Creating a JAR file

Packaging JARs

Recently, I needed to create a .jar file from my Java application in order to use it as a dependency in a Clojure project. This is done with the jar terminal command.

The jar command has a lot of options, and there's a lot of information out there about previous versions, so it took some research to figure out the right approach for me. The solution I came up with was:

cd out
jar -cfe MyHttpServer.jar MyServer.Main .

Explanation

• cd to change directory to out to run the command inside the folder where the compiled class files are
• The c flag denotes that we are creating a new file
• The f flag denotes that we will specify the file name
• MyHttpServer.jsr is the name of the file to be created
• The e flag is to denote that we will specify the entry point of the application
• MyServer.Mainis the specified entry point
• The . means "compile all the class files in this folder"

The e option auto-generates a manifest file that stores metadata about our application, like the entry point, version information, and classpath configuration. It is possible to write a custom manifest file for more complex applications. For my purposes, I found simply using e instead of providing a custom manifest file to be sufficient.