Bytecode Viewer is an Advanced Lightweight Java Bytecode Viewer, GUI Procyon Java Decompiler, GUI CFR Java Decompiler, GUI FernFlower Java Decompiler, GUI Jar-Jar, Hex Viewer, Code Searcher, Debugger and more.
It's written completely in Java, and it's open sourced. It's currently being maintained and developed by Konloch.

There is also a plugin system that will allow you to interact with the loaded classfiles, for example you can write a String deobfuscator, a malicious code searcher, or something else you can think of.
You can either use one of the pre-written plugins, or write your own. It supports groovy, python and ruby scripting. Once a plugin is activated, it will execute the plugin with a ClassNode ArrayList of every single class loaded in BCV, this allows the user to handle it completely using ASM.

Code from various projects has been used, including but not limited to:
    J-RET by WaterWolf
    JHexPane by Sam Koivu
    RSynaxPane by Robert Futrell
    Commons IO by Apache
    ASM by OW2
    FernFlower by Stiver
    Procyon by Mstrobel
    CFR by Lee Benfield
    CFIDE by Bibl

Contributors:
    Konloch
    Bibl
    Fluke
    Righteous
    sahitya-pavurala
    priav03
    If I missed you, please feel free to contact me @Konloch or konloch@gmail.com

Video: http://the.bytecode.club/bytecodeviewer-video/
Source Code: https://github.com/konloch/bytecode-viewer
Bin/Archive: https://github.com/konloch/bytecode-viewer/releases
Java Docs: https://the.bytecode.club/docs/bytecode-viewer/
License (Copyleft): https://raw.githubusercontent.com/Konloch/bytecode-viewer/master/LICENSE
Report Bugs (or below): https://github.com/Konloch/bytecode-viewer/issues
Discussion Forum: https://the.bytecode.club/forumdisplay.php?fid=69

Key Features:
    Java Decompiler - It uses a modified version of FernFlower, Procyon and CFR.
    Bytecode Decompiler - A modified version of CFIDE's.
    Hex Viewer - Powered by JHexPane.
    Each Decompiler/Viewer is toggleable.
    Fully Featured Search System.
    A Plugin System With Built In Plugins. (Show All Strings, Malicious Code Scanner, String Decrypters, etc)
    Fully Featured Scripting System That Supports Groovy, Python And Ruby.
    Recent Files & Recent Plugins.
	EZ-Inject - Graphically insert hooks and debugging code, invoke main and start the program.
    And more! Give it a try for yourself!

Are you a Java Reverse Engineer? Do you want to learn?
Join The Bytecode Club Today!
https://the.bytecode.club

Changelog:
--- Beta 1.0.0 ---:
10/4/2014 - Designed a POC GUI, still needs a lot of work.
10/4/2014 - Started importing J-RET's backend.
10/5/2014 - Finished importing J-RET's backend.
10/6/2014 - Started modifying J-RET's UI.
10/6/2014 - Added several FernFlower options.
10/6/2014 - Fixed the class search function so it doesn't require exact class names.
10/6/2014 - Added save as, it'll save all of the loaded classes into one jar file (GUI Jar-Jar now).
10/6/2014 - Centered the select jar text inside of the file navigator.
10/6/2014 - Properly threaded the open jar function, now fernflower/bytecode decompiler runs in the background.
10/6/2014 - Added a hex viewer (Instead of using Re-Java's, I've decided to use a modified version of JHexEditor).
10/6/2014 - Made all of the viewer (Sourcecode, Bytecode & Hexcode toggleable).
10/7/2014 - Fixed the search function.
10/7/2014 - You can now add new files without it creating a new workspace.
10/7/2014 - Added new workspace button underneath File, this will reset the workspace.
10/7/2014 - Renamed File>Open.. to File>Add..
10/7/2014 - Added recent files.
10/7/2014 - Did some bitch work, the project has no warnings now.
10/7/2014 - Added waiting cursors to anything that will require waiting or loading.
10/8/2014 - Searching now runs in a background thread.
10/8/2014 - Added File>About.
10/8/2014 - The main GUI now starts in the middle of your screen, same with the about window.
10/8/2014 - Made the File Navigator Pane, Workspace Pane & Search Pane a little sexier.
10/9/2014 - Started on a Plugin system
10/9/2014 - Added a malicious code scanner plugin, based off of the one from J-RET, this searches for a multitude of classes/packages that can be used for malicious purposes.
10/9/2014 - Added a show all strings plugin, this grabs all the declared strings and displays them in a nice little window.
10/9/2014 - Fixed a bug with Bytecode Decompiler, where it would it display \r and \n as return carriages.
10/9/2014 - Fixed the Bytecode Decompiler>Debug Instructions option.
10/9/2014 - Save Class Files As is now renamed to Save Files As.
10/9/2014 - Save Files As now saves jar resources, not just classfiles.
10/9/2014 - Added an 'Are you sure' pane when you click on File>New Workspace.
10/9/2014 - Save Files As is no longer dependent on the File System, now if you're on windows and you have a file called AA, and one called Aa, you're fine.
10/11/2014 - Modified the FernFlower library, it no longer spits out System.out.println's while processing a method, this has sped it up quite a lot.
10/12/2014 - Fix an issue when resizing.
10/12/2014 - Modified the core slighty to no longer have a modularized decompiling system (since there are only 2 decompilers anyways).
10/12/2014 - Fixed an issue with decompiling multiple files at once.
10/12/2014 - The Plugin Console now shows the plugin's name on the title.
10/12/2014 - Debug Helpers will now debug all jump instructions by showing what instruction is on the line it's suppose to goto, example: 90. goto 120 // line 120 is PUTFIELD Animable_Sub4.anInt1593 : I
10/12/2014 - Now when you select an already opened file, it will automatically go to that opened pane.
10/14/2014 - Added the option 'exact' to the class finder.
10/14/2014 - Added the option 'exact' to the searcher, now it'll search for .contains when unselected.
10/14/2014 - Stopped the use of StringBuffer, replaced all instances with StringBuilder.
10/14/2014 - Added Labels and Try-Catch blocks to the Bytecode Decompiler.
10/14/2014 - For panes that are not selected, the corresponding decompiler will not execute.
10/14/2014 - Added plugin Show Main Methods, this will show every single public static void main(String[]).
10/14/2014 - Plugins can no longer be ran when there is no loaded classes.
10/14/2014 - The Malicious Code Scanner now has gui option pane before you run it.
10/14/2014 - Added a java/io option to the Malicious Code Scanner.
10/14/2014 - Added save Java files as.
10/15/2014 - Added save as Jar file. (Export as Jar)
10/15/2014 - Added the option to ASCII only strings in the Bytecode Decompiler.
10/15/2014 - External plugins are now fully functional, same with recent plugins.
10/16/2014 - Removed all refences of 'ClassContainer'.
10/16/2014 - Rewrote the tempfile system.
10/16/2014 - Moved the file import to BytecodeViewer.class.
10/16/2014 - Fixed a jTree updating issue.
10/16/2014 - Now if you try search with an empty string, it won't search.
10/16/2014 - Added Replace Strings plugin.
10/16/2014 - Added a loading icon that displays whenever a background task is being executed.
--- Beta 1.1.0 ---:
10/19/2014 - Fixed harcoded \\.
--- Beta 1.2.0 ---:
10/19/2014 - Started importing Procyon and CFR decompilers.
10/19/2014 - Partially finished importing Procyon and CFR, just need to finish export java files as zip.
--- Beta 1.3.0 ---:
10/22/2014 - Imported Bibl's Bytecode Decompiler from CFIDE.
10/22/2014 - Did some changes to the Bytecode Decompiler.
10/23/2014 - Added CFR settings.
10/23/2014 - Updated FernFlower to Intellij's Open Sourced version of FernFlower.
10/24/2014 - Fixed FernFlower save Java files as zip.
10/29/2014 - Added version checker.
10/29/2014 - Added Procyon settings.
10/29/2014 - When saving as jars or zips, it'll automatically append the file extension if it's not added.
10/29/2014 - All the built in plugins no longer set the cursor to busy.
10/29/2014 - Tried to fix the issue with JSyntaxPane by making it create the object in a background thread, it still freezes the UI. Changes kept for later implementation of another syntax highlighter.
10/29/2014 - Sped up start up time
--- Beta 1.3.1 ---:
10/29/2014 - Replaced JSyntaxPane with RSyntaxArea, this sadly removes the search feature inside of source/bytecode files, I'll implement a search function soon. (This also fixes the JRE 1.8 issue)
10/29/2014 - Added a new decompiler option to append brackets to labels.
10/31/2014 - Fixed an issue with the decompiler still running when the source code pane isn't toggled.
--- Beta 1.4.0 ---:
11/1/2014 - Fixed FernFlower save Java files on Unix.
11/1/2014 - FernFlower now uses the settings for save Java files.
11/1/2014 - Added Procyon save Java files (It uses the settings).
11/1/2014 - Updated CFR to cfr_0_89.
11/1/2014 - Added CFR save Java files (It uses the settings), however it relies on the file system, because of this if there is heavy name obfuscation, it could mess up for windows.
--- Beta 1.5.0 ---:
11/1/2014 - Updated and improved the search function, it now prints out more useful information.
11/1/2014 - Fixed a UI issue with the Replace All Strings plugin.
11/2/2014 - Added search function to the Class Viewer.
11/2/2014 - Updated Procyon to procyon-decompiler-0.5.27.
--- Beta 1.5.1 ---:
11/2/2014 - Fixed a CFR issue with packages.
--- Beta 1.5.2 ---:
11/3/2014 - Fixed Refresh Class.
--- Beta 1.5.3 ---:
11/3/2014 - Settings/Temp file are now in a global directory.
11/3/2014 - The GUI setttings now save.
11/3/2014 - Removed the option to disable syntax highlighting (since it's lightweight now).
11/3/2014 - About window now contains the version number and the BCV directory.
11/3/2014 - Added an option to toggle to outdated status.
--- 2.0.0 ---: //Out of beta, WOO
11/4/2014 - Officially been 1 month of development.
11/4/2014 - Replaced ""+ with String.valueOf (cheers bibl).
11/4/2014 - Changed how the temp directory was created.
11/4/2014 - Put a file.seperator  to the end of tempDirectory.
11/4/2014 - Made the exit button work.
11/4/2014 - Added a GUI for all Exception Stack Trace's.
11/4/2014 - The plugin system now shows a message instead of just printing to the console when it's not going to run a plugin.
11/4/2014 - Updated the search function, it's now perfect.
11/5/2014 - Made the Show All Strings plugin instant.
11/5/2014 - Kinda added middle mouse button closes tab (only if you click the exit button).
11/5/2014 - Improved the Malicious Code Scanner, also made it instant.
11/5/2014 - Added icons to the program (cheers Fluke).
--- 2.0.1 ---:
11/7/2014 - Fixed the search function.
11/7/2014 - Removed an unused package containing some unused classes.
--- 2.1.0 ---:
11/5/2014 - Started working on the EZ-Inject plugin.
11/6/2014 - Fixed the ClassNodeDecompiler creating unnessessary objects. (thanks bibl).
11/6/2014 - Finished an alpha version of EZ-Inject.
11/6/2014 - Started working on a basic obfuscator.
11/6/2014 - The Obfuscator now sucessfully renames all field names.
11/6/2014 - Updated CFR to cfr_0_90.
11/8/2014 - Started working on the API for BCV.
11/9/2014 - Decided to make a graphical reflection kit.
11/10/2014 - Made some progress with the obfuscator, almost finished EZ-Injection.
11/14/2014 - Been doing various updates to EZ-Injection, Obfucsation, Reflection Kit and the BCV API.
11/16/2014 - Added the option to launch BCV command line as java -jar bcv.jar C:/test.jar C:/example/whatever.jar
11/17/2014 - Fixed an issue with the out of date checking UI still activating when not selected.
11/19/2014 - Added annotatitons/local variables to the methodnode decompiler (Thanks Bibl).
11/21/2014 - Decided to release it with the obfuscator/reflection kit unfinished, they're currently disabled for future use.
--- 2.1.1 ---:
12/09/2014 - Upated CFR to cfr_0_91.
--- 2.2.0 ---:
12/09/2014 - Added a text search function to the plugin console.
12/09/2014 - When you press enter in the text search bar, it will now search.
12/13/2014 - The Bytecode Decompiler now shows the method's description in a comment.
12/13/2014 - Fixed an issue with the text search function.
12/13/2014 - Search results are now clickable.
--- 2.2.1 ---:
12/13/2014 - Fixed an issue with the Bytecode Decompiler. - Thanks bibl
--- 2.3.0 ---:
12/16/2014 - Started updating the class viewer.
12/18/2014 - Finished a basic concept of the new class viewer.
12/18/2014 - Fixed an error with importing some jars.
12/18/2014 - Fixed the about window.
12/18/2014 - Finished the final concept for the new class viewer.
12/18/2014 - Threaded save Java files as zip, it now runs in a background thread.
12/18/2014 - Save Java files as zip now prompts you to select a decompiler.
12/18/2014 - Removed the cursor waiting for save Java files as zip.
12/18/2014 - Wrapped the save Java files as zip around an exception handler, it will now safely show the exception if any is thrown.
12/18/2014 - Fixed not escaping the Java strings by default for the Bytecode decompiler. - http://i.imgur.com/YrRnZA7.png
12/18/2014 - Used Eclipse's code formatting tool and formatted the code
12/19/2014 - Priav03 fixed the quick class searcher.