Spring编写GET请求接口时报BigInteger无法强转为String/Integer错误咨询

class java.math.BigInteger cannot be cast to class java.lang.String

报错核心是：原生SQL查询返回的数值型字段（如userid、trainerid等）默认被映射为java.math.BigInteger类型，代码中存在类型转换逻辑错误，具体问题点如下：

• Service层中直接将数值类型的字段强转为Integer：(Integer)row[0]、(Integer)row[8]，如果数据库字段类型是bigint/unsigned int，原生查询返回的是BigInteger，无法直接强转成Integer，如果错误的将BigInteger直接转String也会触发本次报错
• Repository层返回值类型定义错误：多字段原生SQL查询每个结果行是Object[]类型，应定义返回值为List<Object[]>，而非List<Object>，类型不匹配会导致后续取值时出现意外的类型转换
• Service层参数多余的@PathVariable注解：该注解仅用于Controller层接收路径参数，Service层参数加该注解无意义且可能触发不可预期的参数解析逻辑

1. 修正Repository层返回值类型 #

@Query(value ="select u.userid as \"studentid\",u.username as \"studentname\",u.Image_url as \"studentImage\",u.addeddate as \"enrolleddate\", u.highestqualification as \"highereducation\",\r\n"
        + "u.college as \"university\",e.employmenttype as \"employement\",e.location,\r\n"
        + "ur.requestedtoid as \"trainerid\" from users u JOIN userexperience e  \r\n"
        + "on u.userid = e.userid  join userrequests ur on u.userid = ur.requestedtoid \r\n"
        + "where u.userid = ur.requestedtoid or u.userid =:trainerId",nativeQuery = true)
// 把返回值从List<Object>改成List<Object[]>
List<Object[]> getListOfStudentsBasedOnTrainerId(int trainerId);

2. 修正Service层的类型转换逻辑 #

// 去掉参数上的@PathVariable注解
public List<TrainerIdResponse> getListOfStudentsBasedOnTrainerId(int trainerId) throws RecordNotFoundException{
    List<Object[]> trainerIdResponse=searchRepository.getListOfStudentsBasedOnTrainerId(trainerId);
    List<TrainerIdResponse> trainerIdList  =new ArrayList<>();
    for(Object[] row : trainerIdResponse) {
        TrainerIdResponse trainerIdResponse1= new TrainerIdResponse();
        // 修正数值类型转换逻辑：先转BigInteger再取int值
        trainerIdResponse1.setStudentid(((BigInteger)row[0]).intValue());
        trainerIdResponse1.setStudentname(String.valueOf(row[1]));
        trainerIdResponse1.setStudentImage(String.valueOf(row[2]));
        trainerIdResponse1.setEnrolleddate(String.valueOf(row[3]));
        trainerIdResponse1.setHighereducation(String.valueOf(row[4]));
        trainerIdResponse1.setUniversity(String.valueOf(row[5]));
        trainerIdResponse1.setEmployement(String.valueOf(row[6]));
        trainerIdResponse1.setLocation(String.valueOf(row[7]));
        // 修正trainerid的类型转换
        trainerIdResponse1.setTrainerid(((BigInteger)row[8]).intValue());
        trainerIdList.add(trainerIdResponse1);
    }
    return trainerIdList;
}

可选优化 #

如果不想手动处理结果映射，可以使用SqlResultSetMapping将原生查询结果直接映射到TrainerIdResponse实体，省去手动遍历赋值的步骤，从根源避免类型转换错误。

内容的提问来源于stack exchange，提问作者Bharat Chaudhari