Java中的List和MySQL中的varchar相互转换的解决方案

package com.examples.handler;

import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;

import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class ListStringTypeHandler extends BaseTypeHandler<List<String>> {

    @Override
    public void setNonNullParameter(PreparedStatement ps, int i, List<String> parameter, JdbcType jdbcType) throws SQLException {
        ps.setString(i, String.join(",", parameter));
    }

    @Override
    public List<String> getNullableResult(ResultSet rs, String columnName) throws SQLException {
        if (rs.getString(columnName) == null) {
            return new ArrayList<>();
        }
        return Arrays.asList(rs.getString(columnName).split(","));
    }

    @Override
    public List<String> getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
        if (rs.getString(columnIndex) == null) {
            return new ArrayList<>();
        }
        return Arrays.asList(rs.getString(columnIndex).split(","));
    }

    @Override
    public List<String> getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
        if (cs.getString(columnIndex) == null) {
            return new ArrayList<>();
        }
        return Arrays.asList(cs.getString(columnIndex).split(","));
    }
}

@Data
public class Student {
    private Long id;
    private String name;
    private List<String> hobbies;
}

public interface StudentMapper {
    void saveStudent(Student student);

    Student queryStudentById(long id);
}

<?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.examples.mapper.StudentMapper">
    <resultMap id="studentMap" type="student">
        <result column="hobbies" property="hobbies" typeHandler="com.examples.handler.ListStringTypeHandler"/>
    </resultMap>
    <insert id="saveStudent" keyProperty="id" useGeneratedKeys="true" keyColumn="id">
        insert into student (name, hobbies)
        values (#{name}, #{hobbies,typeHandler=com.examples.handler.ListStringTypeHandler})
    </insert>

    <select id="queryStudentById" resultType="student" resultMap="studentMap">
        select *
        from student
        where id = #{id}
    </select>
</mapper>

public class StudentTest {

    @Resource
    private StudentMapper studentMapper;

    // 添加
    @Test
    void testSaveStudent() {
        Student student = new Student();
        List<String> hobbiesList = new ArrayList<>();
        hobbiesList.add("篮球");
        hobbiesList.add("阅读");
        hobbiesList.add("写代码");

        student.setName("张三");
        student.setHobbies(hobbiesList);
        studentMapper.saveStudent(student);
    }

    //查询
    @Test
    void testQueryStudentById() {
        Student student = studentMapper.queryStudentById(1L);
        System.out.println(student);
    }
}