仅从 Spring MVC 3 控制器返回字符串消息

Question

Can any one tell me how I can return string message from controller?

If i just return a string from a controller method then spring mvc treating it as a jsp view name.

Answer 1

Annotate your method in controller with @ResponseBody :

@RequestMapping(value="/controller", method=GET)
@ResponseBody
public String foo() {
    return "Response!";
}

From: 15.3.2.6 Mapping the response body with the @ResponseBody annotation :

The @ResponseBody annotation [...] can be put on a method and indicates that the return type should be written straight to the HTTP response body (and not placed in a Model, or interpreted as a view name).

Answer 2

With Spring 4, if your Controller is annotated with @RestController instead of @Controller , you don't need the @ResponseBody annotation.

The code would be

@RestController
public class FooController {

   @RequestMapping(value="/controller", method=GET)
   public String foo() {
      return "Response!";
   }

}

You can find the Javadoc for @RestController here

Answer 3

Although, @Tomasz is absolutely right there is another way:

@RequestMapping(value="/controller", method=GET)
public void foo(HttpServletResponse res) {
    try {       
        PrintWriter out = res.getWriter();
        out.println("Hello, world!");
        out.close();
    } catch (IOException ex) { 
        ...
    }
}

but the first method is preferable. You can use this method if you want to return response with custom content type or return binary type (file, etc...);

Answer 4

This is just a note for those who might find this question later, but you don't have to pull in the response to change the content type. Here's an example below to do just that:

@RequestMapping(method = RequestMethod.GET, value="/controller")
public ResponseEntity<byte[]> displayUploadedFile()
{
  HttpHeaders headers = new HttpHeaders();
  String disposition = INLINE;
  String fileName = "";
  headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);

  //Load your attachment here

  if (Arrays.equals(Constants.HEADER_BYTES_PDF, contentBytes)) {
    headers.setContentType(MediaType.valueOf("application/pdf"));
    fileName += ".pdf";
  }

  if (Arrays.equals(Constants.HEADER_BYTES_TIFF_BIG_ENDIAN, contentBytes)
      || Arrays.equals(Constantsr.HEADER_BYTES_TIFF_LITTLE_ENDIAN, contentBytes)) {
    headers.setContentType(MediaType.valueOf("image/tiff"));
    fileName += ".tif";
  }

  if (Arrays.equals(Constants.HEADER_BYTES_JPEG, contentBytes)) {
    headers.setContentType(MediaType.IMAGE_JPEG);
    fileName += ".jpg";
  }

  //Handle other types if necessary

  headers.add("Content-Disposition", , disposition + ";filename=" + fileName);
  return new ResponseEntity<byte[]>(uploadedBytes, headers, HttpStatus.OK);
}

Answer 5

What about:

PrintWriter out = response.getWriter();
out.println("THE_STRING_TO_SEND_AS_RESPONSE");
return null;

This woks for me.

Answer 6

For outputing String as text/plain use:

@RequestMapping(value="/foo", method=RequestMethod.GET, produces="text/plain")
@ResponseBody
public String foo() {
    return "bar";
}

Answer 7

Simplest solution:

Just add quotes, I really don't know why it's not auto-implemented by Spring boot when response type defined as application/json, but it works great.

@PostMapping("/create")
public String foo()
{
    String result = "something"
    return "\"" + result + "\"";
}

Answer 8

@Controller
public class HelloController {
    @RequestMapping(value = "/", method = RequestMethod.GET)
    ResponseEntity<String> sayHello() {
        return ResponseEntity.ok("Hello");
    }
}

Answer 9

@ResponseBody
@RequestMapping(value="/get-text", produces="text/plain")
public String myMethod() {
     return "Response!";
}

• You see that @ResponseBody ?

It's telling that the method returns some text and not to interpret it as a view etc.

• You see that produces="text/plain" ?

It's just a good practice as it tells what will be returned from the method :)

Answer 10

There are two possible solution

1. Use @Controller and @ResponseBody , to combine HTML page and the string message for different functions

   @Controller @RequestMapping({ "/user/registration"}) public class RegistrationController { @GetMapping public String showRegistrationForm(Model model) { model.addAttribute("user", new UserDto()); return "registration"; //Returns the registration.html } @PostMapping @ResponseBody public String registerUserAccount(@Valid final UserDto accountDto, final HttpServletRequest request) { LOGGER.debug("Registering user account with information: {}", accountDto); return "Successfully registered" // Returns the string }

2. Use @RestController to return String message. In this case, you cannot have functions which returns HTML page.

    @RestController @RequestMapping({ "/user/registration"}) public class RegistrationController { @PostMapping public String registerUserAccount(@Valid @RequestBody final UserDto accountDto, final HttpServletRequest request) { LOGGER.debug("Registering user account with information: {}", accountDto); return "Successfully registered" // Returns the string }