Spring MVC @RequestParam a list of objects

Question

I want to create a page where a person sees a list of users and there are check boxes next to each of them that the person can click to have them deleted.

In my MVC that consumes a REST API, I want to send a List of User objects to the REST API.

Can the @RequestParam annotation support that?

For example:

@RequestMapping(method = RequestMethod.DELETE, value = "/delete")
    public @ResponseBody Integer delete(
            @RequestParam("users") List<Users> list) {
        Integer deleteCount = 0;
        for (User u : list) {
            if (u != null) {
                repo.delete(u);
                ++deleteCount;
            }
        }
        return deleteCount;
    }

In the MVC client, the url would be:

List list = new ArrayList<User>();
....
String url = "http://restapi/delete?users=" + list;

Hazelwood

Answer 1

Request parameters are a Multimap of String to String. You cannot pass a complex object as request param.

But if you just pass the username that should work - see how to capture multiple parameters using @RequestParam using spring mvc?

@RequestParam("users") List<String> list

But I think it would be better to just use the request body to pass information.

Psychognosis

Ahh, yes @RequestBody offers the functionality that I am looking for. – Hazelwood

@RequestBody is not allowed on a GET for Restful APIs. This will cause problems with openapi libs like springdoc – Devi

Answer 2

Spring mvc can support List<Object>, Set<Object> and Map<Object> param, but without @RequestParam.

Take List<Object> as example, if your object is User.java, and it like this:

public class User {
    private String name;
    private int age;

    // getter and setter
}

And you want pass a param of List<User>, you can use url like this

http://127.0.0.1:8080/list?users[0].name=Alice&users[0].age=26&users[1].name=Bob&users[1].age=16

Remember to encode the url, the url after encoded is like this:

http://127.0.0.1:8080/list?users%5B0%5D.name=Alice&users%5B0%5D.age=26&users%5B1%5D.name=Bob&users%5B1%5D.age=16

Example of List<Object>, Set<Object> and Map<Object> is displayed in my github.

Literati

FYI for anyone else confused like me. Using List<User> as parameter for the Controller won't work. Instead a wrapper class containing list should be used a parameter. Check the github link! – Placative

I can not get this to work, tried with the same code as in the github link. I am using Spring Boot 2 and Kotlin, so it is probably one of these causing it. – Brade

Answer 3

Just a reminder, any List of custom objects might require custom converters to be registered, like:

    @Bean
public Converter<String, CustomObject> stringToCustomObjectConverter() {
    return new Converter<>() {
        @Override
        public CustomObject convert(String str) {
            return new ObjectMapper().readValue(str, CustomObject.class);
        }
    };
}

@Bean
public Converter<String, List<CustomObject>> stringToListCustomObjectConverter() {
    return new Converter<>() {
        @Override
        public List<CustomObject> convert(String str) {
            return new ObjectMapper().readValue(str, new TypeReference<>() {
            });
        }
    };
}

So you can cover custom cases like:

 /api/some-api?custom={"name":"Bla 1","age":20}
 /api/some-api?custom={"name":"Bla 1","age":20}&custom={"name":"Bla 2","age":30}
 /api/some-api?custom=[{"name":"Bla 1","age":20},{"name":"Bla 2","age":30}]

where: @RequestParam("custom") List customObjects

Socage