使用ModelMapper映射后获取RequestParam遇空指针异常求助

我用ModelMapper实现了模型对象与实体对象的双向映射，目前在处理GET请求的RequestParam参数时遇到异常，请求帮忙解决。

报错信息 #

Hibernate: select c1_0.id, c1_0.email, c1_0.first_name, c1_0.idp_customer_id,
c1_0.last_name, c1_0.phone from customer_entity as c1_0 where c1_0.idp_customer_id = ?
2022-08-04 22:41:10 [http-nio-8040-exec-4] ERROR - [dispatcherServlet]:175: Servlet.service() for servlet [dispatcherServlet] in context with path [/ca] threw exception [Request processing failed; nested exception is java.lang.IllegalArgumentException: source cannot be null] with root cause
java.lang.IllegalArgumentException: source cannot be null

控制器代码 #

/** GET request to return customer Id_id **/
@RequestMapping( method = RequestMethod.GET)
@ResponseBody
public Customer getCustomerIdpId(@RequestParam(name = "idp_customer_id") String idpCustomerId) {
        return customerMapper.convertToCustomer(customerAccountService.getCustomerIdp(idpCustomerId));
}

CustomerMapper代码 #

public Customer convertToCustomer(CustomerEntity customerEntity) {
    return modelMapper.map(customerEntity, Customer.class);
}

错误的请求方式（GET请求不应携带请求体） #

{
"idpCustomerId": "3940f85e-4601-4870-b30f-c6624e7d4678"
}

问题分析 #

1. 异常核心是source cannot be null，说明调用modelMapper.map时传入的customerEntity为null，也就是customerAccountService.getCustomerIdp(idpCustomerId)没有查询到对应数据，返回了null。
2. 关键问题：你用GET请求携带请求体传递参数，这不符合HTTP规范，后端@RequestParam无法从请求体中获取到idp_customer_id的值，导致查询条件无效，最终返回null。

解决方法 #

1. 修正请求方式：GET请求通过URL参数传递值，比如请求地址改为：

   /ca?idp_customer_id=3940f85e-4601-4870-b30f-c6624e7d4678
   

2. 添加空值校验：在Mapper层增加空判断，避免传入null触发ModelMapper异常：

   public Customer convertToCustomer(CustomerEntity customerEntity) {
       if (customerEntity == null) {
           return null; // 也可根据业务需求返回空的Customer对象
       }
       return modelMapper.map(customerEntity, Customer.class);
   }
   

3. 检查服务层逻辑：确认customerAccountService.getCustomerIdp方法在参数无效或无匹配记录时的处理逻辑，必要时在控制器层先校验参数是否为空，再调用服务查询。

内容的提问来源于stack exchange，提问作者autoboss