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  • New to JEE; architecture suggestions for a service/daemon?

    - by Kate
    I am brand new to the JEE world. As an exercise to try and familiarize myself with JEE, I'm trying to create a tiered web-app, but I'm getting a little stuck on what the best way is to spin up a service in the background that does work. Parameters of the service: It must open and hold a socket connection and receive information from the connected server. There is a 1-to-1 correlation between a user and a new socket connection. So the idea is the user presses a button on the web-page, and somewhere on the server a socket connection is opened. For the remainder of the users session (or until the user presses some sort of disconnect button) the socket remains open and pushes received information to some sort of centralized store that servlets can query and return to the user via AJAX. Is there a JEE type way to handle this situation? Naturally what I would think to do is to just write a Java application that listens on a port that the servlets can connect to and spawns new threads that open these sockets, but that seems very ad-hoc to me. (PS: I am also new to Stack Overflow, so forgive me if it takes me some time to figure the site out!)

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  • Vectors for a 2D/3D World in Java

    - by jax
    I reading about Mathematics in Games and am wondering what is the best way to represent a Vector location in Java. I know there is a Vector class but I don't think this is what I need. There is also a Matrix class which looks like it may be what I want (a 1 dimensional matrix maybe). In particular, if I were to create a location Vector such as: v(x,y,z) where x,y and z are the coordinates in 3D space, what would be the best way to represent this in Java. It would be nice if I could also add, subtract and find the dot-product of Vectors. ideas?

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  • Java: how to take a screenshot fast

    - by user350789
    I am implementing a simple eye tracker, which requires fast screenshoting of what is happening on the screen simultaneously with capturing the video from webcam. The thing is that the way of doing it with Robot, mentioned here: http://stackoverflow.com/questions/2475303/java-library-for-capturing-active-window-screenshot is extremely slow. By the way, retrieving the video from a webcam works much faster and returns the byte array, which is very fast to be processed. Does anybody know a faster solution? C++ libraries, which can be linked to Java for doing this may help as well. Thank you!

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  • Google App Engine, Java, and HTTP Performance

    - by polyclef
    A friend and I are currently working on a turn-based game with chat with both desktop browser and Android clients, with Google App Engine as the server. We're using the Java API for GAE and using HTTP for communication with the server. We've implemented simple chat functionality, and we're getting undesirable latencies 1-3 seconds from both the browser and Android clients while just posting simple one-word chat messages. My friend thought it would be best to use XMPP instead of HTTP, but we want to use a Google Accounts cookie for authentication from the Android client, and according to the GAE documentation, XMPP clients cannot use a Google Accounts cookie and must use the user's password. Does anyone have any suggestions as to where the latency might be coming from, how to troubleshoot it, and/or what to do about it? Also, is anyone aware of any opensource implementations of chat (or something similar) on GAE done in Java? Can't seem to find any.

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  • Create "INSERT" statements from mySQL database in Java

    - by girdus
    Does anyone know of any good libraries or scripts out there which will allow me to point to any mySQL table and automatically get a list of all the INSERT statements for the data in the table? DdlUtils allows me to create an XML file from a database model but I would like to have it in INSERT statements format and preferably the ability to choose a couple of tables instead of dumping the entire database. Thanks. EDIT: I need it to be a Java API because I want to programatically call it from my Java method.

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  • Installing Java SDK on Linux.

    - by Negai
    Hi everyone, I'm currently trying to install Java SDK on my Debian 'Etch'. Even though the installation process has been described a number of times, but still I haven't found the information to solve the problem. Here is, what I'm getting: m@sanctuary:~/distr/java$ fakeroot make-jpkg jdk-6u20-linux-i586.bin Creating temporary directory: /tmp/make-jpkg.sqQPnaxiwl Loading plugins: blackdown-j2re.sh blackdown-j2sdk.sh common.sh ibm-j2re.sh ibm-j2sdk.sh j2re.sh j2sdk-doc.sh j2sdk.sh j2se.sh sun-j2re.sh sun-j2sdk-doc.sh sun-j2sdk.sh Detected Debian build architecture: i386 Detected Debian GNU type: i486-linux-gnu No matching plugin was found. Removing temporary directory: done Could anybody help me? Thanks in advance.

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  • How do I cast from int to generic type Integer?

    - by Rob Kent
    I'm relatively new to Java and am used to generics in C# so have struggled a bit with this code. Basically I want a generic method for getting a stored Android preference by key and this code, albeit ugly, works for a Boolean but not an Integer, when it blows up with a ClassCastException. Can anyone tell me why this is wrong and maybe help me improve the whole routine (using wildcards?)? public static <T> T getPreference(Class<T> argType, String prefKey, T defaultValue, SharedPreferences sharedPreferences) { ... try { if (argType == Boolean.class) { Boolean def = (Boolean) defaultValue; return argType.cast(sharedPreferences.getBoolean(prefKey, def)); } else if (argType == Integer.class) { Integer def = (Integer) defaultValue; return argType.cast(sharedPreferences.getInt(prefKey, def)); } else { AppGlobal.logWarning("getPreference: Unknown type '%s' for preference '%s'. Returning default value.", argType.getName(), prefKey); return defaultValue; } } catch (ClassCastException e) { AppGlobal.logError("Cast exception when reading pref %s. Using default value.", prefKey); return defaultValue; } } I've tried various ways - using the native int, casting to an Integer, but nothing works.

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  • Java date long value changed after insert, select query

    - by StackExploded
    AFAIK, java Date type is independent from Timezone which means that it represents specific moment of time as long typed value. I found really weird thing here. This is the original value i tried to insert. (http-0.0.0.0-9080-4) 1352955600000 <-- long integer. (http-0.0.0.0-9080-4) Thu Nov 15 00:00:00 EST 2012 <-- User Friendly Format. After i finished inserting into Oracle 11g database, the value has changed! (http-0.0.0.0-9080-4) 1352952000000 (http-0.0.0.0-9080-4) Wed Nov 14 23:00:00 EST 2012 How could this happen?? The more weird thing is it only happens specific environments such as Jboss. I'm currently using below environments. java 1.6 ibatis 2.34 jboss-5.1 (server) tomcat 6.0 (local) oracle 11g Is there anybody who can give me a clue or link to be helpful? it really bugging me!!

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  • Best way to notify several java applets/applications of a change on a server

    - by Dustin
    I need to know the best (fastest) way to have a server (preferably a php based one, but a jsp/servlet one could be set up as well using google app engine) notify several java applets/applications that a change has occurred to the data. The way i am picturing this to work will be very similar to that of the way i think an online java game (like Runescape) works User 1: Changes data on server. Server: returns success to User 1, notifies connected computers of change. Connected Computer 1: processes change, returns success to server. Connected Computer 2: processes change, returns success to server. Connected Computer 3: processes change, returns success to server. Connected Computer 4: processes change, returns success to server. I am hoping to have this entire process complete in half a second, and not involve polling as there will be long durations of nothing, followed by a sudden moment where 4 events happen in succession.

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  • java service could not be initialized (debugging help)

    - by vikasde
    I have a jar package that I wrote using netbeans. This package is called from other java file. The jar calls a webservice and is supposed to do something with it. Now everything works fine locally. I compiled the files and locally and uploaded them to the server and when I run it, I get the "Service could not be initialized".I am not sure how to debug this. I am pretty new to java. What is the best approach here to solve the issue?

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  • convert flv to mp3 with Java

    - by krial
    Hi, I'm pretty new in developing programs in Java. I'm currently writing a program that converts a flv video into mp3. I have already written such a program in Visual Studio.net C#, but the Problem is, that it isn't cross platform compatible... I used the ffmpeg binary to convert the video into mp3, but I can't find ffmpeg binaries for Mac and Linux. (if so, I could start the specific binaries from java, depending on the OS) So I tried to convert the video with Xuggle, but the final mp3 has 0 bytes. My current code is the following: IMediaReader reader = ToolFactory.makeReader("video.flv"); reader.addListener(ToolFactory.makeWriter("music.mp3", reader)); while (reader.readPacket() == null) do {} while(false); Thanks in advance. p.s sorry for my bad english

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  • Fractional Calculator in Java

    - by user2888881
    I am trying to create a fractional calculator in Java with inputs of mixed fractions, proper fractions, improper fractions or integers. It should include the four basic operators as well. The program should be set up as a loop where it is continuous until the user types "quit". I have coded the beginning loop but have no idea where to go from there. Please help, I am a beginner and would really appreciate it. Thank you again. This is what I have so far: import java.util.*; public class FractionCalculator { private static Scanner input; public static void main(String[] args) { input = new Scanner(System.in); String x = "quit"; System.out.println("Enter a fraction"); while (true) { String y = input.next(); if (y.equals(x)) { break; } } } }

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  • What ever happened to Java and Sun?

    - by leeand00
    What happened to Java and Sun? The community surrounding them had some of my favorite tools and software to develop with. The Java platform anyway, still looked like it had some promise to it: Groovy and Grails. Why does all of this seem to be going the way of the dodo lately? (Yes, I know their stock price is dropping badly.) Is it just the economy? Or did the lack of cohesion (i.e., not settling on a framework) among the community finally lead to its demise?

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  • Network license control for a Java application

    - by user1461615
    I have been tasked with providing some form of network license control for a Java application. The app would be stored on a network drive and run from a client machine. The basic idea is that it will be able to work out how many times it is being run concurrently and prevent the N+1th user from running the software where N is the number of concurrent licenses the customer has purchased. Is this possible somehow with a Java application? I implemented a "solution" which relied on multi-cast UDP communication between the running instances of the application but this didn't work because on most networks this kind of communication is blocked by security measures. Is there a better way? I don't even mind if it requires JNI/JNA. N.B. The solution does not have to be that sophisticated or highly secure.

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