mybaits入门

1.回顾jdbc开发 orm概述

　　orm是一种解决持久层对象关系映射的规则，而不是一种具体技术。jdbc/dbutils/springdao，hibernate/springorm，mybaits同属于ORM解决方案之一。

2.mybaits

　　mybatis基于jdbc，兼顾难易度和速度。

3.mybatis快速入门

　　导入lib包

　　在src目录下配置mybatis.cfg.xml

<?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>
    <!--加载类路径下的属性文件-->
    <properties resource="db.properties">
    </properties>
    <!--设置类型别名-->
    <typeAliases>
        <typeAlias type="app04.Student" alias="student"/>
    </typeAliases>
    <!--设置默认连接环境信息-->
    <environments default="oracle_developer">
        <!--连接环境信息，取一个唯一的名字-->
        <environment id="mysql_developer">
            <!--事务管理方式-->
            <transactionManager type="jdbc"></transactionManager>
            <!--使用连接池获取-->
            <dataSource type="pooled">
                <!--配置与数据库交互的4个必要属性-->
                <property name="driver" value="${mysql.driver}"/>
                <property name="url" value="${mysql.url}"/>
                <property name="username" value="${mysql.username}"/>
                <property name="password" value="${mysql.password}"/>
            </dataSource>
        </environment>
        <environment id="oracle_developer">
            <!--事务管理方式-->
            <transactionManager type="jdbc"></transactionManager>
            <!--使用连接池获取-->
            <dataSource type="pooled">
                <!--配置与数据库交互的4个必要属性-->
                <property name="driver" value="oracle.jdbc.driver.OracleDriver"/>
                <property name="url" value="jdbc:oracle:thin:@127.0.0.1:1521:orcl"/>
                <property name="username" value="scott"/>
                <property name="password" value="tiger"/>
            </dataSource>
        </environment>
    </environments>
    <!--加载映射文件-->
    <mappers>
        <mapper resource="app04/StudentMapper.xml"/>
        <mapper resource="app09/StudentMapper.xml"/>
        <mapper resource="app10/StudentMapper.xml"/>
        <mapper resource="app11/StudentMapper.xml"/>
    </mappers>
</configuration>

　　实体类

　　配置映射文件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">
    <!--映射实体与表-->
    <!--type表示实体的全路径名
        id为实体与表的映射取一个唯一的编号-->
    <resultMap id="studentMap" type="app04.Student">
        <!--id标签映射主键属性，result标签映射非主键属性
            property表示实体的属性名
            column表示表的字段名-->
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="sal" column="sal"/>
    </resultMap>
    <!--insert属性：要书写insert语句
        id表示为insert语句取一个唯一编号
        parameterType表示要执行的dao中的方法的参数，如果是类的话，必须使用全路径名-->
    <insert id="add1">
        INSERT INTO students(id,name,sal) values(1,"haha",7000)
    </insert>
    <insert id="add2" parameterType="student">
        INSERT INTO students(id,name,sal) values(#{id},#{name},#{sal})
    </insert>
</mapper>

　　获取连接

public class MybatisUtil {
    private static ThreadLocal<SqlSession> threadLocal = new ThreadLocal<SqlSession>();
    private static SqlSessionFactory sqlSessionFactory;
    //加载位于mybatis.xml配置文件
    static{
        try {
            Reader reader = Resources.getResourceAsReader("mybatis.cfg.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    public static SqlSession getSqlSession(){
                SqlSession sqlSession = threadLocal.get();
        if(sqlSession == null){
            sqlSession = sqlSessionFactory.openSession();
            //将session与当前线程绑定在一起
            threadLocal.set(sqlSession);
        }
        return sqlSession;
    }
    //关闭当前sqlsession，与当前线程分离
    public static void closeSqlSession(){
        SqlSession sqlSession = threadLocal.get();
        if(sqlSession!=null){
            sqlSession.close();
            //分离，目的是为了尽早垃圾回收
            threadLocal.remove();
        }
    }

}

　　dao

    public void add1() throws Exception{
        SqlSession sqlSession = null;
        try {
            sqlSession = MybatisUtil.getSqlSession();
            //默认事务开始，读取StudentMapper.xml映射文件中的sql语句
            int i = sqlSession.insert("studentNamespace.add1");
            sqlSession.commit();
            System.out.println("本次操作影响了"+i+"行");
        }catch (Exception e){
            sqlSession.rollback();
            throw e;
        }finally {
            MybatisUtil.closeSqlSession();
        }
    }
    public void add2(Student student) throws Exception{
        SqlSession sqlSession = null;
        try {
            sqlSession = MybatisUtil.getSqlSession();
            //默认事务开始，读取StudentMapper.xml映射文件中的sql语句
            sqlSession.insert("studentNamespace.add2",student);
            sqlSession.commit();
        }catch (Exception e){
            sqlSession.rollback();
            throw e;
        }finally {
            MybatisUtil.closeSqlSession();
        }
    }

4.mybatis工作流程

1）通过Reader对象读取src目录下的mybatis.cfg.xml配置文件(该文本的位置和名字可任意)

2）通过SqlSessionFactoryBuilder对象创建SqlSessionFactory对象

3）从当前线程中获取SqlSession对象

4）事务开始，在mybatis中默认

5）通过SqlSession对象读取StudentMapper.xml映射文件中的操作编号，从而读取sql语句

6）事务提交，必写

7）关闭SqlSession对象，并且分开当前线程与SqlSession对象，让GC尽早回收

5基于MybatisUtil工具类，完成CURD操作

　　映射配置文件

<?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="app09.Student">
    <resultMap id="studentMap" type="app09.Student">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="sal" column="sal"/>
    </resultMap>
    <insert id="add" parameterType="app09.Student">
        INSERT  INTO students(id,name, sal) VALUES(#{id},#{name},#{sal})
    </insert>
    <!--如果参数不是实体，只是普通变量，#中的参数名可以随便写-->
    <select id="findById" parameterType="int" resultType="app09.Student">
        SELECT ID,NAME,SAL FROM students WHERE id = #{xxx}
    </select>

    <select id="findAll" resultType="app09.Student">
        SELECT ID,NAME,SAL FROM students
    </select>

    <update id="update" parameterType="app09.Student">
        UPDATE students SET name=#{name},sal=#{sal} WHERE id=#{id}
    </update>
    <delete id="delete" parameterType="app09.Student">
        DELETE  FROM students WHERE  ID=#{id}
    </delete>
</mapper>

　　dao

    public void add(Student student) throws Exception{
        SqlSession sqlSession = null;
        try {
            sqlSession = MybatisUtil.getSqlSession();
            sqlSession.insert(Student.class.getName()+".add",student);
            sqlSession.commit();
        }catch (Exception e){
            sqlSession.rollback();
            throw e;
        }finally {
            MybatisUtil.closeSqlSession();
        }
    }
    private Student findById(int id) {
        Student student= null;
        SqlSession sqlSession = null;
        try {
            sqlSession = MybatisUtil.getSqlSession();
            student = sqlSession.selectOne(Student.class.getName() + ".findById", id);
            sqlSession.commit();
        }catch (Exception e){
            sqlSession.rollback();
            throw e;
        }finally {
            MybatisUtil.closeSqlSession();
        }
        return student;

    }

    private List<Student> findAll() {
        List<Student> students = new ArrayList<>();
        SqlSession sqlSession = null;
        try {
            sqlSession = MybatisUtil.getSqlSession();
            students = sqlSession.selectList(Student.class.getName() + ".findAll");
            sqlSession.commit();
        }catch (Exception e){
            sqlSession.rollback();
            throw e;
        }finally {
            MybatisUtil.closeSqlSession();
        }
        return students;
    }
    private void update(Student student) {
        SqlSession sqlSession = null;
        try {
            sqlSession = MybatisUtil.getSqlSession();
            sqlSession.update(Student.class.getName()+".update",student);
            sqlSession.commit();
        }catch (Exception e){
            sqlSession.rollback();
            throw e;
        }finally {
            MybatisUtil.closeSqlSession();
        }
    }
    private void delete(Student student) {
        SqlSession sqlSession = null;
        try {
            sqlSession = MybatisUtil.getSqlSession();
            sqlSession.delete(Student.class.getName()+".delete",student);
            sqlSession.commit();
        }catch (Exception e){
            sqlSession.rollback();
            throw e;
        }finally {
            MybatisUtil.closeSqlSession();
        }
    }

6.分页查询(mysql,oracle)

　　映射配置文件

mysql

    <select id="findAllWithFy" parameterType="map" resultMap="studentMap">
        SELECT id,name,sal FROM students LIMIT #{start},#{size}
    </select>

oracle

    <select id="findAllWithFyByOracle" parameterType="map" resultMap="studentMap">
        SELECT ID,NAME,SAL
        FROM (SELECT ROWNUM IDS,ID,NAME,SAL
            FROM STUDENTS
            WHERE ROWNUM &lt; #{end})
        WHERE IDS &gt; #{start}
    </select>

　　dao

    public List<Student> findAllWithFy(int start,int size){
        List<Student> students = new ArrayList<>();
        SqlSession sqlSession = null;
        try {
            sqlSession = MybatisUtil.getSqlSession();
            Map<String, Object> map = new LinkedHashMap<>();
            map.put("start",start);
            map.put("size",size);
            students = sqlSession.selectList(Student.class.getName()+".findAllWithFy",map);
            sqlSession.commit();
            return students;
        }catch (Exception e){
            sqlSession.rollback();
            throw e;
        }finally {
            MybatisUtil.closeSqlSession();
        }
    }

7.动态SQL操作之查询

　　映射配置文件

    <select id="findAll" parameterType="map" resultMap="studentMap">
        SELECT ID,NAME,SAL FROM STUDENTS
        <where>
            <if test="pid!=null">
                and ID = #{pid}
            </if>
            <if test="pname!=null">
                and NAME = #{pname}
            </if>
            <if test="psal != null">
                AND SAL &lt; #{psal}
            </if>
        </where>
    </select>

　　dao

    public List<Student> findAll(Integer id ,String name,Double sal){
        List<Student> students = new ArrayList<>();
        SqlSession sqlSession = null;
        try {
            sqlSession = MybatisUtil.getSqlSession();
            Map<String, Object> map = new LinkedHashMap<>();
            map.put("pid",id);
            map.put("pname",name);
            map.put("psal",sal);
            students = sqlSession.selectList(Student.class.getName()+".findAll",map);
            sqlSession.commit();
            return students;
        }catch (Exception e){
            sqlSession.rollback();
            throw new RuntimeException(e);
        }finally {
            MybatisUtil.closeSqlSession();
        }
    }

8.动态SQL操作之更新

　　映射配置文件

    <update id="update" parameterType="map">
        UPDATE STUDENTS
        <set>
            <if test="pname!=null">
                name = #{pname},
            </if>
            <if test="psal != null">
                sal = #{psal},
            </if>
        </set>
        WHERE id = #{pid}
    </update>

　　dao

    public void update(Student student){
        SqlSession sqlSession = null;
        try {
            sqlSession = MybatisUtil.getSqlSession();
            Map<String, Object> map = new LinkedHashMap<>();
            map.put("pid",student.getId());
            map.put("pname",student.getName());
            map.put("psal",student.getSal());
            sqlSession.update(Student.class.getName()+".update",map);
            sqlSession.commit();
        }catch (Exception e){
            sqlSession.rollback();
            throw new RuntimeException(e);
        }finally {
            MybatisUtil.closeSqlSession();
        }
    }

9.动态SQL操作之删除

　　映射配置文件

   <delete id="deleteAll" >
        DELETE FROM  students WHERE ID IN
        <foreach collection="array" open="(" close=")" separator="," item="ids">
            #{ids}
        </foreach>
    </delete>

　　dao

   public void deleteAll(int... ids)throws Exception{
        SqlSession sqlSession = null;
        try {
            sqlSession = MybatisUtil.getSqlSession();
            sqlSession.delete(Student.class.getName()+".deleteAll",ids);
            sqlSession.commit();
        }catch (Exception e){
            sqlSession.rollback();
            throw new RuntimeException(e);
        }finally {
            MybatisUtil.closeSqlSession();
        }
    }

10.动态SQL操作之插入

　　映射配置文件

    <!--sql片段-->
    <sql id="key">
        <trim suffixOverrides=",">
            <if test="id != null">
                id,
            </if>
            <if test="name != null">
                name,
            </if>
            <if test="sal != null">
                sal,
            </if>
        </trim>
    </sql>
    <sql id="value">
        <trim suffixOverrides=",">
            <if test="id != null">
                #{id},
            </if>
            <if test="name != null">
                #{name},
            </if>
            <if test="sal != null">
                #{sal},
            </if>
        </trim>
    </sql>
    <insert id="insert" parameterType="app11.Student">
        INSERT INTO students(<include refid="key"/>) values (<include refid="value"/>)
    </insert>

　　dao

    public void deleteList(List<Integer> ids)throws Exception{
        SqlSession sqlSession = null;
        try {
            sqlSession = MybatisUtil.getSqlSession();
            sqlSession.delete(Student.class.getName()+".deleteList",ids);
            sqlSession.commit();
        }catch (Exception e){
            sqlSession.rollback();
            throw new RuntimeException(e);
        }finally {
            MybatisUtil.closeSqlSession();
        }
    }