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  • java concurrency: many writers, one reader

    - by Janning
    I need to gather some statistics in my software and i am trying to make it fast and correct, which is not easy (for me!) first my code so far with two classes, a StatsService and a StatsHarvester public class StatsService { private Map<String, Long> stats = new HashMap<String, Long>(1000); public void notify ( String key ) { Long value = 1l; synchronized (stats) { if (stats.containsKey(key)) { value = stats.get(key) + 1; } stats.put(key, value); } } public Map<String, Long> getStats ( ) { Map<String, Long> copy; synchronized (stats) { copy = new HashMap<String, Long>(stats); stats.clear(); } return copy; } } this is my second class, a harvester which collects the stats from time to time and writes them to a database. public class StatsHarvester implements Runnable { private StatsService statsService; private Thread t; public void init ( ) { t = new Thread(this); t.start(); } public synchronized void run ( ) { while (true) { try { wait(5 * 60 * 1000); // 5 minutes collectAndSave(); } catch (InterruptedException e) { e.printStackTrace(); } } } private void collectAndSave ( ) { Map<String, Long> stats = statsService.getStats(); // do something like: // saveRecords(stats); } } At runtime it will have about 30 concurrent running threads each calling notify(key) about 100 times. Only one StatsHarvester is calling statsService.getStats() So i have many writers and only one reader. it would be nice to have accurate stats but i don't care if some records are lost on high concurrency. The reader should run every 5 Minutes or whatever is reasonable. Writing should be as fast as possible. Reading should be fast but if it locks for about 300ms every 5 minutes, its fine. I've read many docs (Java concurrency in practice, effective java and so on), but i have the strong feeling that i need your advice to get it right. I hope i stated my problem clear and short enough to get valuable help.

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  • How to add two java.lang.Numbers?

    - by amit.dev
    I have two Numbers. Eg: Number a = 2; Number b = 3; //Following is an error: Number c = a + b; Why arithmetic operations are not supported on Numbers? Anyway how would I add these two numbers in java? (Of course I'm getting them from somewhere and I don't know if they are Integer or float etc).

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  • Java - Runtime.getRuntime().exec() what's going on?

    - by kunkanwan
    Hi, I have problem with Runtime.exec() in Java My code: String lol = "/home/pc/example.txt"; String[] b = {"touch", lol}; try { Runtime.getRuntime().exec(b); } catch(Exception ex) { doSomething(ex); } It's working good but when I trying changle variable "lol" files doesn't create in hard disk for instance: String lol = x.getPath(); where getPath() returns String What should I do ? Thanks for your reply :)

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  • Japanese fonts in a Java GUI

    - by kakashi
    Hi everyone, Is it possible to write a GUI in Java that would display Japanese fonts correctly regardless of the language settings of the OS it's being run on? I'd like to write a program which is able to do this but I'm not sure how to start going about this. Any advice would be a huge help!

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  • java database backup restore

    - by jawath
    how do i backup /restore any kind of databases inside my java application to flate files.Are there any tools framework available to backup database to flat file like CSV, XML,or secure encrypted file,or restore from csv or xml files to databases ,it should be also capable of dumping table vise restore and backup also

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  • Window z-ordering in java

    - by Aaron
    Is there a way to manage the window z-ordering of JDialog windows within java? I would like to able to assign each window to a layer such that windows on lower layers can never go above and obscure windows on higher layers. Even when they have focus. Similar to the Z-order capability that exists for components but for JDialog windows. The solution does not need to work across all OSes. A linux specific solution is acceptable.

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  • How does java implement inner class closures?

    - by thecoop
    In Java an anonymous inner class can refer to variables in it's local scope: public class A { public void method() { final int i = 0; doStuff(new Action() { public void doAction() { Console.printf(i); // or whatever } }); } } My question is how is this actually implemented? How does i get to the anonymous inner doAction implementation, and why does it have to be final?

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  • Creating and writing file from a FileOutputStream in Java

    - by Althane
    Okay, so I'm working on a project where I use a Java program to initiate a socket connection between two classes (a FileSender and FileReceiver). My basic idea was that the FileSender would look like this: try { writer = new DataOutputStream(connect.getOutputStream()); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } //While we have bytes to send while(filein.available() >0){ //We write them out to our buffer writer.write(filein.read(outBuffer)); writer.flush(); } //Then close our filein filein.close(); //And then our socket; connect.close(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); The constructor contains code that checks to see if the file exists, and that the socket is connected, and so on. Inside my FileReader is this though: input = recvSocket.accept(); BufferedReader br = new BufferedReader(new InputStreamReader(input.getInputStream())); FileOutputStream fOut= new FileOutputStream(filename); String line = br.readLine(); while(line != null){ fOut.write(line.getBytes()); fOut.flush(); line = br.readLine(); } System.out.println("Before RECV close statements"); fOut.close(); input.close(); recvSocket.close(); System.out.println("After RECV clsoe statements"); All inside a try-catch block. So, what I'm trying to do is have the FileSender reading in the file, converting to bytes, sending and flushing it out. FileReceiver, then reads in the bytes, writes to the fileOut, flushes, and continues waiting for more. I make sure to close all the things that I open, so... here comes the weird part. When I try and open the created text file in Eclipse, it tells me "An SWT error has occured ... recommended to exit the workbench... see .log for more details.". Another window pops up saying "Unhandled event loop exception, (no more handles)". However, if I try to open the sent text file in notepad2, I get ThisIsASentTextfile Which is good (well, minus the fact that there should be line breaks, but I'm working on that...). Does anyone know why this is happening? And while we're checking, how to add the line breaks? (And is this a particularly bad way to transfer files over java without getting some other libraries?)

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  • Java Robot class and UAC

    - by bml13
    I am using the Java Robot class to take screenshots, my problem is that in W7 when the UAC dialog is shown (i right click on any application and select run as Admin) it will not appear in the screen shot or the whole screen is just black. Running my application with admin rights or as a service does not solve the problem. Please, does any one know what to do so that i will be able to capture the screen even when the UAC is showing? Thanks

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  • java interfaces

    - by Codenotguru
    write an interface with one method,two classes that implement the interface, and a main method with an array holding an instance from both classes.Using this array variable call the method in a foreach loop.This is a interview question in java anybody?

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  • Java OCR package

    - by pstanton
    what is the best OCR package you've used with java? I need to parse mainly numbers in a single font and am looking for a well architected, lite weight library to use. thanks.

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  • Securing username/password embedded in Java Desktop App

    - by William
    My Java desktop application includes a component for communicating with a web service. We therefore need to include the access details for it within the application, but do not want it to be easily accessible in the event that the code is decompiled (we will be obfuscating). What techniques can we use to secure these details?

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  • java web browser slow

    - by zachary
    org.eclipse.swt.browser.Browser I load the embedded browser into java and have it load a page. It seems to load really slow... is this an issue with the page caching? What can I do to speed this up?

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  • Profiling short-lived Java applications

    - by ejel
    Is there any Java profiler that allows profiling short-lived applications? The profilers I found so far seem to work with applications that keep running until user termination. However, I want to profile applications that work like command-line utilities, it runs and exits immediately. Tools like visualvm or NetBeans Profiler do not even recognize that the application was ran. I am looking for something similar to Python's cProfile, in that the profiler result is returned when the application exits.

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