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  • Generic collection as a Java method argument

    - by Guido
    Is there any way to make this work in Java? public static void change(List<? extends Object> list, int position1, int position2) { Object obj = list.get(position1); list.set(position1, list.get(position2)); list.set(position2, obj); } The only way I've successfully avoided warnings and errors is this: public static <T> T change(List<T> list, int position1, int position2) { T obj = list.get(position1); list.set(position1, list.get(position2)); list.set(position2, obj); return obj; } but I don't like to be forced to return a value.

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  • Java Applet in JAR File

    - by Jared Revik
    I have created a java applet (.class file) and made a .jar with it and digitally signed the .jar file. Now I need to run the .jar as an applet in firefox. What do I put in the html code to run the .jar file as an applet? I tried and it doesn't work, it tries to get a .class file, how do I load and run my applet as a .jar file using the applet tag in Internet Explorer and Firefox? I searched on the internet and could not find an answer.

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  • Java Google App Engine inconsistent data lose after restarting dev server

    - by user259349
    Hello everyone, I am using Java GAE. So far, i'm just scafolding my data objects and i'm seeing an interesting issue. The records that i am playing around with are getting updated properly as long as my dev server is running up. The second that the my dev server gets restarted, i lose all of my changes. That would be not alarming if i lost all of my records, but, there was a point of time where my data persisted through the server restart. I'm worried that i would lose production data if i launched without fixing this potential bugs? ANy idea on wher ei should look?

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  • download zip file using java?

    - by Mohamed
    I am downloading zip file from web server using Java but somehow I am loosing about 2kb in each file. I don't know why since same code works fine with other formats, e.g, text, mp3 and extra. any help is appreciated? here is my code. public void download_zip_file(String save_to) { try { URLConnection conn = this.url.openConnection(); conn.setDoOutput(true); conn.setDoInput(true); conn.setRequestProperty("content-type", "binary/data"); InputStream in = conn.getInputStream(); FileOutputStream out = new FileOutputStream(save_to + "tmp.zip"); byte[] b = new byte[1024]; int count; while ((count = in.read(b)) > 0) { out.write(b, 0, count); } out.close(); in.close(); } catch (IOException e) { e.printStackTrace(); } }

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  • Create Personalized Controls For Java ME

    - by Nathan Campos
    I'm starting to develop a eBook reader for mobile using Java ME, but for the control were the book will be shown I need a personalized control. For this I need to first know how to do one, to workaround with my needs. Then I need to know how can I do a personalized control as we do with Visual Basic. PS: I want to do a personalized TextBox, that in some parts can be in bold, italic, sublined, that supports topics(as the Edit, the MS-DOS Text Editor) and many other things that make a eBook better viewed than a simple plain text

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  • Java 2D clip area to shape

    - by user2923880
    I'm quite new to graphics in java and I'm trying to create a shape that clips to the bottom of another shape. Here is an example of what I'm trying to achieve: Where the white line at the base of the shape is the sort of clipped within the round edges. The current way I am doing this is like so: g2.setColor(gray); Shape shape = getShape(); //round rectangle g2.fill(shape); Rectangle rect = new Rectangle(shape.getBounds().x, shape.getBounds().y, width, height - 3); Area area = new Area(shape); area.subtract(new Area(rect)); g2.setColor(white); g2.fill(area); I'm still experimenting with the clip methods but I can't seem to get it right. Is this current method ok (performance wise, since the component repaints quite often) or is there a more efficient way? Thanks in advance.

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  • Using a JSON web service from a Java client application

    - by user383341
    I am developing a client-side Java application that has a bit of functionality that requires getting data from some web services that transmit in JSON (some RESTful, some not). No JavaScript, no web browser, just a plain JAR file that will run locally with Swing for the GUI. This is not a new or unique problem; surely there must be some open source libraries out there that will handle the JSON data transmission over HTTP. I've already found some that will parse JSON, but I'm having trouble finding any that will handle the HTTP communication to consume the JSON web service. So far I've found Apache Axis2 apparently which might have at least part of the solution, but I don't see enough documentation for it to know if it will do what I need, or how to use it. Maybe part of the problem is that I don't have experience with web services so I'm not able to know a solution when I see it. I hope some of you can point me in the right direction. Examples would be helpful.

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  • sg_map & lsscsi showing old storage version

    - by PratapSingh
    I am using SUN storage and recently upgraded/refreshed my ISCSI LUN storage. We have replicated old storage to new storage and attached to our servers. I can see at SUN storage side that storage is attached to server and also from server when I run the below command it prints the following output : iscsiadm -m session tcp: [1] 10.1.1.10:3260,2 iqn.86-03.com.sun:02:afsfsf58-c56a-6ba8-a944-addd258687cd The above storage is SUN STORAGE 7420 But when I run sg_map or lsscsi command it prints different version: lsscsi disk SUN Sun Storage 7410 1.0 /dev/sda disk SUN Sun Storage 7410 1.0 /dev/sdb disk SUN Sun Storage 7410 1.0 /dev/sdc disk SUN Sun Storage 7410 1.0 /dev/sdd Output of ls on "/dev/disk/by-path/" ls -1 /dev/disk/by-path/ ip-10.1.1.10:3260-iscsi-iqn.86-03.com.sun:02:afsfsf58-c56a-6ba8-a944-addd258687cd-lun-0 ip-10.1.1.10:3260-iscsi-iqn.86-03.com.sun:02:afsfsf58-c56a-6ba8-a944-addd258687cd-lun-0-part1 ip-10.1.1.10:3260-iscsi-iqn.86-03.com.sun:02:afsfsf58-c56a-6ba8-a944-addd258687cd-lun-18 ip-10.1.1.10:3260-iscsi-iqn.86-03.com.sun:02:afsfsf58-c56a-6ba8-a944-addd258687cd-lun-18-part1 ip-10.1.1.10:3260-iscsi-iqn.86-03.com.sun:02:afsfsf58-c56a-6ba8-a944-addd258687cd-lun-2 ip-10.1.1.10:3260-iscsi-iqn.86-03.com.sun:02:afsfsf58-c56a-6ba8-a944-addd258687cd-lun-2-part1 ip-10.1.1.10:3260-iscsi-iqn.86-03.com.sun:02:afsfsf58-c56a-6ba8-a944-addd258687cd-lun-4 ip-10.1.1.10:3260-iscsi-iqn.86-03.com.sun:02:afsfsf58-c56a-6ba8-a944-addd258687cd-lun-4-part1 ip-10.1.1.10:3260-iscsi-iqn.86-03.com.sun:02:afsfsf58-c56a-6ba8-a944-addd258687cd-lun-6 ip-10.1.1.10:3260-iscsi-iqn.86-03.com.sun:02:afsfsf58-c56a-6ba8-a944-addd258687cd-lun-6-part1 I have rebooted server twice but still I am getting the same output as given above.

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  • Selenium server won't start

    - by moff
    I'm getting the following error when trying to start selenium: C:\Temp\selenium-server-1.0.3java -jar selenium-server.jar 22:02:07.615 INFO - Java: Sun Microsystems Inc. 16.0-b13 22:02:07.617 INFO - OS: Windows 7 6.1 x86 22:02:07.625 INFO - v2.0 [a2], with Core v2.0 [a2] 22:02:07.811 INFO - RemoteWebDriver instances should connect to: http://127.0.0. 1:4444/wd/hub 22:02:07.813 INFO - Version Jetty/5.1.x 22:02:07.815 INFO - Started HttpContext[/selenium-server/driver,/selenium-server /driver] 22:02:07.817 INFO - Started HttpContext[/selenium-server,/selenium-server] 22:02:07.818 INFO - Started HttpContext[/,/] 22:02:07.866 INFO - Started org.openqa.jetty.jetty.servlet.ServletHandler@2bbd86 22:02:07.867 INFO - Started HttpContext[/wd,/wd] 22:02:07.870 WARN - Failed to start: [email protected]:4444 Exception in thread "main" org.openqa.jetty.util.MultiException[java.net.SocketE xception: Unrecognized Windows Sockets error: 0: JVM_Bind] at org.openqa.jetty.http.HttpServer.doStart(HttpServer.java:686) at org.openqa.jetty.util.Container.start(Container.java:72) at org.openqa.selenium.server.SeleniumServer.start(SeleniumServer.java:3 96) at org.openqa.selenium.server.SeleniumServer.boot(SeleniumServer.java:23 4) at org.openqa.selenium.server.SeleniumServer.main(SeleniumServer.java:19 8) java.net.SocketException: Unrecognized Windows Sockets error: 0: JVM_Bind at java.net.PlainSocketImpl.socketBind(Native Method) at java.net.PlainSocketImpl.bind(Unknown Source) at java.net.ServerSocket.bind(Unknown Source) at java.net.ServerSocket.(Unknown Source) at org.openqa.jetty.util.ThreadedServer.newServerSocket(ThreadedServer.j ava:391) at org.openqa.jetty.util.ThreadedServer.open(ThreadedServer.java:477) at org.openqa.jetty.util.ThreadedServer.start(ThreadedServer.java:503) at org.openqa.jetty.http.SocketListener.start(SocketListener.java:204) at org.openqa.jetty.http.HttpServer.doStart(HttpServer.java:716) at org.openqa.jetty.util.Container.start(Container.java:72) at org.openqa.selenium.server.SeleniumServer.start(SeleniumServer.java:3 96) at org.openqa.selenium.server.SeleniumServer.boot(SeleniumServer.java:23 4) at org.openqa.selenium.server.SeleniumServer.main(SeleniumServer.java:19 8) Java is installed: C:\Temp\selenium-server-1.0.3java -version java version "1.6.0_18" Java(TM) SE Runtime Environment (build 1.6.0_18-b07) Java HotSpot(TM) Client VM (build 16.0-b13, mixed mode, sharing) Thanks in advance

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  • Dell PERC 5 - RAID-10 keeps rebuilding drive 2 every day

    - by raid question
    I have a Dell PowerEdge 2950 with this card: RAID bus controller [0104]: Dell PowerEdge Expandable RAID controller 5 [1028:0015] and six disks in a RAID-10. I replaced drive 2, because it didn't show up, and then it started to rebuild itself: root@backup01:~# megaraidsas-status -- Arrays informations -- -- ID | Type | Size | Status a0d0 | RAID 10 | 5587GiB | DEGRADED -- Disks informations -- ID | Model | Status | Warnings a0e8s0 | ATA ST2000DM001-9YN1 1863GiB | online | errs: media:0 other:5393 a0e8s1 | ATA ST2000DM001-9YN1 1863GiB | online | errs: media:0 other:5394 a0e8s2 | ATA ST2000DM001-1E61 1863GiB | rebuild | errs: media:0 other:99 a0e8s3 | ATA ST2000DM001-9YN1 1863GiB | online | errs: media:0 other:5393 a0e8s4 | ATA ST2000DM001-9YN1 1863GiB | online | errs: media:0 other:5393 a0e8s5 | ATA ST2000DM001-9YN1 1863GiB | online | errs: media:0 other:5393 The rebuild finishes, then the virtual drive becomes optimal, and drive 2 goes online. Then once a day, drive 2 acts like it's been removed, and the rebuild starts all over again. How do I make this once a day rebuild stop? Event Description: Removed: PD 02(e1/s2) Event Description: Removed: PD 02(e1/s2) Info: enclPd=08, scsiType=0, portMap=04, sasAddr=1221000002000000,0000000000000000 Event Description: State change on VD 00/0 from OPTIMAL(3) to DEGRADED(2) Event Description: VD 00/0 is now DEGRADED1 Event Description: State change on PD 02(e1/s2) from ONLINE(18) to FAILED(11) Event Description: State change on PD 02(e1/s2) from FAILED(11) to UNCONFIGURED_BAD(1) Event Description: Background Initialization failed on VD 00/0 Event Description: Inserted: PD 02(e1/s2) Event Description: Inserted: PD 02(e1/s2) Info: enclPd=08, scsiType=0, portMap=04, sasAddr=1221000002000000,0000000000000000 Event Description: PD 02(e1/s2) is not a certified drive Event Description: State change on PD 02(e1/s2) Event Description: State change on PD 02(e1/s2) from UNCONFIGURED_GOOD(0) to OFFLINE(10) from UNCONFIGURED_BAD(1) to UNCONFIGURED_GOOD(0) Event Description: Rebuild automatically started on PD 02(e1/s2) Event Description: State change on PD 02(e1/s2) from OFFLINE(10) to REBUILD(14)

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  • Java Hibernate/C3P0 error: "Could not obtain connection metadata. An attempt by a client to checkout

    - by Allan
    I'm trying to get some code I was passed up and running. It appears to use the Hibernate framework. I've gotten past most of the errors tweaking the configuration, but this one has me dead stumped. It's trying to connect to two databases: gameapp and gamelog. Both exist. It seems to have issues connecting to gamelog, but none connecting to gameapp (later in the init, it connects to and loads other DBs just fine). Below, I've pasted the error and exception stack dump. I imaging there's something else in the configs, so I've also included the configuration file for that db. I know this is very vague, but I'm hoping some pro can see the stupid mistake I'm missing. <?xml version="1.0" encoding="GBK"?> <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"> <hibernate-configuration> <session-factory> <property name="dialect">org.hibernate.dialect.MySQLDialect</property> <property name="connection.driver_class">com.mysql.jdbc.Driver</property> <property name="connection.url">jdbc:mysql://127.0.0.1:3306/gamelog</property> <property name="connection.username">root</property> <property name="connection.password"></property> <property name="connection.useUnicode">true</property> <property name="connection.characterEncoding">UTF-8</property> <property name="hibernate.jdbc.batch_size">100</property> <property name="jdbc.fetch_size">1</property> <property name="hbm2ddl.auto">none</property><!-- update --> <property name="connection.useUnicode">true</property> <property name="show_sql">true</property> <!-- c3p0-configuration --> <property name="hibernate.connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</property> <property name="hibernate.c3p0.min_size">5</property> <property name="hibernate.c3p0.max_size">10</property> <property name="hibernate.c3p0.timeout">30</property> <property name="hibernate.c3p0.idle_test_period">30</property> <property name="hibernate.c3p0.max_statements">0</property> <property name="hibernate.c3p0.acquire_increment">5</property> </session-factory> </hibernate-configuration> Exception and stack trace: 2010-04-30 17:50:00,411 WARN [org.hibernate.cfg.SettingsFactory] - Could not obtain connection metadata java.sql.SQLException: An attempt by a client to checkout a Connection has timed out. at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:106) at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:65) at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:527) at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:128) at org.hibernate.connection.C3P0ConnectionProvider.getConnection(C3P0ConnectionProvider.java:35) at org.hibernate.cfg.SettingsFactory.buildSettings(SettingsFactory.java:76) at org.hibernate.cfg.Configuration.buildSettings(Configuration.java:1933) at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1216) at com.database.hibernate.util.HibernateFactory.<init>(Unknown Source) at com.database.hibernate.util.HibernateUtil.<clinit>(Unknown Source) at com.server.databaseop.goodOp.GoodOpImpl.initBreedGoods(Unknown Source) at com.server.databaseop.goodOp.GoodOpImpl.access$000(Unknown Source) at com.server.databaseop.goodOp.GoodOpImpl$1.run(Unknown Source) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) at java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:351) at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:178) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:165) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:267) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) at java.lang.Thread.run(Thread.java:636) Caused by: com.mchange.v2.resourcepool.TimeoutException: A client timed out while waiting to acquire a resource from com.mchange.v2.resourcepool.BasicResourcePool@ca470 -- timeout at awaitAvailable() at com.mchange.v2.resourcepool.BasicResourcePool.awaitAvailable(BasicResourcePool.java:1317) at com.mchange.v2.resourcepool.BasicResourcePool.prelimCheckoutResource(BasicResourcePool.java:557) at com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:477) at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:525) ... 18 more

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  • Simple Java networking game engine [on hold]

    - by Florian Peschka
    I want to create a simple java networking game and search a networking engine that eases use of sockets etc. I have already read some questions on here and the internet about java networking for games, but many of them were over 10 years old or not really answered. I have no idea whatsoever about what exactly I need to send in terms of messages, but I figured simple strings or integers will be enough for my purposes. It's basically a peer to peer game, so I don't need a centralized server structure. Messaging doesn't have to have an extremely low ping, yet of course all players need to have a synchronized view. What are the possibilities I have here?

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  • Open source Java CMS for Google App Engine?

    - by markvgti
    I am looking for an open source Java CMS (Web CMS, actually) to run on Google App Engine. I have looked at related older questions on this topic (What CMS runs on Google AppEngine?, CMS over Google App Engine, with SEO etc.) but the problem is that they all largely list Python-based CMSes. Plus these questions are pretty old, and since GAE is a fast-moving target, I thought it might be worthwhile to ask again. I want a CMS for creating some websites (for myself and for others), but would rather not start writing one from scratch. A "good" (very subjective, I know) open source WCMS allows me to start using a product, while still being able to add to/extend the product/project. On the one hand I am looking for a somewhat mature product/project, on the other hand it's easier to start contributing to the development cycle of a young product/project (conflicting, I know :-). Here are some features that would be preferable: [X]HTML/XML/CSS based templating Ability to create multiple blogs Galleries Ability to create a "Downloads" section (is this pretty much standard?) Separate management for digital assets (images, PDFs, binary files etc.) Roles like "Administrator", "Editor", "Contributor" etc. (or their equivalents) Ability to move/reorganize pages Export to PDF Reformat content for printing Is the CMS you are about to suggest especially well-suited to publishing an online book? My idea is that while the book may be offered as a downloadable eBook, the latest, most current version will be the one available on the website.

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  • Java Spotlight Episode 84: Anil Gaur on JavaEE 7

    - by Roger Brinkley
    Tweet Interview with Anil Gaur, VP of Java Platform for Enterprise Edition and GlassFish Server, on JavaEE 7. Joining us this week on the Java All Star Developer Panel are Dalibor Topic, Java Free and Open Source Software Ambassador and Arun Gupta, Java EE Guy. Right-click or Control-click to download this MP3 file. You can also subscribe to the Java Spotlight Podcast Feed to get the latest podcast automatically. If you use iTunes you can open iTunes and subscribe with this link:  Java Spotlight Podcast in iTunes. Show Notes News Tori Wieldt - Judges Selected for Duke's Choice Awards Donald Smith - #OpenJDK interview in Java Magazine Henrik Ståhl - Java 7 adoption at 23% JavaOne Kicks Off with Sunday Keynotes at Masonic Auditorium Jersey 2.0 M4 JSF 2.2 Latest Snapshot NetBeans IDE 7.2 - Deploy to Cloud Events May 30, OTN Java Developer Day, Redwood Shores June 11-14, Cloud Computing Expo, New York City June 12, Boulder JUG June 13, Denver JUG June 13, Eclipse Juno DemoCamp, Redwoood Shore June 13, JUG Münster June 14, Java Klassentreffen, Vienna, Austria June 18-20, QCon, New York City June 26-28, Jazoon, Zurich, Switzerland July 5, Java Forum, Stuttgart, Germany July 30-August 1, JVM Language Summit, Santa Clara Feature InterviewAnil Gaur is the Vice President of Java Platform, Enterprise Edition, and GlassFish Server at Oracle in the Fusion Middleware Group. Is responsible for creation of Java EE Specifications, Reference Implementation, and Compatibility Test Suites. Leading the evolution on Java EE into Cloud and PaaS environment through the Java EE 7 standard. Prior to that, managed the delivery of Java EE 6 Platform and SDK which quickly gained momentum in enterprise application development and deployments. In this episode we talk about GlassFish 3.1 release. Mail Bag What’s Cool RFR (L): Adding core file parsing on Mac OS X to SA Sergio Del Valle @swdelvalle is the 1,000 @JavaSpotlight twitter follower

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  • Java Transaction Service without the application server

    - by johnny
    Is it possible to have a Java standalone application (no application server attached) that exposes some operations that a client can call and be the one to manage the transactions? I was thinking this application to expose JNDI resources and get a hold of a java:comp/UserTransaction from there, get also a bean from there and call methods A, B and C on it and coordinate the transaction from the client? The application I'm writing isn't complex enough so that I need a big application server around it so I'm thinking to have a standalone JTS inside it that the client could interact with from a transactions point of view. I don't have much experience with distributed transactions and don't really know how to tackle the issue. Is it even possible? Am I getting myself into something beyond what a mere mortal (programmer) can handle? How can I approach this?

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  • Feasibility to take over a JavaMe Project by Coders who have no experience in JavaMe

    - by Stephenmjm
    As the original JavaMe team will leave to do other items. The JavaMe project will be taken over by some guys knowing nothing about JavaMe. Transition period: One month About this JavaMe project: about 3.5 million lines of code (more than 180 java file, SourceCode is 8.5KB in total) using the Polish, Proguard document: The JavaMe project itself have no document. No UML map. Difficulties I guess: familiar with the JavaMe, this should be okay In order to do the further development. We need to Read the sourceCode ---- It's not easy to read 3.5 million lines of code having not enough comment Adaptation work for more than 100 phone These are the questions, thank you! In the case of our guys have no experience in JavaMe, Is one month too hasty? In order to take the job in time . What we should ask the original JavaMe team to do . Considering we hava no experience in JavaMe. The complication we taking the Adaptation work without the original JavaMe team? Any other suggestions?

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  • ca-certificates-java fails to install

    - by Jonas
    I use a VPS with Ubuntu Server 10.10. I want to use Jetty and run the command sudo apt-get install jetty but it fails because the installation encounted errors while processing ca-certificates-java. I have tried to install the failed package with: sudo apt-get install ca-certificates-java How can I solve this? I have run sudo apt-get update and sudo apt-get upgrade but I get the same errors after that. I have also installed Ubuntu Server x64 on a VirtualBox, but the two Ubuntu Server 10.10 has different kernel versions (2.6.35 on VirtualBox and 2.6.18 on my VPS). And on VirtualBox I can install Jetty without any problems.

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  • Eloqua API Full Code Example in JAVA

    - by Shawn Spencer
    Is there anyone out there who has mastered to retrieve some data programmatically from Eloqua? First of all, I'm more or less a newbie, as far as JAVA. I can follow tutorials, take directions and will Google till my fingers bleed. I understand the basics and am slightly familiar with OOP. My main problem is that I have a Friday deadline (and tomorrow is Thanksgiving). At any rate, all the Eloqua code snippets (that I've been able to find) illustrate one aspect of a specific issue, and that's it. In my case, I would greatly appreciate a JAVA project of some sort, with all the necessary files to do web services (WSDL, SOAP and perhaps WSIT) and the main class and all that included. No, I don't want you to do my work for me! Just give me enough to find my way around, enter the information I need to retrieve and all that. I'll take it from there. Any pointers, links or suggestions?

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  • Java ExecutorService java heap space ptoblems

    - by Sergey Aganezov jr
    I have a little bit of a problem in a multitasking java department. I have a class, called public class ThreadWorker implements Runnable { //some code in here public void run(){ // invokes some recursion method in the ThreadWorker itself, // which will stop eventually { } all in all, pretty simple "worker" that can work on it's on. To work with threads I'm using public static int THREAD_NUMBER = 4; public static ExecutorServide es = Executors.newFixedThreadPool(THREAD_NUMBER); adding instances of ThreadWroker class happens here: public void recursiveMethod(Arraylist<Integers> elements, MyClass data){ if (elements.size() == 0 && data.qualifies()){ ThreadWorker tw = new ThreadWorker(data); es.execute(tw); return; } for (int i=0; i< elements.size(); i++){ // some code to prevent my problem MyClass data1 = new MyClass(data); MyClass data2 = new MyClass(data); ArrayList<Integer> newElements = (ArrayList<Integer>)elements.clone(); data1.update(elements.get(i)); data2.update(-1 * elements.get(i)); newElements.remove(i); recursiveMethod(newElements, data1); recursiveMethod(newElements, data2); { } and the problem is that the depth of the recursion tree is quite big, so as it's width, so a lot of ThreadWorkers are added to the ExecutorService, so after some time on the big input a get Exception in thread "pool-1-thread-2" java.lang.OutOfMemoryError: Java heap space which is caused, as I think because of a ginormous number of ThreadWorkers i'm adding to ExecutorSirvice to be executed, so it runs out of memory. Every ThreadWorker takes about 40 Mb of RAM for all it needs. Is there a method to get how many threads (instances of classes implementing runnable interface) have been added to ExecutorService? So I can add it in the shown above code (int the " // some code to prevent my problem"), as while ("number of threads in the ExecutorService" > 10){ Thread.sleep(10000); } so I won't go to deep or to broad with my recursion and prevent those exception-throwing situations. Sincerely, Sergey Aganezov jr.

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  • Question about casting a class in Java with generics

    - by Florian F
    In Java 6 Class<? extends ArrayList<?>> a = ArrayList.class; gives and error, but Class<? extends ArrayList<?>> b = (Class<? extends ArrayList<?>>)ArrayList.class; gives a warning. Why is (a) an error? What is it, that Java needs to do in the assignment, if not the cast shown in (b)? And why isn't ArrayList compatible with ArrayList? I know one is "raw" and the other is "generic", but what is it you can do with an ArrayList and not with an ArrayList, or the other way around?

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  • Java: volatile guarantees and out-of-order execution

    - by WizardOfOdds
    Note that this question is solely about the volatile keyword and the volatile guarantees: it is not about the synchronized keyword (so please don't answer "you must use synchronize" for I don't have any issue to solve: I simply want to understand the volatile guarantees (or lack of guarantees) regarding out-of-order execution). Say we have an object containing two volatile String references that are initialized to null by the constructor and that we have only one way to modify the two String: by calling setBoth(...) and that we can only set their references afterwards to non-null reference (only the constructor is allowed to set them to null). For example (it's just an example, there's no question yet): public class SO { private volatile String a; private volatile String b; public SO() { a = null; b = null; } public void setBoth( @NotNull final String one, @NotNull final String two ) { a = one; b = two; } public String getA() { return a; } public String getB() { return b; } } In setBoth(...), the line assigning the non-null parameter "a" appears before the line assigning the non-null parameter "b". Then if I do this (once again, there's no question, the question is coming next): if ( so.getB() != null ) { System.out.println( so.getA().length ); } Am I correct in my understanding that due to out-of-order execution I can get a NullPointerException? In other words: there's no guarantee that because I read a non-null "b" I'll read a non-null "a"? Because due to out-of-order (multi)processor and the way volatile works "b" could be assigned before "a"? volatile guarantees that reads subsequent to a write shall always see the last written value, but here there's an out-of-order "issue" right? (once again, the "issue" is made on purpose to try to understand the semantics of the volatile keyword and the Java Memory Model, not to solve a problem).

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  • Java Cryptography Extension

    - by Adam Tannon
    I was told that in order to support AES256 encryption inside my Java app that I would need the JCE with Unlimited Strength Jurisdiction Policy Files. I downloaded this from Oracle and unzipped it and I'm only seeing 2 JARs: local_policy.jar; and US_export_polic.jar I just want to confirm I'm not missing anything here! My understanding (after reading the README.txt) is that I just drop these two into my <JAVA_HOME>/lib/security/ directory and they should be installed. By the names of these JARs I have to assume that its not the Java Crypto API that cannot handle AES256, but it's in fact a legal issue, perhaps? And that these two JARs basically tell the JRE "yes, it's legally-acceptable to run this level of crypto (AES256)." Am I correct or off-base?

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  • Resources for game networking in Java

    - by pudelhund
    I am currently working on a Java multiplayer game. The game itself (single player) already works perfectly fine and so does the chat. The only thing that is really missing is the multiplayer part. Sadly I am absolutely clueless on where to start with that. I roughly know that I will have to work with packages, and I also know many things about streaming etc (chat is already working). Oh and it should - according to this article - be a UDP server. My problem is that I can't find any resources on how to do this. A tutorial (book or website) would be perfect, alternatively a good example of an open source client/server (in Java of course) would be fine as well. If you feel like doing something helpful I'd also really appreciate someone "privately" teaching me via email or some chat program :) Thank you!

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