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Code Defenders

This is Code Defenders, a mutation testing game. Publicly available at

For information regarding running Code Defenders via docker see the corresponding documentation.


The repository contains a Vagrantfile for use with Vagrant to quickly create a dev(!) environment.

If you have vagrant installed and configured, simply execute vagrant up. This will create a VM with all required software installed, but initially without the codedefenders.war file deployed.
By default port forwarding for the tomcat server to port 8080, JVM remote debugging to port 8000 and for the database port to port 3306 are set up.

The database name, user and password are all codedefenders.
The tomcat manager application (api and web) can be accessed with username and password manager.
Admin access to codedefenders is possible with username and password admin.

Codedefenders can be deployed to the VM e.g. via the maven deployment steps mentioned below and the manager credentials mentioned above. Everything required should already be setup.

Installation & Configuration

Software Requirements

  • Java (Version 1.8 or later)
  • Tomcat Server (Version 9)
  • Apache Maven
  • Apache Ant
  • MySQL (e.g. MariaDB)


This guide assumes:

  • you are running Debian 10 as OS
  • you installed all the required software

Modify the configuration

Copy the file to /var/lib/tomcat9/conf/ and set the values to match your environment.
The only required value is data.dir, all other properties have sensible default values.

Adapt the systemd service

On Debian 10 tomcat9 by default has only very limited write permissions.
To allow the data.dir to be located outside of the /var/lib/tomcat9/webapps/ folder hierarchy you have to systemctl edit tomcat9 and add the following code:

ReadWritePaths="<data.dir path>"

Setup the database

The MySQL or MariaDB database and the user to access the database have to be created before the first run.

Create the data.dir and run the installation script

Create the data.dir folder with the appropriate owner/group and permissions.
CodeDefenders (resp. the tomcat user) requires write permissions to the folder to create missing directories/files and to save the source code files.

To install Code Defenders automatically, execute the script under the installation folder with the appropriate user and pass the file as input.

cd installation
./ /var/lib/tomcat9/conf/

The script performs a basic availability check of required software. The data directory folder structures created. All the required dependencies and files are automatically downloaded.

If any installation step fails, the installation process aborts and prints an error message.

Note: Depending on the chosen data directory and Tomcat installation in place, root access may be necessary to create required folders. Similarly, additional configurations might be needed. For example, if Tomcat runs under a different user, data directory accesses and ownership might be need to be adjusted.

Note: Code Defenders also requires that its MySQL user owns specific privileges to create databases and tables. Additionally, it requires INDEX privileges, otherwise the installation fails with an error message similar to:

ERROR 1142 (42000) at line 183: INDEX command denied to user

Set up Code Defenders admin users

Code Defenders currently relies on the Tomcat authentication system for providing a username-role mapping that can be used to assign admin privileges.

Assigning admin privileges to a Code Defenders users can be done by setting up a mapping between the username (<CODEDEFENDERS_USERNAME>) and the configured auth.admin.role (codedefenders-admin by default) in the tomcat-users.xml file.
This file is per default located in ${CATALINA_HOME}/conf.

  <role rolename="codedefenders-admin"/>
  <user username="<CODEDEFENDERS_USERNAME>" roles="codedefenders-admin"/>

Care should be taken, so the chosen CODEDEFENDERS_USERNAME can not be simply registered by anyone.

All system configuration and privileged features are accessible for admin users under the /admin page. Configurations are organized in three groups:

  • Game management: Create bulk games for an entire class, distribute students among the games, and assign roles to students.
  • User management: Check and update users settings, and forcefully reset passwords.
  • System settings: Customize technical aspects of Code Defenders and include several advanced settings.

Build and Deployment

For successful deployment, both Tomcat and MySQL services must be running.

Tests can be skipped via -DskipTests
If you want to run the tests be sure the library is present on your system as the database tests depend on it.

For additional information on the system- and integration-tests see the Testing document.


To deploy you simply need to copy the codedefenders.war file to the tomcat webapps directory, with the context path as name.
E.g to deploy codedefenders at the tomcat root path (http://localhost:8080/) you can simply cp target/codedefenders.war /var/lib/tomcat9/webapps/ROOT.war

You can either download the codedefenders.war file from the latest release or build it yourself with mvn clean package -DskipTests.

Automatic Deployment via Maven

Alternatively you can automatically deploy with maven. For this, Tomcat requires a user with manager-script role, which can be configured in $CATALINA_BASE/conf/tomcat-users.xml (CATALINA_BASE is the Tomcat installation directory).

The maven deployment is configured via a file. Simply copy the file over and adjust the values to your needs.

<role rolename="manager-script"/>
<user username="<MY_USER>" password="<MY_USER_PASSWORD>" roles="manager-script"/>

Note: This requires the tomcat manager application to be installed, which on Debian is provided by the tomcat9-admin package.

Code Defenders is built and deployed with Maven using the following commands.

mvn clean deploy -DskipTests


This project is supported IMPRESS. Check the official website for a detailed list of supporters.