Making Struts send 500 Internal Server Error when exceptions get thrown

Question

I'm working on an AJAX-enabled JavaScript frontend that makes calls to a Java backend written with Struts. My problem is that when the backend throws an exception, the client still sees a "200 OK" HTTP response code instead of "500 Internal Server Error" like one would expect.

This is tripping me up repeatedly because my 3rd-party client JavaScript library depends on HTTP status codes to determine if something is wrong with an AJAX call, as most modern libraries normally do. The errors pass undetected until my code blows up when it tries to parse what would normally be JSON.

I really want to avoid hacking my client JS library in order to gracefully handle these errors. So then, how can I make Struts give me a 500 status code when there's been an unhandled exception in the backend? Shouldn't this be Struts's default behavior?

Edit: The client-side code is irrelevant in this case. I am needing to fix the server so it sends the appropriate status code when unhandled exceptions happen. Thanks!

Answer 1

I figured out one way to do it. I'm not sure if it's the best or easiest, but it works. I found the Struts Exception Configuration guide and added the following to my <package> inside struts.xml:

<global-results>
  <result name="exception">/exception.jsp</result>
</global-results>

<global-exception-mappings>
  <exception-mapping exception="java.lang.Exception" result="exception" />
</global-exception-mappings>

This causes all unhandled exceptions to be redirected to /exception.jsp. And here are the JSP's contents:

<%@ taglib prefix="s" uri="/struts-tags" %>
<%@ page contentType="application/json; charset=UTF-8" %>
<% response.setStatus(500); %>
{"success": false,"errors": "<s:property value="%{exception.message}"/>"}

You'll note on the 3rd line that I manually set the response code to 500.

This gave me a new problem: exceptions were not being logged any more. As suggested in the aforementioned Struts guide, I solved this by adding the following to my <package> in struts.xml as well:

<interceptors>
    <interceptor-stack name="appDefaultStack">
        <interceptor-ref name="defaultStack">
            <param name="exception.logEnabled">true</param>
             <param name="exception.logLevel">ERROR</param>
        </interceptor-ref>
    </interceptor-stack>
</interceptors>

<default-interceptor-ref name="appDefaultStack" />

Struts: -1 for making such a simple and obvious feature NOT the default, and another -1 for making the solution so obtuse.

Answer 2

Update: I've fixed the <global-results> section (which was missing the httpheader tag)

I like your solution better, but here's another way you could do it if you didn't want to mess w/ setting the response header in the jsp.

1. In struts.xml, create a global exception mapping from "java.lang.Exception" to a result named "exception"
2. In struts.xml, create a global result which maps "exception" to a httpheader result with a value of 500.
3. In web.xml, create an error-page entry that maps error code 500 to your error page location.

So, for struts.xml:

<global-exception-mappings>
    <exception-mapping exception="java.lang.Exception" result="exception" />
</global-exception-mappings>

<global-results>
    <result name="exception" type="httpheader">
        <param name="error">500</param>
    </result>
</global-results>

And for web.xml

<error-page>
    <error-code>500</error-code>
    <location>/exception.jsp</location>
</error-page>

This works but has some big downsides. The servlet container is rendering your error page (not struts) so you wont have access to the original error message or the struts valueStack. Exception logging will still work, however (if you have enabled it).

As an aside, I too find it baffling that struts makes this so difficult. In every other framework I've dealt with the concept of returning an error page and an error code is pretty trivial to implement.