MyBatis

一、MyBatis架构与项目搭建

● 导入Jar

数据库驱动包：mysql-connector-java-5.1.46-bin.jar

mybatis核心包：mybatis-3.4.6.jar

 

mybatis依赖：

● 准备数据库

● db.properties - mysql驱动配置文件（这样可以优化性能）

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/games_db?useUnicode=true&characterEncoding=UTF-8&useSSL=true
jdbc.username=root
jdbc.password=123456

● 引入log4j.properties文件（测试输出需要）

● 添加mybatis映射配置文件 - sqlMapConfig.xml

配置文件中主要是配置连接数据库和事务管理的内容，文件名可以自定义，默认SqlMapConfig.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>
    <!-- 引入外部配置文件 -->
    <properties resource="db.properties"></properties>
    <!-- 配置别名;推荐使用package包形式来配置别名;包的形式会扫描主包及子包中所有文件;以对象类名为别名,大小写不限,推荐使用小写 -->
    <typeAliases>
        <!-- <typeAlias type="com.sikiedu.beans.User" alias="user" /> -->
        <package name="com.sikiedu.beans" />
    </typeAliases>
    <!-- 配置mybatis运行环境 ; 在集成Spring是不用 -->
    <environments default="development">
        <environment id="development">
            <!-- type="JDBC" 代表使用JDBC的提交和回滚来管理事务 -->
            <transactionManager type="JDBC" />
            <!-- 使用连接池连接数据库 - mybatis提供了3种数据源类型，分别是：POOLED,UNPOOLED,JNDI -->
            <!-- POOLED 表示支持JDBC数据源连接池 ; UNPOOLED 表示不支持数据源连接池 ; JNDI 表示支持外部数据源连接池 -->
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}" />
                <property name="url" value="${jdbc.url}" />
                <property name="username" value="${jdbc.username}" />
                <property name="password" value="${jdbc.password}" />
            </dataSource>
        </environment>
    </environments>
    <!--配置映射器的位置 -->
    <mappers>
        <!-- 单个配置 -->
        <!-- <mapper resource="com/sikiedu/mapper/UserMapper.xml" /> -->
        <!-- <mapper url="file:\D:JavaWorkSpaceJavaEE_SSM_Testssm_mybatissrccomsikiedumapperUserMapper.xml" /> -->
        <!-- <mapper class="com.sikiedu.mapper.UserMapper" /> -->
        <!-- 多配置-以包的形式;推荐使用 -->
        <package name="com.sikiedu.mapper" />
    </mappers>
</configuration>

● 创建数据库对应的实体对象

数据库实体对象

package com.sikiedu.beans;

public class Role {

    private Integer id;
    private String name;
    private Integer level;
    private String roletype;
    private Integer userid;

    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 Integer getLevel() {
        return level;
    }

    public void setLevel(Integer level) {
        this.level = level;
    }

    public String getRoletype() {
        return roletype;
    }

    public void setRoletype(String roletype) {
        this.roletype = roletype;
    }

    public Integer getUserid() {
        return userid;
    }

    public void setUserid(Integer userid) {
        this.userid = userid;
    }

    @Override
    public String toString() {
        return "Role [id=" + id + ", name=" + name + ", level=" + level + ", roletype=" + roletype + ", userid="
                + userid + "]";
    }

}

package com.sikiedu.beans;

import java.util.Date;

public class User {

    private Integer id;
    private String username;
    private String userpassword;
    private Float balance;
    private String grgisterdate;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getUserpassword() {
        return userpassword;
    }

    public void setUserpassword(String userpassword) {
        this.userpassword = userpassword;
    }

    public Float getBalance() {
        return balance;
    }

    public void setBalance(Float balance) {
        this.balance = balance;
    }

    public String getGrgisterdate() {
        return grgisterdate;
    }

    public void setGrgisterdate(String grgisterdate) {
        this.grgisterdate = grgisterdate;
    }

    @Override
    public String toString() {
        return "User [id=" + id + ", username=" + username + ", userpassword=" + userpassword + ", balance=" + balance
                + ", grgisterdate=" + grgisterdate + "]";
    }

}

Vo为关联查询需要 - 一对一、一对多

package com.sikiedu.beans;

import java.util.List;

public class RoleVo extends Role {

    private User user;
    private List<Integer> idList;

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    public List<Integer> getList() {
        return idList;
    }

    public void setList(List<Integer> idList) {
        this.idList = idList;
    }

    @Override
    public String toString() {
        return "RoleVo [ID=" + getId() + "	 name=" + getName() + "	 roletype=" + getRoletype() + "	 user=" + user
                + "]";
    }

}

package com.sikiedu.beans;

import java.util.List;

public class UserVo extends User {
    // 维护一个Role集合
    private List<Role> roleList;

    public List<Role> getRole() {
        return roleList;
    }

    public void setRole(List<Role> roleList) {
        this.roleList = roleList;
    }

    @Override
    public String toString() {
        return "UserVo [ID=" + getId() + "	 username=" + getUsername() + "	 Grgisterdate=" + getGrgisterdate()
                + "	 role=" + roleList + "]";
    }

}

● 创建方法接口XxxxMapper.java And 定义操作数据表的sql映射文件XxxMapper.xml

创建方法接口 - 提供简单的增删改查数据信息。

package com.sikiedu.mapper;

import java.util.List;

import com.sikiedu.beans.Role;
import com.sikiedu.beans.RoleVo;

public interface RoleMapper {

    // 查询所有
    public List<Role> selectAllRole();

    // 通过RoleVo一对一关联查询
    public List<RoleVo> selectAllRoleVo();

    // 多条件查询 通过角色对象中的条件查询角色表
    public List<Role> selectRoleListByRole(Role role);

    // 多条件查询 通过角色对象中的条件查询角色表Trim
    public List<Role> selectRoleListByTrim(Role role);

    // 更新角色表
    public void updateSetRole(Role role);

    // 使用多个ID获取角色列表 By array
    public List<Role> selectRoleListByids(Integer[] ids);

    // 使用多个ID获取角色列表 By list
    public List<Role> selectRoleListByList(List<Integer> idList);

    // 使用多个ID获取角色列表 By RoleVo
    public List<Role> selectRoleListByRoleVo(RoleVo roleVo);

}

package com.sikiedu.mapper;

import java.util.List;

import com.sikiedu.beans.User;
import com.sikiedu.beans.UserVo;

public interface UserMapper {

    // 根据ID查询用户
    public User selectUserById(Integer id);

    // 根据用户名模糊查询用户
    public List<User> selectUserLikeUsername(String username);

    // 同过包装类UserVo查询用户
    public User selectUserByUserVoId(UserVo vo);

    // 查询用户总条数
    public Integer selectUserCount();

    // 查询所有用户包装类
    public List<UserVo> selectAllUserVo();
}

定义操作数据表的sql映射文件

<?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="com.sikiedu.mapper.RoleMapper">

    <sql id="myselect">
        SELECT *
        FROM role
    </sql>

    <resultMap type="Role" id="roleRM">
        <id property="id" column="idrole" />
    </resultMap>
    <select id="selectAllRole" resultMap="roleRM">
        <include refid="myselect"></include>
    </select>

    <resultMap type="RoleVo" id="roleVo">
        <id property="id" column="idrole" />
        <result property="name" column="name" />
        <result property="level" column="level" />
        <result property="roletype" column="roletype" />
        <!-- 一对一关系 -->
        <association property="user" javaType="User">
            <id property="id" column="id" />
            <result property="username" column="username" />
        </association>
    </resultMap>
    <!-- 一对一关联查询 -->
    <select id="selectAllRoleVo" resultMap="roleVo">
        SELECT
        r.idrole,
        r.name,
        r.level,
        r.roletype,
        u.id,
        u.username
        FROM role r
        LEFT JOIN user u
        ON r.idrole = u.id
    </select>

    <!-- 多条件查询 通过角色对象中的条件查询角色表 -->
    <select id="selectRoleListByRole" parameterType="Role" resultMap="roleRM">
        <include refid="myselect"></include>
        <where>
            <if test="level!=null and level!=''">
                level = #{level}
            </if>
            <if test="roletype!=null and roletype!=''">
                AND roletype = #{roletype}
            </if>
            <if test="userid!=null">
                AND userid = #{userid}
            </if>
        </where>
    </select>

    <!--多条件查询 通过角色对象中的条件查询角色表Trim -->
    <select id="selectRoleListByTrim" parameterType="Role" resultMap="roleRM">
        <include refid="myselect"></include>
        <trim prefix="WHERE" suffixOverrides="AND">
            <if test="level!=null and level!=''">
                level = #{level} AND
            </if>
            <if test="roletype!=null and roletype!=''">
                roletype = #{roletype} AND
            </if>
            <if test="userid!=null">
                userid = #{userid}
            </if>
        </trim>
    </select>

    <!-- 更新角色表 -->
    <update id="updateSetRole" parameterType="Role">
        UPDATE role
        <set>
            <if test="name != null and name != ''">
                name = '${name}',
            </if>
            <if test="level != null">
                level = ${level},
            </if>
            <if test="roletype != null and roletype != ''">
                roletype = '${roletype}',
            </if>
            <if test="userid != null">
                userid = ${userid}
            </if>
        </set>
        WHERE
        idrole = #{id}
    </update>

    <!-- 使用多个ID获取角色列表 foreach遍历数组 -->
    <select id="selectRoleListByids" resultMap="roleRM">
        <include refid="myselect"></include>
        WHERE idrole IN
        <foreach collection="array" item="id" open="(" separator="," close=")">
            ${id}
        </foreach>
    </select>

    <!-- 使用多个ID获取角色列表 foreach遍历集合 -->
    <select id="selectRoleListByList" resultMap="roleRM">
        <include refid="myselect"></include>
        WHERE idrole IN
        <foreach collection="list" item="id" open="(" separator="," close=")">
            ${id}
        </foreach>
    </select>

    <select id="selectRoleListByRoleVo" resultMap="roleRM">
        <include refid="myselect"></include>
        WHERE idrole IN
        <foreach collection="list" item="id" open="(" separator="," close=")">
            ${id}
        </foreach>
    </select>
    
</mapper>

<?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="com.sikiedu.mapper.UserMapper">

    <!-- 查询用户 -->
    <select id="selectUserById" parameterType="Integer" resultType="com.sikiedu.beans.User">
        SELECT * FROM user WHERE id = #{id}
    </select>
    <!-- #{}占位符 尽量选用#{}来解决问题 -->
    <!-- ${}字符拼接 or1=1 容易被SQL注入 -->
    <select id="selectUserLikeUsername" parameterType="String" resultType="User">
        <!-- SELECT * FROM coke.user WHERE username LIKE '%${value}%' -->
        SELECT * FROM user WHERE username LIKE "%"#{username}"%"
    </select>

    <!-- 添加用户 -->
    <insert id="insertUser" parameterType="com.sikiedu.beans.User">
        INSERT INTO user VALUES(null,#{username},#{userpassword},#{balance},#{grgisterdate})
    </insert>

    <!-- 修改用户 -->
    <update id="updateUser" parameterType="com.sikiedu.beans.User">
        UPDATE user SET username = #{username} WHERE id = #{id}
    </update>

    <!-- 删除用户 -->
    <delete id="deleteUserById" parameterType="Integer">
        DELETE FROM user WHERE id = #{id}
    </delete>

    <!-- 同过包装类UserVo查询用户 -->
    <select id="selectUserByUserVoId" parameterType="UserVo" resultType="user">
        SELECT * FROM user WHERE id = #{id}
    </select>

    <!-- selectUserCount -->
    <select id="selectUserCount" resultType="Integer">
        SELECT COUNT(*) FROM user
    </select>

    <resultMap type="UserVo" id="userVo">
        <id property="id" column="id" />
        <result property="username" column="username" />
        <result property="grgisterdate" column="grgisterdate" />
        <!-- 一对多关系 -->
        <collection property="roleList" ofType="Role">
            <id property="id" column="idrole" />
            <result property="name" column="name" />
            <result property="roletype" column="roletype" />
        </collection>
    </resultMap>
    <!-- 一对多关联查询 -->
    <select id="selectAllUserVo" resultMap="userVo">
        SELECT
        u.id,
        u.username,
        u.grgisterdate,
        r.idrole,
        r.name,
        r.roletype
        FROM user u
        LEFT JOIN role r
        ON u.id = r.userid
    </select>

</mapper>

映射配置文件里注册映射文件

<!--配置映射器的位置 -->
<mappers>
    <!-- 单个配置 -->
    <!-- <mapper resource="com/sikiedu/mapper/UserMapper.xml" /> -->
    <!-- <mapper url="file:\D:JavaWorkSpaceJavaEE_SSM_Testssm_mybatissrccomsikiedumapperUserMapper.xml" /> -->
    <!-- <mapper class="com.sikiedu.mapper.UserMapper" /> -->
    <!-- 自动扫描包内的Mapper接口与配置文件 - 以包的形式;推荐使用 -->
    <package name="com.sikiedu.mapper" />
</mappers>

● Dao原始开发方式

原始dao开发思路比较简单，写个dao接口和dao实现类即可。

需要向dao实现类中注入sqlSessionFactory，在方法体内通过sqlSessionFactory创建sqlSession。操作完成之后，关闭资源。

为什么在方法体内创建呢？

因为mybatis中sqlSession是线程不安全的。如果在方法外面以成员变量的方式创建，可能会引发线程安全问题。

① dao层接口

package com.sikiedu.dao;

import java.util.List;

import com.sikiedu.beans.User;
import com.sikiedu.beans.UserVo;

public interface UserDao {

    // 根据ID查询用户
    public User selectUserById(Integer id);

    // 根据用户名模糊查询用户
    public List<User> selectUserLikeUsername(String username);

    // 同过包装类UserVo查询用户
    public User selectUserByUserVoId(UserVo vo);

    // 查询用户总条数
    public Integer selectUserCount();

    // 查询所有用户包装类
    public List<UserVo> selectAllUserVo();

}

② dao层接口实现类

package com.sikiedu.dao;

import java.util.List;

import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;

import com.sikiedu.beans.User;
import com.sikiedu.beans.UserVo;

public class UserDaoImpl implements UserDao {

    // SQLSession工厂
    private SqlSessionFactory ssf;

    // 通过构造给ssf赋值
    public UserDaoImpl(SqlSessionFactory ssf) {
        super();
        this.ssf = ssf;
    }

    @Override
    public User selectUserById(Integer id) {

        // 生产一个session
        SqlSession sqlSession = ssf.openSession();
        // 操作数据库
        return sqlSession.selectOne("selectUserById", id);
    }

    @Override
    public List<User> selectUserLikeUsername(String username) {
        SqlSession sqlSession = ssf.openSession();
        return sqlSession.selectList("selectUserLikeUsername", username);
    }

    @Override
    public User selectUserByUserVoId(UserVo vo) {
        SqlSession sqlSession = ssf.openSession();
        return sqlSession.selectOne("selectUserByUserVoId", vo);
    }

    @Override
    public Integer selectUserCount() {
        SqlSession sqlSession = ssf.openSession();
        return sqlSession.selectOne("selectUserCount");
    }

    @Override
    public List<UserVo> selectAllUserVo() {
        SqlSession sqlSession = ssf.openSession();
        return sqlSession.selectList("selectAllUserVo");
    }

}

③ JUnit的测试类

package com.sikiedu.test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import com.sikiedu.beans.User;
import com.sikiedu.beans.UserVo;
import com.sikiedu.dao.UserDaoImpl;

public class UserDaoTest {

    // sqlSession工厂
    private static SqlSessionFactory ssf;

    static {
        String resource = "sqlMapConfig.xml";
        try {
            // 读取配置文件
            InputStream inputStream = Resources.getResourceAsStream(resource);
            // 创建sqlSession工厂
            ssf = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Test // 根据ID查询用户
    public void test1() {

        UserDaoImpl dao = new UserDaoImpl(ssf);
        User user = dao.selectUserById(1);
        System.out.println(user);
    }

    @Test // 同过包装类UserVo查询用户
    public void test2() {

        UserDaoImpl dao = new UserDaoImpl(ssf);
        List<User> list = dao.selectUserLikeUsername("");
        for (User user : list) {
            System.out.println(user);
        }
    }

    @Test // 查询用户总条数
    public void test3() {

        UserDaoImpl dao = new UserDaoImpl(ssf);
        Integer count = dao.selectUserCount();
        System.out.println(count);
    }

    @Test // 查询所有用户包装类
    public void test4() {

        UserDaoImpl dao = new UserDaoImpl(ssf);
        List<UserVo> list = dao.selectAllUserVo();
        for (UserVo vo : list) {
            System.out.println(vo);
        }
    }
}

● 原始Dao开发存在的问题

1、dao接口实现类方法中存在大量重复代码，从设计上来看，应该抽取。
2、调用sqlSession方法时，将satement的id硬编码了，即类似于”test.findUserById”这种，都写死了。
3、sqlSession的方法中，要求传入的参数是Object类型的(泛型)，也就是说如果我传错了参数，编译不会报错，执行的时候才会报错，不利于开发。

● Dao动态代理开发方式

Mapper接口开发方式是基于入门程序的基础上，对 控制程序 进行分层开发，程序员只需要 编写mapper接口 和 Mappe.xml 配置文件即可。

程序员编写mapper接口需要遵循一些开发规范，mybatis可以自动生成mapper接口实现类代理对象。

二、SqlSession的使用范围

● SqlSessionFactoryBuilder

通过SqlSessionFactoryBuilder创建会话工厂SqlSessionFactory
将SqlSessionFactoryBuilder当成一个工具类使用即可，不需要使用单例管理SqlSessionFactoryBuilder。
在需要创建SqlSessionFactory时候，只需要new一次SqlSessionFactoryBuilder即可。

● SqlSessionFactory

通过SqlSessionFactory创建SqlSession，使用单例模式管理sqlSessionFactory（工厂一旦创建，使用一个实例）。
将来mybatis和spring整合后，使用单例模式管理sqlSessionFactory。

● SqlSession

SqlSession是一个面向用户（程序员）的接口。
SqlSession中提供了很多操作数据库的方法：如：selectOne(返回单个对象)、selectList（返回单个或多个对象）、。
SqlSession是线程不安全的，在SqlSesion实现类中除了有接口中的方法（操作数据库的方法）还有数据域属性。
SqlSession最佳应用场合在方法体内，定义成局部变量使用。

三、增删改查操作

读取配置文件，创建sqlSessionFactory，获取sqlSession

// 读取配置文件
String resource = "sqlMapConfig.xml";
InputStream in = Resources.getResourceAsStream(resource);

// 需要sqlSessionFactoryBuilder
SqlSessionFactoryBuilder ssfb = new SqlSessionFactoryBuilder();

// 创建sqlSessionFactory
SqlSessionFactory ssf = ssfb.build(in);

// 生产一个sqlSession
SqlSession sqlSession = ssf.openSession();

♦ 增

<insert id="insertUser" parameterType="com.sikiedu.beans.User">
    INSERT INTO user VALUES(null,#{username},#{userpassword},#{balance},#{grgisterdate})
</insert>

User user = new User();
user.setUsername("天猫");
user.setUserpassword("123456");
user.setBalance(Float.valueOf(1000));
user.setGrgisterdate(new SimpleDateFormat("yyyy-MM-dd").format(new Date(System.currentTimeMillis())));
sqlSession.insert("com.sikiedu.mapper.UserMapper.insertUser", user);
sqlSession.commit();

♦ 删

<delete id="deleteUserById" parameterType="Integer">
    DELETE FROM user WHERE id = #{id}
</delete>

sqlSession.delete("com.sikiedu.mapper.UserMapper.deleteUserById", 100);
sqlSession.commit();

♦ 改

<update id="updateUser" parameterType="com.sikiedu.beans.User">
    UPDATE user SET username = #{username} WHERE id = #{id}
</update>

User user = new User();
user.setId(44);
user.setUsername("阿羊");
sqlSession.update("com.sikiedu.mapper.UserMapper.updateUser", user);
sqlSession.commit();

♦ 查

<!-- #{}占位符 尽量选用#{}来解决问题 -->
<!-- ${}字符拼接 or1=1 容易被SQL注入 -->
<select id="selectUserById" parameterType="Integer" resultType="com.sikiedu.beans.User">
    SELECT * FROM user WHERE id = #{id}
</select>
<select id="selectUserLikeUsername" parameterType="String" resultType="User">
    <!-- SELECT * FROM coke.user WHERE username LIKE '%${value}%' -->
    SELECT * FROM user WHERE username LIKE "%"#{username}"%"
</select>

// 查询用户
// 操作数据库;参数1-要操作的sql语句；参数2-sql语句参数
User user = sqlSession.selectOne("com.sikiedu.mapper.UserMapper.selectUserById", 3);
System.out.println(user);

// 通过username模糊 查询用户
List<User> users = sqlSession.selectList("com.sikiedu.mapper.UserMapper.selectUserLikeUsername", "天");
for (User user : users) {
    System.out.println(user);
}