MyBatis获取参数值的两种方式（重点）代码
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MyBatis Code

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pom.xml

<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>top.qaqaq.mybatis</groupId>
  <artifactId>MyBatis_demo2</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>MyBatis_demo2</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>

    <!-- 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>8.0.31</version>
    </dependency>
    <!-- log4j日志 -->
    <dependency>
      <groupId>log4j</groupId>
      <artifactId>log4j</artifactId>
      <version>1.2.17</version>
    </dependency>

  </dependencies>
</project>

resources

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 resource="jdbc.properties" />

    <typeAliases>
        <package name="top.qaqaq.mybatis.pojo"/>
    </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="top.qaqaq.mybatis.mapper"/>
    </mappers>
</configuration>

jdbc.properties

jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mybatis
jdbc.username=root
jdbc.password=123456

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>

resources/mapper

ParameterMapper.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="top.qaqaq.mybatis.mapper.ParameterMapper">
    
    <!--List<User> getAllUser();-->
    <select id="getAllUser" resultType="User">
        select * from t_user
    </select>

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

    <!--User checkLogin(String username, String password);-->
    <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>

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

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

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

</mapper>

mapper

ParameterMapper .java

package top.qaqaq.mybatis.mapper;

import org.apache.ibatis.annotations.Param;
import top.qaqaq.mybatis.pojo.User;

import java.util.List;
import java.util.Map;

public interface ParameterMapper {

    /**
     * 验证登录（使用@Param）
     */
    User checkLoginByParam(@Param("username") String username, @Param("password") String password);

    /**
     * 添加用户信息
     */
    int insertUser(User user);

    /**
     * 验证登录（参数为map）
     */
    User checkLoginByMap(Map<String, Object> map);

    /**
     * 验证登录
     */
    User checkLogin(String username, String password);

    /**
     * 根据用户名查询用户信息
     */
    User getUserByUsername(String username);

    /**
     * 查询所有的员工信息
     */
    List<User> getAllUser();

}

pojo

User .java

package top.qaqaq.mybatis.pojo;

/**
 * @author RichieZhang
 * @create 2023-01-01 15:37
 */
public class User {

    private Integer id;
    private String username;
    private String password;
    private Integer age;
    private String sex;
    private String email;

    public User() {
    }

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

    public void setSex(String sex) {
        this.sex = sex;
    }

    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 +
                ", sex='" + sex + '\'' +
                ", email='" + email + '\'' +
                '}';
    }
}

utils

SqlSessionUtils .java

package top.qaqaq.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;

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) {
            throw new RuntimeException(e);
        }
        return sqlSession;
    }
}

test

ParameterMapperTest .java

package top.qaqaq.mybatis.test;

import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import top.qaqaq.mybatis.mapper.ParameterMapper;
import top.qaqaq.mybatis.pojo.User;
import top.qaqaq.mybatis.utils.SqlSessionUtils;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class ParameterMapperTest {

    /**
     * MyBatis获取参数值的两种方式：${} 和 #{}
     * ${} 本质字符串拼接
     * #{} 本质占位符赋值
     * MyBatis获取参数值的各种情况：
     * 1、mapper接口方法的参数为单个的字面量类型
     * 可以通过 ${} 和 #{} 以任意的名称获取参数值，但需要注意 ${} 的单引号问题
     * 2、mapper接口方法的参数为多个时
     * 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 #{} 和 ${} 以键的方式访问值即可，但需要注意 ${} 的单引号问题
     * 3、若mapper接口方法的参数有多个时，可以手动将这些参数放在一个map中存储
     * 只需要通过 #{} 和 ${} 以键的方式访问值即可，但需要注意 ${} 的单引号问题
     * 4、mapper接口方法的参数是实体类类型的参数
     * 只需要通过 #{} 和 ${} 以属性的方式访问值即可，但需要注意 ${} 的单引号问题
     * 5、使用@Param注解命名参数
     * 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 #{} 和 ${} 以键的方式访问值即可，但需要注意 ${} 的单引号问题
     */

    @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 testInsertUser() {
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        ParameterMapper mapper = sqlSession.getMapper(ParameterMapper.class);
        int result = mapper.insertUser(new User(null, "李四", "123", 23, "男", "123@qq.com"));
        System.out.println(result);
    }

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

    @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 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("","","");
        //PreparedStatement ps = connection.prepareStatement("select * from t_user where username = '" + username + "'");
        PreparedStatement ps = connection.prepareStatement("select * from t_user where username = ?");
        ps.setString(1, username);
    }
}
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