title: Order of Tomcat Classloaders: common, shared, and server
body: <p>The Tomcat <a href="http://tomcat.apache.org/tomcat-7.0-doc/class-loader-howto.html" rel="nofollow noreferrer">Class Loader HOW-TO</a> documentation describes 4 different class loaders:</p>
  
  <ol>
  <li>Bootstrap</li>
  <li>System</li>
  <li>Common</li>
  <li>Webapp</li>
  </ol>
  
  <p>In the default catalina.properties file, however, there are properties defined for a shared and server class loader as well.  In the default version of the file both of these properties are empty and the comments say: </p>
  
  <blockquote>
    <p>If left as blank, the "common" loader
    will be used as Catalina's
    "shared"/"server" loader.</p>
  </blockquote>
  
  <p>I have not been able to find any additional documentation about these class loaders.  My question is, in which order are the shared and system loaders searched relative to the common loader?  And additionally, what is the intended use for these class loaders?</p>