Spring MVC - How to return simple String as JSON in Rest Controller

java

best-practices

json-handling

rest-controllers

byNikita Barsukov·Jan 24, 2025

In Spring MVC, to return a String as JSON using a RestController, use the @RestController and @GetMapping annotations. The produces attribute of the @GetMapping annotation should be set to MediaType.APPLICATION_JSON_VALUE. Look at this quick example:

@RestController
public class SimpleController {

    @GetMapping(value = "/stringAsJson", produces = MediaType.APPLICATION_JSON_VALUE)
    public String getStringAsJson() {
        return "{\"message\":\"Hello, World!\"}";
    }
}

This creates a JSON-formatted string when /stringAsJson is accessed. Thanks to @RestController, there's no need for @ResponseBody.

But wait! It gets better – no need for manually adding quotes anymore. Let's dive into the comprehensive solutions.

Best Practices for JSON String Response

Wrapping a String in an Object

Get classy and avoid manual quote escapes:

@RestController
public class ClassResponseController {

    @GetMapping("/classStringAsJson")
    public Response getMessage() {
        return new Response("When life gives you classes, make objects.");
    }
    
    static class Response {
        private final String message;
        
        public Response(String message) {
            this.message = message;
        }
        
        public String getMessage() {
            return this.message;
        }
    }
}

Fancy ResponseEntity

With ResponseEntity, gain extra control:

@RestController
public class ResponseEntityController {

    @GetMapping("/responseEntityAsString")
    public ResponseEntity<String> getResponseEntityAsString() {
        return ResponseEntity.ok()
                             .contentType(MediaType.APPLICATION_JSON)
                             .body(JSONObject.quote("When life gives you lemons, JSONify them!"));
    }
}

Here JSONObject.quote() ensures its input turns into a valid JSON text.

JSONify it with Collections.singletonMap

Perfect for a one-off key-value JSON object:

@RestController
public class SingletonMapController {

    @GetMapping("/singletonMap")
    public Map<String, String> getSingletonMap() {
        return Collections.singletonMap("message", "Hello, Singleton World!");
    }
}

Delve Deeper with Advanced Configuration

To take JSON conversion into our own hands:

@Configuration
public class WebConfig implements WebMvcConfigurer {

    @Override
    public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
        // Sorting hat code to choose Jackson converter over String converter
    }
}

Mastering the Art of JSON Handling

RestyGWT Compatibility

Work with RestyGWT? Make sure the returned JSON is appetizing:

@GetMapping(value = "/restyGwtFriendly", produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<Object> getRestyGWTCompatibleString() {
    return ResponseEntity.ok(new JSONObject(Map.of("response", "Respecting the Rest(yGWT)!")));
}

Debugging Served on a Platter

Just like ketchup to fries, a logger nicely accompanies debugging:

private static final Logger logger = LoggerFactory.getLogger(YourController.class);

@GetMapping("/loggableStringAsJson")
public Map<String, String> getLoggableStringAsJson(HttpServletRequest request) {
    logger.info("Received order from {}", request.getRemoteAddr());
    return Collections.singletonMap("response", "Order up! Hello, World!");
}

Handle Content with Elegance

Give your content negotiation a VIP upgrade:

@GetMapping("/negotiatedStringAsJson")
public ResponseEntity<String> getNegotiatedStringAsJson() {
    HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.APPLICATION_JSON);
    return new ResponseEntity<>("{\"message\":\"The Art of Negotiation, JSON style!\"}", headers, HttpStatus.OK);
}

Taking the JSON Path with Custom Conversion

Snap StringHttpMessageConverter out of default conversion for pure JSONness:

@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
    converters.removeIf(httpMessageConverter -> httpMessageConverter instanceof StringHttpMessageConverter);
    // Configure your mighty Jackson converter
}