Return Hashmap from Spring Rest API

Question

I want to use this code to get some data from Rest API:

public Map<Integer, String> getCategoriesList() {

        Map<Integer, String> list = new HashMap<>();
        list.put(1, "Electronics");
        list.put(2, "Outdoor and Sports");
        list.put(3, "Home and Garden");
        list.put(4, "Home appliances");
        list.put(5, "Air conditioners and heaters");
        list.put(6, "IT accessories");
        list.put(7, "Photo and Video");
        list.put(8, "TV Video and Gaming");

        return list;
    }

@GetMapping("categories")
public ResponseEntity<List<String>> getCategoriesList() {

    return (ResponseEntity<List<String>>) categoriesService.getCategoriesList();
}

I get error: class java.util.HashMap cannot be cast to class org.springframework.http.ResponseEntity

What is the appropriate way to return this data as a response?

Miron Balcerzak · Accepted Answer · 2020-09-28 22:40:43Z

2

You cannot cast one type to another like that...try this

ResponseEntity type:

@GetMapping("categories")
public ResponseEntity<Map<Integer, String>> getCategoriesList() {
    return new ResponseEntity<Map<Integer,String>>(categoriesService.getCategoriesList(), HttpStatus.OK);
}

Without ResponseEntity wrapper

@GetMapping("categories")
@ResponseStatus(code = HttpStatus.OK)
public Map<Integer, String> getCategoriesList() {
    return categoriesService.getCategoriesList();
}

Since both types of map are known to jackson (I presume that's what you are using in spring for serialization/deserialization), no need to do anything more.

Reference: https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/http/ResponseEntity.html

edited Sep 28, 2020 at 22:40

answered Sep 28, 2020 at 22:26

Miron Balcerzak

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6 Comments

Peter Penzov Over a year ago

I get Cannot infer arguments

Miron Balcerzak Over a year ago

Well ... alright - you need to do the casting in this scenario -- but what do u want to achieve? Do you want to return hashmap (as per question) or list as per code?

Peter Penzov Over a year ago

I want to return a hashmap - key - value pairs.

Miron Balcerzak Over a year ago

however...you can just return Map from the method - you do not need to use ResponseEntity type - I've edit my answer

Peter Penzov Over a year ago

Is it a good practice to use ResponseEntity wrapper? What are the benefits?

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