Lee Benfield's Java decompiler CFR is straight forward and can even batch decompile jar container.
- Download the most recent version of CFR (crf 0.1.15 at the time of writing)
wget http://www.benf.org/other/cfr/cfr_0_115.jar
- Run decompile with output into terminal
java -jar cfr_0_115.jar javaclasstodecompiles.class
2a. Run this if you want to export it into a separate Java file
java -jar cfr_0_115.jar javaclasstodecompiles.class > javaclasstodecompiles.java
- To decomplile a complete jar container
java -jar cfr_0_115.jar javacontainer.jar --outputdir ./javacontainer
Caveat: When using "--ouputdir" the directory path is not relative to the folder CFR runs in. So make sure you either use an absolute path or the "." for relative paths.
Alternativie decompiler: javadecompilers.com