java - 无法将类型 'java.lang.String' 的值转换为所需的模型对象类型

Question

我正在尝试通过以 JSON 格式提供所需的请求来使用 postman 访问服务:

 {
    "baseParam": {
        "userId": "u1234"
    },
    "resource": {
        "name": "resource"
    }
}

连同一个多部分文件，如下面的 postman 屏幕所示

Postman screen

但是我得到了错误:

'无法将“java.lang.String”类型的值转换为所需类型“SampleRequestObject”；嵌套异常是 java.lang.IllegalStateException:无法将类型 [java.lang.String] 的值转换为所需类型'

Controller

   @RequestMapping(method = RequestMethod.POST, value = "/sample/resource", 
   produces = "application/json")
   @ResponseBody
   public final ResponseObject sampleResource(@RequestParam("request") final 
   SampleRequestObject requestObject,@RequestParam("file") final 
   MultipartFile file,BindingResult result ) throws IOException {

   String success = “SUCCESS”;
   requestObject.setFile(file);
   String id=sampleService.sampleResourceService(resourceObject);   
   //sampleService Object has been autowired earlier in controller              
    return  success;                                                                                                       


    }  
    }

SampleRequestObject – 模型类

    public class SampleRequestObject extends SampleMainObject {

    @NotNull
    @IsValid(baseParam = { "userId"})
    private BaseParam baseParam;

    @NotNull    
    private SampleResource resource;   // ANOTHER OBJECT OF SAMPLE RESOURCE 
                                          CLASS
    private MultipartFile file;

    public SampleResource getResource() {
    return resource;
    }

    public void setResource(SampleResource resource) {
    this.resource = resource;
    }

    @Override

    public Param getBaseParam() {

    return baseParam;
    }

    public final void setBaseParam(final BaseParam baseParam) {
    this.baseParam = baseParam;
    }

    public MultipartFile getFile() {
    return file;
    }

    public void setFile(MultipartFile file) {
    this.file = file;
    }   
    }

SampleServiceImpl.class 中的函数(SampleService 实现)

    @Override
    @Transactional
    public final String sampleResourceService( SampleRequestObject 
    requestObject) {throws IOException
    String Id=null;

    try
    {

    MainResourceObject resourceObject = new MainResourceObject();
    resourceObject.setActualName(requestObject.getFile()
    .getOriginalFilename());
    resourceObject.setName(requestObject.getResource().getName()); );   
        .
        .
        .
        .  
        .
        .
        .
        .  

        .  
    }
    catch (Exception e) {
    log.error("Service Execution failed",e);
    }
    }

我还尝试提供 @ModelAttribute 而不是 @RequestParam。然后，可以进入 Controller 和服务，但是 requestObject(在 Controller 中)的所有值都被填充为空值。因此，它从服务实现中抛出 NullPointeException。

请提供解决方案。

Answer 1

你能试试这个吗

public final ResponseObject sampleResource(SampleRequestObject request,
       @RequestParam("file") final MultipartFile file,
       BindingResult result ) throws IOException {
...

我刚刚删除了 @RequestParam 并将变量更改为 request