As a developer who splits his time between the .NET and Java platforms, I have been surprised and dismayed by the lackluster selection of decompilers in the Java ecosystem. Jad (no longer maintained, ...
jd-cmd is a command line Java Decompiler which uses JD Core from Java Decompiler project. You can use the jd-cli.bat (Windows) or jd-cli (Linux/Unix) scripts to run the the JAR file. Usage: java -jar ...