title: What does "HttpServletResponse is committed" mean?
body: <p>As stated in title, what does it mean that HttpServletResponse is committed?</p>
  
  <p>I have some request interceptor, extending <code>HandlerInterceptorAdapter</code>, that overrides <code>postHandle</code> method. Post handle method takes parameter <code>final HttpServletResponse response</code>. In method body there is an <code>if</code> statement checking if <code>response.isCommitted()</code>, what exactly does that check?</p>
  
  <pre><code>private static final String voidResponse = "null";
  
  @Override
      public void postHandle(final HttpServletRequest request, final HttpServletResponse response, final Object handler,
              final ModelAndView modelAndView) throws IOException {
          if (!response.isCommitted()) {
              if (DefaultServletHttpRequestHandler.class == handler.getClass()) {
                  return;
              }
              response.setStatus(200);
              response.setCharacterEncoding("UTF-8");
              response.setContentType("application/json");
              try (final Writer writer = response.getWriter()) {
                  writer.write(voidResponse);
              }
              log.info("void method called, respond with 200 and null");
  
              response.flushBuffer();
          }
      }
  </code></pre>