discussion about #RequestParam and #RequestBody - spring

Question

I have a class:
public class user{
private String id;
private MultiPartFile file;
**Getters And Setters**
}
And in the Controller:
#PostMapping(value="/upload)
public void upload(User user){
}
In the front end I post data with form-data.I can get the user object.
But when I add #RequestBody and #RequestParam,it can't works.
in my opinion，#RequestParam is used to binding parameter to simple class . when I use #RequestBody ,spring will find HttpMessageConverter to convert http request body to class.But I'm not sure about that.Does anyone can explain to me?

Answer 1

So, I believe we are talking about org.springframework.web.multipart.MultipartFile, which is to be used together with #RequestParam variable. The mechanism is somewhat special in this case.
I had a similar problem, and what I ended up using was org.springframework.web.multipart.commons.CommonsMultipartResolver. From frontend I've constructed multipart request with two parts, in your scenario it could be user (containing just JSON data) and file (containing the file itself), e.g.:
#PostMapping(value="/upload")
public void upload(#RequestParam("user") User user, #RequestParam("file") MultipartFile file){
...
}
But then, you need to configure custom serialization of the User part, which can be done using org.springframework.web.multipart.commons.CommonsMultipartResolver. You can configure it using bean config like this:
#Configuration
public class MappingConfig {
#Order(Integer.MIN_VALUE)
#Bean(name = "multipartResolver")
public CommonsMultipartResolver multipartResolver() {
return new CommonsMultipartResolver();
}
#Bean
public Converter<String, User> stringToUser() {
return new Converter<String, User>() {
#Override
public User convert(String jsonString) {
return new Gson().fromJson(jsonString, User.class);
}
};
}
...
}
Also, as you can see I am using Gson manually, I couldn't find a better way how to do it. Also, it doesn't play with Java 8 lambdas, so it cannot be shortened (because of explicit types are needed for it to work).
I hope that this will at least points you to a right path.