I have a sample RestController in Spring Boot:
@RestController
@RequestMapping("/api")
class MyRestController
{
@GetMapping(path = "/hello")
public JSONObject sayHello()
{
return new JSONObject("{'aa':'bb'}");
}
}
I am using the JSON library org.json
When I hit API /hello
, I get an exception saying :
Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.IllegalArgumentException: No converter found for return value of type: class org.json.JSONObject] with root cause
java.lang.IllegalArgumentException: No converter found for return value of type: class org.json.JSONObject
What is the issue? Can someone explain what exactly is happening?
This question is related to
java
json
spring-boot
response
use ResponseEntity<ResponseBean>
Here you can use ResponseBean or Any java bean as you like to return your api response and it is the best practice. I have used Enum for response. it will return status code and status message of API.
@GetMapping(path = "/login")
public ResponseEntity<ServiceStatus> restApiExample(HttpServletRequest request,
HttpServletResponse response) {
String username = request.getParameter("username");
String password = request.getParameter("password");
loginService.login(username, password, request);
return new ResponseEntity<ServiceStatus>(ServiceStatus.LOGIN_SUCCESS,
HttpStatus.ACCEPTED);
}
for response ServiceStatus or(ResponseBody)
public enum ServiceStatus {
LOGIN_SUCCESS(0, "Login success"),
private final int id;
private final String message;
//Enum constructor
ServiceStatus(int id, String message) {
this.id = id;
this.message = message;
}
public int getId() {
return id;
}
public String getMessage() {
return message;
}
}
Spring REST API should have below key in response
you will get final response below
{
"StatusCode" : "0",
"Message":"Login success"
}
you can use ResponseBody(java POJO, ENUM,etc..) as per your requirement.
More correct create DTO for API queries, for example entityDTO:
@GetMapping(produces=MediaType.APPLICATION_JSON_VALUE) @ResponseStatus(HttpStatus.OK) public List<EntityDto> getAll() { return entityService.getAllEntities(); }
But if you need return different Map parameters you can use next two examples
2. For return one parameter like map:
@GetMapping(produces=MediaType.APPLICATION_JSON_VALUE) public ResponseEntity<Object> getOneParameterMap() { return ResponseEntity.status(HttpStatus.CREATED).body( Collections.singletonMap("key", "value")); }
@GetMapping(produces = MediaType.APPLICATION_JSON_VALUE) public ResponseEntity<Object> getSomeParameters() { return ResponseEntity.status(HttpStatus.OK).body(Map.of( "key-1", "value-1", "key-2", "value-2", "key-3", "value-3")); }
you can also use a hashmap for this
@GetMapping
public HashMap<String, Object> get() {
HashMap<String, Object> map = new HashMap<>();
map.put("key1", "value1");
map.put("results", somePOJO);
return map;
}
@RequestMapping("/api/status")
public Map doSomething()
{
return Collections.singletonMap("status", myService.doSomething());
}
PS. Works only for 1 value
The reason why your current approach doesn't work is because Jackson is used by default to serialize and to deserialize objects. However, it doesn't know how to serialize the JSONObject
. If you want to create a dynamic JSON structure, you can use a Map
, for example:
@GetMapping
public Map<String, String> sayHello() {
HashMap<String, String> map = new HashMap<>();
map.put("key", "value");
map.put("foo", "bar");
map.put("aa", "bb");
return map;
}
This will lead to the following JSON response:
{ "key": "value", "foo": "bar", "aa": "bb" }
This is a bit limited, since it may become a bit more difficult to add child objects. Jackson has its own mechanism though, using ObjectNode
and ArrayNode
. To use it, you have to autowire ObjectMapper
in your service/controller. Then you can use:
@GetMapping
public ObjectNode sayHello() {
ObjectNode objectNode = mapper.createObjectNode();
objectNode.put("key", "value");
objectNode.put("foo", "bar");
objectNode.put("number", 42);
return objectNode;
}
This approach allows you to add child objects, arrays, and use all various types.
If you need to return a JSON object using a String, then the following should work:
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.http.ResponseEntity;
...
@RestController
@RequestMapping("/student")
public class StudentController {
@GetMapping
@RequestMapping("/")
public ResponseEntity<JsonNode> get() throws JsonProcessingException {
ObjectMapper mapper = new ObjectMapper();
JsonNode json = mapper.readTree("{\"id\": \"132\", \"name\": \"Alice\"}");
return ResponseEntity.ok(json);
}
...
}
You can either return a response as String
as suggested by @vagaasen or you can use ResponseEntity
Object provided by Spring as below. By this way you can also return Http status code
which is more helpful in webservice call.
@RestController
@RequestMapping("/api")
public class MyRestController
{
@GetMapping(path = "/hello", produces=MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<Object> sayHello()
{
//Get data from service layer into entityList.
List<JSONObject> entities = new ArrayList<JSONObject>();
for (Entity n : entityList) {
JSONObject entity = new JSONObject();
entity.put("aa", "bb");
entities.add(entity);
}
return new ResponseEntity<Object>(entities, HttpStatus.OK);
}
}
Source: Stackoverflow.com