How to write ResponseEntity to HttpServletResponse?

Question

How to write ResponseEntity to HttpServletResponse (as it makes @ResponseBody)?

For example I have authentication success handler:

@Override
public void onAuthenticationSuccess(HttpServletRequest request, HttpServletResponse response, Authentication authentication) throws IOException, ServletException {
    Map responseMap = new HashMap();
    responseMap.put("user", "my_user_name");
    ResponseEntity responseEntity = new ResponseEntity(response, HttpStatus.OK);
}

If use MappingJackson2HttpMessageConverter I have error: "Could not write content: not in non blocking mode."

Code:

HttpOutputMessage outputMessage = new ServletServerHttpResponse(response);
messageConverter.write(responseEntity, null, outputMessage);

What are the best practices of implementation handlers with HttpServletResponse?

Answer 1

You can use a custom response object, convert it to a JSON string using the Jackson's ObjectMapper and write the result into the request.

---

Example

MyResponseObject.java

private String user;

public String getUser() {
    return user;
}

public void setUser(String user) {
    this.user = user;
}

MyAuthenticationSuccessHandler.java

@Override
public void onAuthenticationSuccess(HttpServletRequest request, HttpServletResponse response, Authentication authentication) throws IOException, ServletException {
    MyResponseObject responseObj = new MyResponseObject();
    responseObj.setUser("my_user_name");

    String json = new ObjectMapper().writeValueAsString(responseObj);

    httpServletResponse.setStatus(HttpStatus.OK.value());
    httpServletResponse.getWriter().write(json);
    httpServletResponse.flushBuffer();
}  

Answer 2

Based on andrearro88's answer, I have made this generic function to copy a ResponseEntity to a HttpServletResponse:

public static void populateResponse(ResponseEntity<String> responseEntity, HttpServletResponse servletResponse)
        throws IOException {
    for (Map.Entry<String, List<String>> header : responseEntity.getHeaders().entrySet()) {
        String chave = header.getKey();
        for (String valor : header.getValue()) {
            servletResponse.addHeader(chave, valor);                
        }
    }

    servletResponse.setStatus(responseEntity.getStatusCodeValue());
    servletResponse.getWriter().write(responseEntity.getBody());
}