How to extract the source code from a *.jar file on a Mac?

Question

I'm very confused. I downloaded a *.jar file as a bit of software. So, I would like to extract the source code to look at it

I used the command jar xf filename.jar

which returned two more *.jar files and a *.class file. I still cannot open these in the terminal with standard text editors.

Perhaps this is not open source software? Is there an alternative to see what has been done here?

A .class file is Java object code, *not* source code. A jar need not contain any source code. — President James K. Polk, Sep 19 '16 at 00:23
@JamesKPolk I see. There's no way to see what code they wrote? — ShanZhengYang, Sep 19 '16 at 00:24
Looks like you have downloaded the lib rather than src, use jar tf filename.jar to view the contents — chifer, Sep 19 '16 at 00:25

score 24 · Accepted Answer · edited Oct 27 '22 at 17:38

24

Download FernFlower.jar: https://the.bytecode.club/fernflower.jar //the fernflower.jar site changed from http to https
Documentation: http://the.bytecode.club/fernflower.txt
Repository: https://github.com/JetBrains/intellij-community/tree/master/plugins/java-decompiler/engine/src/org/jetbrains/java/decompiler

Run "java -jar fernflower.jar -dgs=true JarToDecompile.jar DecompiledJar"

This is what Intelli-J & Android-Studio Decompiler does.

Note: Fernflower extracts the .java files to a .jar file. You can either Unzip the jar file as a regular zip file (if your version of Archive Utility on OSX allows it -- It doesn't do it for me on OSX Sierra but works on El Capitan) OR you can do jar xf DecompiledJar and it'll extract it.

Example (all in one command -- multiple commands separated by &&):

java -jar fernflower.jar -dgs=true JarToDecompile.jar DecompiledJar && cd DecompiledJar && jar xf DecompiledJar.jar && cd ../

edited Oct 27 '22 at 17:38

answered Sep 19 '16 at 00:33

Brandon

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`java -jar fernflower.jar -dgs=true JarToDecompile.jar DecompiledJar` just gives me a subdirectory with the exact same jar file in question – ShanZhengYang Sep 19 '16 at 00:55
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Open the file you got in the sub directory. It's just a zip file that contains a bunch of Java source files. – Brandon Sep 19 '16 at 00:58
Should I rename it as a zip file and unzip it? – ShanZhengYang Sep 19 '16 at 00:58
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Yeah. Rename it and unzip it. – Brandon Sep 19 '16 at 00:58

score 4 · Answer 2 · answered Jul 23 '18 at 11:57

4

Easy solution:

If you have eclipse just add the jar file in the classpath of current project u can see all the packages and source code in the jar. You no need to install and use the commands. You will get a better view of all files

answered Jul 23 '18 at 11:57

saravanan saminathan

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For intellij Idea: Right click on a project-> Open module sttings->Dependencies tab->'+' button->Jars or libraries->Select your jar->Save. Then you can see jar content in project navigation window in External Libraries. – noriks Jan 21 '22 at 08:43
@noriks - thank you. Is there ANY way that I can edit files after importing decompiled *.jar code? – Jordan MacLachlan Feb 24 '23 at 04:26

score 2 · Answer 3 · answered Oct 06 '21 at 05:27

Adding to the solution provided by @saravanan.

Another solution is to use Eclipse IDE to extract the files.

Open the Eclipse
Paste the jar file in any of the projects.
Right-click on the jar file under Package Explorer.
Extract the file to the desired location.

score 1 · Answer 4 · answered Sep 19 '16 at 00:30

A jar file may contain source code, but more commonly contains only class files. Class files are normally for execution, not for extracting source.

You can decompile class files into source code, but the decompiled code will not be nearly as helpful as the original source code.

If it is open source, go back to the site where you downloaded the jar files and look for the source. It might be in Zip files to be downloaded, it might be in jar files to be downloaded, and it might be in some kind of repository, like Git, that you can connect to with the right software.

score 1 · Answer 5 · answered Jul 23 '21 at 09:41

Another solution is to use JD for OSX (http://java-decompiler.github.io/). For Java 11 with BigSur version, make sure to fix a common error by adding the line export JAVA_HOME=$(/usr/libexec/java_home -v11) into the file /Applications/JD-GUI.app/Contents/MacOS/universalJavaApplicationStub.sh as suggested in https://github.com/java-decompiler/jd-gui/issues/332

How to extract the source code from a *.jar file on a Mac?

5 Answers5