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• Java memory mapped files and swap

  - by MarkS

  I'm looking at some memory mapped files in Java. Let's say I have a heap size set to 2gb, and I memory map a file that is 50gb - far more than the physical memory on the machine. The OS will cache parts of that 50gb file in the os file cache, the java process will have 2gb of heap space. What I'm curious about is how does the OS decide how much of the 50gb file to cache? For instance, if I have another java process, also with a 2gb heap size, will that 2gb be swapped out to allow the os to cache parts of the memory mapped file? Will parts of the heap space of the first process be swapped out to allow the OS to cache? Is there any way to tell the OS not to swap heap space for OS caching? If the OS doesn't swap out main processes, how does it determine how big its file cache should be?

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• Binding a Java Integer to JavaScriptEngine doesn't work

  - by rplantiko

  To see how binding Java objects to symbols in a dynamic language works, I wrote the following spike test, binding a java.lang.Integer to the symbol i to be changed in JavaScript: @Test public void bindToLocalVariable() throws ScriptException { javax.script.ScriptEngineManager sem = new javax.script.ScriptEngineManager(); javax.script.ScriptEngine engine = sem.getEngineByName("JavaScript"); Integer i = new Integer(17); engine.put( "i", i ); engine.eval( "i++;" ); // Now execute JavaScript assertEquals( 18, i.intValue() ); } Unfortunately, I get a failure. java.lang.AssertionError: expected:<18> but was:<17> JavaScript knows the symbol i (otherwise it would have thrown a ScriptException which is not the case), but the increment operation i++ is not performed on the original Integer object. Any explanations?

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• How to handle all exceptions in a web java project

  - by Nick Donovan

  I am doing an web java project about an hotel reservation. I am using, sql, hibernate, java server pages. I want to know how can I redirect an incoming exception to an error.jsp file . There are a lot of java code , and a lot of jsp file. So I want to rederict every exception that I haven't handle to an error page, is there any way to do it ? An exception can come from everywhere and I can't know and handle them all ( for example an user can write to much data in an textfield, and it will generate me an sql exception for data to long) Thank you, sorry for my english.

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• How to Use Eclipse to Debug JNI code (Java & C/C++)

  - by tkryger

  While I can debug my application with the Eclipse JDT debugger for Java code and GDB for C code, I would prefer to use a single tool for all my debugging. I found several projects that enable "mixed-mode" debugging in Eclipse and include support for single stepping between Java and native code. Intel's Integrated Debugger for Java/JNI Environments Mariot Chauvin's Summer of Code Project: Support Seamless Debugging between JDT & CDT Unfortunately, one claims to be pre-release quality and the other is currently unmaintained. Are there any plug-ins that bring mixed mode debugging functionality to Eclipse in a reliable way or should I continue to use two separate debuggers?

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• Preferred Windows Java Development Environment

  - by JF

  I've been a Linux Java developer for years and have loved it. I just got a new laptop which is running Windows 7. I could wipe the drive and go back to my typical Linux dev setup: vim for editing, tabbed Bash windows running javac and java for smaller projects, ant for big projects That said, I'm really thinking it couldn't hurt to learn to develop in a new environment. So, with that in mind, are there any Windows-based Java devs out there? What setup do you like to use to get things done? It'd be interesting to hear both ways to emulate my Linux-based environment as well as completely different styles that I might benefit from trying.

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• java jdbc connection to mysql problem

  - by fatnjazzy

  Hi, I am trying to connect to mysql from java web application in eclipse. Connection con = null; try { //DriverManager.registerDriver(new com.mysql.jdbc.Driver()); Class.forName("com.mysql.jdbc.Driver"); con = DriverManager.getConnection("jdbc:mysql://localhost/db_name","root" ,""); if(!con.isClosed()) System.out.println("Successfully connected to " + "MySQL server using TCP/IP..."); } catch(Exception e) { System.err.println("Exception: " + e.getMessage()); } finally { try { if(con != null) con.close(); } catch(SQLException e) { System.out.println(e.toString()); } } I am always getting the Exception: com.mysql.jdbc.Driver I have downloaded this jar http://forums.mysql.com/read.php?39,218287,220327 import it to the "java build path/lib" the mysql version is 5.1.3 under. running: mysql 5.1.3 (db is up and running queries form PHP) windows XP java jee Thanks

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• Teaching a mainframe COBOL programmer Java?

  - by Jared

  I’m trying to help someone learn Java who’s only programming experience is COBOL on the mainframe. I was wondering if anyone knew any good resources for object oriented concepts. I learned how to program with C++ so just understand the theory behind basic OOP. I’m more concerned about a way to get the basic concepts across, such as encapsulation and inheritance rather then Java syntax. I think it’d be better to teach the concepts of OOP then a language rather then trying to cram both a new language and paradigm in at the same time. Does anyone have any resources or ideas that could help this person learn OOP followed by Java?

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• Java session facade not being found via InitialContext lookups

  - by Hugh Buchanan

  I have a project that is Java EE 5 running on Glassfish. The IDE is Netbeans 6.7.1. We periodically have a very annoying problem with new session facades not being located via InitialContext: javax.naming.NameNotFoundException: No object bound to name java:comp/env/GlobalConfigEntityFacadeLocal In my class (within the same EJB container), I can use the other session facades just fine. This sort of problem happens periodically, and a mixture of clean&build and deleting the build-impl.xml files from nbproject sometimes resolve this. We are not using ejb-jar.xml (stopped using that over a year ago, it is now an empty The code that is calling this is very straight forward: GlobalConfigEntityFacadeLocal globalConfigEntityFacade = null; try { InitialContext ic = new InitialContext(); globalConfigEntityFacade = (GlobalConfigEntityFacadeLocal) ic.lookup("java:comp/env/GlobalConfigEntityFacadeLocal"); ... } catch ( ... ) {} Any advice would be appreciated!!!! Cheers

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• port binding "problem" with Eclipse, Java, & Windows

  - by Jay

  Hi All, I use eclipse to develop a web based java application. My normal course of business is grab the next task tracking ticket. If there is a problem that needs to correcting, I run the application locally, which loads of a Jetty webserver, and binds to port 8080. After verifying the problem, I fix the problem, rebuild, and the re-run the application. The problem is, I far too often forget to close the jetty server before re-running. This generates the Java bind error: WARNING: failed [email protected]:8080: java.net.BindException: Address already in use: JVM_Bind I work in Windows, and was looking to see if there is command I could run to un-bind the port, but couldn't find an answer there. Does anyone here have a good idea of how to fix my problem, other than remember to shut down the old jetty instance before starting a new one? Thanks, Jay

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• SNMP in Java, specifically to be JMX adapter.

  - by Ben

  Hi, I have a few JAVA application that I monitor using JMX. I would like to write an SNMP client for these applications that wraps the JMX interface and by discovery exposes the same attributes that are exposed in JMX, through SNMP. I have no problem writing the client if I just figure out how to write SNMP clients in JAVA. Is there a free SNMP library for JAVA that I can use? Is there a good free SNMP adapter for JMX? (Tried "WebNMS SNMP Adapter for JMX" trial unsuccessfully) Thank you!

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• Why is String final in Java?

  - by Alex

  From when I learned that the class java.lang.String is declared as final in Java, I was wondering why is that? I didn't find any answer back then, but this post: How to create a replica of String class in Java? reminded me of my query. Sure, String provides all the functionality I ever needed, and never thought of any operation that would require an extension of class String, but still you'll never know what someone might need! So, does anyone know what was the intent of the designers when they decided to make it final? See also: Why is String a sealed class in C#?

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• Running a java program in linux terminal with -class path

  - by Arya

  Hello I've been trying for an hour to run the following program with a the postgresql classpath class Test{ public static void main(String[] args){ try { Class.forName("org.postgresql.Driver"); } catch (ClassNotFoundException cnfe) { System.err.println("Couldn't find Postgresql driver class!"); } } } The program compiled fine with the javac command, but I'm having a hard time running it with the postgresql classpath. I have "postgresql-9.0-801.jdbc4.jar" in the same directory as the file and I tried the following, but non of them worked java -classpath ./postgresql-9.0-801.jdbc4.jar Test java -classpath postgresql-9.0-801.jdbc4.jar Test java -classpath "postgresql-9.0-801.jdbc4.jar" Test What am I doing wrong? Regards!

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• ZeroMQ Java Installation Problem

  - by Ivan

  Hi everyone, I'm trying to install ZeroMQ's Java library but I've been having problem. First error was ./configure complained about JAVA_HOME which everything seemed to be fine but I couldn't manage to solve it but I've found a particular solution in ZeroMQ's chat logs. The suggested solution was; JAVA_HOME="/System/Library/Frameworks/JavaVM.framework/Home" ./configure However it doesn't work for me. The error message I've been receiving is checking for jni.h in /Library/Java/Home/include... configure: error: cannot find jni.h in /Library/Java/Home/include. I've tried JAVA_HOME="/System/Library/Frameworks/JavaVM.framework/Home" ./configure and JAVA_HOME="/System/Library/Frameworks/JavaVM.framework/Versions/1.6/Home" ./configure as well but still no luck. I'd like to hear StackOverflowers' thoughts about how I can solve this. Thanks.

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• How to Initialise a static Map in Java

  - by fahdshariff

  How would you initialise a static Map in Java? Method one: Static initialiser Method two: instance initialiser (anonymous subclass) or some other method? What are the pros and cons of each? Here is an example illustrating two methods: import java.util.HashMap; import java.util.Map; public class Test { private static final Map<Integer, String> myMap = new HashMap<Integer, String>(); static { myMap.put(1, "one"); myMap.put(2, "two"); } private static final Map<Integer, String> myMap2 = new HashMap<Integer, String>(){ { put(1, "one"); put(2, "two"); } }; }

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• How to open files in Java Swing without JFileChooser

  - by ron

  I'm using Java Swing (GUI) and I want to add a button to my project for opening files . I don't like the JFileChooser since it opens a small window for browsing through the files of the directories . Can I use something else , instead of the JFileChooser under Java Swing ? I've tried to use elements of SWT but it didn't work , meaning is the use of the button object and then use it inside the Jframe , but that failed , so I guess SWT and Swing don't mix together? Here is the example of Java Swing with JFileChooser and I'm looking for something like this to put in my JFrame.

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• Building a code search engine for java code in git repositories

  - by zero1

  I'm trying to build a Java code search engine. Apart from just searching for keywords, I would also like cross-referencing between classes to work. It should work the way eclipse's referencing works - click on anything to open the definition. Bonus would be if something like search-all-usages-of-foo works. I'm thinking of using Apache Solr to index the files and build the basic search. But I'm not sure how I'd do the crossreferencing part since Solr doesn't understand Java code. Any suggestions on what I could use here? EDIT: I mainly want to index a lot of java git repositories.

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• execute java class with ant

  - by cateof

  I want my ant script to execute the command java -cp libs/a.jar:libs/b.jar org.stack.class1 --package pName --out classes new.wsdl How can I do it with an Ant script? The following does not work <?xml version="1.0" encoding="UTF-8"?> project name="class" default="compile"> <target name="compile"> <java classname="org.stack.class1" fork="true"> <classpath> <pathelement location="libs/a.jar"/> <pathelement location="libs/b.jar"/> </classpath> <arg value="--package pName --out classes new.wsdl"/> </java> </target>

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• parsing primitive types using java.util.Scanner

  - by Rich Fluckiger

  I'm new to java so forgive the noob question. I have created a swing application that basically has three input strings in JTextFields: loanAmount, interestRate and loanYears and a single submit button with the EventAction. I'm trying to use the java.util.Scanner to parse the input to primitive types that I can use in calculations. I'm getting an error in NetBeans indicating that my variables are not recognized? should I not be calling System.in? private void submitButtonActionPerformed(java.awt.event.ActionEvent evt) { Scanner keyInput = new Scanner(System.in); while (true) try{ double amount = keyInput.nextDouble(loanAmount.getText()); double interest = keyInput.nextDouble(interestRate.getText()); int years = keyInput.nextInt(loanYears.getText()); } catch (NumberFormatException nfe){ } }

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• Alternatives to Java bytecode instrumentation

  - by Rafael Regis

  I'm starting a project that will have to instrument java applications for coverage purposes (definition-usage of variables, etc). It has to add trace statements and some logic to the application and maybe remove statements. I have searched for ways of instrument Java code and what I always find is about bytecode instrumentation. My question is: It's the only way to instrument Java applications? There is any other way to do that? What are the advantages of bytecode instrumentation over the others? I'll probably use the bytecode solution, but I want to know what are the problems with the other approaches (if any) to decide precisely. Thanks!

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• setting java classpath for Libre Office Base in Fedora 16

  - by foampile

  using Fedora 16 OS. i want to use Libre Office Base to connect to MySQL. when i set up the JDBC connection, it asks me for the driver, however, it cannot be loaded (because it doesn't see it in the classpath). does anybody know how to set the classpath for Libre Office? is there like a config util tool for that? e.g. my driver is [B]com.mysql.jdbc.Driver [/B]situated in[B] /usr/share/java/mysql-connector-java-5.1.17.jar[/B]. it works fine when i connect from other JDBC clients, like straight Java or Eclipse Quantum plugin. the problem is that Libre Office does not ask me for the (class)path of where it can find the driver and i do not know where and how to set it so that it becomes visible. thanks

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• Java Webservice with generic methods

  - by danby

  Hi, I was wondering if it is possible to make a generic webservice method in java like this: @WebMethod public <T extends Foo> void testGeneric(T data){ However when I try to consume this with a Java client I get an error stating: [ERROR] Schema descriptor {http://####/}testGeneric in message part "parameters" is not defined and could not be bound to Java. I know it is possible to make a method that takes a parameter such as List and this generates correctly using JAX-WS. I don't mind if there is a solution that means I am tied to using only a particular technology. Thanks, Dan.

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• cross domain DOM access and manipulation in Java ?

  - by gaqer

  In my Java app, how can I incorporate the browser (which loads and renders URLs) in Swing and access it's DOM and manipulate HTML ? How can you embed such browser in a Rich Internet Application and access it's DOM ? More specifically, Vaadin ? Is there a HTTP proxy class that can load an external URL, and render it to the user ? This was what I was doing on LAMP stack....but I want to switch to Vaadin or some Java web framework where I can just use Java to do everything from server-side to client-side logic design, so I can focus more on application logic. (aka looking for developer friendly frameworks like Vaadin). Thank you and have a great weekend !

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• Generics and reflection in Java

  - by Ragesh

  This is probably a very basic question, but I'm really new to generics in Java and I'm having a hard time altering my thought process from the way things are done in C#, so bear with me. I'm trying to build a generic repository in Java. I've created an IRepository interface that looks like this: public interface IRepository<T extends IEntity> And a Repository class that looks like this: public class Repository<T extends IEntity> implements IRepository<T> Now, from within the constructor of my Repository class, I'd like to be able to "divine" the exact type of T. For example, if I instantiated a repository like this: IRepository<MyClass> repo = new Repository<MyClass>(); I'd like to know that T is actually MyClass. This is trivial in C#, but obviously generics are a totally different beast in Java and I can't seem to find anything that would help me do this.

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• Archiving Database Tables using Java

  - by HonorGod

  My application demands archiving database tables between sybase and db2 and vice-a-versa and within(db2 to db2 and sybase to sybase) using java. I am trying to understand the best strategies around in terms performance, implementation, ease of use and scalability. Here is my current process - source and destination tables with the acceptable parameters (from java) are defined within xml. the application reads the source and destination configurations and execute them sequentially. destination is sometime optional when source is just deleting data from a specific table or when the source is just calling a stored procedure. dataset between source and destination is extremely large (in millions) From top of my head, it looks like I can define dependencies between multiple source and destination combination and have them execute in parallel in multiple treads. But will this improve any performance(i hope it will)? Are there any open-source frameworks for data archiving using java? Any other thoughts on the implements side will be really helpful. Thanks

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• handling Javascript actions in PDF with Java

  - by Stroboskop

  I'm trying to make PDF forms (aka AcroForms) editable in Java. So far i got the GUI editing and printing working using Bruno Lowagie's iText and Sun's pdf-renderer. But now i'm close to scrapping it all, because after switching from try & error to reading the PDF specification, i realized that it's all worthless unless i can make the multitude of possible JavaScript actions work as well. I don't think iText can do that. So in short: are there any Java libraries that do proper form handling including actions? Or maybe even a Java GUI component to edit form data?

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