Local development

To run the code for your challenge locally, you’ll need java & mvn installed. Our test runners use Java 21 (as of November 2023).

The script for your challenge (like ./your_bittorrent.sh) will automatically compile your code using mvn before executing it. It’ll look something like this:

set -e
mvn -B --quiet package -Ddir=/tmp/codecrafters-redis-target
exec java -jar /tmp/codecrafters-redis-target/java_redis.jar "$@"

When running tests on our servers, the mvn command will only be run once and then commented out. This ensures that each test only runs the java -jar ... line.

File structure

  • The files for your solution are placed in the src/main/java directory.
  • src/main/java/Main.java contains the main function, which is what the test runner executes.

Adding more files

You can add more files and directories to src/main/java. The test runner will include them when compiling your code.

For example, if you added a file at src/main/java/Foo.java, you could use it like so:

By default, all files in src/main/java are in the default package. If you want to extract files into a different package, you’ll need to add a package declaration to the top of the file and change its location. Here’s what that’d look like:

Let’s say you wanted to extract Foo.java into the com.example package. Store Foo.java at src/main/java/com/example/Foo.java and add the following lines:

Use an IDE like IntelliJ IDEA which will automatically offer to move your file to a directory matching the package name.

Adding dependencies

You can add dependencies to your project by adding them to your pom.xml file.

For example, to add the gson library, add the following to the <dependencies> section in your pom.xml:


When you push your code next, the runner will automatically download the dependency.