MyBatis使用总结和整合Spring

MyBatis 本是apache的一个开源项目iBatis, 2010年这个项目由apache software foundation 迁移到了google code，并且改名为MyBatis 。2013年11月迁移到Github。iBATIS一词来源于“internet”和“abatis”的组合，是一个基于Java的持久层框架。

MyBatis是支持普通SQL查询，存储过程和高级映射的优秀持久层框架。MyBatis消除了几乎所有的JDBC代码和参数的手工设置以及对结果集的检索封装。MyBatis可以使用简单的XML或注解用于配置和原始映射，将接口和Java的POJO（Plain Old Java Objects，普通的Java对象）映射成数据库中的记录。

1 第一个MyBatis程序

　　然后需要在test数据库中新建测试表user，sql语句如下所示：

create table users (
    id int primary key auto_increment,
    name varchar(20),
    age int
);
insert into users (name, age) values('Tom', 12);
insert into users (name, age) values('Jack', 11);

1.1 定义表对应的实体类

public class User {

    private int id;
    private String name;
    private int age;

    public User() { }

    public User(int id, String name, int age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }

    public int getId() {
        return id;
    }

    public void setId(int 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;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

1.2 定义MyBatista的mybatisConfig.xml配置文件和user表的sql映射文件userMapper.xml

mybatisConfig.xml文件，该文件是在src目录下新建的。

<?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="development">
    <!-- development:开发环境 work:工作模式 -->
    <environment id="development">
        <transactionManager type="JDBC" />
        <!-- 数据库连接方式 -->
        <dataSource type="POOLED">
            <property name="driver" value="com.mysql.jdbc.Driver" />
            <property name="url" value="jdbc:mysql://192.168.1.150/test" />
            <property name="username" value="root" />
            <property name="password" value="123456" />
        </dataSource>
    </environment>
</environments>

<!-- 注册表映射文件 -->
<mappers>
    <mapper resource="com/mybatis/userMapper.xml"/>
</mappers>

</configuration>

userMapper.xml文件，该配置文件在com.mybatis包下，user表对应的实体类User也在com.mybatis包下。

<?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.mybatis.userMapper">
    <!-- 根据id查询一个User对象 -->
    <select id="getUser" parameterType="int" resultType="com.mybatis.User">
        select * from users where id=#{id}
    </select>
    <select id="getUserAll" resultType="com.mybatis.User">
        select * from users
    </select>

    <!-- 插入一个User对象 -->
    <insert id="insertUser" parameterType="com.mybatis.User">
        insert into users (name, age) value(#{name}, #{age})
    </insert>

    <!-- 删除一个User对象 -->
    <delete id="deleteUser" parameterType="int">
        delete from users where id=#{id}
    </delete>

    <!-- 更新一个User对象-->
    <update id="updateUser" parameterType="com.mybatis.User">
        update users set name=#{name}, age=#{age} where id=#{id}
    </update>
</mapper>

测试代码如下：

public class mybaitstest {

    SqlSessionFactory sessionFactory = null;
    SqlSession sqlSession = null;

    {
        String resource = "mybatisConfig.xml";
        // 加载mybatis的配置文件（它也加载关联的映射文件）
        Reader reader = null;
        try {
            reader = Resources.getResourceAsReader(resource);
        } catch (IOException e) {
            e.printStackTrace();
        }
        // 构建sqlSession的工厂
        sessionFactory = new SqlSessionFactoryBuilder().build(reader);
        // 创建能执行映射文件中sql的sqlSession，默认是手动提交事务的，使用自动提交的话加上参数 true
        sqlSession = sessionFactory.openSession(true);
    }

    public void testSelectUser() {
        // 映射sql的标识字符串
        String statement = "com.mybatis.userMapper" + ".getUser";
        // 执行查询返回一个唯一user对象的sql
        User user = sqlSession.selectOne(statement, 1);
        System.out.println(user);
    }

    public void testSelectAll() {
        List<User> users = sqlSession.selectList("com.mybatis.userMapper.getUserAll");
        System.out.println(users);
    }

    public void testInsertUser(User user) {
        int insert = sqlSession.insert("com.mybatis.userMapper.insertUser", user);
        // 如果不是自动提交的话，需要使用 sqlSession。commit()
        System.out.println(insert);
    }

    public void testDeleteUser(int id) {
        int delete = sqlSession.delete("com.mybatis.userMapper.deleteUser", id);
        System.out.println(delete);
    }

    public void testUpdateUser(User user) {
        int update = sqlSession.update("com.mybatis.userMapper.updateUser", user);
        System.out.println(update);
    }

    public static void main(String[] args) throws IOException {

        new mybaitstest().testSelectUser();
    }
}

最后输出结果为：

2 基于注解的方式使用MyBatis

　　基于注解的方式使用MyBatis，首先定义对应表的sql映射接口。

public interface IUserMapper {

    @Insert("insert into users (name, age) value(#{name}, #{age})")
    public int add(User user);

    @Delete("delete from users where id=#{id}")
    public int deleteById(int id);

    @Update("update users set name=#{name}, age=#{age} where id=#{id}")
    public int update(User user);

    @Select("select * from users where id=#{id}")
    public User getById(int id);

    @Select("select * from users")
    public List<User> getAll();
}

　　然后在mybatisConfig.xml配置文件中注册该接口：

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<!-- 注册表映射文件 -->
<mappers>
    <mapper class="com.mybatis.IUserMapper"/>
</mappers>

测试示例：

/**
 * 使用注解测试的方法
 */
public void test() {
    IUserMapper userMapper = sqlSession.getMapper(IUserMapper.class);

    User user = userMapper.getById(1);
    System.out.println(user);
}

3 如何简化配置操作

　　以上两个程序示例都是直接在配置文件中写连接数据库的信息，其实还可以专门把数据库连接信息写到一个db.proteries文件中，然后由配置文件来读取该db.properies文件信息。db.proteries文件内容如下：

user=root
password=123456
driverClass=com.mysql.jdbc.Driver
jdbcUrl=jdbc:mysql://192.168.1.150/test

　　然后在mybatisConfig.xml配置文件中将数据库环境信息更改为如下所示：

<properties resource="db.properties"/>

<environments default="development">
    <!-- development:开发环境 work:工作模式 -->
    <environment id="development">
        <transactionManager type="JDBC" />
        <!-- 数据库连接方式 -->
        <dataSource type="POOLED">
            <property name="driver" value="${driverClass}" />
            <property name="url" value="${jdbcUrl}" />
            <property name="username" value="${user}" />
            <property name="password" value="${password}" />
        </dataSource>
    </environment>
</environments>

　　配置表对应的sql映射文件时，可以使用别名来简化配置，在mybatisConfig.xml中添加如下配置，在userMapper中parameterType就可以配置为"_User"。

<typeAliases>
    <typeAlias type="com.mybatis.User" alias="_User"/>
</typeAliases>

4 字段名与实体类属性名不匹配的冲突

　　新建表和数据，在test数据库中执行以下SQL语句：

create table orders (
    order_id int primary key auto_increment,
    order_no varchar(20),
    order_price float
);
insert into orders (order_no, order_price) values('aaa', 12);
insert into orders (order_no, order_price) values('bbb', 13);
insert into orders (order_no, order_price) values('ccc', 14);

　　创建对应表的类：

public class Order {

    private int i;
    private String no;
    private float price;

    public Order() { }

    public Order(int i, String no, float price) {
        this.i = i;
        this.no = no;
        this.price = price;
    }

    public int getI() {
        return i;
    }

    public void setI(int i) {
        this.i = i;
    }

    public String getNo() {
        return no;
    }

    public void setNo(String no) {
        this.no = no;
    }

    public float getPrice() {
        return price;
    }

    public void setPrice(float price) {
        this.price = price;
    }
}

　　mybaitsConfig.xml配置如下：

<?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>

    <properties resource="db.properties"/>

    <typeAliases>
        <typeAlias type="com.mybatis.Order" alias="Order"/>
    </typeAliases>

    <environments default="development">
        <!-- development:开发环境 work:工作模式 -->
        <environment id="development">
            <transactionManager type="JDBC" />
            <!-- 数据库连接方式 -->
            <dataSource type="POOLED">
                <property name="driver" value="${driverClass}" />
                <property name="url" value="${jdbcUrl}" />
                <property name="username" value="${user}" />
                <property name="password" value="${password}" />
            </dataSource>
        </environment>
    </environments>

    <!-- 注册表映射文件 -->
    <mappers>
        <mapper resource="com/mybatis/orderMapper.xml"/>
    </mappers>

</configuration>

　　接下来配置orderMapper.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="com.mybatis.orderMapper">

    <!-- 根据id查询一个Order对象 -->
    <select id="getOrder" parameterType="int" resultType="Order">
      SELECT order_id id, order_no no, order_price price FROM orders WHERE order_id=#{id}
    </select>

    <!-- 这种解决字段与属性冲突方式较常用 -->
    <select id="getOrder2" parameterType="int" resultType="Order" resultMap="getOrder2Map">
        SELECT * FROM orders WHERE order_id=#{id}
    </select>
    <!--
        resultMap 封装映射关系
            id    专门针对主键
            result 针对一般字段
    -->
    <resultMap id="getOrder2Map" type="Order">
        <id property="id" column="order_id"/>
        <result property="no" column="order_price"/>
        <result property="price" column="order_price"/>
    </resultMap>

</mapper>

测试用例：

public class MyBaitsMain {
    SqlSessionFactory sessionFactory = null;
    SqlSession sqlSession = null;

    {
        String resource = "mybatisConfig.xml";
        // 加载mybatis的配置文件（它也加载关联的映射文件）
        Reader reader = null;
        try {
            reader = Resources.getResourceAsReader(resource);
        } catch (IOException e) {
            e.printStackTrace();
        }
        // 构建sqlSession的工厂
        sessionFactory = new SqlSessionFactoryBuilder().build(reader);
        // 创建能执行映射文件中sql的sqlSession，默认是手动提交事务的，使用自动提交的话加上参数 true
        sqlSession = sessionFactory.openSession(true);
    }

    public static void main(String[] args) {
        String statement = "com.mybatis.orderMapper.getOrder";
        String statement2 = "com.mybatis.orderMapper.getOrder2";

        Order order = new MyBaitsMain().sqlSession.selectOne(statement, 2);
        System.out.println(order);
        order = new MyBaitsMain().sqlSession.selectOne(statement2, 2);
        System.out.println(order);
    }
}

输出结果为：

5 实现关联表查询

5.1 一对一关联

　　这里实现班级id查询班级信息，班级信息中包括老师信息。首先创建表结构：

CREATE TABLE teacher(
    t_id INT PRIMARY KEY AUTO_INCREMENT, 
    t_name VARCHAR(20)
);
CREATE TABLE class(
    c_id INT PRIMARY KEY AUTO_INCREMENT, 
    c_name VARCHAR(20), 
    teacher_id INT
);
ALTER TABLE class ADD CONSTRAINT fk_teacher_id FOREIGN KEY (teacher_id) REFERENCES teacher(t_id);    

INSERT INTO teacher(t_name) VALUES('LS1');
INSERT INTO teacher(t_name) VALUES('LS2');

INSERT INTO class(c_name, teacher_id) VALUES('bj_a', 1);
INSERT INTO class(c_name, teacher_id) VALUES('bj_b', 2);

　　定义表对应的实体类：

public class Teacher {

    private int id;
    private String name;

    public Teacher() {
    }

    public Teacher(int id, String name) {
        this.id = id;
        this.name = name;
    }

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Teacher{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}

Teacher类

public class Classes {

    private int id;
    private String name;
    private Teacher teacher;

    public Classes() {
    }

    public Classes(int id, String name, Teacher teacher) {
        this.id = id;
        this.name = name;
        this.teacher = teacher;
    }

    public int getId() {
        return id;
    }

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

    public Teacher getTeacher() {
        return teacher;
    }

    public void setTeacher(Teacher teacher) {
        this.teacher = teacher;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Classes{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", teacher=" + teacher +
                '}';
    }
}

Classes类

　　定义sql映射文件，需要在mybatisConfig.xml中注册该表映射文件。

<?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.mybatis.classesMapper">

    <!-- 根据班级id查询班级信息（包括老师信息） -->
    <select id="getClasses" parameterType="int" resultMap="ClassesMap">
        SELECT * FROM class c, teacher t WHERE c.teacher_id = t.t_id and c.c_id = #{id}
    </select>
    <!-- 联表查询 -->
    <resultMap id="ClassesMap" type="com.mybatis.Classes">
        <id property="id" column="c_id"/>
        <result property="name" column="c_name"/>
        <association property="teacher" column="teacher_id" javaType="com.mybatis.Teacher">
            <id property="id" column="t_id"/>
            <result property="name" column="t_name"/>
        </association>
    </resultMap>

    <!-- 嵌套查询 -->
    <select id="getClasses2" parameterType="int" resultMap="ClassesMap2">
        SELECT * FROM class WHERE c_id=#{id}
    </select>
    <select id="getTeacher" parameterType="int" resultType="com.mybatis.Teacher">
        SELECT t_id id, t_name  FROM teacher WHERE t_id=#{id}
    </select>
    <resultMap id="ClassesMap2" type="com.mybatis.Classes">
        <id property="id" column="c_id"/>
        <result property="name" column="c_name"/>
        <association property="teacher" column="teacher_id" select="getTeacher">
        </association>
    </resultMap>

</mapper>

classesMapper.xml文件

测试类：

public class MyBaitsMain {
    SqlSessionFactory sessionFactory = null;
    SqlSession sqlSession = null;

    {
        String resource = "mybatisConfig.xml";
        // 加载mybatis的配置文件（它也加载关联的映射文件）
        Reader reader = null;
        try {
            reader = Resources.getResourceAsReader(resource);
        } catch (IOException e) {
            e.printStackTrace();
        }
        // 构建sqlSession的工厂
        sessionFactory = new SqlSessionFactoryBuilder().build(reader);
        // 创建能执行映射文件中sql的sqlSession，默认是手动提交事务的，使用自动提交的话加上参数 true
        sqlSession = sessionFactory.openSession(true);
    }

    public static void main(String[] args) {

        String statement = "com.mybatis.classesMapper.getClasses";
        String statement2 = "com.mybatis.classesMapper.getClasses2";

        Classes classes = new MyBaitsMain().sqlSession.selectOne(statement, 1);
        System.out.println(classes);
        classes = new MyBaitsMain().sqlSession.selectOne(statement2, 1);
        System.out.println(classes);
    }
}

MyBatisMain测试类

输出结果：

5.2 一对多关联

　　这里实现班级id查询班级信息，班级信息中包括老师信息和学生信息。首先创建表结构：

CREATE TABLE student(
    s_id INT PRIMARY KEY AUTO_INCREMENT, 
    s_name VARCHAR(20), 
    class_id INT
);
INSERT INTO student(s_name, class_id) VALUES('xs_A', 1);
INSERT INTO student(s_name, class_id) VALUES('xs_B', 1);
INSERT INTO student(s_name, class_id) VALUES('xs_C', 1);
INSERT INTO student(s_name, class_id) VALUES('xs_D', 2);
INSERT INTO student(s_name, class_id) VALUES('xs_E', 2);
INSERT INTO student(s_name, class_id) VALUES('xs_F', 2);

　　定义表对应的实体类：

public class Student {

private int id;
private String name;

public Student( int id, String name) {
this.id = id;
this.name = name;
}

public Student() {
}

public int getId() {

return id;
}

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

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

@Override
public String toString() {
return "Student{" +
"id =" + id +
", name = ' " + name + '\ '' +
' } ' ;
}
}

　　定义sql映射文件，需要在mybatisConfig.xml中注册该表映射文件。

<?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.mybatis.classesMapper2">

    <select id="getClasses" parameterType="int" resultMap="ClassesMap">
        SELECT * FROM class c, student s, teacher t WHERE c.c_id=s.class_id AND c.c_id=#{id}
    </select>
    <resultMap id="ClassesMap" type="com.mybatis.Classes">
        <id property="id" column="c_id"/>
        <result property="name" column="c_name"/>
        <association property="teacher" javaType="com.mybatis.Teacher">
            <id property="id" column="t_id"/>
            <result property="name" column="t_name"/>
        </association>
        <!--
            collection: 做一对多关联查询的
                ofType: 指定集合中元素对象的类型
        -->
        <collection property="students" ofType="com.mybatis.Student">
            <id property="id" column="s_id"/>
            <result property="name" column="s_name"/>
        </collection>
    </resultMap>

    <!-- 第二种方式 -->
    <select id="getClasses2" resultMap="ClassesMap2">
        SELECT * FROM class WHERE c_id=#{id}
    </select>
    <select id="getTeacher" resultType="com.mybatis.Teacher">
        SELECT t_id id, t_name name FROM teacher WHERE  t_id=#{id}
    </select>
    <select id="getStudent" resultType="com.mybatis.Student">
        SELECT s_id id, s_name name FROM student WHERE  class_id=#{id}
    </select>
    <resultMap id="ClassesMap2" type="com.mybatis.Classes">
        <id property="id" column="c_id"/>
        <result property="name" column="c_name"/>
        <association property="teacher" column="teacher_id" select="getTeacher">
        </association>
        <collection property="students" column="c_id" select="getStudent">
        </collection>
    </resultMap>

</mapper>

　　测试类：

public class MyBaitsMain {
    SqlSessionFactory sessionFactory = null;
    SqlSession sqlSession = null;

    {
        String resource = "mybatisConfig.xml";
        // 加载mybatis的配置文件（它也加载关联的映射文件）
        Reader reader = null;
        try {
            reader = Resources.getResourceAsReader(resource);
        } catch (IOException e) {
            e.printStackTrace();
        }
        // 构建sqlSession的工厂
        sessionFactory = new SqlSessionFactoryBuilder().build(reader);
        // 创建能执行映射文件中sql的sqlSession，默认是手动提交事务的，使用自动提交的话加上参数 true
        sqlSession = sessionFactory.openSession(true);
    }

    public static void main(String[] args) {

        String statement = "com.mybatis.classesMapper2.getClasses";
        String statement2 = "com.mybatis.classesMapper2.getClasses2";

        Classes classes = new MyBaitsMain().sqlSession.selectOne(statement, 1);
        System.out.println(classes);
        classes = new MyBaitsMain().sqlSession.selectOne(statement2, 1);
        System.out.println(classes);
    }
}

输出结果：