[
    {
        "id": 1,
        "name": «Голубь Шуо Цзы»,
        "roles": [
            «Представитель класса физики»,
            «Представитель математического класса»
        ]
    }
]

SELECT stu.*,
       (SELECT group_concat(r.role_name) AS roles
        FROM stud_role sr
                 left join role r on sr.role_id = r.role_id
        WHERE sr.stu_id = stu.id) AS roles
FROM student stu;

package com.shuo.mpth.handler;

import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;
import org.apache.ibatis.type.MappedJdbcTypes;
import org.apache.ibatis.type.MappedTypes;
import org.springframework.util.StringUtils;

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

/**
 * @author : wshuo
 * @date : 2023/1/11 15:59
 */
@MappedJdbcTypes(JdbcType.VARCHAR)
@MappedTypes({List.class})
public class ListTypeHandler extends BaseTypeHandler<List<String>> {

    private static final String DELIM = ",";

    @Override
    public void setNonNullParameter(PreparedStatement preparedStatement, int i, List<String> strings, JdbcType jdbcType) throws SQLException {
        String value = StringUtils.collectionToDelimitedString(strings, DELIM);
        preparedStatement.setString(i, value);
    }

    @Override
    public List<String> getNullableResult(ResultSet resultSet, String s) throws SQLException {
        String value = resultSet.getString(s);
        return Arrays.asList(StringUtils.tokenizeToStringArray(value, DELIM));
    }

    @Override
    public List<String> getNullableResult(ResultSet resultSet, int i) throws SQLException {
        String value = resultSet.getString(i);
        return Arrays.asList(StringUtils.tokenizeToStringArray(value, DELIM));
    }

    @Override
    public List<String> getNullableResult(CallableStatement callableStatement, int i) throws SQLException {
        String value = callableStatement.getString(i);
        return Arrays.asList(StringUtils.tokenizeToStringArray(value, DELIM));
    }
}

@Data
public class Student {
    /**
     * студенческий билет
     */
    private Integer id;
    /**
     * имя студента
     */
    private String name;
    /**
     * Роль, которую играет ученик
     */
    @TableField(typeHandler = ListTypeHandler.class)
    private List<String> roles;
}

mybatis-plus:
  mapper-locations: classpath*:mapper/*.xml
  type-aliases-package: com.shuo.mpth.**.entity
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
  type-handlers-package: com.shuo.mpth.handler