Spring MVC #RequestParam a list of objects - spring

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;

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.

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.

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