[Java知识库]MyBatis学习

一、准备工作
新建maven项目
连接mysql数据库
修改pom.xml:
1.设置打包方式为jar

  <groupId>com.atguigu.mybatis</groupId>
    <artifactId>MyBatis_demo1</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>

2.导入mysql、junit、mybatis、log4j依赖

 <dependencies>
        <!-- Mybatis核心 -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.7</version> </dependency>
        <!-- junit测试 -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
        <!-- MySQL驱动 -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.15</version>
        </dependency>
        <!-- log4j日志 --> <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.17</version>
    </dependency>
     </dependencies>

把log4j.xml放在resources下

<?xml version="1.0" encoding="GB2312" ?>
<!DOCTYPE log4j:configuration SYSTEM "http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/xml/doc-files/log4j.dtd">
<log4j:configuration debug="true">
<appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
        <param name="Encoding" value="UTF-8"/>
        <layout class="org.apache.log4j.PatternLayout">
            <param name="ConversionPattern" value="%-5p %d{MM-dd HH:mm:ss,SSS} %m (%F:%L) \n"/>
        </layout>
</appender>
    <logger name="java.sql">
        <level value="debug"/>
    </logger>
    <logger name="org.apache.ibatis">
        <level value="info"/>
    </logger>
    <root>
        <level value="debug"/>
        <appender-ref ref="STDOUT"/>
    </root>
</log4j:configuration>

二、pojo与mapper
pojo

public class User {
    private Integer id;
    private  String username;
    private  String password;
    private Integer age;
    private  String sex;
    private  String email;}

mapper接口

public interface UserMapper {
    /*
    * 1、映射文件的namespace 要和mapper接口的全类名保持一致
    * 2、映射文件中的SQL语句的id要和mapper接口中的方法名保持一致
    * */
    int insertUser();
    /**
     * 修改用户信息
     */
    void updateUser();
    void deleteUser();
    User getUserById();
    List<User> getAllUser();
}

三、创建映射文件模板
1、jdbc.properties

jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mybatis?serverTimezone=GMT%2B8
jdbc.username=root
jdbc.password=root

2、核心配置文件mybatis-config.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>
    <!--
    properties?,settings?,typeAliases?,
    typeHandlers?,objectFactory?,objectWrapperFactory?,
    reflectorFactory?,plugins?,environments?,
    databaseIdProvider?,mappers?)".-->

    <!--引入properties文件-->
    <properties resource="jdbc.properties"/>
    <!--设置类型别名,不区分大小写，若不设置默认类名，且不区分大小写-->
    <typeAliases>

        <!--<typeAlias type="com.atguigu.mybatis.pojo.User" alias="User"></typeAlias> -->
        <!--以包位单位，设置默认类型别名，即类名且不区分大小写-->
        <package name="com.atguigu.mybatis.pojo"/>
    </typeAliases>
    <!--配置连接数据库的环境-->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <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>
    <!--引入映射文件-->
    <mappers>
        <!--<mapper resource="mappers/UserMapper.xml"/>-->
        <!--以包为单位引入映射文件
        1、mapper接口所在的包要和映射文件所在的包一致
        2、mapper接口和映射文件的名字一致
        -->
        <package name="com.atguigu.mybatis.mapper"/>

    </mappers>
</configuration>

3、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.atguigu.mybatis.mapper.UserMapper">
    <!--insertUser-->
<insert id="insertUser">
    insert  into t_user values (null,'admin',123456,23,'男','12345@qq.com')
</insert>
    <!--updateUser()-->
    <update id="updateUser">
        update t_user set username='张四' where id = 4
    </update>
    <!--deleteUser-->
    <delete id="deleteUser">
        delete from  t_user where id=5
    </delete>
    <!--getUserById-->
    <!--
    查寻功能的标签必须设置resultType或者resultMap
    resultType:设置默认的映射关系
    resultMap:设置自定义的映射关系
    -->
    <select id="getUserById" resultType="User">
        select * from t_user where id=3
    </select>
    <!--getAllUser-->
    <select id="getAllUser" resultType="User">
        select * from t_user
    </select>
</mapper>

四、SqlSessionUtils工具类和测试
SqlSessionUtil

public class SqlSessionUtils {
    public static SqlSession getSqlSession(){
        SqlSession sqlSession=null;
        try {
            InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
            sqlSession = sqlSessionFactory.openSession(true);
        } catch (IOException e) {
            e.printStackTrace();
        }
      return  sqlSession;
    }

测试

public class ParameterMapperTest {
    @Test
    public void testgetAllUser(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        ParameterMapper mapper = sqlSession.getMapper(ParameterMapper.class);
        List<User> list = mapper.getAllUser();
        list.forEach(user -> System.out.println(user));

    }
}

五、MyBatis获取参数

/**
     * MyBatis获取参数的两种方法：${}和#{}
     * ${}本质是字符串拼接  问题：1.sql注入，2、手动输入单引号
     * #{}本质是占位符赋值  用这个
     * MyBatis获取参数各种情况
     * 1、mapper接口方法的参数为单个的字面量类型
     * 可以通过${}和#{}以任意的字符串获取参数值，但是需要注意${}的单引号问题
     * 2、如果mapper接口方法参数为多个
     *此时MyBatis会将这些参数放在一个map集合中，以两种方式进行存储
     * a>以arg0,arg1....为键，以参数为值
     * b>以param1,param2...为键，以参数为值
     * 因此只需要通过#{}或${}以键的方式访问值即可， 但是需要注意${}的单引号问题
     * 3、若mapper接口方法的参数有多个时，可以手动将参数放在一个map中来存储
     * 只需要通过#{}或${}以键的方式访问值即可， 但是需要注意${}的单引号问题
     *4、mapper接口方法的参数是一个实体类类型的参数
     * 只需要通过#{}或${}以属性的方式访问属性值即可， 但是需要注意${}的单引号问题
     * 5、使用@param命名参数
     *此时MyBatis会将这些参数放在一个map集合中，以两种方式进行存储
     * a>以@Param注解的值为键，以参数为值
     * b>以param1,param2...为键，以参数为值
     * 因此只需要通过#{}或${}以键的方式访问值即可， 但是需要注意${}的单引号问题
     * */

接口

public interface ParameterMapper {
   //验证登录
    User checkLogin(String username,String password);
    //使用map验证登录
    User checkLoginByMap(Map<String,Object>map);
    //添加一个用户信息
    int insertUser(User user);
    //验证登录（使用@Param注解）
    User checkLoginByParam(@Param("username") String username,@Param("password") String password);
    User GetUserByUsername(String username);
    List<User> getAllUser();
}

映射

<!--getAllUser-->
    <select id="getAllUser" resultType="User">
        select * from t_user
    </select>


    <select id="GetUserByUsername" resultType="User">
<!--select * from t_user where username= #{username-->
select * from t_user where username='${name}'
    </select>


<select id="checkLogin" resultType="User">
    select * from t_user where username=#{arg0} and password=#{arg1}
<!--select * from t_user where username=#{param1} and password=#{param2}-->
<!--select * from t_user where username='${arg0}' and password='${arg1}'-->
</select>


    <select id="checkLoginByMap" resultType="User">
        select * from t_user where username=#{username} and password=#{password}
    </select>


<insert id="insertUser">
    insert into t_user values(null,#{username},#{password},#{age},#{sex},#{email});
</insert>


    <select id="checkLoginByParam" resultType="User">
        select * from t_user where username=#{username} and password=#{password}
    </select>

测试

 @Test
    public void testgetUserByUsername(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        ParameterMapper mapper = sqlSession.getMapper(ParameterMapper.class);
        User user = mapper.GetUserByUsername("admin");
        System.out.println(user);

    }
    @Test
    public void testLogin(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        ParameterMapper mapper = sqlSession.getMapper(ParameterMapper.class);
        User user = mapper.checkLogin("admin","123456");
        System.out.println(user);

    }
    @Test
    public void testCheckLoginByMap(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        ParameterMapper mapper = sqlSession.getMapper(ParameterMapper.class);
        Map<String,Object> map=new HashMap<>();
        map.put("username","admin");
        map.put("password","123456");
        User user = mapper.checkLoginByMap(map);
        System.out.println(user);

    }
    @Test
    public void testInsertUser(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        ParameterMapper mapper = sqlSession.getMapper(ParameterMapper.class);
        int result=mapper.insertUser(new User(null,"李9","32323",23,"男","6328378@qq.com"));
        System.out.println(result);

    }
    @Test
    public void testcheckLoginByParam(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        ParameterMapper mapper = sqlSession.getMapper(ParameterMapper.class);
       User user=mapper.checkLoginByParam("admin","123456");
        System.out.println(user);

    }
    @Test
    public void testgetAllUser(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        ParameterMapper mapper = sqlSession.getMapper(ParameterMapper.class);
        List<User> list = mapper.getAllUser();
        list.forEach(user -> System.out.println(user));

    }


    @Test
    public void testJDBC() throws Exception {
        String username="admin";
        Class.forName("");
        Connection connection= DriverManager.getConnection("","","");
        //字符串拼接
        //PreparedStatement preparedStatement = connection.prepareStatement("select  * from t_user where username= '" + username + "'");
        //占位符赋值
        PreparedStatement ps = connection.prepareStatement("select * from t_user where username=?");
        ps.setString(1,username);

    }