Java: Newer and supported decompilers (not JAD)

**Aaron** · 20-Sep-2013, 11:48 AM

To clarify, Beyond Compare 3 does not ship with a decompiler for Java class files. Our File Formats are able to be customized to use External Conversion command lines, such as JAD, to help convert from one file type into plain text.

We do have some previously created formats available for download (including a JAD based one) on our website. We can certainly review the resources you've posted here to see if we can update or create an alternate format, but Scooter Software does not directly support JAD or the other external programs used by the File Formats.

If you are comfortable and familiar with using any of the above resources from the command line, all you would need to do is create a new Text format in the Tools menu -> File Formats dialog, with an external conversion command line which takes in a source file (file.class) and outputs a target temp text file (temp.txt). The target temp file is the one that would be opened in BC3, using %s and %t to represent the files in the External Conversion. We have a sample KB article (detailing a custom format for *.resx files) here:
http://www.scootersoftware.com/suppo...rnalconversion

**bc_for_life** · 23-Sep-2013, 12:00 AM

Thanks Aaron.
(1) I wonder how many people feel that the seamless comparison of Java warfiles / jarfiles is a "killer feature" for this product ? (I know that I do)
(2) Java 6, 7, 8 ... changes. Bytecodes change. JAD is not supported.
(3) I'm guessing that I must have downloaded "these extra formats", as you mentioned. ( " ... We do have some previously created formats available for download ... ").
If so, then I find your Java decompiler formats extremely important.
(4) I did a quick peek-under-the-covers, and here is what I can see, without going to too much effort.
Perhaps others are also interested.
---------------
BeyondCompare >> Tools >> File Formats

###############################################
(1) Name: Java Class to Source
###############################################
Mask: *.class
Description:
{
- Compares Java class files decompiled to source.
- Uses Java decompiler, Jad:
http://www.kpdus.com/jad.html
}
Tab:Coversion/Loading: Helpers\Java\CLASS_to_JAVA.bat %s %t

Where: C:\Program Files (x86)\Beyond Compare 3\Helpers\Java\CLASS_to_JAVA.bat"
{
Helpers\Java\jad.exe -p %1 > %2
}

Tab:Grammar
{
Keyword=LOTS_OF_STUFF
Identifier=LOTS_OF_STUFF
Number=LOTS_OF_STUFF
String=LOTS_OF_STUFF
String=LOTS_OF_STUFF
Comment=LOTS_OF_STUFF
Comment=LOTS_OF_STUFF
Operator=LOTS_OF_STUFF
}

###############################################
(2) Java Class to Source Tidied
###############################################
Mask: *.class
Descriptions:
{
- Compares Java class files decompiled to tidied source.
- Uses Java decompiler, Jad: , http://www.kpdus.com/jad.html
- Uses freeware converter, Jalopy: , http://jalopy.sourceforge.net
- Requires Java JRE: , http://java.sun.com
}

Tab:Conversion/Loading: Helpers\Java\CLASS_to_JAVA_tidied.bat %s %t

Where: "C:\Program Files (x86)\Beyond Compare 3\Helpers\Java\CLASS_to_JAVA_tidied.bat"
{
:GetTempName

set tmpfile=%TMP%.\JadTidied-%RANDOM%-%TIME:~6,5%.tmp
if exist "%tmpfile%" goto :GetTempName
Helpers\Java\jad.exe -p %1 > "%tmpfile%"
for %%F in (%tmpfile%) do set size=%%~zF
if /I %size% equ 0 goto :SkipJalopy
type "%tmpfile%" | java -classpath Helpers\Java\jalopy\lib\getopt.jar;Helpers\Java\ja lopy\lib\jalopy.jar;Helpers\Java\jalopy\lib\jalopy-console.jar;Helpers\Java\jalopy\lib\log4j.jar de.hunsicker.jalopy.plugin.console.ConsolePlugin > %2

:SkipJalopy
del "%tmpfile%"

}

**dr_barnowl** · 21-Jan-2015, 03:49 AM

The main problem is that JAD will not decompile newer Java class files.

There are hacks like a program that "downgrades" the classes so that JAD has an easier time of it, but really, what's needed is a Java decompiler that copes with modern classes.

This claims to fit the bill :

http://jd.benow.ca/

.. but it's not distributable for commercial purposes, and not open-source. Alas, there's no command-line variant that just takes a class file and dumps it to a Java source file - just a monolithic executable and an Eclipse plugin.

Perhaps Scooter could enter into partnership with this guy and license his software? Wouldn't even mind a small extra license fee to buy this as a plugin for BC.

**dr_barnowl** · 21-Jan-2015, 04:02 AM

Slightly more laborious : manual mode

What this application will do, is open a JAR file and save all the sources as a zip archive.

So you can use the manual method ...

* Open a JAR
* Use the "Save all source" command
* Do this for another JAR
* Compare the two ZIP files in BC

If only you could use this on the command line...

... looking at the innards of the Eclipse plugin (which helpfully comes with libraries and source code) it ought to be possible to rig up a command line utility to produce Java output. But because of the licensing, people would have to do this for themselves (at least assemble it themselves like a kit).

**Zoë** · 21-Jan-2015, 12:29 PM

I can't find the work I did on it previously, but the one we'd likely switch to would be the FernFlower decompiler included with IntelliJ. It's open source, can run from the command line, and produces good results. What I remember from testing was that it was substantially slower than JAD though, which is why we haven't pursued it more actively.

Edit: To clarify, the speed difference was annoying but manageable for a single pair of files, but added up quickly if you did a rules-based comparison of an entire .jar.

**bluebossa63** · 07-Feb-2016, 07:28 AM

Support for Java Decompiler supporting Java 8

I have written an addition to the Java Decompiler JD.
Please find the ready to use bcpkg formats.

**Crack** · 12-Apr-2016, 04:41 AM

Wow, I was just trying to use JD and found your work. Thanks!

**yunlei** · 03-Nov-2019, 03:27 AM

The following plugin was made based on fernflower.jar.
https://github.com/caiyunlei/BeyondC...lugin/releases

**typesafe** · 14-Jan-2020, 07:18 AM

There is also a way to use FernFlower decompiler online at http://www.decompiler.com/

**Crack** · 09-Jul-2022, 03:32 PM

You can also use Fernflower by writing a simple wrapper. I'd like to improve upon it a bit, but probably won't find motivation as this works for me.

Script below requires you to get IntelliJ IDEA or compile it yourself (https://github.com/JetBrains/intelli...ompiler/engine), and adjust paths to match your system:

Code:

@echo off

set JAVA_HOME=C:\Program Files\JetBrains\IntelliJ IDEA 2022.1.1\jbr
set FERNFLOWER_HOME=C:\Program Files\JetBrains\IntelliJ IDEA 2022.1.1\plugins\java-decompiler\lib

set CLASS_NAME=%~n1
set JAVA_FILE=%CLASS_NAME%.java

echo [%DATE% %TIME%] decompile '%1' to '%2' > decompile.log
echo [%DATE% %TIME%] expecting .java file '%JAVA_FILE%' >> decompile.log

echo [%DATE% %TIME%] "%JAVA_HOME%\bin\java" -cp "%FERNFLOWER_HOME%\java-decompiler.jar" org.jetbrains.java.decompiler.main.decompiler.ConsoleDecompiler "%1" . >> decompile.log
"%JAVA_HOME%\bin\java" -cp "%FERNFLOWER_HOME%\java-decompiler.jar" org.jetbrains.java.decompiler.main.decompiler.ConsoleDecompiler "%1" . 2>> decompile.log
if %errorlevel% == 0 (
  move /y "%JAVA_FILE%" "%2" >> decompile.log
) else (
  set EL=%errorlevel%
  echo "Failed (%EL%)"
  copy /y decompile.log "%2"
  exit /b %EL%
)

Save to eg. class_to_java.cmd, and add as en external conversion program, calling it as "class_to_java.cmd %s %t".