Tomcat8 Custom ClassLoader
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Tomcat8 Custom ClassLoader

It is just a very simple project.

If you had ever been angry with this issue as I had, these small codes will be helpful

What's the problem

You should read this thread (Warning: TL;DR)


  • Tomcat 8 has a sensitive startup performance penalty if you use unpackWARs="false"

  • Mark Thomas (from Tomcat) do not like this options

  • They do not plan to solve this problem, and leave a guide as

    • use unique appBase values per Host
    • place the WARs outside all appBases
    • use context.xml files to add apps to a Host
    • leave unpackWARs as the default of true
  • They even want to remove it in future

What it solves

Now use a custom loader from this project (currently 0.5) fix some problems:

  • Startup performance

    Testing on a little test war from springframework about 7MB, the loading time

    • Using default loader: about 31 seconds
    • Using custom loader: about 8 seconds
  • CustomClassLoader's getURLs returns file:yy.jar URLs instead of jar:xx.war!/WEB-INF/yy.jar URLs

    That helps discovering classes in apps more easily

How to use

Build the project first, using

mvn package


mvn install


  1. drop the jar from target to your tomcat's ${catalina.base}/lib

  2. edit ${catalina.base}/conf/context.xml

  3. add this line to context.xml

    <Loader loaderClass="com.github.lwr.tomcat8.CustomWebappClassLoader"/>

    (after edited)

    <!-- The contents of this file will be loaded for each web application -->
        ... ...
        <!-- Bellow is the added new line -->
        <Loader loaderClass="com.github.lwr.tomcat8.CustomWebappClassLoader"/>
  4. start / restart your tomcat to check the load time