How to run a JAR file
To execute a JAR file, use the straightforward command:
This requires Java being installed and java being set in your system's PATH.
Notably, this instruction assumes that a Main-Class attribute, which serves as the application's entry point, is specified in the JAR's manifest file. The manifest file should end with a newline to parse correctly. Here's how to package your compiled .class files into an executable JAR:
Ensure the class name defined in Main-Class is your application's entry point and is properly referenced in the manifest.
Nailing the fundamentals
Before proceeding, confirm Java JDK installation. Compile your .java files using:
The process: From source code to JAR
Follow these steps to create a JAR file, with the main class set as the entry point:
-
Craft your
manifest.mf—define the main class appropriately: -
The manifest must always end with a newline character. It's not pedantic—it's standard.
-
Bundle the classes in a JAR:
Launch and troubleshoot
To execute the JAR, the typical command is:
Encountering trouble? Verify your manifest file is nested in the META-INF directory and the package structure aligns with the class definitions.
Deciphering the Manifest
- Check for a valid manifest version with
Manifest-Version: 1.0. - Ensure the entry point in the
Main-Classdefinition matches the actual class name.
Get the nitty-gritty with the Command Line
Run your JAR in the command line rather than double-clicking for extended error logs—enjoy the bittersweet symphony of bug fixing!
Alternative launching processes
Alternate methods to run your JAR include:
- Using classpath:
java -cp awesome-app.jar your.package.MainClass. - If the ZIP utility was a person, it would be your new best friend—employ it to modify the manifest post-creation.
Behold, the non-executable JARs
For non-executable JARs, you'll have to call the main class directly:
Was this article helpful?