Spring Ioc源碼分析系列--Ioc容器BeanFactoryPostProcessor後置處理器分析前言上一篇文章Spring Ioc源碼分析系列--Ioc源碼入口分析已經介紹到Ioc容器的入口refresh()方法，並且分析了refresh()方法裡面的前三個子方法分析了一下。還記得分 ...

Mybatis快速入門

Mybatis開發步驟

添加依賴坐標

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.11</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.1</version>
        </dependency>

編寫POJO映射文件，如UserMapper.xml 可放在resource資源目錄下，註意.和/的區別

<?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="userMapper">
    <select id="findAll" resultType="com.rsk.entity.User">
        select * from user
    </select>
</mapper>

編寫mybatis配置文件，mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <!--數據源環境-->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/test_db?serverTimezone=GMT%2B8"/>
                <property name="username" value="root"/>
                <property name="password" value=""/>
            </dataSource>
        </environment>
    </environments>
    <!--載入映射文件-->
    <mappers>
        <mapper resource="com/rsk/mapper/UserMapper.xml"></mapper>
    </mappers>
</configuration>

編寫測試類

public class Test1 {
    @Test
    public void test1() throws IOException {
        //獲得核心配置文件
        InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");
        //獲得sqlSession工廠
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        //獲得session會話對象
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //執行操作
        List<User> users = sqlSession.selectList("userMapper.findAll");
        System.out.println(users);
        //釋放資源
        sqlSession.close();

    }
}

Mybatis傳統增刪改查方式

mapper.xml

<mapper namespace="userMapper">
    <!--查詢操作-->
    <select id="findAll" resultType="com.rsk.entity.User">
        select * from user
    </select>
    <!--插入操作-->
    <insert id="addUser" parameterType="com.rsk.entity.User">
        insert into user values(#{id},#{name},#{pwd})
    </insert>
    <!--更新操作-->
    <update id="update" parameterType="com.rsk.entity.User">
        update user set name=#{name},pwd=#{pwd} where id=#{id}
    </update>
    <!--刪除操作-->
    <delete id="delete" parameterType="java.lang.Integer">
        delete from user where id=#{id}
    </delete>
</mapper>

Test.java

 //獲得核心配置文件
        InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");
        //獲得sqlSession工廠
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        //獲得session會話對象
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //查詢操作
        //List<User> users = sqlSession.selectList("userMapper.findAll");
        //插入操作
        //int insert = sqlSession.insert("userMapper.addUser", user);
        //更新操作
        //sqlSession.update("userMapper.update", user);
        //刪除操作
        sqlSession.delete("userMapper.delete", 26);
        sqlSession.commit();
        //釋放資源
        sqlSession.close();

Mybatis核心標簽

properties：載入外部的properties文件

 <!--通過標簽載入外部properties文件-->
 <properties resource="jdbc.properties"></properties>

typeAliases：設置類型別名,該標簽必須在environments標簽上面

    <!--別名設置-->
    <typeAliases>
        <typeAlias type="com.rsk.entity.User" alias="user"></typeAlias>
    </typeAliases>

mappers：載入映射配置

    <!--載入映射文件-->
    <mappers>
        <mapper resource="com/rsk/mapper/UserMapper.xml"></mapper>
    </mappers>

enviroments：資料庫環境配置標簽

  <!--數據源環境-->
    <environments default="development">
        <environment id="development">
            <!--指定事務管理類型，為JDBC(依賴數據源獲得連接來管理事務)或者MANAGED(讓容器管理事務，預設情況下會關閉連接)-->
            <transactionManager type="JDBC"></transactionManager>
            <!--指定數據源類型，UNPOOLED(數據源每次被請求時候打開或者關閉連接，POOLED(利用連接池將JDBC對象組織起來)，JNDI(用於EJB或者應用伺服器容器使用))-->
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}"/>
                <property name="url" value="${jdbc.url}?serverTimezone=GMT%2B8"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value=""/>
            </dataSource>
        </environment>
    </environments>

Mybatis代理實現DAO層

採用Mybatis的代理開發實現DAO層，我們只需要編寫Mapper介面（相當於DAO介面），然後由Mybatis框架根據介面定義創建介面的動態代理對象，該動態代理對象的方法體相當於是DAO層的實現類方法。遵循以下規範：

Mapper.xml中的namespace與mapper介面的全限定名稱相同
Mapper.xml中的每個statement的id和Mapper介面方法名相同
Mapper.xml中的每個sql的parameterType與和Mapper介面方法的輸入參數類型相同
Mapper.xml中的每個sql的resultType與和Mapper介面方法的返回參數類型相同

編寫DAO介面UserMapper.class

public interface UserMapper {
    public List<User> findAll() throws IOException;
    public User findById(int id);
}

編寫映射文件UserMapper.xml，namespace需要指定到DAO介面的位置

<?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.rsk.dao.UserMapper">
    <!--查詢操作-->
    <select id="findAll" resultType="user">
        select * from user
    </select>
    <select id="findById" parameterType="int" resultType="user">
        select * from user where id=#{id}
    </select>
    <!--插入操作-->
    <insert id="addUser" parameterType="com.rsk.entity.User">
        insert into user values(#{id},#{name},#{pwd})
    </insert>
    <!--更新操作-->
    <update id="update" parameterType="com.rsk.entity.User">
        update user set name=#{name},pwd=#{pwd} where id=#{id}
    </update>
    <!--刪除操作-->
    <delete id="delete" parameterType="java.lang.Integer">
        delete from user where id=#{id}
    </delete>
</mapper>

Service調用sqlSession的getMapper方法

public class ServiceDemo {
    public static void main(String[] args) throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();

        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        List<User> all = userMapper.findAll();
        User user = userMapper.findById(1);
        System.out.println(all);
        System.out.println(user.getName());

    }
}

動態sql

面對複雜的業務邏輯，SQL需要進行動態調整，如果對每個不同條件專門寫一條sql則需要寫多個介面中的方法，因此可以選擇動態生成SQL語句，從而減少代碼量

<where><if></if></where>標簽：條件判斷後拼接

    <!--動態SQL查詢-->
    <select id="findByCondition" parameterType="user" resultType="user">
        select * from user
        <where>
            <if test="id!=0">
                and id=#{id}
            </if>
            <if test="name!=null">
                and name=#{name}
            </if>
            <if test="pwd!=null">
                and pwd=#{pwd}
            </if>
        </where>
    </select>

對應的介面中的方法：

    //條件查詢
    public List<User> findByCondition(User user);

測試環境中的代碼：

    @Test
    public void test2(){
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        //條件對象
        User user = new User();
        user.setId(1);

        List<User> all = mapper.findByCondition(user);
        System.out.println(all);
    }

<foreach>標簽：迴圈拼接

    <!--動態SQL查詢-->
    <select id="findByIds" parameterType="list" resultType="user">
        select * from user
        <where>
            <foreach collection="list" open="id in(" close=")" item="id" separator=",">
                #{id}
            </foreach>
        </where>
    </select>

對應介面中的方法：

    public List<User> findByIds(List<Integer> ids);

對應測試代碼：

    @Test
    public void tests(){
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        //條件對象
        List<Integer> ids = new ArrayList<Integer>();
        ids.add(1);
        ids.add(2);
        List<User> all = mapper.findByIds(ids);
        System.out.println(all);
    }

sql語句抽取

將動態SQL共用的sql語句代碼段進行提取，避免修改表名時修改全部的sql,達到sql片段重用的目的

    <!--sql語句片段抽取-->
    <sql id="selectUser">select * from user</sql>

    /*sql語句片段引入*/
    <include refid="selectUser"></include>

一對一查詢

主要難點在於查詢出來的數據包含兩個實體類的屬性，需要利用resultMap標簽進行配置，course類實體需要擁有user成員對象

CourseMapper.xml

    <resultMap id="courseMap" type="com.rsk.entity.Course">
        <!--手動指定欄位與實體屬性間的映射關係-->
        <id column="cid" property="id"></id>
        <result column="cno" property="cno"></result>
        <result column="cname" property="cname"></result>
        <!--配置外鍵所在表的映射關係-->
        <association property="user" javaType="com.rsk.entity.User">
            <id column="uid" property="id"></id>
            <result column="name" property="name"/>
            <result column="pwd" property="pwd"/>
        </association>
    </resultMap>

    <select id="findAll" resultMap="courseMap">
        select *, c.id cid
        from course c, user u where c.uid=u.id
    </select>

test

    @Test
    public void test5(){
        CourseMapper mapper = sqlSession.getMapper(CourseMapper.class);
        List<Course> all = mapper.findAll();
        System.out.println(all);
    }

Mybatis快速上手