title: "Servlet is currently unavailable" error on Tomcat
body: <p>I'm trying to write a simple Java EE app in Eclipse EE Juno. Here is the file hierarchy of my project:</p>
  
  <p><img src="https://i.stack.imgur.com/QtjBL.png" alt="project file hierarchy"></p>
  
  <p>index.jsp:</p>
  
  <pre><code>&lt;jsp:forward page="/departments.do"/&gt;
  </code></pre>
  
  <p>web.xml</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0"&gt;
    &lt;display-name&gt;UniBudget&lt;/display-name&gt;
    &lt;welcome-file-list&gt;
      &lt;welcome-file&gt;index.html&lt;/welcome-file&gt;
      &lt;welcome-file&gt;index.htm&lt;/welcome-file&gt;
      &lt;welcome-file&gt;index.jsp&lt;/welcome-file&gt;
      &lt;welcome-file&gt;default.html&lt;/welcome-file&gt;
      &lt;welcome-file&gt;default.htm&lt;/welcome-file&gt;
      &lt;welcome-file&gt;default.jsp&lt;/welcome-file&gt;
    &lt;/welcome-file-list&gt;
    &lt;servlet&gt;
      &lt;servlet-name&gt;Do&lt;/servlet-name&gt;
      &lt;servlet-class&gt;control.Controller&lt;/servlet-class&gt;
    &lt;/servlet&gt;
    &lt;servlet-mapping&gt;
      &lt;servlet-name&gt;Do&lt;/servlet-name&gt;
      &lt;url-pattern&gt;*.do&lt;/url-pattern&gt;
    &lt;/servlet-mapping&gt;
  &lt;/web-app&gt;
  </code></pre>
  
  <p>The error I get:</p>
  
  <pre><code>HTTP Status 503 - Servlet Do is currently unavailable
  </code></pre>
  
  <p>And the question: why is this happening and how can I fix it?</p>