CODEWITHSUNDEEP
javapython-2.7decompiler
Niranga Sandaruwan
Niranga Sandaruwan

Reputation: 711

How to decompile .class and jar file using Storyyeller/Krakatau

I am trying to decompile a file using Storyyeller/Krakatau decompiler. I have already downloaded the relevant file and placed it inside a folder. I tried decompile the file using below syntax using command prompt.

=== Decompilation ===

Usage:

python Krakatau\decompile.py [-nauto] [-path PATH] [-out OUT] [-r] [-skip]
target

PATH: An optional list of directories, jars, or zipfiles to search for classes in. Krakatau will attempt to automatically detect and add the jar containing core language classes, but you can disable this with the -nauto option. For multiple jars, you can either pass a semicolon seperated list of jars or pass the -path option multiple times.

OUT: Directory name where source files are to be written. Defaults to the current directory. If the name ends in .zip or .jar, the output will be a zip file instead.

-r: Decompiles all .class files found in the directory target (recursively)

-skip: Continue upon errors. If an error occurs while decompiling a specific method, the trace back will be printed as comments in the source file. If the error occurs while decompiling at the class level, no source file will be emitted and an error message will be printed to the console.

target: Class name or jar name to decompile. If a jar is specified, all classes in the jar will be decompiled. If -r is specified, this should be a directory.

But I always get errors.I don't understand the above syntax.

Please explain this syntax

python Krakatau\decompile.py [-nauto] [-path PATH] [-out OUT] [-r] [-skip]
target

using a simple example.

Upvotes: 4

Views: 6943

Answers (1)

Antimony
Antimony

Reputation: 39451

The easiest and normal way to decompile with Krakatau is to decompile a jar.

Say you have a jar file named Luyten.jar in the current directory and you want to decompile every class in the jar and output it to the directory temp. Then you'd do something like

pypy -O Krakatau\decompile.py -skip -out temp Luyten.jar

Depending on whether you have JDK installed and where, you may need to explicitly pass the location of the jre in the path argument. For example

pypy -O Krakatau\decompile.py -skip -out temp -path "C:\Program Files (x86)\Java\jre7\lib\rt.jar" Luyten.jar

If you want to decompile a specific class within the jar, you can add the jar to the path and specify the classname. If you need to specify a path to rt.jar as in the previous example, you can pass the -path argument multiple times or a single time separated by semicolons. For example to decompile only the class com.beust.jcommander.FuzzyMap$IKey,

pypy -O Krakatau\decompile.py -skip -out temp -path Luyten.jar com.beust.jcommander.FuzzyMap$IKey

You can also decompile classfiles that are outside of a jar, but it's a lot more annoying, because you have to make sure the directory layout is correct. You need to specify the directory that is the root relative to where the classes will be found.

For example, suppose you have a classfile located at ./Foo/Bar/com/beust/jcommander/FuzzyMap$IKey.class

pypy -O Krakatau\decompile.py -skip -out temp -path Foo/Bar com.beust.jcommander.FuzzyMap$IKey

In this case, the directory has to match the fully qualified classname exactly. A common mistake is to try to decompile with the wrong root directory. The nice thing about jars is that having the correct directory structure is automatic.

Upvotes: 5

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