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  • [java] Efficiency of while(true) ServerSocket Listen

    - by Submerged
    I am wondering if a typical while(true) ServerSocket listen loop takes an entire core to wait and accept a client connection (Even when implementing runnable and using Thread .start()) I am implementing a type of distributed computing cluster and each computer needs every core it has for computation. A Master node needs to communicate with these computers (invoking static methods that modify the algorithm's functioning). The reason I need to use sockets is due to the cross platform / cross language capabilities. In some cases, PHP will be invoking these java static methods. I used a java profiler (YourKit) and I can see my running ServerSocket listen thread and it never sleeps and it's always running. Is there a better approach to do what I want? Or, will the performance hit be negligible? Please, feel free to offer any suggestion if you can think of a better way (I've tried RMI, but it isn't supported cross-language. Thanks everyone

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  • Java - Highest, Lowest and Average

    - by Emily
    Right, so why does Java come up with this error: Exception in thread "main" java.lang.Error: Unresolved compilation problem: Type mismatch: cannot convert from double to int at rainfall.main(rainfall.java:38) From this: public class rainfall { /** * @param args */ public static void main(String[] args) { int[] numgroup; numgroup = new int [12]; ConsoleReader console = new ConsoleReader(); int highest; int lowest; int index; int tempVal; int minMonth; int minIndex; int maxMonth; int maxIndex; System.out.println("Welcome to Rainfall"); // Input (index now 0-based) for(index = 0; index < 12; index = index + 1) { System.out.println("Please enter the rainfall for month " + index + 1); tempVal = console.readInt(); while (tempVal100 || tempVal<0) { System.out.println("The rating must be within 0...100. Try again"); tempVal = console.readInt(); } numgroup[index] = tempVal; } lowest = numgroup[0]; highest = numgroup[0]; int total = 0.0; // Loop over data (using 1 loop) for(index = 0; index < 12; index = index + 1) { int curr = numgroup[index]; if (curr < lowest) { lowest = curr; minIndex = index; } if (curr highest) { highest = curr; maxIndex = index; } total += curr; } float avg = (float)total / numgroup.length; System.out.println("The average monthly rainfall was " + avg); // +1 to go from 0-based index to 1-based month System.out.println("The lowest monthly rainfall was month " + minIndex + 1); System.out.println("The highest monthly rainfall was month " + maxIndex + 1); System.out.println("Thank you for using Rainfall"); } private static ConsoleReader ConsoleReader() { return null; } }

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  • Java resource as file

    - by Martin Riedel
    Is there a way in Java to construct a File instance on a resource retrieved from a jar through the classloader? My application uses some files from the jar (default) or from a filesystem directory specified at runtime (user input). I'm looking for a consistent way of a) loading these files as a stream b) listing the files in the user-defined directory or the directory in the jar respectively Edit: Apparently, the ideal approach would be to stay away from java.io.File altogether. Is there a way to load a directory from the classpath and list its contents (files/entities contained in it)?

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  • How Can I create different selectors for accepting new connection in java NIO

    - by Deepak
    I want to write java tcp socket programming using java NIO. Its working fine. But I am using the same selector for accepting reading from and writing to the clients. How Can I create different selectors for accepting new connection in java NIO, reading and writing. Is there any online help. Actually when I am busy in reading or writing my selector uses more iterator. So If more number of clients are connected then performance of accepting new coneection became slow. But I donot want the accepting clients to be slow // Create a selector and register two socket channels Selector selector = null; try { // Create the selector selector = Selector.open(); // Create two non-blocking sockets. This method is implemented in // e173 Creating a Non-Blocking Socket. SocketChannel sChannel1 = createSocketChannel("hostname.com", 80); SocketChannel sChannel2 = createSocketChannel("hostname.com", 80); // Register the channel with selector, listening for all events sChannel1.register(selector, sChannel1.validOps()); sChannel2.register(selector, sChannel1.validOps()); } catch (IOException e) { } // Wait for events while (true) { try { // Wait for an event selector.select(); } catch (IOException e) { // Handle error with selector break; } // Get list of selection keys with pending events Iterator it = selector.selectedKeys().iterator(); // Process each key at a time while (it.hasNext()) { // Get the selection key SelectionKey selKey = (SelectionKey)it.next(); // Remove it from the list to indicate that it is being processed it.remove(); try { processSelectionKey(selKey); } catch (IOException e) { // Handle error with channel and unregister selKey.cancel(); } } } public void processSelectionKey(SelectionKey selKey) throws IOException { // Since the ready operations are cumulative, // need to check readiness for each operation if (selKey.isValid() && selKey.isConnectable()) { // Get channel with connection request SocketChannel sChannel = (SocketChannel)selKey.channel(); boolean success = sChannel.finishConnect(); if (!success) { // An error occurred; handle it // Unregister the channel with this selector selKey.cancel(); } } if (selKey.isValid() && selKey.isReadable()) { // Get channel with bytes to read SocketChannel sChannel = (SocketChannel)selKey.channel(); // See e174 Reading from a SocketChannel } if (selKey.isValid() && selKey.isWritable()) { // Get channel that's ready for more bytes SocketChannel sChannel = (SocketChannel)selKey.channel(); } } Thanks Deepak

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  • Java 'Prototype' pattern - new vs clone vs class.newInstance

    - by Guillaume
    In my project there are some 'Prototype' factories that create instances by cloning a final private instance. The author of those factories says that this pattern provides better performance than calling 'new' operator. Using google to get some clues about that, I've found nothing really relevant about that. Here is a small excerpt found in a javdoc from an unknown project javdoc from an unknown project Sadly, clone() is rather slower than calling new. However it is a lot faster than calling java.lang.Class.newInstance(), and somewhat faster than rolling our own "cloner" method. For me it's looking like an old best practice of the java 1.1 time. Does someone know more about this ? Is this a good practice to use that with 'modern' jvm ?

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  • fastest (low latency) method for Inter Process Communication between Java and C/C++

    - by Bastien
    Hello, I have a Java app, connecting through TCP socket to a "server" developed in C/C++. both app & server are running on the same machine, a Solaris box (but we're considering migrating to Linux eventually). type of data exchanged is simple messages (login, login ACK, then client asks for something, server replies). each message is around 300 bytes long. Currently we're using Sockets, and all is OK, however I'm looking for a faster way to exchange data (lower latency), using IPC methods. I've been researching the net and came up with references to the following technologies: - shared memory - pipes - queues but I couldn't find proper analysis of their respective performances, neither how to implement them in both JAVA and C/C++ (so that they can talk to each other), except maybe pipes that I could imagine how to do. can anyone comment about performances & feasibility of each method in this context ? any pointer / link to useful implementation information ? thanks for your help

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  • Are there macro facility for Java or C#?

    - by h2g2java
    Macros are useful. Therefore, I occasionally bemoan the absence of macros in Java and C#. Macros allow me to force in-line but allow me the code-manageability of non-macro code. Is there any Java- or C#-based project/product somewhere out there that effectively allow macros or specifying in-line expansion. I am thinking of something like @macro public void hello(int x){ ... } or when I call a method, an @inline annotation preceding the call would effect the called-method to be in-lined. or, should I need to know that I should just trust the compiler to make the best the decision for me that at the best of its analysis it might in-line a call. I hope this question will not lead to debating the pro/cons/usefulness of macros.

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  • java.util.regex.* Recursive matching

    - by amit.bhayani
    Hi Guys, I have been using the java.util.regex.* classes for Regular Expression in Java and all good so far. But today I have a different requirement. For example consider the pattern to be "aabb". Now if the input String is aa it will definitely not match, however there is still possibility that if I append bb it becomes aabb and it matches. However if I would have started with cc, no matter what I append it will never match. I have explored the Pattern and Matcher class but didn't find any way of achieving this. The input will come from user and system have to wait till pattern matches or it will never match irrespective of any input further. Any clue? Thanks.

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  • Convert JSON String to Java Object or HashMap

    - by Priyank
    Hi. I am writing an android app. I want to pass some data across the intents/activities and I feel that a conversion to and from JSON is probably a more optimal way at this point. I am able to convert a java hashmap to a json string successfully using JSONObject support. However i need to convert back this JSON string to a java object or a hashmap. What is the best way to go about it. Is parcelable really a change worth doing; if I have simple 5 field object? What are the other ways to transfer data between intents. Cheers

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  • SSL HandShake on Java Client

    - by JKV
    I have a very basic doubt in SSL HandShake. Assume that we have a server S which uses self signed certificates. I write a Java client C which connects to the S. When C connects to S, C gets certificates from S and saves them to its truststore and the remaining part of the communication proceeds. After some time I use the same C to connect to the S, so will S send the certificates again to C, or C will use the certificates already stored in truststore. I am not good in SSL and underlying implementation of Truststore functionality in Java. Will S send the certificates to C invariable of whether the C has certificates on its truststore?? I believe that if I have certificates in truststore C trusts S and C will not ask for certificates when I connect again?? Is my assumption right?? Is the process same for self-signed certificates and CA certificates?? Thanks in advance.

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  • Java - Google App Engine - InvalidClassException when I change a class that was stored in session sc

    - by Spines
    I updated my User class, and now whenever someone that had the old version of the User class stored in their session scope accesses my site, I get an InvalidClassException. javax.servlet.ServletException: java.lang.RuntimeException: java.io.InvalidClassException: User; local class incompatible: stream classdesc serialVersionUID = 4949038118012519093, local class serialVersionUID = -971500502189813151 How do I stop this error from happening for those users? I could probably invalidate everyone's sessions every time I want to update a class that gets stored in session scope, but is there a better way, so that my user's don't have to login again?

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  • Best language to learn complementing java

    - by danielrutledge
    Hi all, I'm a somewhat experienced java ee developer, and I wish to complement my background by learning a newish language. I'm recently out of school where I did a ton of scientific computing and some functional programming, so I'm pretty comfortable with those families of languages. If at all possible, I'd like to pick a language with some market value, though I know this is tough to gauge. After snooping around a bit, the consensus seems to be one of Python/Ruby/Perl; how would each of these work with java in a web application environment, and in your opinion which complements it best? Any other suggestions for languages would also be welcome.

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  • Converting Json to Java

    - by Binaryrespawn
    Hi all, I want to be able to access properties from a json string within my java action method. The string is available by simply saying myJsonString = object.getJson(); Below is an example of what the string can look like: {'title': 'Computing and Information systems','id':1,'children': 'true','groups': [{'title': 'Level one CIS','id':2,'children': 'true','groups':[{'title': 'Intro To Computing and Internet','id':3,'children': 'false','groups':[]}]}]} In this string every json object contains an array of other json objects. The intention is to extract a list of id's where any given object possessing a group property that contains other json objects. I looked at google's Gson as a potential json plugin. Can anyone offer some form of guidance as to how I can generate java from this json string? Thank you, Kind regards.

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  • Java: Sockets or RMI?

    - by StillLearning
    Hi, I need to separate our application into a light-weight gui application and a business logic application. This won't be a client/server setup as such, as the 'server' component will only have one client. The other limitation in the application is that it has only one entry/exit point. Therefore if we were to use RMI, it would only ever be on one function. All form data is already wrapped up into a string and passed through one transport area. Should I just use Java Sockets to enhance this application, or go with RMI? Or some other Java technology? I made a previous post outlining the requirements of our application, however it went unanswered. http://stackoverflow.com/questions/2604528/terminal-panel-pc-single-server-solution-client-server-or-rdp Cheers.

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  • Java, searching through folders to match a name

    - by Nick
    Hi folks, I using java to search for a file or folder that matches a specific case. For instance i want to search through all the files and folders and iterate through them as many times as necessary untill i find a result. The catch I searching for files and folders through a binary image of a file system. This means i doubt there are any preexisting classes such java.file.* to do it for me. If it helps i can tell you that i can tell the difference between files and folders easily enough. (a folder is flagged as 0x20) The only way i can think of is to do a standard loop and iterated several times but this limits me if a file or folder is several folders deep. All input greatly welcome

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  • Building Java projects with circular imports in Eclipse

    - by Buggieboy
    I have a legacy Java (not my native language) app that I'm trying to build in Eclipse Galileo. As it's not my own, I can't speak to the quality of the design, but I am coming across a number of instances where I'll have something like this: In a project called, say, "lib_a", I'll have a file containing this: import com.acme.lib_b.onething; Project "lib_b" on the other hand, will contain: import com.acme.lib_a.anotherthing; Of course, the problem is that one project can't be built because the errors prevent me from creating a .jar file that can be added as an external archive to the other project, and vice versa. It seems to me that this must be a fairly common occurence in building Java applications. Rewriting it from scratch is not an option here, so I'd like to know "what other folks do."

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  • telling java to accept self-signed ssl certificate

    - by Nikita Rybak
    It looks like a standard question, but I couldn't find clear directions anywhere. I have java code trying to connect server with probably self-signed (or expired) certificate. It gives something like this [HttpMethodDirector] I/O exception (javax.net.ssl.SSLHandshakeException) caught when processing request: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target As I understand, I have to play around with keytool and tell java that it's ok to allow this connection. But all comments I've found assume I'm fully proficient with keytool, like "generate private key for server and import it into keystore". And I'm not. Is there anybody who could post detailed instructions? I'm running unix, so bash script would be best. Not sure if it's important, but code executed in jboss. Thanks a lot!

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  • Problem with greek characters using java

    - by Subhendu Mahanta
    I am trying to write greek characters to a file using java like this: String greek = "\u03c1\u03ae\u03bc. \u03c7\u03b1\u03b9\u03c1\u03b5\u03c4\u03ce"; try { BufferedWriter out = new BufferedWriter(new FileWriter("E:\\properties\\outfilename.txt")); out.write(greek); out.close(); } catch (IOException e) { } Not working. Tried to use javac -encoding ISO-8859-7. Also tried java -Dfile.encoding=ISO-8859-7. Assuming that as I do not have greek font in my pc, I downloaded achillies (greek font - Ach4.ttf).Installed it by going to control panel fonts. Any ideas?

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  • check for naming convention in java.

    - by Vivart
    through java reflection how to check that method name is in camelCase? e.g. import java.lang.reflect.*; public class TestClass { private int simpleMethod( Object p, int x) throws NullPointerException { if (p == null) throw new NullPointerException(); return x; } public static void main(String args[]) { try { Class cls = Class.forName("method1"); Method methlist[] = cls.getDeclaredMethods(); for (int i = 0; i < methlist.length; i++) { Method m = methlist[i]; System.out.println("name= " + m.getName()); } } catch (Throwable e) { System.err.println(e); } } } here i am getting method names simpleMethod and main i have to check that these names are in camelCase.

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  • Creating a desktop icon using JWS JNLP for a JavaFX app.

    - by Sleepycat
    I am trying to get a custom destop icon to be displayed for my app but for some reason no matter what I do the same default java icon shows up. I have tried everything I can think of and gone and compared my jnlp file with others whose icons seem to work ok. According to everything I have read the following should work fine. But of course, it doesn't: <information> <title>MikesApp</title> <vendor>Mike</vendor> <homepage href="http://www.mikesapp.com/"/> <description>Mikes App.</description> <icon kind="shortcut" href="res/icon64x64.png" width="64" height="64"/> <offline-allowed/> <shortcut> <desktop/> </shortcut> </information> Any ideas would be greatly appreciated.

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