Need to call servlet from javascript along with parameters

Question

I have session key that is a javascript variable which i get from a Rest api call. I need to call a servlet and pass that key as a parameter. What Javascript function can I use to do that?

Answer 1

No JavaScript function per se, but browsers usually* provide an XMLHttpRequest object and you can go through that.

Libraries such as YUI and jQuery provide helper functions to simplify its usage.

* for a value of "usually" that includes pretty much any browser that supports JavaScript and was released since Netscape 4 died

Answer 2

Several ways:

1. Use window.location to fire a GET request. Caveat is that it's synchronous (so the client will see the current page being changed).

   window.location = 'http://example.com/servlet?key=' + key;
   

2. Use form.submit() to fire a GET or POST request. The caveat is also that it's synchronous.

   document.formname.key.value = key;
   document.formname.submit();
   

   With

   <form name="formname" action="servlet" method="post">
       <input type="hidden" name="key">
   </form>
   

   Alternatively you can also only set the hidden field of an existing form and just wait until the user submits it.

3. Use XMLHttpRequest#send() to fire an asynchronous request in the background (also known as Ajax).

   var xhr = new XMLHttpRequest();
   xhr.open('GET', 'http://example.com/servlet?key=' + key, true);
   xhr.send(null);
   

4. Use jQuery to send a crossbrowser compatible Ajax request (above works in real browsers only, for MSIE compatibility, you'll need to add some clutter ;) ).

   $.get('http://example.com/servlet?key=' + key);
   

Either way, the key will be just available by request.getParameter("key") in the servlet. To learn more about communication between Java/JSP and JavaScript, you may find this article useful as well.