5、Mybatis之获取参数值

5.1、创建新module

5.1.1、右击SSM文件夹，创建新module

5.1.2、选择maven

5.1.3、配置module名称和路径

5.1.4、module初始状态

5.1.5、复制打包方式和依赖

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.rain</groupId>
    <artifactId>mybatis_parameter</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>

    <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>5.1.49</version>
        </dependency>
        <!-- log4j日志 -->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
    </dependencies>

</project>

5.1.6、复制配置文件

• jdbc.properties

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/ssm?characterEncoding=utf-8
jdbc.username=root
jdbc.password=root

• log4j.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
    <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>

5.1.7、复制并修改Mybatis核心配置文件

注意：别名包值和映射文件包值，目前是悬空状态

<?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="jdbc.properties"/>

    <typeAliases>
        <package name=""/>
    </typeAliases>

    <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>

    <mappers>
        <package name=""/>
    </mappers>

</configuration>

5.1.8、创建mapper接口和映射文件

• mapper接口

• 映射文件目录

注意目录分隔符是“/”，而且路径和mapper接口路径一致

• 映射文件

注意：映射文件名称要和mapper接口名称一致，映射文件mapper标签的namespace属性值是对应mapper接口的全限定名

<?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="org.rain.mybatis.mapper.UserMapper">

</mapper>

5.1.9、创建实体类

++++++++++++++++++++++++++++++++分割线++++++++++++++++++++++++++++++++

++++++++++++++++++++++++++++++++分割线++++++++++++++++++++++++++++++++

package org.rain.mybatis.pojo;

/**
 * @author liaojy
 * @date 2023/5/22 - 23:56
 */
public class User {
    private Integer id;

    private String username;

    private String password;

    private Integer age;

    private String gender;

    private String email;

    public User() {
    }

    public User(Integer id, String username, String password, Integer age, String gender, String email) {
        this.id = id;
        this.username = username;
        this.password = password;
        this.age = age;
        this.gender = gender;
        this.email = email;
    }

    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 getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

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

}

5.1.10、更新核心配置文件的包引用

5.1.11、创建SqlSession工具类

package org.rain.mybatis.utils;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;
import java.io.InputStream;

/**
 * @author liaojy
 * @date 2023/5/19 - 7:41
 */
public class SqlSessionUtils {
    public static SqlSession getSqlSession(){
        SqlSession sqlSession = null;

        try {
            //读取MyBatis核心配置文件的输入流
            InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
            //创建SqlSessionFactoryBuilder对象
            SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
            //通过核心配置文件所对应的字节输入流创建工厂类SqlSessionFactory，用于生产SqlSession对象
            SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(is);
            //创建自动提交事务的SqlSession对象
            sqlSession = sqlSessionFactory.openSession(true);
        } catch (IOException e) {
            e.printStackTrace();
        }
        return sqlSession;
    }
}

5.1.12、创建测试类

5.2、单个字面量类型的参数

字面量：基本数据类型及其包装类，和字符串都属于字面量

5.2.1、接口方法

package org.rain.mybatis.mapper;

import org.rain.mybatis.pojo.User;

/**
 * @author liaojy
 * @date 2023/5/22 - 23:53
 */
public interface UserMapper {

    User getUserByUsername(String username);
}

5.2.2、映射文件

实际上，mybatis只知道方法传的参数值，而不知道参数名，所以可以用任意名获取参数值，如${abc}；

但为了可读性，推荐使用方法的参数名${username}。

    <!--User getUserByUsername(String username);-->
    <select id="getUserByUsername" resultType="User">
        select * from t_user where username = #{username}
    </select>

5.2.3、测试方法

注意：在这个示例中，数据库中username字段的值只能有一个“root”

package org.rain.mybatis.test;

import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import org.rain.mybatis.mapper.UserMapper;
import org.rain.mybatis.pojo.User;
import org.rain.mybatis.utils.SqlSessionUtils;

/**
 * @author liaojy
 * @date 2023/5/23 - 7:54
 */
public class ParameterTest {

    @Test
    public void testGerUserByUsername(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        User user = userMapper.getUserByUsername("root");
        System.out.println(user);
        sqlSession.close();
    }
}

5.2.4、执行效果

从控制台的sql日志可知，#{}的本质是占位符赋值

5.2.5、字符串赋值

从上图控制台的sql日志可知，${}的本质是字符串拼接，会存在字符串参数值的单引号问题；解决方法见下图，手动加单引号

5.3、多个字面量类型的参数

5.3.1、接口方法

User checkLogin(String username,String password);

5.3.2、映射文件

注意：当mapper接口方法的参数为多个字面量时，mybatis会以两种map集合的形式存储参数值；

一种map集合的键为arg0、arg1等，另一种map集合的键为param1、param2等；

    <!--User checkLogin(String username,String password);-->
    <select id="checkLogin" resultType="User">
        select * from t_user where username = #{arg0} and password = #{arg1}
    </select>

5.3.3、测试方法

    @Test
    public void testCheckLogin(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        User user = userMapper.checkLogin("root","123");
        System.out.println(user);
        sqlSession.close();
    }

5.3.4、执行效果

5.3.5、字符串拼接

5.4、map集合类型的参数

5.4.1、接口方法

User checkLoginByMap(Map<String,Object> map);

5.4.2、测试方法

    @Test
    public void testCheckLoginByMap(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        Map<String,Object> map = new HashMap<String, Object>();
        map.put("username","root");
        map.put("password","123");
        User user = userMapper.checkLoginByMap(map);
        System.out.println(user);
        sqlSession.close();
    }

5.4.3、映射文件

注意：可以自定义map集合，然后通过自定义map集合中的键来获取参数值

    <!--User checkLoginByMap(Map<String,Object> map);-->
    <select id="checkLoginByMap" resultType="User">
        select * from t_user where username = #{username} and password = #{password}
    </select>

5.4.4、执行效果

5.5、实体类类型的参数

5.5.1、接口方法

void insertUser(User user);

5.5.2、测试方法

    @Test
    public void testInsertUser(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        Map<String,Object> map = new HashMap<String, Object>();
        User user = new User();
        user.setUsername("zhangsan");
        user.setPassword("123");
        user.setAge(55);
        user.setGender("男");
        user.setEmail("123@qq.com");
        userMapper.insertUser(user);
        sqlSession.close();
    }

5.5.3、映射文件

通过用${}和#{}访问实体类对象中的属性名来获取对应的属性值；

注意：属性名是实体类的getter或setter方法去掉get或set之后的首字母小写部分，和成员变量无关

    <!--void insertUser(User user);-->
    <insert id="insertUser">
        insert into t_user values (null ,#{username},#{password},#{age},#{gender},#{email});
    </insert>

5.5.4、执行效果

+++++++++++++++++++++++++++++分割线+++++++++++++++++++++++++++++

5.6、使用@Param标识参数

5.6.1、接口方法

用@Param注解标识mapper接口中的方法参数，可以自定义mybatis中map集合的键；

这样，只需要通过${}或#{}访问map集合的自定义键就可以获取对应的参数值

User checkLoginByParam(@Param("username") String username, @Param("password") String password);

5.6.2、映射文件

    <!--User checkLoginByParam(@Param("username") String username, @Param("param") String password);-->
    <select id="checkLoginByParam" resultType="User">
        select * from t_user where username = #{username} and password = #{password}
    </select>

5.6.3、测试方法

    @Test
    public void testCheckLoginByParam(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        User user = userMapper.checkLoginByParam("root","123");
        System.out.println(user);
        sqlSession.close();
    }

5.6.4、执行效果