duì)象（代理對(duì)象）UserMapper userMapper = sqlSession.getMapper(UserMapper.class);System.out.println('userMapper = ' +userMapper);// 6. 調(diào)用接口的方法根據(jù)id查詢用戶User user = userMapper.findUserById(1);System.out.println('user = ' + user);// 7. 關(guān)閉會(huì)話，釋放資源。sqlSession.close();}}

你會(huì)發(fā)現(xiàn)在這倆個(gè)方法中有很多相似的代碼，每次寫都要重新寫，關(guān)鍵是還沒有啥軟用，現(xiàn)在來(lái)看看優(yōu)化之后的代碼

package com.vg.test;import com.vg.dao.UserMapper;import com.vg.entity.User;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import org.junit.After;import org.junit.Before;import org.junit.BeforeClass;import org.junit.Test;import java.io.IOException;import java.io.InputStream;import java.util.List;/** * 測(cè)試類 */public class TestUserMapper {private static SqlSessionFactory sqlSessionFactory =null;private SqlSession sqlSession =null;private UserMapper userMapper =null;// 該方法在所有測(cè)試方法執(zhí)行之前執(zhí)行1次@BeforeClasspublic static void init() throws Exception {// 1. 通過(guò)Resources類，加載sqlMapConfig.xml，得到文件輸入流對(duì)InputStream in = Resources.getResourceAsStream('sqlMapConfig.xml');// 2. 實(shí)例化會(huì)話工廠創(chuàng)建類SqlSessionFactoryBuilder對(duì)象SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();// 3. 根據(jù)字節(jié)輸入流獲取SqlSessionFactory對(duì)象sqlSessionFactory = builder.build(in);}// 該方法會(huì)在每個(gè)測(cè)試方法執(zhí)行之前執(zhí)行1次@Beforepublic void before(){// 4. 獲取SqlSession對(duì)象，等價(jià)連接對(duì)象// true:事務(wù)自動(dòng)提交，false:不自動(dòng)提交,默認(rèn)值sqlSession = sqlSessionFactory.openSession();// 5. 創(chuàng)建接口 實(shí)現(xiàn)類對(duì)象 userMapper = sqlSession.getMapper(UserMapper.class);}/** * 測(cè)試方法：查詢所有學(xué)生 * SqlSessionFactoryBuilder => SqlSessionFactory => SqlSession：相當(dāng)于JDBC中的Connection對(duì)象，提供了操作數(shù)據(jù)庫(kù)的CRUD方法 */@Testpublic void testFindAllUsers() throws Exception{List<User> userList = userMapper.findAllUsers();for (User user : userList) {System.out.println(user);}}@Testpublic void testFindUserById()throws Exception{// 6. 調(diào)用接口的方法根據(jù)id查詢用戶User user = userMapper.findUserById(1);System.out.println('user = ' + user);}@Afterpublic void after() {// 7. 關(guān)閉會(huì)話，釋放資源。sqlSession.close();}}

這樣子是不是比以前的代碼簡(jiǎn)單起來(lái)了呢?

以上就是本文的全部?jī)?nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持好吧啦網(wǎng)。