Can you call a servlet with a link?

Question

Can you call a servlet with a link? For example

<a href="/servletName">link text</a>

And possibly pass parameters to the request object by adding them to the querystring.

If not, I have seen this kind of thing:

RequestDispatcher dispatcher = getServletContext().getRequestDispatcher(/MyServlet); 
dispatcher.include(request,response); 

But how would I trigger this? For example if it was JavaScript code I could put it within a jQuery click function, or if this was a servlet I would put it into a method.

But how do I call this code from within a JSP. As far as I know you can't call Java code with JavaScript events.

Answer 1

<a href="servletUrl?param=value">click</a>

is perfectly legal and will work.

That will make the doGet(..) method of the servlet be called, and you can get the parameter using request.getParameter("param")

Answer 2

Just to clear a misconception:

As far as I know you can't call Java code with Javascript events.

You can perfectly call Java code with JavaScript code (and events). To the point, you just need to let JavaScript send a fullworthy HTTP request to the server side. There are basically 3 ways for this.

1. The first way is to simulate invocation of an existing link/button/form. E.g.

   <a id="linkId" href="http://www.google.com/search?q=balusc">Link</a>
   
   <script type="text/javascript">
       document.getElementById('linkId').click();
   </script>
   

   and

   <form id="formId" action="http://www.google.com/search">
       <input type="text" id="inputId" name="q">
   </form>
   
   <script type="text/javascript">
       document.getElementById('inputId').value = 'balusc';
       document.getElementById('formId').submit();
   </script>
   

2. The second way is to use window.location to fire a plain GET request. For example:

   <script type="text/javascript">
       var search = 'balusc';
       window.location = 'http://www.google.com/search?q=' + search;
   </script>
   

3. The third way is to use XMLHttpRequest object to fire an asynchronous request and process the results. This technique is the base idea of "Ajax". Here's a Firefox compatible example:

   <script type="text/javascript">
       function getUrl(search) {
           var xhr = new XMLHttpRequest();
           xhr.onreadystatechange = function() {
               if (xhr.readyState == 4) {
                   var responseJson = eval('(' + xhr.responseText + ')');
                   var url = responseJson.responseData.results[0].unescapedUrl;
                   var link = document.getElementById('linkId');
                   link.href = link.firstChild.nodeValue = url;
                   link.onclick = null;
               }
           }
           var google = 'http://ajax.googleapis.com/ajax/services/search/web?v=1.0&q='
           xhr.open('GET', google + search, true);
           xhr.send(null);
       }
   </script>
   
   <p>My homepage is located at: <a id="linkId" href="#" onclick="getUrl('balusc')">click me!</a></p>
   

   This can be rewritten in a shorter and crossbrowsercompatible manner with jQuery.

Just substitute http://www.google.com/search with your own servlet to get the above examples to work in your environment.

For more background information, you may find this article useful as well.