Return only string message from Spring MVC 3 Contr

问题:

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.

回答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).

回答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

回答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...);

回答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);
}

回答5:

What about:

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

This woks for me.

回答6:

For outputing String as text/plain use:

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