Error message from Java to Ajax is not returned properly

Question

When the java program does not find the required information I want to return an appropriate error message (could be one of a number of identified reasons). My java code is:

}else{
    response.sendError(response.SC_BAD_REQUEST, "Captcha description not correct");
    response.getWriter().write("Captcha description incorrect.");
}

And the ajax is:

$.ajax({
    type: "POST",
    url: "AccountRecoveryQuestionsView",
    cache: false,
    data: $(questionForm).serialize(),
    success: function(data){
        $('#ajaxGetUserServletResponse').text(data);
    },
    error: function(data) {
        $("#accountName").focus();
        //$('#ajaxGetUserServletResponse').text('An error occured validating the questions.');
        $('#ajaxGetUserServletResponse').text(data);
    }
});

The error function is triggered; however, the message is not displayed.

I have changed the code to:

          statusCode: {
                400: function(jqXHR, textStatus, errorThrown){
                    alert(jqXHR.status);
                    alert(textStatus);
                    alert(errorThrown);
                    $("#accountName").focus();
                    $('#ajaxGetUserServletResponse').text(errorThrown);
                }
            },

And the result is 400, error, blank.

I have changed the ajax to:

          .fail (function(jqXHR, textStatus, errorThrown) {
                alert(jqXHR.status);
                alert(textStatus);
                alert(errorThrown);
                alert(jqXHR.statusText);
                alert(jqXHR.responseText);
                $("#accountName").focus();
                //$('#ajaxGetUserServletResponse').text('An error occured validating the questions.');
                //$('#ajaxGetUserServletResponse').text(errorThrown);
                $('#ajaxGetUserServletResponse').text(jqXHR.responseText);
            });

And alert(jqXHR.responseText); is returning:

<!doctype html><html lang="en"><head><title>HTTP Status [400] – [Bad Request]</title><style type="text/css">h1 {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:22px;} h2 {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:16px;} h3 {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:14px;} body {font-family:Tahoma,Arial,sans-serif;color:black;background-color:white;} b {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;} p {font-family:Tahoma,Arial,sans-serif;background:white;color:black;font-size:12px;} a {color:black;} a.name {color:black;} .line {height:1px;background-color:#525D76;border:none;}</style></head><body><h1>HTTP Status [400] – [Bad Request]</h1><hr class="line" /><p><b>Type</b> Status Report</p><p><b>Message</b> Captcha description not correct</p><p><b>Description</b> The server cannot or will not process the request due to something that is perceived to be a client error (e.g., malformed request syntax, invalid request message framing, or deceptive request routing).</p><hr class="line" /><h3>Apache Tomcat/8.5.15</h3></body></html>

How do I just get the error message "Captcha description not correct". This is contained in the above.

`SC_BAD_REQUEST` is `400` and you should do: `$.ajax({ statusCode: { 400: function() { //do something } } });` — Aniket Sahrawat, Mar 26 '18 at 04:48
In regard of `#sendError`: "If the response has already been committed, this method throws an IllegalStateException. After using this method, the response should be considered to be committed and _should not be written to_." — Kristin, Mar 26 '18 at 04:51
Thanks @Aniket Sahrawat. This works. Is there a way to return a different error message for each exception as I have around five different exceptions that can occur (e.g., incorrect captcha name, question not answered correctly, email address not on file). — Glyn, Mar 26 '18 at 05:10
If you are throwing exceptions for them then it is not a correct way of handling client errors. You should just write a proper response code and message and send it back to the client whenever a client error occurred. — Aniket Sahrawat, Mar 26 '18 at 05:20
I am doing this statusCode: { 400: function() {$('#ajaxGetUserServletResponse').text("Captch not correct.");} }, — Glyn, Mar 26 '18 at 05:21
Is there a way to return a different error code for each type of error? Only one type of error will be returned. Or how do I return the error message? — Glyn, Mar 26 '18 at 05:23
Don't do that, instead map the response code inside your `error` function. Here is the example: https://stackoverflow.com/a/6700873/6099347 — Aniket Sahrawat, Mar 26 '18 at 05:25
Hi Aniket, I have made the change as edited above. The displayed is "400, error, blank". — Glyn, Mar 26 '18 at 07:21

Kristin · Accepted Answer · 2018-03-28T04:55:23.160

The HttpServletResponse object should not be written to after #sendError has been called, as stated

If the response has already been committed, this method throws an IllegalStateException. After using this method, the response should be considered to be committed and should not be written to.

hence:

response.sendError(...);
response.getWriter().write(...); // Should not be done

You should use the static field access of the error codes. In your code, you use response.SC_BAD_REQUEST, when you should use HttpServletResponse.SC_BAD_REQUEST. Writing the int code yourself, e.g. sendError(400, ...), does not change the outcome.

The .error call for the $.ajax-function in jQuery, has been removed since version 3.0, so do not use it. Instead, you should use .done, .fail and .always. .done is the equivalent of .success, while .fail is the equivalent of .error, and .always is kinda like a finally-block in a try-catch (will, as the name implies, always run, regardless).

$.ajax always returns a jQuery XMLHttpRequest object, jqXHR. You can thus run method calls directly on the $.ajax-call, like

var jqxhrobj = $.ajax({
    type: "POST",
    url: "AccountRecoveryQuestionsView",
    cache: false,
    data: $(questionForm).serialize()
})
.done(function(jqXHR, textStatus, errorThrown) {
    // Success here
    $('#ajaxGetUserServletResponse').text(jqXHR.responseText);
})
.fail(function(jqXHR, textStatus, errorThrown) {
    // Fail, do something about the error
    // Since you have several error codes you want to handle
    // you could for instance use a switch case
    switch(jqXHR.status) {
        case "400":
            // It might be an int, or even "400 Bad request",
            // change accordingly

            // Do something to handle the error
            break;
        default:
            // Handle errors not specified with a case
            break;
    }
});


// Later in the js code

jqxhrobj.always(function() {
    // Execute something here, regardless of success/failure of the $.ajax-call
});

Further information on the jqXHR object can be read here.

The responseText will contain a fully formatted html-output, with head, body and so on. If you look at the body of the responseText, it looks like this:

<body>
    <h1>HTTP Status [errorCode] – [errorCode description]</h1>
    <hr class="line" />
    <p><b>Type</b> Status Report</p>
    <p><b>Message</b> [message passed as 2nd argument in the sendError-call]</p>
    <p><b>Description</b> [full errorCode description]</p>
    <hr class="line" />
    <h3>Apache Tomcat/8.5.15</h3>
</body>

You could use .find (see here) on the jqXHR.responseText - find the p-tags inside of the body. You should have 3 elements returned; the message will be inside the 2nd result element. You might want to do some sort of substr, to get rid of <b>Message</b>.

A simple but naive approach, that relies on the output to always have exactly the same structure:

var message = jqXHR.responseText.find("p:eq(1)").text();
// text() will not return the <b>-tags, just "Message [msg passed as argument]"
// We'll just substr from the end of "Message"
message = message.substr(7));
// Remove any leading/trailing whitespace
message = message.trim();
// message now contains the error message from #sendError
alert(message);

I have made the change. Please see my edit above. However, I am unable to get the error message to display. It is embedded in the long string of HTML. — Glyn, Mar 26 '18 at 21:20
I could replace "response.sendError(response.SC_BAD_REQUEST, "Captcha description not correct");" with "response.sendError(401, "Captcha description not correct");" using a different error code (e.g., 401. 402, 403) for each error test use the case to test for each and display the appropriate error message. Is that a correct approach or a bad hack? — Glyn, Mar 26 '18 at 21:56
I've added a suggestion of how to get the error message, although it does not include a written example. If you need help with it, you'll have to ask. I also included information regarding the usage of the static fields (e.g. SC_BAD_REQUEST), at the top, after the code block with `response.sendError...` — Kristin, Mar 26 '18 at 23:11
I am having trouble starting on this. I have tried var message = $(jqXHR.responseText).find("p"); alert(message) and this returns "[object Object]". — Glyn, Mar 27 '18 at 01:32
A small btw: you do not have to add the jQuery-selector syntax `$()`, if you're handling a jQuery object (which jqXHR is in this case). You can just call any jQuery-related function against it, like you see in my example above, where I use the `find()` method. — Kristin, Mar 27 '18 at 03:01
How about "includes" is that acceptable: if(jqXHR.responseText.includes('Captcha description not correct')){ $('#ajaxGetUserServletResponse').text('Captcha description not correct'); }else{ $('#ajaxGetUserServletResponse').text('An error occured.'); } — Glyn, Mar 27 '18 at 04:51
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/167610/discussion-between-eli-and-glyn). — Kristin, Mar 27 '18 at 08:42

davidluckystar · Answer 2 · 2018-03-26T05:13:15.420

0

Try to flush and close your writer

...
response.getWriter().flush();
response.getWriter().close();

If it didnt help, make sendError call the last one like this

response.getWriter().write("Captcha description incorrect.");
response.sendError(response.SC_BAD_REQUEST, "Captcha description not correct");

edited Mar 26 '18 at 05:13

answered Mar 26 '18 at 04:48

davidluckystar

928
5
15

oh, I just realized, mb sendError is flushing the buffer, so you should make it last - see my update – davidluckystar Mar 26 '18 at 05:13

score 0 · Answer 3 · answered Mar 26 '18 at 05:39

0

you can return the following

Response.status(500).entity("Captcha description incorrect. ").build();

Modify the error code based on your requirement,

answered Mar 26 '18 at 05:39

Harshita Sethi

2,035
3
24
46

Sorry harshita, this does not answer the OP. You seem to be lost by the wording in OP. – Aniket Sahrawat Mar 26 '18 at 05:47

Error message from Java to Ajax is not returned properly

3 Answers3