Send error message as JSON object

问题:

I have two servlet: first servlet is similar to a client and creates an HttpURLConnection to call the second servlet.

I would like send a special error, formatted like a JSON object, so I call sendError method in this way:

response.sendError(code, "{json-object}")

But in the first servlet when I read error with getResponseMessage method I just get standard HTTP message and not my json object as a string.

How I can get my json string?

回答1:

From the HttpServletResponse#sendError() javadoc:

The server defaults to creating the response to look like an HTML-formatted server error page containing the specified message, setting the content type to "text/html", leaving cookies and other headers unmodified. If an error-page declaration has been made for the web application corresponding to the status code passed in, it will be served back in preference to the suggested msg parameter.

So with this approach you have no other option than extracting the message from the HTML response yourself. JSoup may however be useful in this.

To achieve what you want, you need to set the error code and write the response yourself, e.g.

response.setStatus(code);
response.setContentType("application/json");
response.setCharacterEncoding("UTF-8");
response.getWriter().write(json);

Instead of code you could by the way also use one of the HttpServletResponse.SC_XXX constants for this.