How to decompile a whole Jar file?

Question

Does anyone know of a free decompiler that can decompile an entire Jar file instead of a single class? I have a problem with sub classes like name$1.class name$2.class name.class

Answer 1

2023: splashout suggests in the comments the Vineflower/vineflower decompiler (releases), renaming from Quiltflower to Vineflower.

java -jar vineflower.jar -dgs=1 c:\Temp\binary\library.jar c:\Temp\souce

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2022 update: QuiltMC/quiltflower is the latest most advanced Java decompiler:

Quiltflower is a modern, general purpose decompiler focused on improving code quality, speed, and usability.
Quiltflower is a fork of Fernflower and Forgeflower.

Changes include:

• New language features (Try with resources, switch expressions, pattern matching, and more)
• Better control flow generation (loops, try-catch, and switch, etc.)
• More configurability
• Better error messages
• Javadoc application
• Multithreading
• Optimization
• Many other miscellaneous features and fixes

Originally intended just for use with the QuiltMC toolchain with Minecraft, Quiltflower quickly expanded to be a general purpose java decompiler aiming to create code that is as accurate and clean as possible.

If the name sounds familiar it's because Quiltflower is a fork of Fernflower, the (in)famous decompiler that was developed by Stiver, maintained by Jetbrains, and became the default decompiler in Intellij IDEA.
Fernflower also quickly found its way into many other tools.

Over the past year, Quiltflower has added support for features such as modern string concatenation, a code formatter, sealed classes, pattern matching, switch expressions, try-with-resources, and more. Quiltflower also focuses on the code quality of the decompiled output, and takes readability very seriously.

See output examples.

Runs nice with jbang

https://github.com/QuiltMC/quiltflower/releases/download/1.8.1/quiltflower-1.8.1.jar

Or:

java -jar quiltflower.jar -dgs=1 c:\Temp\binary\library.jar c:\Temp\binary\Boot.class c:\Temp\source\

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2009: JavaDecompiler can do a good job with a jar: since 0.2.5, All files, in JAR files, are displayed.

See also the question "How do I “decompile” Java class files?".

The JD-Eclipse doesn't seem to have changed since late 2009 though (see Changes).
So its integration with latest Eclipse (3.8, 4.2+) might be problematic.

JD-Core is actively maintained.

Both are the result of the fantastic work of (SO user) Emmanuel Dupuy.

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2018: A more modern option, mentioned in the comments by David Kennedy Araujo:

JetBrains/intellij-community/plugins/java-decompiler/engine

Fernflower is the first actually working analytical decompiler for Java and probably for a high-level programming language in general.

java -jar fernflower.jar [-<option>=<value>]* [<source>]+ <destination>

java -jar fernflower.jar -hes=0 -hdc=0 c:\Temp\binary\ -e=c:\Java\rt.jar c:\Temp\source\

See also How to decompile to java files intellij idea for a command working with recent IntelliJ IDEA.

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2022 update: Florian Wendelborn suggests in the comments

this one works well: jdec.app from Leonardo Santos.

Answer 2

First of all, it's worth remembering that all Java archive files (.jar/.war/etc...) are all basically just fancy.zip files, with a few added manifests and metadata.

Second, to tackle this problem I personally use several tools which handle this problem on all levels:

• Jad + Jadclipse while working in IDE for decompiling .class files
• WinRAR, my favorite compression tool natively supports Java archives (again, see first paragraph).
• Beyond Compare, my favorite diff tool, when configured correctly can do on-the-fly comparisons between any archive file, including jars. Well worth a try.

The advantage of all the aforementioned, is that I do not need to hold any other external tool which clutters my work environment. Everything I will ever need from one of those files can be handled inside my IDE or diffed with other files natively.

Answer 3

If you happen to have both a bash shell and jad:

JAR=(your jar file name)
unzip -d $JAR.tmp $JAR
pushd $JAR.tmp
for f in `find . -name '*.class'`; do
    jad -d $(dirname $f) -s java -lnc $f
done
popd

I might be a tiny, tiny bit off with that, but it should work more or less as advertised. You should end up with $JAR.tmp containing your decompiled files.

Answer 4

I have had reasonable success with a tool named (frustratingly) "JD: Java Decompiler".

I have found it better than most decompilers when dealing with classes compiled for Java 5 and higher. Unfortunately, it can still have some hiccups where JAD would normally succeed.

Answer 5

Something like:

jar -xf foo.jar && find . -iname "*.class" | xargs /opt/local/bin/jad -r

maybe?

Answer 6

Insert the following into decompile.jar.sh

# Usage: decompile.jar.sh some.jar [-d]

# clean target folders
function clean_target {
  rm -rf $unjar $src $jad_log
}

# clean all debug stuff
function clean_stuff {
  rm -rf $unjar $jad_log
}

# the main function
function work {
  jar=$1
  unjar=`basename $jar.unjar`
  src=`basename $jar.src`
  jad_log=jad.log

  clean_target

  unzip -q $jar -d $unjar
  jad -d $src -ff -r -lnc -o -s java $unjar/**/*.class > $jad_log 2>&1

  if [ ! $debug ]; then
    clean_stuff
  fi

  if [ -d $src ] 
    then
      echo "$jar has been decompiled to $src"
    else
      echo "Got some problems check output or run in debug mode"
  fi
}

function usage {
  echo "This script extract and decompile JAR file"
  echo "Usage: $0 some.jar [-d]"
  echo "    where: some.jar is the target to decompile"
  echo "    use -d for debug mode"
}

# check params
if [ -n "$1" ]
  then
    if [ "$2" == "-d" ]; then
      debug=true
      set -x
    fi
    work $1
  else
    usage
fi

• chmod +x decomplie.jar.sh //executable
• ln -s ./decomplie.jar.s /usr/bin/dj

Ready to use, just type dj your.jar and you will get your.jar.src folder with sources. Use -d option for debug mode.

Answer 7

Note: This solution only works for Mac and *nix users.

I also tried to find Jad with no luck. My quick solution was to download MacJad that contains jad. Once you downloaded it you can find jad in [where-you-downloaded-macjad]/MacJAD/Contents/Resources/jad.

Answer 8

You extract it and then use jad against the dir.