JsonMappingException: Can not construct instance of CommonsMultipartFile

Question

I am using Spring-MVC 3.0, and in my application, I am sending some information with multiple attachments, and each one of these files have title, Id etc. So, I made one DTO as follows ``` public class MyDTO { Long id; Integer age; MultipartFile infoFile; // getter setter ``` I am just creating one `JSON` object according to the above DTO class in my `JS` file. Here is my `Controller` mapping: ``` @RequestMapping(value = "/saveInfo", method = RequestMethod.POST) public @ResponseBody String saveInfo( @RequestParam(value = "data", required = true) String stdData, @RequestParam(value = "fileData", required = false) MultipartFile[] files, HttpSession session,HttpServletRequest request) { MyDTO dto; try { dto = mapper.readValue(stdData, new TypeReference<MyDTO>() {}); } catch (JsonParseException e) { e.printStackTrace(); } catch (JsonMappingException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } ``` But I am getting following errors: ``` org.codehaus.jackson.ma…

Accepted Answer

Actually I find the answer for myself. We can't send file directly in JSON object. A `File` object doesn't hold a file, it holds the path to the file, ie. C:/hi.txt. If that's what we put in our JSON, it'll produce

`{"File" : "C:/hi.txt"}`

It won't contain the file content. So we might as well just put the file path directly

```
JSONObject my_data = new JSONObject();
my_data.put("User", "Avi");
my_data.put("Date", "22-07-2013");
my_data.put("File", "C:/hi.txt");
```

If you're trying to do a file upload with JSON, one way is to read the bytes from the file with Java 7's NIO

```
byte[] bytes = Files.readAllBytes(file_upload .toPath());
```

Base64 encode those bytes and write them as a String in the JSONObject. Using Apache Commons Codec

```
Base64.encodeBase64(bytes);
my_data.put("File", new String(bytes));
```

There are `94 Unicode` characters which can be represented as one byte according to the JSON spec (if your JSON is transmitted as UTF-8).

JsonMappingException: Can not construct instance of CommonsMultipartFile

Solution

Problem