Is there a java classfile / bytecode editor to edit instructions?

Question

Is there a utility (or eclipse plugin) for editing java class files? I'd like to manipulate the bytecode of a java class file without recompiling it nor having a complete buildpath.

E.g. to rename methods, add/delete instructions, change constants etc.

The only utilities I found are:

classeditor but it's very limited in functionality (e.g. renaming of things and manipulating instructions isn't possible).
jbe doesn't save changes (maybe because class verifying fails - before I made any changes, although the class runs perfectly)

(jbe initially had a classpath issue, adding the class path to the jbe.bat file helped)

What's wrong with _jbe_? It's Java so it should run anywhere. — musiKk, Jul 22 '10 at 11:43
@musikk An exception is thrown: Exception in thread "main" java.lang.NoClassDefFoundError: ee/ioc/cs/jbe/browser /BrowserApplication — MRalwasser, Jul 22 '10 at 11:44
@Thorbjørn Ravn Andersen: jbe had a classpath issue when using the shipped jbe.bat. I altered it, now it runs, but I still cannot use it (see edited text above) — MRalwasser, Jul 22 '10 at 12:23
I generally discard a project if I cannot get the provided get-started-examples to run. If _that_ doesn't run, then what else doesn't? — Thorbjørn Ravn Andersen, Aug 09 '10 at 11:48
@Thorbjørn Ravn Andersen: This is one of the reasons why I am asking for other utilities than the above mentioned. — MRalwasser, Aug 09 '10 at 12:48
possible duplicate of [java bytecode editor?](http://stackoverflow.com/questions/2395574/java-bytecode-editor) — Ciro Santilli OurBigBook.com, Nov 04 '13 at 21:56

score 24 · Answer 1 · edited Jun 16 '14 at 13:58

24

I use reJ for editing class files directly.

It allows you to edit instructions, methods, constant pool, diff classes, and a split view with a hex editor.

It's ridiculously awesome.

edited Jun 16 '14 at 13:58

Eugene Loy

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answered Jan 29 '11 at 16:29

nahsra

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reJ seems to be dead (last release took place in 2007) – MRalwasser Jun 17 '14 at 11:32
reJ would be awesome if editing worked. I've just tried to insert an "ifne" instruction that requires a parameter, I get a NullPointerException because its graphical user interface remains unfinished, it doesn't allow to pass the expected branch offset. Actually, I would advise to use reJ to display the instructions, Java Decompiler to check whether the changes are understood and a plain hexadecimal editor to edit the class file(s). – gouessej Feb 20 '18 at 10:24
By the way, JByteMod just works, it does what reJ fails to do: https://grax.info/ I've used it to patch JOGL 2.3.2 :) – gouessej Feb 20 '18 at 10:57

score 10 · Accepted Answer · edited Oct 03 '17 at 06:04

10

I have not seen any byte code -> byte code frontends, but plenty backends.

I would suggest that you have a look at the many byte code manipulation libraries like javassist which allow loading byte code, manipulate it, and save it back to disk, and then write a small main that does exactly that.

edited Oct 03 '17 at 06:04

evandrix

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answered Jul 22 '10 at 11:55

Thorbjørn Ravn Andersen

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score 9 · Answer 3 · answered Dec 18 '12 at 16:49

I wrote an open source Java assembler and dissasembler you may find useful.

It lets you disassemble a classfile into human readable assembly, edit it, and then reassemble it into a class. It was originally designed for writing obfuscated crackmes, so there are a lot of obscure features it supports that many other tools don't. If you need any features it doesn't currently support, feel free to contact me and I'll see what I can do.

score 3 · Answer 4 · answered Jul 22 '10 at 15:37

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Find this list of byte code manipulation/code generation libraries helpful?

answered Jul 22 '10 at 15:37

Guy Sensei

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I need working tools, I don't have the time to code such a tool by myself (neither with the help of those libraries). – MRalwasser Jul 30 '10 at 13:39

Is there a java classfile / bytecode editor to edit instructions?

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