title: how to -- url mapping in filter?
body: <p>I already have an unaswered question here that how and when .do is appended in any url when we use servlets...</p>
  
  <p>Today when i learnt about filters, another doubt occured:</p>
  
  <pre><code>&lt;filter-mapping&gt;
          &lt;filter-name&gt;struts2&lt;/filter-name&gt;
          &lt;url-pattern&gt;/*&lt;/url-pattern&gt;
      &lt;/filter-mapping&gt;
  </code></pre>
  
  <p>In this case what is /*, if it means that it will check all the requests? Besides when an action is invoked the <code>url says: http://..../myapp/register.action.</code> Like <code>.do</code>,  <code>.action</code> is appended and it is not even mentioned in mapping. Please clear this doubt and if possible the <code>.do</code> doubt also...</p>