CFR will decompile modern Java features - Java 8 lambdas (pre and post
Java beta 103 changes), Java 7 String switches etc, but is written
entirely in Java 6. (FAQ)

To use, simply run the cfr command, with the class name you want to
decompile (either as a path to a class file, or as a fully qualified
classname on your classpath), and optionally the method name. (--help
to list arguments).

Alternately, to decompile an entire jar, simply provide the jar path,
and if you want to emit files (which you probably do!) add --outputdir
/tmp/putithere