1.0 使用 Dao 的實現類,操作數據庫

1.0.1 Dao 開發

（0）定義接口StudentDao 及創建接口的映射文件StudentDao .xm

package com.zep.dao;import com.zep.domain.Student;import java.util.List;public interface StudentDao {List<Student> selectStudents();int insertStudent(Student student);int updateStudent(Student student);int deleteStudent(int id); } <?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.zep.dao.StudentDao"><select id="selectStudents" resultType="com.zep.domain.Student">select * from student order by id;</select><insert id="insertStudent">insert into student values(#{id},#{name},#{email},#{age})</insert><update id="updateStudent">update student set age = #{age} where id=#{id}</update><delete id="deleteStudent">delete from student where id=#{studentId}</delete> </mapper>

（1） 創建 Dao 接口實現類

public class StudentDaoImpl implements StudentDao

（2） 實現接口中 select 方法

@Overridepublic List<Student> selectStudents() {// 1.獲取SqlSession對象SqlSession sqlSession = MybatisUtils.getSqlSession();String sqlId = "com.zep.dao.StudentDao.selectStudents";// 2.執行sql語句，使用SqlSession類的方法List<Student> students = sqlSession.selectList(sqlId);/*for (Student student : students) {System.out.println(student);}*/// 3.關閉sqlSession.close();return students;}

測試查詢操作:
MyBatisTest 類中創建 StudentDaoImpl 對象

public class TestMybatis {@Testpublic void testSelectStudents() {StudentDaoImpl dao = new StudentDaoImpl();List<Student> students = dao.selectStudents();for (Student student : students) {System.out.println(student);}} }

（3） 實現接口中 insert 方法

@Overridepublic int insertStudent(Student student) {// 1.獲取SqlSession對象SqlSession sqlSession = MybatisUtils.getSqlSession();String sqlId = "com.zep.dao.StudentDao.insertStudent";// 2.執行sql語句，使用SqlSession類的方法int nums = sqlSession.insert(sqlId,student);// 3.提交事務sqlSession.commit();// 4.關閉sqlSession.close();return nums;}

測試 insert

@Testpublic void testInsertStudent() {StudentDaoImpl dao = new StudentDaoImpl();Student student = new Student();student.setId(1003);student.setName("zep");student.setEmail("zep@qq.com");student.setAge(22);int nums = dao.insertStudent(student);System.out.println("添加對象的數量：" + nums);}

（4） 實現接口中 update 方法

@Override public int updateStudent(Student student) {SqlSession session = MybatisUtils.getSqlSession();int nums = session.update("com.zep.dao.StudentDao.updateStudent",student);session.commit();session.close();return nums;}

測試 update

@Test public void testUpdateStudent() {StudentDaoImpl dao = new StudentDaoImpl();Student student = new Student();student.setId(1004);student.setAge(222);int nums = dao.updateStudent(student);System.out.println("使用Dao修改數據：" + nums);}

（5） 實現接口中 delete 方法

@Override public int deleteStudent(int id) {SqlSession session = MybatisUtils.getSqlSession();int nums = session.delete("com.zep.dao.StudentDao.deleteStudent",id);session.commit();session.close();return nums;}

測試 delete

@Testpublic void testDeleteStudent() {StudentDaoImpl dao = new StudentDaoImpl();int nums = dao.deleteStudent(1005);System.out.println("使用Dao刪除的數據：" + nums);}

項目完整代碼如下：

pom.xml:

<?xml version="1.0" encoding="UTF-8"?><project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>com.zep</groupId><artifactId>ch02-mybatis-dao</artifactId><version>1.0-SNAPSHOT</version><properties><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding><maven.compiler.source>1.8</maven.compiler.source><maven.compiler.target>1.8</maven.compiler.target></properties><dependencies><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.11</version><scope>test</scope></dependency><!--mybatis依賴--><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.5.1</version></dependency><!--mysql驅動--><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.1.9</version></dependency></dependencies><build><resources><resource><directory>src/main/java</directory><!--所在的目錄--><includes><!--包括目錄下的.properties,.xml 文件都會掃描到--><include>**/*.properties</include><include>**/*.xml</include></includes><filtering>false</filtering></resource></resources><plugins><plugin><artifactId>maven-compiler-plugin</artifactId><version>3.1</version><configuration><source>1.8</source><target>1.8</target></configuration></plugin></plugins></build></project>

Student .java:

package com.zep.domain; // 推薦和表名一樣，容易記憶 public class Student {// 定義屬性，目前要求是 屬性名和列名保持一致private Integer id;private String name;private String email;private Integer age;public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getEmail() {return email;}public void setEmail(String email) {this.email = email;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}@Overridepublic String toString() {return "Student{" +"id=" + id +", name='" + name + '\'' +", email='" + email + '\'' +", age=" + age +'}';} }

mybatis.xml:

<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration><!--mybatis.xml 文件加入日志配置，可以在控制臺輸出執行的 sql 語句和參數--><settings><setting name="logImpl" value="STDOUT_LOGGING"/></settings><environments default="mysql"><environment id="mysql"><transactionManager type="JDBC"/><dataSource type="POOLED"><!--數據庫的驅動類名--><property name="driver" value="com.mysql.jdbc.Driver"/><!--連接數據庫的url字符串--><property name="url" value="jdbc:mysql://localhost:3306/ssm"/><!--訪問數據庫的用戶名--><property name="username" value="root"/><!--密碼--><property name="password" value="root"/></dataSource></environment></environments><mappers><mapper resource="com/zep/dao/StudentDao.xml"/></mappers> </configuration>

MybatisUtils .java:

package com.zep.utils;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 java.io.IOException; import java.io.InputStream;public class MybatisUtils {private static SqlSessionFactory factory = null;/*靜態代碼塊：執行優先級高于非靜態的初始化塊，它會在類初始化的時候執行一次，執行完成便銷毀*///使用 靜態塊 創建一次 SqlSessionFactorystatic {String config = "mybatis.xml"; //需要和你的項目中的文件名一樣try {//讀取配置文件InputStream in = Resources.getResourceAsStream(config);//創建SqlSessionFactory對象，使用SqlSessionFactoryBuilderfactory = new SqlSessionFactoryBuilder().build(in);} catch (IOException e) {e.printStackTrace();}}// 獲取SqlSession對象的方法public static SqlSession getSqlSession() {SqlSession sqlSession = null;if (factory != null) {sqlSession = factory.openSession(); // 非自動提交事務}return sqlSession;} }

StudentDao .java:

package com.zep.dao;import com.zep.domain.Student;import java.util.List;public interface StudentDao {List<Student> selectStudents();int insertStudent(Student student);int updateStudent(Student student);int deleteStudent(int id); }

StudentDao.xml:

<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.zep.dao.StudentDao"><select id="selectStudents" resultType="com.zep.domain.Student">select * from student order by id;</select><insert id="insertStudent">insert into student values(#{id},#{name},#{email},#{age})</insert><update id="updateStudent">update student set age = #{age} where id=#{id}</update><delete id="deleteStudent">delete from student where id=#{studentId}</delete> </mapper>

StudentDaoImpl .java:

package com.zep.dao.Impl;import com.zep.dao.StudentDao; import com.zep.domain.Student; import com.zep.utils.MybatisUtils; import org.apache.ibatis.session.SqlSession;import java.util.List;public class StudentDaoImpl implements StudentDao {@Overridepublic List<Student> selectStudents() {// 1.獲取SqlSession對象SqlSession sqlSession = MybatisUtils.getSqlSession();String sqlId = "com.zep.dao.StudentDao.selectStudents";// 2.執行sql語句，使用SqlSession類的方法List<Student> students = sqlSession.selectList(sqlId);/*for (Student student : students) {System.out.println(student);}*/// 3.關閉sqlSession.close();return students;}@Overridepublic int insertStudent(Student student) {// 1.獲取SqlSession對象SqlSession sqlSession = MybatisUtils.getSqlSession();String sqlId = "com.zep.dao.StudentDao.insertStudent";// 2.執行sql語句，使用SqlSession類的方法int nums = sqlSession.insert(sqlId,student);// 3.提交事務sqlSession.commit();// 4.關閉sqlSession.close();return nums;}public int updateStudent(Student student) {SqlSession session = MybatisUtils.getSqlSession();int nums = session.update("com.zep.dao.StudentDao.updateStudent",student);session.commit();session.close();return nums;}@Overridepublic int deleteStudent(int id) {SqlSession session = MybatisUtils.getSqlSession();int nums = session.delete("com.zep.dao.StudentDao.deleteStudent",id);session.commit();session.close();return nums;} }

TestMybatis .java:

package com.zep;import com.zep.dao.Impl.StudentDaoImpl; import com.zep.domain.Student; import org.junit.Test;import java.util.List;public class TestMybatis {@Testpublic void testSelectStudents() {//com.zep.dao.StudentDaoStudentDaoImpl dao = new StudentDaoImpl();/*** 調用List<Student> students = dao.selectStudents();* 1.dao對象，類型是StudentDao,可以獲取到它的全限定類名為：com.zep.dao.StudentDao* 這個全限定名稱和StudentDao.xml文件中mapper的namespace的值是一樣的** 2.方法名稱，selectStudents，這個方法就是StudentDao.xml文件中mapper標簽下的子標簽中id的值selectStudents** 3.通過dao中方法的返回值也可以確定Mybatis要調用的SqlSession的方法* 如果返回值是List,調用的是SqlSession.selectList()方法。* 如果返回值是int,或者是非List的，看mapper文件中的標簽是<insert>,<update>* 就會調用SqlSession的insert()，update()等方法** mybatis的動態代理：mybatis根據dao的方法調用，獲取執行sql語句的信息。* mybatis根據你的dao接口，創建出一個dao接口的實現類，并創建這個類的對象來完成* SqlSession調用方法，訪問數據庫。*/List<Student> students = dao.selectStudents();for (Student student : students) {System.out.println(student);}}@Testpublic void testInsertStudent() {StudentDaoImpl dao = new StudentDaoImpl();Student student = new Student();student.setId(1005);student.setName("zep");student.setEmail("zep@qq.com");student.setAge(22);int nums = dao.insertStudent(student);System.out.println("添加對象的數量：" + nums);}@Testpublic void testUpdateStudent() {StudentDaoImpl dao = new StudentDaoImpl();Student student = new Student();student.setId(1004);student.setAge(222);int nums = dao.updateStudent(student);System.out.println("使用Dao修改數據：" + nums);}@Testpublic void testDeleteStudent() {StudentDaoImpl dao = new StudentDaoImpl();int nums = dao.deleteStudent(1005);System.out.println("使用Dao刪除的數據：" + nums);}}

1.0.2 傳統 Dao 開發方式的分析

在前面例子中自定義 Dao 接口實現類時發現一個問題：Dao 的實現類其實并沒有干什么實質性的工作，它僅僅就是通過 SqlSession 的相關 API 定位到映射文件 mapper （StudentDao.xml）中相應 id 的 SQL 語句，真正對 DB 進行操作的工作其實是由框架通過 mapper 中的 SQL 完成的。

所以，MyBatis 框架就拋開了 Dao 的實現類，直接定位到映射文件 mapper 中的相應 SQL 語句，對DB 進行操作。這種對 Dao 的實現方式稱為 Mapper 的動態代理方式。

Mapper 動態代理方式無需程序員實現 Dao 接口，不需要我們自己編寫Dao接口的實現類。接口是由 MyBatis 結合映射文件自動生成的動態代理實現的

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