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• Tuning JVM (GC) for high responsive server application

  - by elgcom

  I am running an application server on Linux 64bit with 8 core CPUs and 6 GB memory. The server must be highly responsive. After some inspection I found that the application running on the server creates rather a huge amount of short-lived objects, and has only about 200~400 MB long-lived objects(as long as there is no memory leak) After reading http://java.sun.com/javase/technologies/hotspot/gc/gc_tuning_6.html I use these JVM options -Xms2g -Xmx2g -XX:MaxPermSize=256m -XX:NewRatio=1 -XX:+UseConcMarkSweepGC Result: the minor GC takes 0.01 ~ 0.02 sec, the major GC takes 1 ~ 3 sec the minor GC happens constantly. How can I further improve or tune the JVM? larger heap size? but will it take more time for GC? larger NewSize and MaxNewSize (for young generation)? other collector? parallel GC? is it a good idea to let major GC take place more often? and how?

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• dozer custom convertors for primitive types

  - by koti

  the below url has an example on dozer custom convertors.. http://stackoverflow.com/questions/1931212/map-collection-size-in-dozer but when i tried that example its giving the exception like this.. Type: null Source parent class: dozerPackage.Source Source field name: images Source field type: class java.util.ArrayList Source field value: [www, eee] Dest parent class: dozerPackage.Destination Dest field name: numOfImages Dest field type: int org.dozer.MappingException: Destination Type (int) is not accepted by this Custom Converter (dozerPackage.TestCustomFieldConverter)! is there any way that i can return the primitive types from dozer custom convertors..

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• XHTML editor wanted!

  - by stolsvik

  I need an editor that outputs clean HTML, and preferably strict XHTML with CSS, as I am going to display the resulting pages as help pages in a java application using xhmtlrenderer ("Flying Saucer") which apparently very much prefers XHTML with CSS 2.1. Having searched stackoverflow for HTML editor and XHTML editor, I've found several mentioned. Aptana is one, Eclipse's Web Tools is another, and KompoZer is a third. I am going to try these out. With this question, I ask whether there are other good options that would satisfy my requirements, and if there are any one of these mentioned or new ones that you'd recommend in particular, that I should focus a bit extra on?

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• Maven and db4o dependency

  - by Jens Jansson

  I'm intrigued to test new frameworks in the Java world, and decided to create a new project that takes advantage of Maven and db4o. I'm starting to get a hang of Maven, but I have a hard time adding db4o as a dependency to the project. First problem is that db4o doesn't exist in the official Maven repositories. Next up comes the problem that db4o seem to have recently restructured their whole site's URI:s, so I'm getting 'site not found' messages all the time when I try to navigate their site. I found somewhere a potential Maven repository that should be at https://source.db4o.com/maven but I get all the time "Error reading archetype catalog https://source.db4o.com/maven Unable to locate resource in repository" when I try to access it. So, any suggestions on how I'll get db4o up through Maven? I've managing Maven through Eclipse with the M2Eclipse plugin.

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• How can I determine if a file I want to read from actually exists?

  - by Imray

  I'm learning Java, and I'm trying to write a program that can read from a .ser file, which I've already created with a writeTo method. I want to know a given file exists in the system before I tell the program to read from it. My code looks like this: public boolean readFromSerializedFile(String fileName){ FileInputStream fileInStream = null; ObjectInputStream objectInStream = null; try{ fileInStream = new FileInputStream(fileName); objectInStream = new ObjectInputStream(fileInStream); Is there a simple way I can determine if the file with the name of the parameter exists in the root directory (or wherever else specified)?

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• Which Maven Glassfish plugin to use?

  - by Nick Klauer

  I've been trying to integrate deploying java .war's in Glassfish V3 through Maven. While I have found a few plugins, none of them look to be very active: Maven Glassfish Plugin Eskato's Wordpress Blog on Maven And I got the most information out of Eskato's Blog, it was written March 2008, so I don't know what the state of Glassfish Maven integration is, nor can I find a suitable plugin to work with. With the Maven Glassfish Plugin I have had some success, but it still doesn't work entirely well for all goals it says it supports, which makes some of the commands ineffective. Has anyone else been able to integrate Glassfish V3 and Maven successfully? If so, what resources did you use to get it done?

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• JUnit4 + Eclipse "An internal error occured during Launching"

  - by Mike

  Hello I'm trying to run JUnit4 test cases on Eclipse 3.4.2 but it's not even starting for me. I am sure that I properly have junit-4.7.jar in my build path and the test application. Here is a simple example that illustrates my problem package test; import org.junit.Before; import org.junit.Test; public class UTest { @Test public void test() { } @Before public void setUp() throws Exception { } } This compiles fine Then I do "Run JUnit Test case" from Eclipse and I get an error dialog with this message "Launching UTest' has encountered a problem An internal error occurred during: "Launching UTest". java.lang.NullPointerException I'm not sure how to figure out what exactly generating this NullPointerException. Some pointers would be appreciated

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• What are the pro and cons of having localization files vs hard coded variables in source code?

  - by corgrath

  Definitions: Files: Having the localization phrases stored in a physical file that gets read at application start-up and the phrases are stored in the memory to be accessed via util-methods. The phrases are stored in key-value format. One file per language. Variables: The localization texts are stored as hard code variables in the application's source code. The variables are complex data types and depending on the current language, the appropriate phrase is returned. Background: The application is a Java Servlet and the developers use Eclipse as their primary IDE. Some brief pro and cons: Since Eclipse is use, tracking and finding unused localizations are easier when they are saved as variables, compared to having them in a file. However the application's source code becomes bigger and bloated. What are the pro and cons of having localization text in files versus hard coded varibles in source code? What do you do and why?

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• Client or server side invocation to google API?

  - by Raffo

  I'm writing a web application with GWT and I've to call google calendar's API to retrieve some information. I now have this dilemma: Is it better to use a client side invocation (using javascript or gwt-gdata library) or using the standard google library for java to call the service at server side and then passing all the data to the client via an async call?? I'm not able to understand pros and cons of the two approaches... In particular, I need to call several time the calendar API to retrieve events and let users add new ones, etc. Can you help me?

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• ClassCastException in webclient

  - by narendra

  I am using web client for getting page source. First time i am getting page source. After i use the same object for getting page source for different URL it's showing an Exception like: java.lang.ClassCastException: com.gargoylesoftware.htmlunit.UnexpectedPage cannot be cast to com.gargoylesoftware.htmlunit.html.HtmlPage This is the code which i am using. HtmlPage firstPage = webClient.getPage("firsturl"); HtmlPage downloadPage = null; try { webClient.setJavaScriptEnabled(true); downloadPage = (HtmlPage) webClient.getPage("secondurl"); } catch (Exception e) { e.printStackTrace(); } Thx in advance

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• Other SecurityManager implementations available?

  - by mhaller

  Is there any other implementation (e.g. in an OSS project) of a Java SecurityManager available which has more features than the one in the JDK? I'm looking for features like configurable at runtime policies updateable at runtime, read from other data sources than a security.policy file Thread-aware, e.g. different policies per Thread Higher-level policies, e.g. "Disable network functions, but allow JDBC traffic" Common predefined policies, e.g. "Allow read-access to usual system properties like file.encoding or line.separator, but disallow read-access to user.home" Monitoring and audit trace logging, e.g. "Log all file access, log all network access going NOT to knownhost.example.org" Blocking jobs "requesting" a permission until an administrator grants permission, letting the thread/job continue ... I'm pretty sure that application servers (at least the commercial ones) have their own SecurityManager implementation or at least their own policy configuration. I'm wondering if there is any free project with similar requirements.

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• Porting WebSphere code to get remote credentials to Tomcat

  - by Glenn Lawrence

  I have been asked to look into porting some code from a web app under IBM WAS 7 so that it will run under Tomcat 7. This is part of a larger SPNEGO/Kerberos SSO system but for purposes of discussion I have distilled the code down to the following that shows the dependencies on the two WebSphere classes AccessController and WSSubject: GSSCredential clientCreds = (GSSCredential) com.ibm.ws.security.util.AccessController.doPrivileged(new java.security.PrivilegedAction() { public Object run() { javax.security.auth.Subject subject = com.ibm.websphere.security.auth.WSSubject.getCallerSubject(); GSSCredential clientCreds = (GSSCredential) subject.getPrivateCredentials(GSSCredential.class).iterator().next(); return clientCreds; } }); I'd like to be able to do this in Tomcat.

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• How useful is a 'pure' MVC implementation?

  - by Matt1776

  I work at a company that provides custom made 'CRM'-like software. We are currently redesigning/redeveloping the software with the hopes that it will look more modern and be easier to develop and customize for future clients. Currently it takes a long time to customize each new application. There is a presumption that the reason it takes so long is because of the amount of business logic that is present in the 'view' layer. To some extent I can vouch for this being true, but symptoms don't always reliably point out a cause. There was a suggestion that if we just move the business logic to the controller layer and use pure view (we use java J2EE and struts) as in implementing struts tags instead of calling the bean layer and iterating objects right on the jsp - etc etc. Before I start advocating we go forward with this, I wanted to get a feeling for what other people thought. Does a "pure" implementation of the MVC (especially emphasis on decoupling the controller and the view) provide a cleaner, easier to develop and change code base?

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• Programming Contest Question: Counting Polyominos

  - by Martijn Courteaux

  Hi, An example question for a programming contest was to write a program that finds out how much polyominos are possible with a given number of stones. So for two stones (n = 2) there is only one polyominos: XX You might think this is a second solution: X X But it isn't. The polyominos are not unique if you can rotate them. So, for 4 stones (n = 4), there are 7 solutions: X X XX X X X X X X XX X XX XX XX X X X XX X X XX The application has to be able to find the solution for 1 <= n <=10 PS: Using the list of polyominos on Wikipedia isn't allowed ;) EDIT: Of course the question is: How to do this in Java, C/C++, C#

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• Netbeans GUI Form corrupted?

  - by hubpages-my

  I was making a java gui application through netbeans IDE. All was working fine but yesterday when I opened the form in Netbeans, it said that the form had been corrupted and it could only open that form in read-only mode. When I opened that form in read-only mode, I found that the code was incomplete as severals lines of coding wasn't there at the end. Could anybody tell me how to recover the form. The form is perfect in lookwise but the generated code is incomplete. The code is too long to write it again. The Netbeans told me to get help from http://wiki.netbeans.org/FormGuardedBlockError but I didn't find any helpful information there.

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• XMLEncoder and PersistenceDelegate

  - by Johannes Rössel

  I'm trying to use XMLEncoder to write an object graph (tree in my case) to a file. However, one class contained in it is not actually a Java bean and I don't particularly like making its guts publicly accessible. It's accessed more like a list and has appropriate add methods. I've already written a custom PersistenceDelegate to deal with that. However, is there any way for XMLEncoder to pick it up on its own or do I really need to add it whenever I use an encoder to write a graph that may contain said class?

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• C++: Create abstract class with abstract method and override the method in a subclass

  - by Martijn Courteaux

  Hi, How to create in C++ an abstract class with some abstract methods that I want to override in a subclass? How should the .h file look? Is there a .cpp, if so how should it look? In Java it would look like this: abstract class GameObject { public abstract void update(); public abstract void paint(Graphics g); } class Player extends GameObject { @Override public void update() { // ... } @Override public void paint(Graphics g) { // ... } } // In my game loop: for (int i = 0; i < objects.size(); i++) { objects.get(i).update(); } for (int i = 0; i < objects.size(); i++) { objects.get(i).paint(g); } Translating this code to C++ is enough for me.

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• Monitoring Reasoning Progress using the Pellet Reasoner

  - by Nico

  I am currently constructing an OWL ontology, which - until very recently classified rapidly using the Pellet reasoner. However, since the introduction of several new classes, the reasoning performance has slowed to a crawl. Although the reasoner completes and the ontology does not contain any unsatisfiable concepts etc, the time the reasoning takes is unacceptable. I am currently trying to track down the offending classes/class that may have led to the slowdown. Here's my question: is it possible to log the reasoning progreess of Pellet? I.e. is it possible to produce some output that will document how long pellet has spent on certain reasoning tasks/traces how long reasoning over any given class and axiom takes? If so, does anyone have some java code they could post up? Thanks in advance for your answers!

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• getResourceAsStream not loading resource

  - by Michal Gorecki

  The project that I am currently working on utilizes an old application contained within a .jar file. One of the responsibilities of this application is that it updates the database when changes to the configuration files are made. Every time I try to run this file (which is a simple Ant Task extension), I get an exception thrown early in the process. I decompiled the Java file responsible, and found that the exception being thrown happens here. I do not know what the issue is, as "hibernate.cfg.xml" is contained within the same .jar file as the .class throwing the exception. ClassLoader loader = Thread.currentThread().getContextClassLoader(); InputStream in = loader.getResourceAsStream("hibernate.cfg.xml"); if (in == null) { throw new RuntimeException("Couldn't find built in hibernate config"); } If anyone has any ideas, even pointing me in the right direction, I would be grateful. Of course, any solution will have to be external, as the client already has this build of the program in production use.

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• Ant failed to build

  - by eyal

  Hi, I have build a Java appliction which is using ant.jar (ant 1.8.2) classes for building android application from it's build.xml file with release as target. My Android project has been built by using android create project command, using sdk 2.2. When I run my application for building the Android application I get the following message - build.xml:46: taskdef class com.android.ant.SetupTask cannot be found I have verified the sdk.dir path and the sdk-location path and both are correct. How it can be solved? Thanks, Eyal.

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• Why is conversion from UTF-8 to ISO-8859-1 not the same in Windows and Linux?

  - by user1895307

  I have the following in code to convert from UTF-8 to ISO-8859-1 in a jar file and when I execute this jar in Windows I get one result and in CentOS I get another. Might anyone know why? public static void main(String[] args) { try { String x = "Ä, ä, É, é, Ö, ö, Ãœ, ü, ß, «, »"; Charset utf8charset = Charset.forName("UTF-8"); Charset iso88591charset = Charset.forName("ISO-8859-1"); ByteBuffer inputBuffer = ByteBuffer.wrap(x.getBytes()); CharBuffer data = utf8charset.decode(inputBuffer); ByteBuffer outputBuffer = iso88591charset.encode(data); byte[] outputData = outputBuffer.array(); String z = new String(outputData); System.out.println(z); } catch(Exception e) { System.out.println(e.getMessage()); } } In Windows, java -jar test.jar test.txt creates a file containing: Ä, ä, É, é, Ö, ö, Ü, ü, ß, «, » but in CentOS I get: ??, ä, ??, é, ??, ö, ??, ü, ??, «, » Help please!

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• What is a good practice to access class attributes in class methods?

  - by Clem

  I always wonder about the best way to access a class attribute from a class method in Java. Could you quickly convince me about which one of the 3 solutions below (or a totally different one :P) is a good practice? public class Test { String a; public String getA(){ return this.a; } public setA(String a){ this.a = a; } // Using Getter public void display(){ // Solution 1 System.out.println(this.a); // Solution 2 System.out.println(getA()); // Solution 3 System.out.println(this.getA()); } // Using Setter public void myMethod(String b, String c){ // Solution 1 this.a = b + c; // Solution 2 setA(b + c); // Solution 3 this.setA(b + c); } }

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• How created method with signature as List

  - by London

  Hi all, I'm very new to Java programming language so this is probably dumb question but I have to ask it because I can't figure it out on my own. Here is the deal. I want to create method which extracts certain object type from a list. So the method should receive List as argument, meaning list should contain either Object1 or Object2. I've tried like this : public Object1 extractObject(List<?>){ //some pseudo-code ... loop trough list and check if list item is instance of object one return that instance } The problem with declaring method with List<?> as method argument is that I receive compilation error from eclipse Syntax error on token ">", VariableDeclaratorId expected after this token. How do I set the method signature properly to accept object types either Object1 or Object2 ? Thank you

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• Pros and cons of sorting data in DB?

  - by Roman

  Let's assume I have a table with field of type VARCHAR. And I need to get data from that table sorted alphabetically by that field. What is the best way (for performance): add sort by field to the SQL-query or sort the data when it's already fetched? I'm using Java (with Hibernate), but I can't tell anything about DB engine. It could be any popular relational database (like MySQL or MS Sql Server or Oracle or HSQL DB or any other). The amount of records in table can vary greatly but let's assume there are 5k records.

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• Write a function in c that includes the following sequence of statements [Wont Compile]

  - by Cody

  There is a question in my programming languages textbook that is as follows: Write a C function that includes the following sequence of statements: x = 21; int x; x = 42; Run the program and explain the results. Rewrite the same code in C++ and Java and compare the results. I have written code, and played with it in all three languages but I can not even get it to compile. This includes declaring x above the three lines as well as in the calling function (as this question is obviously attempting to illustrate scoping issues) I'd like to explain the results and do the comparisons on my own, as it is an assignment question but I was wondering if anyone had any insight as to how to get this code to compile? Thanks

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