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• Staggering java linux process startup to prevent OOM

  - by ctennis

  I am running a number of java processes on a single Linux machine. From a memory and computing standpoint, everything is fine when things are static. However, periodically we use a configuration management package up upgrade the jar or war files, and restart the java process. The problem is, that is restarts them all relatively quickly, and so we get 10 or so java VMs restarting all at the same time (we use daemontools for the service stops/starts), which wreaks havoc on the machine, in terms of OOMs or just really slow. This is because it's spawning the JVM 10x at the same time. Other than trying to stagger the startups, is there a smarter way of handling this? Maybe a sysctl tuning performance parameters, or a JVM parameter?

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• Java sound doesn't work under Linux

  - by Cliff

  I just installed Fedora 12 and after downloading and running the Java Sound Demo I get exceptions. If I run just a vanilla Java program that plays a .wav file it runs silently with no sound and no exceptions. Every other app seems to play sound. I also took some advice from this thread in the Ubuntu forums which almost seemed to work. (Installing aoss got rid of the initial exceptions in the sound demo but I still hear nothing when I play.) I'm getting frustrated by the individual hoops I have to go through to eek sound out of my speakers when running Java apps on Linux platforms! Can somebody help me figure out what's wrong?

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• powershell run java process problem

  - by Limited Atonement

  Dear Sirs, I'm trying to run a java process via Powershell in Windows XP. Here's the command: java.exe -cp .;./common.jar -Dcontext=atest1 -Dresourcepath=. DW_Install So, the classpath is . and .\common.jar (I think java takes the wrong slashes, right?) There are two environment variables, one "atest1" the other "." and the class to execute main on is DW_Install (in the default package). This command works in cmd.exe, but doesn't is PS. What's going on? What is PS doing while parsing this command that CMD doesn't do (or vice versa)? Aaron

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• Java JRE: Setting default heap size

  - by AndiDog

  I'm having trouble with Java on a virtual server, it always gives me the following error: # java Error occurred during initialization of VM Could not reserve enough space for object heap Could not create the Java virtual machine. I first solved this by using the CACAO virtual machine (of OpenJDK, by putting it first in jvm.cfg), but then I run into problems with my web application (Play! framework based, gives me nasty LinkageErrors). So I cannot use that VM. Instead I'd like to just use the normal server VM and set -Xmx128M by default. How can I do that? Related: this question

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• Firefox hangs with java in Linux

  - by Xolve

  I am using Firefox 3.6 on Linux and I haveJava 6 update 15. Obviously I am using the newer plugin type. Whenever I open a page with Java applet it just becoms unresponsive and hangs. I tried with Chrome. I think it detects the Java plugin from mozilla's plugins folder. Due to multiprocess architecture it doesn't hang and shows the initial applet loading window but then it reports that the plugin has crashed. The only way I can run Java applets is to download the class file and make an html file and run the applet using applet viewer.

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• Java login through LDAP

  - by Salda

  I am starting to write an application for our office and the first step is authentication through LDAP where all users already exist. Everything I need is a code in Java to check if the pair <nick,password> is right. Google found me many links, but I think that I will find here the most sofisticate, short and up to date solution (I don't want to read all articles like 2 whole days to do something so simple). I have written many dkBs of code in C++, but in Java I am total noob and I haven't coded anything with LDAP yet so try to be simple if speaking in Java and LDAP terms if possible.

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• Java and Sendmail HELO requires domain address

  - by ealgestorm

  I am trying to set up emailing from a java web application hosted on a linux server (Cent OS) in apache. Sendmail is working fine from the command line as root on localhost but when trying to send emails from the java web app (also on the same server from localhost) the following java exception is thrown. 501 5.0.0 HELO requires domain address EDIT: I have read that some people have found this is due to an incorrect hosts entry currently the hosts file contains 127.0.0.1 Centos-VPS localhost.localdomain localhost and i'm not sure what the Centos-VPS bit at the start is for but this is a clients hosted server so don't really want to break stuff EDIT see the RFC is helpful ... 501 Syntax error in parameters or arguments Now I know what the problem is! (note the sarcasm people.)

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• Java Hint in NetBeans for Identifying JOptionPanes

  - by Geertjan

  I tend to have "JOptionPane.showMessageDialogs" scattered through my code, for debugging purposes. Now I have a way to identify all of them and remove them one by one, since some of them are there for users of the application so shouldn't be removed, via the Refactoring window: Identifying instances of code that I'm interested in is really trivial: import org.netbeans.spi.editor.hints.ErrorDescription; import org.netbeans.spi.java.hints.ConstraintVariableType; import org.netbeans.spi.java.hints.ErrorDescriptionFactory; import org.netbeans.spi.java.hints.Hint; import org.netbeans.spi.java.hints.HintContext; import org.netbeans.spi.java.hints.TriggerPattern; import org.openide.util.NbBundle.Messages; @Hint( displayName = "#DN_ShowMessageDialogChecker", description = "#DESC_ShowMessageDialogChecker", category = "general") @Messages({ "DN_ShowMessageDialogChecker=Found \"ShowMessageDialog\"", "DESC_ShowMessageDialogChecker=Checks for JOptionPane.showMes" }) public class ShowMessageDialogChecker { @TriggerPattern(value = "$1.showMessageDialog", constraints = @ConstraintVariableType(variable = "$1", type = "javax.swing.JOptionPane")) @Messages("ERR_ShowMessageDialogChecker=Are you sure you need this statement?") public static ErrorDescription computeWarning(HintContext ctx) { return ErrorDescriptionFactory.forName( ctx, ctx.getPath(), Bundle.ERR_ShowMessageDialogChecker()); } } Stick the above class, which seriously isn't much code at all, in a module and run it, with this result: Bit trickier to do the fix, i.e., add a bit of code to let the user remove the statement, but I looked in the NetBeans sources and used the System.out fix, which does the same thing:  import com.sun.source.tree.BlockTree; import com.sun.source.tree.StatementTree; import com.sun.source.util.TreePath; import java.util.ArrayList; import java.util.Iterator; import java.util.List; import org.netbeans.api.java.source.CompilationInfo; import org.netbeans.api.java.source.WorkingCopy; import org.netbeans.spi.editor.hints.ErrorDescription; import org.netbeans.spi.editor.hints.Fix; import org.netbeans.spi.java.hints.ConstraintVariableType; import org.netbeans.spi.java.hints.ErrorDescriptionFactory; import org.netbeans.spi.java.hints.Hint; import org.netbeans.spi.java.hints.HintContext; import org.netbeans.spi.java.hints.JavaFix; import org.netbeans.spi.java.hints.TriggerPattern; import org.openide.util.NbBundle.Messages; @Hint( displayName = "#DN_ShowMessageDialogChecker", description = "#DESC_ShowMessageDialogChecker", category = "general") @Messages({ "DN_ShowMessageDialogChecker=Found \"ShowMessageDialog\"", "DESC_ShowMessageDialogChecker=Checks for JOptionPane.showMes" }) public class ShowMessageDialogChecker { @TriggerPattern(value = "$1.showMessageDialog", constraints = @ConstraintVariableType(variable = "$1", type = "javax.swing.JOptionPane")) @Messages("ERR_ShowMessageDialogChecker=Are you sure you need this statement?") public static ErrorDescription computeWarning(HintContext ctx) { Fix fix = new FixImpl(ctx.getInfo(), ctx.getPath()).toEditorFix(); return ErrorDescriptionFactory.forName( ctx, ctx.getPath(), Bundle.ERR_ShowMessageDialogChecker(), fix); } private static final class FixImpl extends JavaFix { public FixImpl(CompilationInfo info, TreePath tp) { super(info, tp); } @Override @Messages("FIX_ShowMessageDialogChecker=Remove the statement") protected String getText() { return Bundle.FIX_ShowMessageDialogChecker(); } @Override protected void performRewrite(TransformationContext tc) throws Exception { WorkingCopy wc = tc.getWorkingCopy(); TreePath statementPath = tc.getPath(); TreePath blockPath = tc.getPath().getParentPath(); while (!(blockPath.getLeaf() instanceof BlockTree)) { statementPath = blockPath; blockPath = blockPath.getParentPath(); if (blockPath == null) { return; } } BlockTree blockTree = (BlockTree) blockPath.getLeaf(); List<? extends StatementTree> statements = blockTree.getStatements(); List<StatementTree> newStatements = new ArrayList<StatementTree>(); for (Iterator<? extends StatementTree> it = statements.iterator(); it.hasNext();) { StatementTree statement = it.next(); if (statement != statementPath.getLeaf()) { newStatements.add(statement); } } BlockTree newBlockTree = wc.getTreeMaker().Block(newStatements, blockTree.isStatic()); wc.rewrite(blockTree, newBlockTree); } } } Aside from now being able to use "Inspect & Refactor" to identify and fix all instances of JOptionPane.showMessageDialog at the same time, you can also do the fixes per instance within the editor:

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• Java EE 7 Roadmap

  - by Linda DeMichiel

  The Java EE 6 Platform, released in December 2009, has seen great uptake from the community with its POJO-based programming model, lightweight Web Profile, and extension points. There are now 13 Java EE 6 compliant appserver implementations today! When we announced the Java EE 7 JSR back in early 2011, our plans were that we would release it by Q4 2012. This target date was slightly over three years after the release of Java EE 6, but at the same time it meant that we had less than two years to complete a fairly comprehensive agenda — to continue to invest in significant enhancements in simplification, usability, and functionality in updated versions of the JSRs that are currently part of the platform; to introduce new JSRs that reflect emerging needs in the community; and to add support for use in cloud environments. We have since announced a minor adjustment in our dates (to the spring of 2013) in order to accommodate the inclusion of JSRs of importance to the community, such as Web Sockets and JSON-P. At this point, however, we have to make a choice. Despite our best intentions, our progress has been slow on the cloud side of our agenda. Partially this has been due to a lack of maturity in the space for provisioning, multi-tenancy, elasticity, and the deployment of applications in the cloud. And partially it is due to our conservative approach in trying to get things "right" in view of limited industry experience in the cloud area when we started this work. Because of this, we believe that providing solid support for standardized PaaS-based programming and multi-tenancy would delay the release of Java EE 7 until the spring of 2014 — that is, two years from now and over a year behind schedule. In our opinion, that is way too long. We have therefore proposed to the Java EE 7 Expert Group that we adjust our course of action — namely, stick to our current target release dates, and defer the remaining aspects of our agenda for PaaS enablement and multi-tenancy support to Java EE 8. Of course, we continue to believe that Java EE is well-suited for use in the cloud, although such use might not be quite ready for full standardization. Even today, without Java EE 7, Java EE vendors such as Oracle, Red Hat, IBM, and CloudBees have begun to offer the ability to run Java EE applications in the cloud. Deferring the remaining cloud-oriented aspects of our agenda has several important advantages: It allows Java EE Platform vendors to gain more experience with their implementations in this area and thus helps us avoid risks entailed by trying to standardize prematurely in an emerging area. It means that the community won't need to wait longer for those features that are ready at the cost of those features that need more time. Because we have already laid some of the infrastructure for cloud support in Java EE 7, including resource definition metadata, improved security configuration, JPA schema generation, etc., it will allow us to expedite a Java EE 8 release. We therefore plan to target the Java EE 8 Platform release for the spring of 2015. This shift in the scope of Java EE 7 allows us to better retain our focus on enhancements in simplification and usability and to deliver on schedule those features that have been most requested by developers. These include the support for HTML 5 in the form of Web Sockets and JSON-P; the simplified JMS 2.0 APIs; improved Managed Bean alignment, including transactional interceptors; the JAX-RS 2.0 client API; support for method-level validation; a much more comprehensive expression language; and more. We feel strongly that this is the right thing to do, and we hope that you will support us in this proposed direction.

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• javax.servlet.ServletException - how could i get to the cause?

  - by Michal

  Hi, i'm getting a very strange error while opening one of the pages in my web app. The application is built on Seam 2.2 and is using JSF (RichFaces) as a view technology. I run it on Tomcat 6. The error i'm describing doesn't occur on my machine (Mac OS X), but it does on my client's dev machines (Windows) and on the server (Linux Debian). I'm sure i'm running the same version on each system and i have tried connecting to the same database... In logs everything looks fine - each next JSF Phase executes normally, and after the last one, there is this moment when the request starts processing for the SEAM debug page... And this is the stack trace i see on the debug page (nothing is logged): Exception during request processing: Caused by javax.servlet.ServletException with message: "Servlet execution threw an exception" org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:313) org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:83) org.jboss.seam.web.IdentityFilter.doFilter(IdentityFilter.java:40) org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69) org.jboss.seam.web.MultipartFilter.doFilter(MultipartFilter.java:90) org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69) org.jboss.seam.web.ExceptionFilter.doFilter(ExceptionFilter.java:64) org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69) org.jboss.seam.web.RedirectFilter.doFilter(RedirectFilter.java:45) org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69) org.ajax4jsf.webapp.BaseXMLFilter.doXmlFilter(BaseXMLFilter.java:178) org.ajax4jsf.webapp.BaseFilter.handleRequest(BaseFilter.java:290) org.ajax4jsf.webapp.BaseFilter.processUploadsAndHandleRequest(BaseFilter.java:388) org.ajax4jsf.webapp.BaseFilter.doFilter(BaseFilter.java:515) org.jboss.seam.web.Ajax4jsfFilter.doFilter(Ajax4jsfFilter.java:56) org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69) org.jboss.seam.web.LoggingFilter.doFilter(LoggingFilter.java:60) org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69) org.jboss.seam.web.HotDeployFilter.doFilter(HotDeployFilter.java:53) org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69) org.jboss.seam.servlet.SeamFilter.doFilter(SeamFilter.java:158) org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) pl.mgibowski.alterium.util.LoggingFilter.doFilter(LoggingFilter.java:18) org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:465) org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298) org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:852) org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588) org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) java.lang.Thread.run(Thread.java:619) Exception without any cause... I was trying to catch the exception with my custom Filter (LoggingFilter.java that you can see on the strack trace), using this code: try { filterChain.doFilter(servletRequest, servletResponse); } catch (Throwable e) { e.printStackTrace(); System.out.println("Stack trace:"); System.out.println(e.getStackTrace()); System.out.println("Cause:"); System.out.println(e.getCause()); } But it doesn't catch anything, the line 18 from the stack trace is this one: filterChain.doFilter(servletRequest, servletResponse); nothing gets caught by the try block. Anybody has any ideas about how could i get closer to the real cause?

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• RMI applet is making requests on random ports and blocked consequently

  - by Dan

  /// I have set up RMI system successfully on local ubuntu srver. Registry port 1099 and remote object export on 1100(fixed by calling super(1100)) Now I am trying to make it work on Ubuntu over internet with a public IP. I could bind service properly with public ip.But the client applet is trying to connect to ubuntu server at random ports. Below is the error thrown by client applet: // Exception network: Connecting public-ip:1100 with proxy=DIRECT network: Connecting public-ip/cgi-bin/java-rmi.cgi?forward=1099 with proxy=DIRECT network: Connecting public-ip:3733 with proxy=DIRECT network: Connecting public-ip:3721 with proxy=DIRECT // java.rmi.ConnectException: Connection refused to host: public-ip; nested exception is: java.net.ConnectException: Connection refused: connect at sun.rmi.transport.tcp.TCPEndpoint.newSocket(Unknown Source)Source) at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source) ... // // I have only 2 ports open on server, i.e., 1099(registry) and 1100(export). How can I fix ports in applet requests such that it does always connect server on same open port? // // Another issue.As I have bound service on public IP i.e. //public-ip:1099/ServiceName, a job running on server to send message to clinets is not able to make request to RMI service. public-ip URL does not work on same machine,i.e., server.Do you think I should use fixed socket factory?If so please give me code snippet and guide me how i can set it up. //Exception java.rmi.ConnectException: Connection refused to host: public-ip; nested exception is: java.net.ConnectException: Connection refused at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:619) at sun.rmi.transport.tcp.TCPChannel.createConnection(TCPChannel.java:216) at sun.rmi.transport.tcp.TCPChannel.newConnection(TCPChannel.java:202) at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:128) at java.rmi.server.RemoteObjectInvocationHandler.invokeRemoteMethod(RemoteObjectInvocationHandler.java:194) at java.rmi.server.RemoteObjectInvocationHandler.invoke(RemoteObjectInvocationHandler.java:148) at $Proxy5.getUserID(Unknown Source) at rmi.source.xxxxxx$JobScheduler.run(xxxxServerImpl.java:293) at java.util.TimerThread.mainLoop(Timer.java:555) at java.util.TimerThread.run(Timer.java:505) Caused by: java.net.ConnectException: Connection refused at java.net.PlainSocketImpl.socketConnect(Native Method) at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:337) at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:198) at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:180) at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:391) at java.net.Socket.connect(Socket.java:579) at java.net.Socket.connect(Socket.java:528) at java.net.Socket.(Socket.java:425) at java.net.Socket.(Socket.java:208) at sun.rmi.transport.proxy.RMIDirectSocketFactory.createSocket(RMIDirectSocketFactory.java:40) at sun.rmi.transport.proxy.RMIMasterSocketFactory.createSocket(RMIMasterSocketFactory.java:146) at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:613) ... 9 more Coould you please help me? Thanks a lot in advance. Dan

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• Java MapReduce read data

  - by Tatiana

  Hi I am having following map-reduce code by which I am trying to read records from my database. There's code: import java.io.*; import java.util.ArrayList; import java.util.List; import org.apache.hadoop.fs.*; import org.apache.hadoop.io.*; import org.apache.hadoop.mapred.*; import org.apache.hadoop.mapred.lib.db.DBConfiguration; import org.apache.hadoop.mapred.lib.db.DBInputFormat; import org.apache.hadoop.mapred.lib.db.DBWritable; import org.apache.hadoop.util.*; import org.apache.hadoop.conf.*; public class Connection extends Configured implements Tool { public int run(String[] args) throws IOException { JobConf conf = new JobConf(getConf(), Connection.class); conf.setInputFormat(DBInputFormat.class); DBConfiguration.configureDB(conf, "com.sun.java.util.jar.pack.Driver", "jdbc:postgresql://localhost:5432/polyclinic", "postgres", "12345"); String[] fields = { "name" }; DBInputFormat.setInput(conf, MyRecord.class, "doctors", null, null, fields); conf.setMapOutputKeyClass(LongWritable.class); conf.setMapOutputValueClass(MyRecord.class); conf.setOutputKeyClass(LongWritable.class); conf.setOutputValueClass(TextOutputFormat.class); TextOutputFormat.setOutputPath(conf, new Path(args[0])); JobClient.runJob(conf); return 0; } public static void main(String[] args) throws Exception { int exitCode = ToolRunner.run(new Connection(), args); System.exit(exitCode); } } Class Mapper: import java.io.IOException; import org.apache.hadoop.io.IntWritable; import org.apache.hadoop.io.LongWritable; import org.apache.hadoop.io.Text; import org.apache.hadoop.mapred.MapReduceBase; import org.apache.hadoop.mapred.Mapper; import org.apache.hadoop.mapred.OutputCollector; import org.apache.hadoop.mapred.Reporter; public class MyMapper extends MapReduceBase implements Mapper<LongWritable, MyRecord, Text, IntWritable> { public void map(LongWritable key, MyRecord val, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException { output.collect(new Text(val.name), new IntWritable(1)); } } Class Record: import java.io.DataInput; import java.io.DataOutput; import java.io.IOException; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import org.apache.hadoop.io.Text; import org.apache.hadoop.io.Writable; import org.apache.hadoop.mapred.lib.db.DBWritable; class MyRecord implements Writable, DBWritable { String name; public void readFields(DataInput in) throws IOException { this.name = Text.readString(in); } public void readFields(ResultSet resultSet) throws SQLException { this.name = resultSet.getString(1); } public void write(DataOutput out) throws IOException { } public void write(PreparedStatement stmt) throws SQLException { } } After this I got error: WARN mapred.JobClient: No job jar file set. User classes may not be found. See JobConf(Class) or JobConf#setJar(String). Can you give me any suggestion how to solve this problem?

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• Questions related to writing your own file downloader using multiple threads java

  - by Shekhar

  Hello In my current company, i am doing a PoC on how we can write a file downloader utility. We have to use socket programming(TCP/IP) for downloading the files. One of the requirements of the client is that a file(which will be large in size) should be transfered in chunks for example if we have a file of 5Mb size then we can have 5 threads which transfer 1 Mb each. I have written a small application which downloads a file. You can download the eclipe project from http://www.fileflyer.com/view/QM1JSC0 A brief explanation of my classes FileSender.java This class provides the bytes of file. It has a method called sendBytesOfFile(long start,long end, long sequenceNo) which gives the number of bytes. import java.io.File; import java.io.IOException; import java.util.zip.CRC32; import org.apache.commons.io.FileUtils; public class FileSender { private static final String FILE_NAME = "C:\\shared\\test.pdf"; public ByteArrayWrapper sendBytesOfFile(long start,long end, long sequenceNo){ try { File file = new File(FILE_NAME); byte[] fileBytes = FileUtils.readFileToByteArray(file); System.out.println("Size of file is " +fileBytes.length); System.out.println(); System.out.println("Start "+start +" end "+end); byte[] bytes = getByteArray(fileBytes, start, end); ByteArrayWrapper wrapper = new ByteArrayWrapper(bytes, sequenceNo); return wrapper; } catch (IOException e) { throw new RuntimeException(e); } } private byte[] getByteArray(byte[] bytes, long start, long end){ long arrayLength = end-start; System.out.println("Start : "+start +" end : "+end + " Arraylength : "+arrayLength +" length of source array : "+bytes.length); byte[] arr = new byte[(int)arrayLength]; for(int i = (int)start, j =0; i < end;i++,j++){ arr[j] = bytes[i]; } return arr; } public static long fileSize(){ File file = new File(FILE_NAME); return file.length(); } } Second Class is FileReceiver.java - This class receives the file. Small Explanation what this file does This class finds the size of the file to be fetched from Sender Depending upon the size of the file it finds the start and end position till the bytes needs to be read. It starts n number of threads giving each thread start,end, sequence number and a list which all the threads share. Each thread reads the number of bytes and creates a ByteArrayWrapper. ByteArrayWrapper objects are added to the list Then i have while loop which basically make sure that all threads have done their work finally it sorts the list based on the sequence number. then the bytes are joined, and a complete byte array is formed which is converted to a file. Code of File Receiver package com.filedownloader; import java.io.File; import java.io.IOException; import java.util.ArrayList; import java.util.Collections; import java.util.Comparator; import java.util.List; import java.util.zip.CRC32; import org.apache.commons.io.FileUtils; public class FileReceiver { public static void main(String[] args) { FileReceiver receiver = new FileReceiver(); receiver.receiveFile(); } public void receiveFile(){ long startTime = System.currentTimeMillis(); long numberOfThreads = 10; long filesize = FileSender.fileSize(); System.out.println("File size received "+filesize); long start = filesize/numberOfThreads; List<ByteArrayWrapper> list = new ArrayList<ByteArrayWrapper>(); for(long threadCount =0; threadCount<numberOfThreads ;threadCount++){ FileDownloaderTask task = new FileDownloaderTask(threadCount*start,(threadCount+1)*start,threadCount,list); new Thread(task).start(); } while(list.size() != numberOfThreads){ // this is done so that all the threads should complete their work before processing further. //System.out.println("Waiting for threads to complete. List size "+list.size()); } if(list.size() == numberOfThreads){ System.out.println("All bytes received "+list); Collections.sort(list, new Comparator<ByteArrayWrapper>() { @Override public int compare(ByteArrayWrapper o1, ByteArrayWrapper o2) { long sequence1 = o1.getSequence(); long sequence2 = o2.getSequence(); if(sequence1 < sequence2){ return -1; }else if(sequence1 > sequence2){ return 1; } else{ return 0; } } }); byte[] totalBytes = list.get(0).getBytes(); byte[] firstArr = null; byte[] secondArr = null; for(int i = 1;i<list.size();i++){ firstArr = totalBytes; secondArr = list.get(i).getBytes(); totalBytes = concat(firstArr, secondArr); } System.out.println(totalBytes.length); convertToFile(totalBytes,"c:\\tmp\\test.pdf"); long endTime = System.currentTimeMillis(); System.out.println("Total time taken with "+numberOfThreads +" threads is "+(endTime-startTime)+" ms" ); } } private byte[] concat(byte[] A, byte[] B) { byte[] C= new byte[A.length+B.length]; System.arraycopy(A, 0, C, 0, A.length); System.arraycopy(B, 0, C, A.length, B.length); return C; } private void convertToFile(byte[] totalBytes,String name) { try { FileUtils.writeByteArrayToFile(new File(name), totalBytes); } catch (IOException e) { throw new RuntimeException(e); } } } Code of ByteArrayWrapper package com.filedownloader; import java.io.Serializable; public class ByteArrayWrapper implements Serializable{ private static final long serialVersionUID = 3499562855188457886L; private byte[] bytes; private long sequence; public ByteArrayWrapper(byte[] bytes, long sequenceNo) { this.bytes = bytes; this.sequence = sequenceNo; } public byte[] getBytes() { return bytes; } public long getSequence() { return sequence; } } Code of FileDownloaderTask import java.util.List; public class FileDownloaderTask implements Runnable { private List<ByteArrayWrapper> list; private long start; private long end; private long sequenceNo; public FileDownloaderTask(long start,long end,long sequenceNo,List<ByteArrayWrapper> list) { this.list = list; this.start = start; this.end = end; this.sequenceNo = sequenceNo; } @Override public void run() { ByteArrayWrapper wrapper = new FileSender().sendBytesOfFile(start, end, sequenceNo); list.add(wrapper); } } Questions related to this code 1) Does file downloading becomes fast when multiple threads is used? In this code i am not able to see the benefit. 2) How should i decide how many threads should i create ? 3) Are their any opensource libraries which does that 4) The file which file receiver receives is valid and not corrupted but checksum (i used FileUtils of common-io) does not match. Whats the problem? 5) This code gives out of memory when used with large file(above 100 Mb) i.e. because byte array which is created. How can i avoid? I know this is a very bad code but i have to write this in one day -:). Please suggest any other good way to do this? Thanks Shekhar

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• What's the cause of (and treatment for) this java MySQL exception?

  - by justkevin

  I'm getting the following exception when executing the first preparedstatement after a period of inactivity: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure The last packet successfully received from the server was 2,855,054 milliseconds ago. The last packet sent successfully to the server was 123 milliseconds ago. at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:406) at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1074) at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3052) at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2938) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3481) at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1959) at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2109) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2648) at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2077) at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:2228) This only shows up if my application hasn't communicated with MySQL recently. Subsequent queries execute normally. I suspect it's some kind of timeout issue, but the periods of inactivity are way below the 8 hour timeout for MySQL. Any suggestions?

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• How do I keep a scanner from throwing exceptions when the wrong type is entered? (java)

  - by David

  Here's some sample code: import java.util.Scanner; class In { public static void main (String[]arg) { Scanner in = new Scanner (System.in) ; System.out.println ("how many are invading?") ; int a = in.nextInt() ; System.out.println (a) ; } } if i run the program and give it an int like 4then everything goes fine. if, on the other hand, i answer too many it doesn't laugh at my funny joke. instead i get this: (as expected) Exception in thread "main" java.util.InputMismatchException at java.util.Scanner.throwFor(Scanner.java:819) at java.util.Scanner.next(Scanner.java:1431) at java.util.Scanner.nextInt(Scanner.java:2040) at java.util.Scanner.nextInt(Scanner.java:2000) at In.main(In.java:9) is there a way so that i can make it so that it either ignores entries that aren't ints or re prompts with "how many are invading?"? i'd like to know how to do both of these.

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• java graphics display help

  - by java

  I know that i am not calling the graphics paint command in the mainframe in order to display it. but i'm not sure how. thanks in advance import java.awt.*; import javax.swing.*; public class MainFrame extends JFrame { private static Panel panel = new Panel(); public MainFrame() { panel.setBackground(Color.white); Container c = getContentPane(); c.add(panel); } public void paint(Graphics g) { g.drawString("abc", 20, 20); } public static void main(String[] args) { MainFrame frame = new MainFrame(); frame.setVisible(true); frame.setSize(600, 400); frame.setResizable(false); frame.setLocationRelativeTo(null); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); } }

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• Java ME SDK 3.2 is now live

  - by SungmoonCho

  Hi everyone, It has been a while since we released the last version. We have been very busy integrating new features and making lots of usability improvements into this new version. Datasheet is available here. Please visit Java ME SDK 3.2 download page to get the latest and best version yet! Some of the new features in this version are described below. Embedded Application SupportOracle Java ME SDK 3.2 now supports the new Oracle® Java ME Embedded. This includes support for JSR 228, the Information Module Profile-Next Generation API (IMP-NG). You can test and debug applications either on the built-in device emulators or on your device. Memory MonitorThe Memory Monitor shows memory use as an application runs. It displays a dynamic detailed listing of the memory usage per object in table form, and a graphical representation of the memory use over time. Eclipse IDE supportOracle Java ME SDK 3.2 now officially supports Eclipse IDE. Once you install the Java ME SDK plugins on Eclipse, you can start developing, debugging, and profiling your mobile or embedded application. Skin CreatorWith the Custom Device Skin Creator, you can create your own skins. The appearance of the custom skins is generic, but the functionality can be tailored to your own specifications.  Here are the release highlights. Implementation and support for the new Oracle® Java Wireless Client 3.2 runtime and the Oracle® Java ME Embedded runtime. The AMS in the CLDC emulators has a new look and new functionality (Install Application, Manage Certificate Authorities and Output Console). Support for JSR 228, the Information Module Profile-Next Generation API (IMP-NG). The IMP-NG platform is implemented as a subset of CLDC. Support includes: A new emulator for headless devices. Javadocs for the following Oracle APIs: Device Access API, Logging API, AMS API, and AccessPoint API. New demos for IMP-NG features can be run on the emulator or on a real device running the Oracle® Java ME Embedded runtime. New Custom Device Skin Creator. This tool provides a way to create and manage custom emulator skins. The skin appearance is generic, but the functionality, such as the JSRs supported or the device properties, are up to you. This utility only supported in NetBeans. Eclipse plugin for CLDC/MIDP. For the first time Oracle Java ME SDK is available as an Eclipse plugin. The Eclipse version does not support CDC, the Memory Monitor, and the Custom Device Skin Creator in this release. All Java ME tools are implemented as NetBeans plugins. As of the plugin integrates Java ME utilities into the standard NetBeans menus. Tools > Java ME menu is the place to launch Java ME utilities, including the new Skin Creator. Profile > Java ME is the place to work with the Network Monitor and the Memory Monitor. Use the standard NetBeans tools for debugging. Profiling, Network monitoring, and Memory monitoring are integrated with the NetBeans profiling tools. New network monitoring protocols are supported in this release: WMA, SIP, Bluetooth and OBEX, SATSA APDU and JCRMI, and server sockets. Java ME SDK Update Center. Oracle Java ME SDK can be updated or extended by new components. The Update Center can download, install, and uninstall plugins specific to the Java ME SDK. A plugin consists of runtime components and skins. Bug fixes and enhancements. This version comes with a few known problems. All of them have workarounds, so I hope you don't get stuck in these issues when you are using the product. It you cannot watch static variables during an Eclipse debugging session, and sometimes the Variable view cannot show data. In the source code, move the mouse over the required variable to inspect the variable value. A real device shown in the Device Selector is deleted from the Device Manager, yet it still appears. Kill the device manager in the system tray, and relaunch it. Then you will see the device removed from the list. On-device profiling does not work on a device. CPU profiling, networking monitoring, and memory monitoring do not work on the device, since the device runtime does not yet support it. Please do the profiling with your emulator first, and then test your application on the device. In the Device Selector, using Clean Database on real external device causes a null pointer exception. External devices do not have a database recognized by the SDK, so you can disregard this exception message. Suspending the Emulator during a Memory Monitor session hangs the emulator. Do not use the Suspend option (F5) while the Memory Monitor is running. If the emulator is hung, open the Windows task manager and stop the emulator process (javaw). To switch to another application while the Memory Monitor is running, choose Application > AMS Home (F4), and select a different application. Please let us know how we can improve it even better, by sending us your feedback. -Java ME SDK Team

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• How can I move from Java and ColdFusion to Ruby on Rails?

  - by Ciaran Archer

  Currently I work with ColdFusion 9+ and some Java in a Windows environment. Prior to ColdFusion, my background was in Java and JSP. I'm considering a move towards Ruby on Rails, as I think it would be a real challenge, keep things fresh, and provide more job opportunities. In order to get into it, I started to build my personal website in Rails 3.0. But what else can I do to make this transition from what I know now to Ruby and Rails? Are there specific or idiomatic aspects of Ruby or Rails I should keep in mind when switching over from a ColdFusion and Java mindset?

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• Do I need to know servlets and JSP to learn spring or hibernate or any other java web frameworks?

  - by KyelJmD

  I've been asking a lot of people where to start learning java web development, I already know core java (Threading,Generics,Collections, a little experience with (JDBC)) but I do not know JSPs and servlets. I did my fair share of development with several web based applications using PHP for server-side and HTML,CSS,Javascript,HTML5 for client side. Most people that I asked told me to jump right ahead to Hibernate while some told me that I do not need to learn servlets and jsps and I should immediately study the Spring framework. Is this true? do I not need to learn servlets and JSPs to learn hibernate or Spring? All of their answers confused me and now I am completely lost what to learn or study. I feel that if I skipped learning JSP and servlets I would missed a lot of important concepts that will surely help me in the future. So the question, do I need to have foundation/know servlets and JSP to learn spring or hibernate or any other java web frameworks.?

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• Hot Java Content

  - by Tori Wieldt

  It's August, summertime in the United States, and time for many of us to go on vacation. (You'll have to find my personal account to see more photos of the Monterey Bay Aquarium.) Here's some great Java content that you may have missed while I was gone: Blogs  Project Jigsaw: Late for the train: The Q&A JSR 355 Final Release, and moves JCP to version 2.9Oracle releases JDK for Linux ARM, JRE for Mac OS XArchitects and Architecture at JavaOne 2012Java Champions at JavaOne 2012 Podcasts & Videos Java Spotlight Episode 96: Johan Vos on Glassfish and JavaFXJava Spotlight Episode 94: Kirk Pepperdine on Java Performance TuningJava Spotlight Episode 93: Jonathan Giles on JavaFX 2.2 UI ControlsVideo: JavaFX Canvas Node July/August Java Magazine (free subscription) Developer Power: Web-based Development ToolsFork/Join Framework for Client Java ApplicationsIntro to Web Service SecurityHow to Modify javacOracle's Berkeley DB Java Edition's Java API and more. Java Magazine is available on the App Store and the Android Market. Get all this great Java content while it's as hot as a North American (non-San Franciscian) summer. 

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• Web services, Java EE, Spring, DB integration project ideas - maybe data mining related?

  - by saral jain

  I am a graduate Computer Science student (Data Mining and Machine Learning) and have good exposure to core Java (3 years). I have read up on a bunch of stuff on the following topics: Design patterns, Java EE Web services (SOAP and REST), Spring, and Hibernate Java Concurrency - advanced features like Task and Executors. I would now like to do a project combining this stuff -- over my free time of course -- to get a better understanding of these things and to kind of make an end to end software (to learn the best design principles etc + SVN, maven). Any good project ideas would be really appreciated. I just want to build this stuff to learn, so I don't really mind re-inventing the wheel. Also, anything related to data mining would be an added bonus as it fits with my research but is absolutely not necessary since this project is more to learn to do large scale software development.

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• What are the most commonly used enterprise Java technologies, and what would you want a non technical audience to understand about them?

  - by overstood

  I have been asked to give a presentation to a non-technical audience on what Java technologies are currently being used in the enterprise world. The goal is to give this non-technical audience the background they need to understand what engineers are talking about. It's part of a broader series of talks that I'm giving. I'm primarily a .NET and C++ dev, so I thought I'd try to get some input from some Java devs. What technologies do you use? What Java related acronyms would you like to be able to use around non-coders? What would you like non-coders to understand about them?

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• What is the difference between Java 6 and PHP 5.4? [closed]

  - by Mashael

  First of all, let me explain the matter. I'm in a class where we learn Java 6 OOP fundamentals. However, my goal is to learn PHP (the last version) next. So, my question: Is there a big difference between PHP and Java 6 in OOP concepts? Meaning that after I finish the OOP class in Java will I find a lot of things that need to be learned in PHP regarding OOP? Update: *My goal of learning PHP next is to build dynamic sites* (I'm not sure of other options) and to follow OOP.

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• Do I have to write a lot of boilerplate code if I keep working using Java?

  - by edem

  I'm working for a company writing ERP applications. My problem is that I have to write tons of boilerplate code. I came up with ideas to automatize/prevent the drudgery but only some of them were accepted. I have been told by the lead developer that my ideas tend to be go far afield and I should write code everyone can understand. I had a discussion about this lately and it seems to me that this kind of code ramp is within java's philosophy. I have to write lots of code to achiveve simple things not because it is necessary but because this is the way most of the people at the company think. Is this universally applicable to most of the companies out there using java or this is just my company's view? Do I have to get used to the drudgery if I keep working for java-based firms?

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• Java update

  - by JuergenKress

  Oracle has just released Security Alert CVE-2012-4681 to address 3 distinct but related vulnerabilities and one security-in-depth issue affecting Java running in desktop browsers.  These vulnerabilities are: CVE-2012-4681, CVE-2012-1682, CVE-2012-3136, and CVE-2012-0547.  These vulnerabilities are not applicable to standalone Java desktop applications or Java running on servers, i.e. these vulnerabilities do not affect any Oracle server based software." (Read more at https://blogs.oracle.com/security/entry/security_alert_for_cve_20121) Updates are available at http://www.oracle.com/technetwork/java/javase/overview/index.html or Check your Java version online: http://www.java.com/de/download/testjava.jsp WebLogic Partner Community For regular information become a member in the WebLogic Partner Community please visit: http://www.oracle.com/partners/goto/wls-emea ( OPN account required). If you need support with your account please contact the Oracle Partner Business Center. Blog Twitter LinkedIn Mix Forum Wiki Technorati Tags: Java,Java Security,Java update,WebLogic,WebLogic Community,Oracle,OPN,Jürgen Kress

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