How to Decompile a JAR File into .java Source Files Using Command Prompt

How can I use the command prompt to decompile a JAR file into .java files?

java -jar fernflower.jar input.jar output_directory

Decompiling a JAR file into Java source files can be achieved using various tools. This guide will focus on using command-line tools for decompilation, specifically the Fernflower decompiler, which is an open-source tool widely used for this task.

java -jar fernflower.jar input.jar output_directory

Causes

• The need for inspecting the source code of a JAR file for debugging or learning purposes.
• No direct access to the original .java files from compiled bytecode.

Solutions

• Download and set up the Fernflower decompiler as a JAR file from its GitHub repository.
• Use the command prompt to navigate to the directory containing the Fernflower JAR and the JAR file you want to decompile.
• Execute the decompilation command pointing to the input JAR file and specifying the output directory for the .java files.

Mistake: Forgetting to specify the correct path to the Fernflower JAR file.

Solution: Always ensure that you provide the correct path relative to your command prompt location.

Mistake: Not having the necessary permissions to write to the output directory.

Solution: Make sure you have write permissions in the specified output directory.

Mistake: Using an incompatible JAR file format with the decompiler.

Solution: Ensure that the JAR file is a valid Java archive and not an executable or corrupted file.