DDevelopment & Design

How to create a native Java App

Recently, I stumbled upon JCGO, an interesting project, which translates Java 1.4 code into C.
In this article, I show how to create a native Windows app out of a small Java app.

The Java app I will use is NetCat (https://github.com/rafalrusin/netcat). You can download precompiled executable, netcat.exe, from https://github.com/rafalrusin/netcat/downloads.

So the first step is to download all dependencies. I will use MinGW, MinGW GCC, jcgo-lib-1_14.tar.gz, jcgo-src-1_14.tar.bz2, classpath-0.93 (http://ftp.gnu.org/gnu/classpath/classpath-0.93.tar.gz) and Java sources for the app with dependent libraries: https://github.com/rafalrusin/netcat, commons cli 1.2 (http://commons.apache.org/cli/download_cli.cgi). You need to put all this in the same directory, so it’ll have structure like this:

auxbin
classpath-0.93
commons-cli-1.2-src
dlls
goclsp
src
jcgo
jcgo.exe
jcgo.jar
libs
miscsrc
netcat
out
rflg_out
stdpaths.in

Then, you need to run Java to C translator by using command:

jcgo.exe -sourcepath netcat/src -sourcepath commons-cli-1.2-src/src/java netcat.NetCat @stdpaths.in -d out

Initializing...

Analysis pass...

Output pass...

Writing class tables...
Creating main file...
Parsed: 293 java files (2699 KiB). Analyzed: 3067 methods.
Produced: 640 c/h files (3769 KiB).
Contains: 1490 java methods, 4119 normal and 288 indirect calls.
Done conversion in 1 seconds. Total heap size: 36572 KiB.
 
Next step is to compile it into final executable. Following command does this:
 
gcc -DJCGO_INET -DJCGO_NOFP -DJCGO_WIN32 -DJCGO_THREADS -I src/include/ -I src/include/boehmgc/ -I src/native/ out/Main.c -o netcat.exe libs/x86/mingw/libgcmt.a -lws2_32
 
I used some switches, which are suitable for this particular app. For example, by default JCGO doesn’t use multithreading or networking. This has to be enabled explicitly. 
 
And that’s it. Now you can try out the app by calling google.com, like this:
 
$ netcat.exe google.com -p 80
Connecting to google.com port 80
GET
HTTP/1.0 302 Found
Location: http://www.google.pl/
Cache-Control: private
Content-Type: text/html; charset=UTF-8
Set-Cookie: PREF=ID=2f3085ac38771e98:FF=0:TM=1345885031:LM=1345885031:S=8A-IkreMgCogMsey; expires=Mon, 25-Aug-2014 08:57:11 GMT; path=/; domain=.google.com
Set-Cookie: NID=63=O_QZ4bDrzYNiiE0DY8RT-34c_pGt_OZagP3gzrzqCAx_Xo2kO7s9zVrUOx7FVz4TyAEY7Wx9UhglYZSX9UHSdzT7c9mUKzfkJFp5lk5FyfiMIcKITLhgSX4__3QwEYBS; expires=Sun
, 24-Feb-2013 08:57:11 GMT; path=/; domain=.google.com; HttpOnly
P3P: CP="This is not a P3P policy! See http://www.google.com/support/accounts/bin/answer.py?hl=en&answer=151657 for more info."
Date: Sat, 25 Aug 2012 08:57:11 GMT
Server: gws
Content-Length: 218
X-XSS-Protection: 1; mode=block
X-Frame-Options: SAMEORIGIN


<HTML><HEAD><meta http-equiv="content-type" content="text/html;charset=utf-8">
<TITLE>302 Moved</TITLE></HEAD><BODY>
<H1>302 Moved</H1>
The document has moved
<A HREF="http://www.google.pl/">here</A>.
</BODY></HTML>

I like the approach of translating Java code into C, because compared to other tools, which generate C++ code, this is more suitable for embedded devices. For example it is possible to generate code for iOS, because Objective C is a superset of C.

One feature I would like to see though is to be able to use reference counting instead of full gc. This is because one of the advantages of C over Java is that it doesn’t have GC hangs. So then the programmer would have to make sure there’s no cycles in orphaned object structure.

Update: Ivan Maidansky, an author of JCGO, has put some interesting comments regarding this article. In particular, he is aware of some apps in Apple Store, which do this kind of translation. Also, reference counting is discouraged due to multithreading issues. These comments can be found here: https://github.com/ivmai/JCGO/issues/2

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DDevelopment & Design

Super Confitura Man

How Super Confitura Man came to be :)

Recently at TouK we had a one-day hackathon. There was no main theme for it, you just could post a project idea, gather people around it and hack on that idea for a whole day - drinks and pizza included.

My main idea was to create something that could be fun to build and be useful somehow to others. I’d figured out that since Confitura was just around a corner I could make a game, that would be playable at TouK’s booth at the conference venue. This idea seemed good enough to attract Rafał Nowak @RNowak3 and Marcin Jasion @marcinjasion - two TouK employees, that with me formed a team for the hackathon.

Confitura 01

The initial plan was to develop a simple mario-style game, with preceduraly generated levels, random collectible items and enemies. One of the ideas was to introduce Confitura Man as the main character, but due to time constraints, this fall through. We’ve decided to just choose a random available sprite for a character - hence the onion man :)

Confitura 02

How the game is played?

Since we wanted to have a scoreboard and have unique users, we’ve printed out QR codes. A person that would like to play the game could pick up a QR code, show it against a camera attached to the play booth. The start page scanned the QR code and launched the game with username read from paper code.

The rest of the game was playable with gamepad or keyboard.

Confitura game screen

Technicalities

Writing a game takes a lot of time and effort. We wanted to deliver, so we’ve decided to spend some time in the days before the hackathon just to bootstrap the technology stack of our enterprise.

We’ve decided that the game would be written in some Javascript based engine, with Google Chrome as a web platform. There are a lot of HTML5 game engines - list of html5 game engines and you could easily create a game with each and every of them. We’ve decided to use Phaser IO which handles a lot of difficult, game-related stuff on its own. So, we didn’t have to worry about physics, loading and storing assets, animations, object collisions, controls input/output. Go see for yourself, it is really nice and easy to use.

Scoreboard would be a rip-off from JIRA Survivor with stats being served from some web server app. To make things harder, the backend server was written in Clojure. With no experience in that language in the team, it was a bit risky, but the tasks of the server were trivial, so if all that clojure effort failed, it could be rewritten in something we know.

Statistics

During the whole Confitura day there were 69 unique players (69 QR codes were used), and 1237 games were played. The final score looked like this:

  1. Barister Lingerie 158 - 1450 points
  2. Boilerdang Custardbath 386 - 1060 points
  3. Benadryl Clarytin 306 - 870 points

And the obligatory scoreboard screenshot:

Confitura 03

Obstacles

The game, being created in just one day, had to have problems :) It wasn’t play tested enough, there were some rough edges. During the day we had to make a few fixes:

  • the server did not respect the highest score by specific user, it was just overwritting a user’s score with it’s latest one,
  • there was one feature not supported on keyboard, that was available on gamepad - turbo button
  • server was opening a database connection each time it got a request, so after around 5 minutes it would exhaust open file limit for MongoDB (backend database), this was easily fixed - thou the fix is a bit hackish :)

These were easily identified and fixed. Unfortunately there were issues that we were unable to fix while the event was on:

  • google chrome kept asking for the permission to use webcam - this was very annoying, and all the info found on the web did not work - StackOverflow thread
  • it was hard to start the game with QR code - either the codes were too small, or the lighting around that area was inappropriate - I think this issue could be fixed by printing larger codes,

Technology evaluation

All in all we were pretty happy with the chosen stack. Phaser was easy to use and left us with just the fun parts of the game creation process. Finding the right graphics with appropriate licensing was rather hard. We didn’t have enough time to polish all the visual aspects of the game before Confitura.

Writing a server in clojure was the most challenging part, with all the new syntax and new libraries. There were tasks, trivial in java/scala, but hard in Clojure - at least for a whimpy beginners :) Nevertheless Clojure seems like a really handy tool and I’d like to dive deeper into its ecosystem.

Source code

All of the sources for the game can be found here TouK/confitura-man.

The repository is split into two parts:

  • game - HTML5 game
  • server - clojure based backend server

To run the server you need to have a local MongoDB installation. Than in server’s directory run: $ lein ring server-headless This will start a server on http://localhost:3000

To run the game you need to install dependencies with bower and than run $ grunt from game’s directory.

To launch the QR reading part of the game, you enter http://localhost:9000/start.html. After scanning the code you’ll be redirected to http://localhost:9000/index.html - and the game starts.

Conclusion

Summing up, it was a great experience creating the game. It was fun to watch people playing the game. And even with all those glitches and stupid graphics, there were people vigorously playing it, which was awesome.

Thanks to Rafał and Michał for great coding experience, and thanks to all the players of our stupid little game. If you’d like to ask me about anything - feel free to contact me by mail or twitter @zygm0nt

Recently at TouK we had a one-day hackathon. There was no main theme for it, you just could post a project idea, gather people around it and hack on that idea for a whole day - drinks and pizza included.

My main idea was to create something that could be fun to build and be useful somehow to others. I’d figured out that since Confitura was just around a corner I could make a game, that would be playable at TouK’s booth at the conference venue. This idea seemed good enough to attract >Conclusion