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View a Java Class File using a decompiler

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created March 22, 2001 · complexity intermediate · author bhaskar_v_k · version 5.7

Do you wish you could view a Java Class File using Vim?

First of all you will need a Java Decompiler to decompile the Class File. I would suggest the JAD decompiler by Pavel Kouznetsov

It's a command line decompiler and absolutely free.

Next create a vimscript file called jad.vim:

augr class
au bufreadpost,filereadpost *.class %!d:jad.exe -noctor -ff -i -p %
au bufreadpost,filereadpost *.class set readonly
au bufreadpost,filereadpost *.class set ft=java
au bufreadpost,filereadpost *.class normal gg=G
au bufreadpost,filereadpost *.class set nomodified
augr END

Note: Keep the Jad.exe in a directory without white spaces. The -p options directs JAD to send the output to standard output instead of a .jad file. Other options are described on the JAD site.

Next add the following line in the vimrc file.

so jad.vim

Next time you do vim abc.class, you have the source code for abc.class.

NOTE: I have written the script so as to open the class file read only, So that you don't accidentally modify it. You can also extend this script to unjar a jar file and then view each file in the JAR file.


I modified this a little bit to use the improved file runtime organisation of vim60, I don't know if other will like it better but here it is: I added to filetype.vim:

augroup filetypedetect
au! BufRead,BufNewFile *.jad setfiletype java
au! BufRead,BufNewFile *.class setfiletype class
augroup END

and created in ftplugin a class.vim with

%!jad.exe -noctor -ff -i -p %
set readonly
set ft=java
normal gg=G
set nomodified

If you don't want to 'hit ENTER' after every decompilation, you can add 'silent' to some of the lines:

au bufreadpost,filereadpost *.class silent %!jad -noctor -ff -i -p %

and maybe even:

au bufreadpost,filereadpost *.class silent normal gg=G

I can now select any class file, right click, and select the "Edit with Vim" option to view the source.

I'm just wondering, how do I change this to if I do the same to a jar file, and it will show me the contents of the jar file, as in a jar -tf, and if I select any of the entries, I can view the source?

I tried opening the jar file using WinZip, and if I view any of the entries in it using vim, I'll get something like this: JavaClassFileReadException: can't open input file on `C:\Documents' JavaClassFileReadException: can't open input file on `and' JavaClassFileReadException: can't open input file on `Settings\gwunwai\Local' JavaClassFileReadException: can't open input file on `Settings\Temp\Version.class'

I think that's because WinZip extracts the zip entries into my temp directory, which contains white spaces.

Is there some way around this?

you can change the command to %!jad.exe -noctor -ff -i -p "%" (enclosed the % with quotes). It worked for me

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