myBatis

一，初识mybatis

1.声明对应表的实体类

package com.mybatis.bean; public class Student { private String id; private String name; private int age; public Student(String id,String name,int age){ this.id = id; this.name = name; this.age = age; } public String getId() { return id; } public void setId(String id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } }

2.声明映射文件表StudentMapper.xml

<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="studentNameSpace"> <!-- resultMap:表示实体类与映射表 type：实体类全路徑名 id:为实体类与表的映射取一个唯一的编码 --> <resultMap type="com.mybatis.bean.Student" id="studentMap"> <!-- id标签：映射主键属性 property:实体类的属性名 column:表的字段名 --> <id property="id" column="id"/> <!-- result标签：映射非主键的属性 --> <result property="name" column="name"/> <result property="age" column="age"/> </resultMap> <!-- 插入语句 parameterType:参数类型 --> <insert id="add" parameterType="com.mybatis.bean.Student"> insert into student(id,name,age) values(#{id},#{name},#{age}); </insert> </mapper>

3.Dao文件

public class StudentDao { public void add(Student student){ SqlSession sqlSession = MyBatisUtil.getSqlSession(); sqlSession.insert("studentNameSpace.add",student); sqlSession.commit(); } }

4.MyBatisUtil文件

public class MyBatisUtil { private static ThreadLocal<SqlSession> threadLocal = new ThreadLocal<SqlSession>(); private static SqlSessionFactory sqlSessionFactory; /** * 加载位于src/mybatis.xml配置文件 */ static{ try { Reader reader = Resources.getResourceAsReader("mybatis.xml"); sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader); } catch (IOException e) { e.printStackTrace(); throw new RuntimeException(e); } } /** * 禁止外界通过new方法创建 */ private MyBatisUtil(){} /** * 获取SqlSession */ public static SqlSession getSqlSession(){ //从当前线程中获取SqlSession对象 SqlSession sqlSession = threadLocal.get(); //如果SqlSession对象为空 if(sqlSession == null){ //在SqlSessionFactory非空的情况下，获取SqlSession对象 sqlSession = sqlSessionFactory.openSession(); //将SqlSession对象与当前线程绑定在一起 threadLocal.set(sqlSession); } //返回SqlSession对象 return sqlSession; } /** * 关闭SqlSession与当前线程分开 */ public static void closeSqlSession(){ //从当前线程中获取SqlSession对象 SqlSession sqlSession = threadLocal.get(); //如果SqlSession对象非空 if(sqlSession != null){ //关闭SqlSession对象 sqlSession.close(); //分开当前线程与SqlSession对象的关系，目的是让GC尽早回收 threadLocal.remove(); } } }

5.配置mabatis连接数据库的文件

<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration> <environments default="mysql_development"> <environment id="mysql_development"> <transactionManager type="JDBC"/> <dataSource type="POOLED"> <property name="driver" value="com.mysql.jdbc.Driver"/> <property name="url" value="jdbc:mysql://127.0.0.1:3306/mydb4"/> <property name="username" value="root"/> <property name="password" value="123"/> </dataSource> </environment> </environments> <mappers> <mapper resource="com/mybatis/bean/StudentMapper.xml"></mapper> </mappers> </configuration>

6.测试

public static void main(String[] args) { //测试数据库配置文件是否正确 Connection conn = MyBatisUtil.getSqlSession().getConnection(); System.out.println(conn!=null?"连接成功":"连接失败"); //测试插入一条数据 StudentDao dao = new StudentDao(); dao.add(new Student("0001","daMing",20)); }

二，myBatist的增删改查

1.studentMapper.xml文件的配置

<!-- 插入语句 parameterType:参数类型 --> <insert id="add" parameterType="com.mybatis.bean.Student"> insert into student(id,name,age) values(#{id},#{name},#{age}); </insert> <!-- resultMap:解决bean类和表字段不一致导致的映射问题 --> <select id="add" parameterType="int" resultMap="studentMap"> select s_id,s_name,s_age from student where s_id = #{id}; </select> <!--查询语句 parameterType:请求参数类型 resultType:返回值类型 --> <select id="findById" parameterType="string" resultType="com.mybatis.bean.Student"> select id,name,age from student where id = #{id}; </select> <!-- 查询所有 如果返回结果为list，那么resultType只需要写list里面的类型 --> <select id="findAll" resultType="com.mybatis.bean.Student"> select id,name,age from student; </select> <!-- 更新操作 --> <update id="update" parameterType="com.mybatis.bean.Student"> update student set age = #{age},name = #{name} where id = #{id}; </update> <!--删除--> <delete id="deleteById" parameterType="string"> delete from student where id = #{id}; </delete> <!-- 多参数查询 map:封装多个查询参数 --> <select id="findByLimit" parameterType="map" resultMap="studentMap"> select id,name,age from student limit #{start},#{size}; </select>

2.dao文件

//添加学生 public void add(Student student){ SqlSession sqlSession = MyBatisUtil.getSqlSession(); sqlSession.insert("studentNameSpace.add",student); sqlSession.commit(); } //根据id查询学生 public Student findById(String id){ SqlSession sqlSession = MyBatisUtil.getSqlSession(); try { Student student = sqlSession.selectOne("studentNameSpace.findById",id); sqlSession.commit(); return student; } catch (Exception e) { // TODO: handle exception System.out.println(e.toString()); sqlSession.rollback(); }finally{ MyBatisUtil.closeSqlSession(); } return null; } //查询多个学生 public List<Student> findAll(){ SqlSession sqlSession = MyBatisUtil.getSqlSession(); try { List<Student> students = sqlSession.selectList("studentNameSpace.findAll"); sqlSession.commit(); return students; } catch (Exception e) { // TODO: handle exception System.out.println(e.toString()); sqlSession.rollback(); }finally{ MyBatisUtil.closeSqlSession(); } return null; } //更新学生 public void update(Student student){ SqlSession sqlSession = MyBatisUtil.getSqlSession(); try { sqlSession.update("studentNameSpace.update",student); sqlSession.commit(); } catch (Exception e) { // TODO: handle exception System.out.println(e.toString()); sqlSession.rollback(); }finally{ MyBatisUtil.closeSqlSession(); } } //删除学生 public void deleteById(String id){ SqlSession sqlSession = MyBatisUtil.getSqlSession(); try { sqlSession.delete("studentNameSpace.deleteById",id); sqlSession.commit(); } catch (Exception e) { // TODO: handle exception System.out.println(e.toString()); sqlSession.rollback(); }finally{ MyBatisUtil.closeSqlSession(); } } //分页查询 public List<Student> findByLimit(int start,int size){ SqlSession sqlSession = MyBatisUtil.getSqlSession(); try { Map<String,Integer> map = new HashMap<String, Integer>(); map.put("start", start); map.put("size", size); List<Student> students = sqlSession.selectList("studentNameSpace.findByLimit",map); sqlSession.commit(); return students; } catch (Exception e) { // TODO: handle exception System.out.println(e.toString()); sqlSession.rollback(); }finally{ MyBatisUtil.closeSqlSession(); } return null; }

3.测试

StudentDao dao = new StudentDao(); // dao.add(new Student("0002","xiaoLong",10)); // dao.add(new Student("0003","哈哈",10)); // dao.add(new Student("0004","呵呵",10)); // Student student = dao.findById("0001"); // System.out.println(student.getName()+":"+student.getAge()); /** List<Student> students = dao.findAll(); for (Student student : students) { System.out.println(student.getName()+":"+student.getAge()); }*/ // dao.update(new Student("0003","hehe",10)); dao.deleteById("0004");