回调函数没有在jquery中执行

Question

I was learning to send a get request in jquery. The following is the block of code which makes the get request. I checked in my servlet that the get request was made successfully but the callback function was not invoked. I can't figure out the problem.

$.get('http://localhost:8080/PC_controlo/StatusServlet?id=1001',
function(data){
alert('hello');
});

And the browsers network tab shows this

[01:21:26.759] GET http://localhost:8080/PC_controlo/StatusServlet?id=1001 [HTTP/1.1 200 OK 1ms]

+

This is what I have done in my servlet.

PrintWriter out = response.getWriter();
            out.write("Working");
            out.close();

and .fail(msg){ alert('Failed with message:'+JSON.stringify(msg)); gave the following message

Failed with message: {"readyState":0,"responseText":"","status":0,"statusText":"error"}

Thanks in advance :).

Answer 1

I did a few tests with replacing the URL with Google.com, and I encountered the same problem. I noticed if you use .done(), .always(), and .error(), you might have better luck figuring out exactly what is going on. Check out this JSFiddle:

http://jsfiddle.net/gQfsd/

$.get('http://www.google.com/')
.done(function(data) {
    alert('Success! Data loaded: ' + data);   
})
.fail(function(msg) {
    alert('Failed with message: ' + JSON.stringify(msg));
})
.always(function() {
    alert('Always Alerts');
});

Answer 2

The most likely scenario is that your request did not complete successfully, so your success handler function callback is not called, because there was no success.

According to the jQuery docs $.get 's success handler function is: (emphasis mine)

A callback function that is executed if the request succeeds.

To get more control over the error handling of the AJAX request, It's usually recommended to use $.ajax instead, which you can read the documentation for here . This will allow you to use an error callback that will trigger when the request wont complete for some reason.

$.get is just a shortcut method that delegates to $.ajax under the covers.

---

Why is your request failing? No clue. That's between your browser and the server you are talking to. It could be a million things. Check the network tab of your browser development console and see what the request and response looks like.

Answer 3

Probably a communication error with the call itself, or the call failed for some reason. Check for failures too:

$.get('http://localhost:8080/PC_controlo/StatusServlet?id=1001')
 .success(function(result) {alert('success'); })
.error(function(jqXHR, textStatus, errorThrown) {alert(textStatus) });