使用PrintWriter时已为此响应调用getOutputStream（）

Question

I'm working on this Java Sprint 3.0 application where I'm passing data to a dataTable. Everything works fine, but every so often I see this error:

ERROR [[dispatcher]] Servlet.service() for servlet dispatcher threw exception
java.lang.IllegalStateException: getOutputStream() has already been called

for this response.

Here is my code:

@PreAuthorize("hasRole('ADMIN')")
@RequestMapping(value = "/dataTable", method = RequestMethod.GET)
public void serverSide(Model model, HttpServletRequest request, HttpServletResponse response) throws IOException {

  response.setContentType("application/json");
  response.setHeader("Cache-Control", "no-store");

  PrintWriter out = response.getWriter();
  out.print(dataTableService.viewUsers(request));
}

I have tried adding the following:

out.flush();
out.close();
return;

I have also tried using response.getOutputStream().print(dataTableService.viewUsers(request)) and response.getWriter().append(dataTableService.viewUsers(request)) instead of using a PrintWriter but nothing seems to fix it.

EDIT:

Here is the stacktrace:

Answer 1

The basics are:

1. headers must be written first;
2. then the content must be written using either getOutputStream or getWriter .

What still can go wrong:

• Basic errors like using both response.getOutputStream() and response.getWriter() - very unlikely here.

• Control flow:

   if (...) { ... redirect // Missing return } ... normal output 

• A filter or interceptor: ordinarily unlikely; though here are annotations.

   out.flush(); // OKAY // Probably NOT OKAY: out.close(); 

• Servlet fields being used. The service methods should be stateless in themselves.