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• Difficulty setting ArrayList to java.sql.Blob to save in DB using hibernate

  - by me_here

  I'm trying to save a java ArrayList in a database (H2) by setting it as a blob, for retrieval later. If this is a bad approach, please say - I haven't been able to find much information on this area. I have a column of type Blob in the database, and Hibernate maps to this with java.sql.Blob. The code I'm struggling with is: Drawings drawing = new Drawings(); try { ByteArrayOutputStream bos = new ByteArrayOutputStream(); ObjectOutputStream oos = null; oos = new ObjectOutputStream(bos); oos.writeObject(plan.drawingPane21.pointList); byte[] buff = bos.toByteArray(); Blob drawingBlob = null; drawingBlob.setBytes(0, buff); drawing.setDrawingObject(drawingBlob); } catch (Exception e){ System.err.println(e); } The object I'm trying to save into a blob (plan.drawingPane21.pointList) is of type ArrayList<DrawingDot>, DrawingDot being a custom class implementing Serializable. My code is failing on the line drawingBlob.setBytes(0, buff); with a NullPointerException. Help appreciated.

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• Using ServletOutputStream to write very large files in a Java servlet without memory issues

  - by Martin

  I am using IBM Websphere Application Server v6 and Java 1.4 and am trying to write large CSV files to the ServletOutputStream for a user to download. Files are ranging from a 50-750MB at the moment. The smaller files aren't causing too much of a problem but with the larger files it appears that it is being written into the heap which is then causing an OutOfMemory error and bringing down the entire server. These files can only be served out to authenticated users over https which is why I am serving them through a Servlet instead of just sticking them in Apache. The code I am using is (some fluff removed around this): resp.setHeader("Content-length", "" + fileLength); resp.setContentType("application/vnd.ms-excel"); resp.setHeader("Content-Disposition","attachment; filename=\"export.csv\""); FileInputStream inputStream = null; try { inputStream = new FileInputStream(path); byte[] buffer = new byte[1024]; int bytesRead = 0; do { bytesRead = inputStream.read(buffer, offset, buffer.length); resp.getOutputStream().write(buffer, 0, bytesRead); } while (bytesRead == buffer.length); resp.getOutputStream().flush(); } finally { if(inputStream != null) inputStream.close(); } The FileInputStream doesn't seem to be causing a problem as if I write to another file or just remove the write completly the memory usage doesn't appear to be a problem. What I am thinking is that the resp.getOutputStream().write is being stored in memory until the data can be sent through to the client. So the entire file might be read and stored in the resp.getOutputStream() causing my memory issues and crashing! I have tried Buffering these streams and also tried using Channels from java.nio, none of which seems to make any bit of difference to my memory issues. I have also flushed the outputstream once per iteration of the loop and after the loop, which didn't help.

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• String length differs from Javascript to Java code

  - by François P.

  I've got a JSP page with a piece of Javascript validation code which limits to a certain amount of characters on submit. I'm using a <textarea> so I can't simply use a length attribute like in a <input type="text">. I use document.getElementById("text").value.length to get the string length. I'm running Firefox 3.0 on Windows (but I've tested this behavior with IE 6 also). The form gets submitted to a J2EE servlet. In my Java servlet the string length of the parameter is larger than 2000! I've noticed that this can easily be reproduced by adding carriage returns in the <textarea>. I've used Firebug to assert the length of the <textare> and it really is 2000 characters long. On the Java side though, the carriage returns get converted to UNIX style (\r\n, instead of \n), thus the string length differs! Am I missing something obvious here or what ? If not, how would you reliably (cross-platform / browser) make sure that the <textarea> is limited.

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• Persisting Joda DateTime instead of Java Date in hibernate

  - by Tauren

  My entities currently contain java Date properties. I'm starting to use Joda Time for date manipulation and calculations quite frequently. This means that I'm constantly having to convert my Dates into Joda DateTime objects and back again. So I was wondering, is there any reason I shouldn't just change my entities to store Joda DateTime objects instead of Java Date objects? Please note that these entities are persisted via Hibernate. I found the jodatime-hibernate project, but I also was reading on the Joda mailing list that it wasn't compatible with newer versions of hibernate. And it seems like it isn't very well maintained. So I'm wondering if it would be best to just continue converting between Date and DateTime, or if it would be wise to start persisting DateTime objects. My concern is being reliant on a poorly maintained library. Edit: Note that one of my objectives is to be better able to store timezone information. Storing just a Date appears to save the date in the local timezone. As my application can be used globally, I need to know the timezone as well. Joda Time Hibernate seems to address this as well in the user guide.

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• Maven:install jar file during build process

  - by Venkata

  I have got a requirement as follows. I need to run ant build file during maven build process. I need to invoke the build.xml from my pom.xml file. I have done that using maven-antrun-plugin. Now I need to install the ant build generated jar file automatically into my local repository before maven compiles my project source. I tried using build-helper-maven-plugin but it did not help. Either I am doing something wrong, or i am not doing right. Please help. Update Thank you. ant maven tasks worked for me as well. However I am runing into the following exception at the end of the build process. Any help is highly appreciated. org.apache.tools.ant.ExitException: Permission (java.lang.RuntimePermission exitVM) was not granted. at org.apache.tools.ant.types.Permissions$MySM.checkExit(Permissions.java:196) at java.lang.Runtime.exit(Runtime.java:99) at java.lang.System.exit(System.java:275) at org.codehaus.classworlds.Launcher.main(Launcher.java:376) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:37) at java.lang.reflect.Method.invoke(Method.java:599) at org.apache.tools.ant.taskdefs.ExecuteJava.run(ExecuteJava.java:217) at org.apache.tools.ant.taskdefs.ExecuteJava.execute(ExecuteJava.java:152) at org.apache.tools.ant.taskdefs.Java.run(Java.java:771) at org.apache.tools.ant.taskdefs.Java.executeJava(Java.java:221) at org.apache.tools.ant.taskdefs.Java.executeJava(Java.java:135) at org.apache.tools.ant.taskdefs.Java.execute(Java.java:108) at org.apache.maven.artifact.ant.Mvn.execute(Mvn.java:81) at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:291) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:37) at java.lang.reflect.Method.invoke(Method.java:599) at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:106) at org.apache.tools.ant.Task.perform(Task.java:348) at org.apache.tools.ant.Target.execute(Target.java:390) at org.apache.tools.ant.Target.performTasks(Target.java:411) at org.apache.tools.ant.Project.executeSortedTargets(Project.java:1399) at org.apache.tools.ant.Project.executeTarget(Project.java:1368) at org.apache.tools.ant.helper.DefaultExecutor.executeTargets(DefaultExecutor.java:41) at org.apache.tools.ant.Project.executeTargets(Project.java:1251) at org.apache.tools.ant.Main.runBuild(Main.java:809) at org.apache.tools.ant.Main.startAnt(Main.java:217) at org.apache.tools.ant.launch.Launcher.run(Launcher.java:280) at org.apache.tools.ant.launch.Launcher.main(Launcher.java:109)

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• Java: Handling cookies when logging in with POST

  - by Cris Carter

  I'm having quite some trouble logging in to any site in Java. I'm using the default URLconnection POST request, but I'm unsure how to handle the cookies properly. I tried this guide: http://www.hccp.org/java-net-cookie-how-to.html But couldn't get it working. I've been trying basically for days now, and I really need help if anyone wants to help me. I'll probably be told that it's messy and that I should use a custom library meant for this stuff. I tried downloading one, but wasn't sure how to get it set up and working. I've been trying various things for hours now, and it just won't work. I'd rather do this with a standard URLconnection, but if anyone can help me get another library working that's better for this, that would be great, too. I would really appreciate if someone could post a working source that I could study. What I need is: POST login data to site - Get and store the cookie from the site - use cookie with next URLconnection requests to get logged-in version of the site. Can anyone help me with this? Would be EXTREMELY appreciated. It really does mean a lot. If anyone wants to actually help me out live, please leave an instant-messenger address. Thank you a lot for your time.

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• Spelling correction for data normalization in Java

  - by dareios

  I am looking for a Java library to do some initial spell checking / data normalization on user generated text content, imagine the interests entered in a Facebook profile. This text will be tokenized at some point (before or after spell correction, whatever works better) and some of it used as keys to search for (exact match). It would be nice to cut down misspellings and the like to produce more matches. It would be even better if the correction would perform well on tokens longer than just one word, e.g. "trinking coffee" would become "drinking coffee" and not "thinking coffee". I found the following Java libraries for doing spelling correction: JAZZY does not seem to be under active development. Also, the dictionary-distance based approach seems inadequate because of the use of non-standard language in social network profiles and multi-word tokens. APACHE LUCENE seems to have a statistical spell checker that should be much more suited. Question here would how to create a good dictionary? (We are not using Lucene otherwise, so there is no existing index.) Any suggestions are welcome!

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• JAVA vs .NET - Choice for way to go further [closed]

  - by Sarang

  I have my subject .Net acedemically. I also learned core Java and did a project as well. I took training from a Java firm. Now, as a skill I do have knowledge as both language. But, it is creating a large problem to me that, which field I should chhose? Even if having better OOP fundamentals, will it be easier for me to transfer from one to another in the future ? Please suggest me a way. Also, we do have may technologies available at both side, like JSP, JSF, J2ME, Share Point, SilverLight etc. Which is better as per their reliabity point of view? Which are fast growing and useful technologies used mostly in current IT corporate world ? Are they easier to learn at fresher's point of view? Please answer. Perhaps, this answer may help me mostly to create my way to learn them and go further. Every IT developer, please help to find me my way.

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• Java Collections and Garbage Collector

  - by Anth0

  A little question regarding performance in a Java web app. Let's assume I have a List<Rubrique> listRubriques with ten Rubrique objects. A Rubrique contains one list of products (List<product> listProducts) and one list of clients (List<Client> listClients). What exactly happens in memory if I do this: listRubriques.clear(); listRubriques = null; My point of view would be that, since listRubriques is empty, all my objects previously referenced by this list (including listProducts and listClients) will be garbage collected pretty soon. But since Collection in Java are a little bit tricky and since I have quite performance issues with my app i'm asking the question :) edit : let's assume now that my Client object contains a List<Client>. Therefore, I have kind of a circular reference between my objects. What would happen then if my listRubrique is set to null? This time, my point of view would be that my Client objects will become "unreachable" and might create a memory leak?

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• Cannot parse persistence unit from class path resource

  - by Grzegorz S

  so I have this problem in running my Spring WS app which implements JPA ( or should implement..) I have a problem with running a WS, it looks like my Spring context can't find file persistence.xml Which i am able to believe because i did not have generated META-INF folder in my template (which is Maven project template with archetype org.springframework.ws) I have created META-INF manually. Here is the HTTP 500: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'caChainDao' defined in file [E:\STS\vfabric-tc-server-developer-2.7.2.RELEASE\zz\wtpwebapps\FCAWSv4\WEB-INF\classes\pl\famoc\test\ws\db\dao\caChainDao.class]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in ServletContext resource [/WEB-INF/spring-ws-servlet.xml]: Invocation of init method failed; nested exception is java.lang.IllegalArgumentException: Cannot parse persistence unit from class path resource [persistence.xml] org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:527) org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456) org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:294) org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:225) org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:291) org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193) org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:609) org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:918) org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:469) org.springframework.web.servlet.FrameworkServlet.configureAndRefreshWebApplicationContext(FrameworkServlet.java:631) org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:588) org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:645) org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:508) org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:449) org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:133) javax.servlet.GenericServlet.init(GenericServlet.java:160) org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472) org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99) org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:929) org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407) org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1002) org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:585) org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310) java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) java.lang.Thread.run(Thread.java:722) Here it is my persistence.xml <?xml version="1.0" encoding="UTF-8" ?> <persistence xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd" version="2.0" xmlns="http://java.sun.com/xml/ns/persistence"> <persistence-unit name="persistenceUnit" transaction-type="RESOURCE_LOCAL" /> </persistence> here it is where i am looking for it <property name="persistenceXmlLocation" value="classpath:persistence.xml" /> and here it is path to this xml in my classpath: src/main/webapp/META-INF/persistence.xml Could anyone give me a hint what am i missing?

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• How does Java handle ArrayList refrerences and assignments?

  - by Jonathan

  Hey all- I mostly write in C but am using Java for this project. I want to know what Java is doing here under the hood. ArrayList<Integer> prevRow, currRow; currRow = new ArrayList<Integer>(); for(i =0; i < numRows; i++){ prevRow = currRow; currRow.clear(); currRow.addAll(aBunchOfItems); } Is the prevRow = currRow line copying the list or does prevRow now point to the same list as currRow? If prevRow points to the same list as currRow, I should create a new ArrayList instead of clearing.... private ArrayList<Integer> someFunction(ArrayList<Integer> l){ Collections.sort(l); return l; } main(){ ArrayList<Integer> list = new ArrayList<Integer>(Integer(3), Integer(2), Integer(1)); list = someFunction(list); //Option 1 someFunction(list); //Option 2 } In a similar question, do Option 1 and Option 2 do the same thing in the above code? Thanks- Jonathan

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• Embedded SQL in OO languages like Java

  - by Steve De Caux

  One of the things that annoys me working with SQL in OO languages is having to define SQL statements in strings. When I used to work on IBM mainframes, the languages used an SQL preprocessor to parse SQL statements out of the native code, so the statements could be written in cleartext SQL without the obfuscation of strings, for instance in Cobol there is a EXEC SQL .... END-EXEC syntax construct that allows pure SQL statements to be embedded in the Cobol code. <pure cobol code, including assignment of value to local variable HOSTVARIABLE> EXEC SQL SELECT COL_A, COL_B, COL_C INTO :COLA, :COLB, :COLC FROM TAB_A WHERE COL_D = :HOSTVARIABLE END_EXEC <more cobol code, variables COLA, COLB, COLC have been set> ...this makes the SQL statement really easy to read & check for errors. Between the EXEC SQL .... END-EXEC tokens there are no constraints on indentation, linebreaking etc., so you can format the SQL statement according to taste. Note that this example is for a single-row select, when a multiple-row resultset is expected, the coding is different (but still v. easy to read). So, taking Java as an example What made the "old COBOL" approach undesirable ? Not only SQL, but system calls could be made much more readable with that approach. Let's call it the embedded foreign language preprocessor approach. Would an embedded foreign language preprocessor for SQL be useful to implement ? Would you see a benefit in being able to write native SQL statements inside java code ? Edit I'm really asking if you think SQL in OO languages is a throwback, and if not then what could be done to make it better.

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• Connection details & timeouts in a java web service client

  - by f1sh

  Hello fellow Coders, I have to implement a webservice client to a given WSDL file. I used the SDK's 'wsimport' tool to create Java classes from the WSDL as well as a class that wrap's the webservice's only method (enhanceAddress(auth, param, address)) into a simple java method. So far, so good. The webservice is functional and returning results correcty. The code looks like this: try { EnhancedAddressList uniservResponse = getWebservicePort().enhanceAddress(m_auth, m_param, uniservAddress); //Where the Port^ is the HTTP Soap 1.2 Endpoint }catch (Throwable e) { throw new AddressValidationException("Error during uniserv webservice request.", e); } The Problem now: I need to get Information about the connection and any error that might occur in order to populate various JMX values (such as COUNT_READ_TIMEOUT, COUNT_CONNECT_TIMEOUT, ...) Unfortunately, the method does not officially throw any Exceptions, so in order to get details about a ConnectException, i need to use getCause() on the ClientTransportException that will be thrown. Even worse: I tried to test the read timeout value, but there is none. I changed the service's location in the wsdl file to post the request to a php script that simply waits forever and does not return. Guess what: The web service client does not time out but waits forever as well (I killed the app after 30+ minutes of waiting). That is not an option for my application as i eventually run out of tcp connections if some of them get 'stuck'. The enhanceAddress(auth, param, address) method is not implemented but annotated with javax.jws.* Annotations, meaning that i cannot see/change/inspect the code that is actually executed. Do i have any option but to throw the whole wsimport/javax.jsw-stuff away and implement my own soap client?

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• Documentation for java.util.concurrent.locks.ReentrantReadWriteLock

  - by Andrei Taptunov

  Disclaimer: I'm not very good at Java and just comparing read/writer locks between C# and Java to understand this topic better & decisions behind both implementations. There is JavaDoc about ReentrantReadWriteLock. It states the following about upgrade/downgrade for locks: Lock downgrading ... However, upgrading from a read lock to the write lock is not possible. It also has the following example that shows manual upgrade from read lock to write lock: // Here is a code sketch showing how to exploit reentrancy // to perform lock downgrading after updating a cache void processCachedData() { rwl.readLock().lock(); if (!cacheValid) { // upgrade lock manually #1: rwl.readLock().unlock(); // must unlock first to obtain writelock #2: rwl.writeLock().lock(); if (!cacheValid) { // recheck ... } ... } use(data); rwl.readLock().unlock(); Does it mean that actually the sample from above may not behave correctly in some cases - I mean there is no lock between lines #1 & #2 and underlying structure is exposed to changes from other threads. So it can not be considered as the correct way to upgrade the lock or do I miss something here?

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• Good patterns for loose coupling in Java?

  - by Eye of Hell

  Hello. I'm new to java, and while reading documentation so far i can't find any good ways for programming with loose coupling between objects. For majority of languages i know (C++, C#, python, javascript) i can manage objects as having 'signals' (notification about something happens/something needed) and 'slots' (method that can be connected to signal and process notification/do some work). In all mentioned languages i can write something like this: Object1 = new Object1Class(); Object2 = new Object2Class(); Connect( Object1.ItemAdded, Object2.OnItemAdded ); Now if object1 calls/emits ItemAdded, the OnItemAdded method of Object2 will be called. Such loose coupling technique is often referred as 'delegates', 'signal-slot' or 'inversion of control'. Compared to interface pattern, technique mentioned don't need to group signals into some interfaces. Any object's methods can be connected to any delegate as long as signatures match ( C++Qt even extends this by allowing only partial signature match ). So i don't need to write additional interface code for each methods / groups of methods, provide default implementation for interface methods not used etc. And i can't see anything like this in Java :(. Maybe i'm looking a wrong way?

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• Java operator overloading

  - by nimcap

  Not using operators makes my code obscure. (aNumber / aNother) * count is better than aNumber.divideBy(aNother).times(count) After 6 months of not writing a single comment I had to write a comment to the simple operation above. Usually I refactor until I don't need comment. And this made me realize that it is easier to read and perceive math symbols and numbers than their written forms. For example TWENTY_THOUSAND_THIRTEEN.plus(FORTY_TWO.times(TWO_HUNDERED_SIXTY_ONE)) is more obscure than 20013 + 42*261 So do you know a way to get rid of obscurity while not using operator overloading in Java? Update: I did not think my exaggeration on comments would cause such trouble to me. I am admitting that I needed to write comment a couple of times in 6 months. But not more than 10 lines in total. Sorry for that. Update 2: Another example: budget.plus(bonusCoefficient.times(points)) is more obscure than budget + bonusCoefficient * points I have to stop and think on the first one, at first sight it looks like clutter of words, on the other hand, I get the meaning at first look for the second one, it is very clear and neat. I know this cannot be achieved in Java but I wanted to hear some ideas about my alternatives.

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• Calling webservice via server causes java.net.MalformedURLException: no protocol

  - by Thomas

  I am writing a web-service, which parses an xml file. In the client, I read the whole content of the xml into a String then I give it to the web-service. If I run my web-service with main as a Java-Application (for tests) there is no problem, no error messages. However when I try to call it via the server, I get the following error: java.net.MalformedURLException: no protocol I use the same xml file, the same code (without main), and I just cannot figure out, what the cause of the error can be. here is my code: DOMParser parser=new DOMParser(); try { parser.setFeature("http://xml.org/sax/features/validation", true); parser.setFeature("http://apache.org/xml/features/validation/schema",true); parser.setFeature("http://apache.org/xml/features/validation/dynamic",true); parser.setErrorHandler(new myErrorHandler()); parser.parse(new InputSource(new StringReader(xmlFile))); document=parser.getDocument(); xmlFile is constructed in the client so: String myFile ="C:/test.xml"; File file=new File(myFile); String myString=""; FileInputStream fis=new FileInputStream(file); BufferedInputStream bis=new BufferedInputStream(fis); DataInputStream dis=new DataInputStream(bis); while (dis.available()!=0) { myString=myString+dis.readLine(); } fis.close(); bis.close(); dis.close(); Any suggestions will be appreciated!

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• passing java mail message object from between applications

  - by jezhilvalan

  I'm using java mail api 1.4.1 to obtain new emails. Two classes are being used to obtain emails and then parsing it. "GetMail" class communicates with mail server(Gmail,yahoo etc) and obtains the message object. Then the message object is passed to yet another class "MailFormatter" class, which then parses the message object, obtains the email headers (From,To,Subject etc) and then it parses the Multipart content to obtain the main body and attachments.Since both "Mail getting" and "Mail formatting" process are very resource intensive, these classes are going to be implemented as separate web applications.This application is going to monitor new emails for numerous email ids.If these ("GetMail" and "MailFormatter") are implemented as separate web applications, how can I pass the message object from "GetMail" app to "MailFormatter" app ? Is there a way through which I can persist the obtained message object in a certain location (a location which is common to both "GetMail" and "MailFormatter" applications), so that "GetMail" can persist the message object in that location, and then "MailFormatter" app can read "Message" objects from that location and carry out the parsing process. Message objects cannot be serialized. If they cannot be serialized how can I persist the state of java mail message object? please do help me to resolve this issue.

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• deploying gwt web application on jetty

  - by Azhar

  Hi I am deploying my web application created in Gwt on the jetty. I have used mongodb as my database.After starting the server it starts deploying the weapp.war and gives following error - 694 [main] INFO org.mortbay.log - Extract /usr/share/jetty/webapps/myapp.war to /tmp/Jetty_0_0_0_0_8090_myapp.war__myapp__n6yltk/webapp 3567 [main] WARN org.mortbay.log - failed Startup: java.lang.LinkageError: loader constraint violation: loader (instance of org/mortbay/jetty/webapp/WebAppClassLoader) previously initiated loading for a different type with name "javax/management/MBeanServer" at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:634) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) at java.net.URLClassLoader.defineClass(URLClassLoader.java:277) at java.net.URLClassLoader.access$000(URLClassLoader.java:73) at java.net.URLClassLoader$1.run(URLClassLoader.java:212) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:205) at org.mortbay.jetty.webapp.WebAppClassLoader.loadClass(WebAppClassLoader.java:392) at org.mortbay.jetty.webapp.WebAppClassLoader.loadClass(WebAppClassLoader.java:363) at com.mongodb.DBPortPool$Holder.get(DBPortPool.java:58) at com.mongodb.DBTCPConnector._set(DBTCPConnector.java:458) at com.mongodb.DBTCPConnector.<init>(DBTCPConnector.java:46) at com.mongodb.Mongo.<init>(Mongo.java:137) at com.mongodb.Mongo.<init>(Mongo.java:123)

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• Java Performance measurement

  - by portoalet

  Hi, I am doing some Java performance comparison between my classes, and wondering if there is some sort of Java Performance Framework to make writing performance measurement code easier? I.e, what I am doing now is trying to measure what effect does it have having a method as "synchronized" as in PseudoRandomUsingSynch.nextInt() compared to using an AtomicInteger as my "synchronizer". So I am trying to measure how long it takes to generate random integers using 3 threads accessing a synchronized method looping for say 10000 times. I am sure there is a much better way doing this. Can you please enlighten me? :) public static void main( String [] args ) throws InterruptedException, ExecutionException { PseudoRandomUsingSynch rand1 = new PseudoRandomUsingSynch((int)System.currentTimeMillis()); int n = 3; ExecutorService execService = Executors.newFixedThreadPool(n); long timeBefore = System.currentTimeMillis(); for(int idx=0; idx<100000; ++idx) { Future<Integer> future = execService.submit(rand1); Future<Integer> future1 = execService.submit(rand1); Future<Integer> future2 = execService.submit(rand1); int random1 = future.get(); int random2 = future1.get(); int random3 = future2.get(); } long timeAfter = System.currentTimeMillis(); long elapsed = timeAfter - timeBefore; out.println("elapsed:" + elapsed); } the class public class PseudoRandomUsingSynch implements Callable<Integer> { private int seed; public PseudoRandomUsingSynch(int s) { seed = s; } public synchronized int nextInt(int n) { byte [] s = DonsUtil.intToByteArray(seed); SecureRandom secureRandom = new SecureRandom(s); return ( secureRandom.nextInt() % n ); } @Override public Integer call() throws Exception { return nextInt((int)System.currentTimeMillis()); } } Regards

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• Filling combobox from database by using hibernate in Java

  - by denny

  Heyy; I am developing a small swing based application with hibernate in java. And I want fill combobox from database coloumn.How i can do that ? And I don't know in where(under initComponents, buttonActionPerformd) i need to do. For saving i'am using jbutton and it's code is here : private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) { int idd=Integer.parseInt(jTextField1.getText()); String name=jTextField2.getText(); String description=jTextField3.getText(); Session session = null; SessionFactory sessionFactory = new Configuration().configure() .buildSessionFactory(); session = sessionFactory.openSession(); Transaction transaction = session.getTransaction(); try { ContactGroup con = new ContactGroup(); con.setId(idd); con.setGroupName(name); con.setGroupDescription(description); transaction.begin(); session.save(con); transaction.commit(); } catch (Exception e) { e.printStackTrace(); } finally{ session.close(); } }

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• puzzled with java if else performance

  - by user1906966

  I am doing an investigation on a method's performance and finally identified the overhead was caused by the "else" portion of the if else statement. I have written a small program to illustrate the performance difference even when the else portion of the code never gets executed: public class TestIfPerf { public static void main( String[] args ) { boolean condition = true; long time = 0L; int value = 0; // warm up test for( int count=0; count<10000000; count++ ) { if ( condition ) { value = 1 + 2; } else { value = 1 + 3; } } // benchmark if condition only time = System.nanoTime(); for( int count=0; count<10000000; count++ ) { if ( condition ) { value = 1 + 2; } } time = System.nanoTime() - time; System.out.println( "1) performance " + time ); time = System.nanoTime(); // benchmark if else condition for( int count=0; count<10000000; count++ ) { if ( condition ) { value = 1 + 2; } else { value = 1 + 3; } } time = System.nanoTime() - time; System.out.println( "2) performance " + time ); } } and run the test program with java -classpath . -Dmx=800m -Dms=800m TestIfPerf. I performed this on both Mac and Linux Java with 1.6 latest build. Consistently the first benchmark, without the else is much faster than the second benchmark with the else section even though the code is structured such that the else portion is never executed because of the condition. I understand that to some, the difference might not be significant but the relative performance difference is large. I wonder if anyone has any insight to this (or maybe there is something I did incorrectly). Linux benchmark (in nano) performance 1215488 performance 2629531 Mac benchmark (in nano) performance 1667000 performance 4208000

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• Noob question about a statement in a Java program

  - by happysoul

  I am beginner to java and was trying out this code puzzle from the book head first java which I solved as follows and got the output correct :D class DrumKit { boolean topHat=true; boolean snare=true; void playSnare() { System.out.println("bang bang ba-bang"); } void playTopHat() { System.out.println("ding ding da-ding"); } } public class DrumKitTestDriver { public static void main(String[] args) { DrumKit d =new DrumKit(); if(d.snare==true) { d.playSnare(); } d.playTopHat(); } } Output is :: bang bang ba-bang ding ding da-ding Now the problem is that in that code puzzle one code snippet is left that I did not include..it's as follows d.snare=false; Even though I did not write it , I got the output like the book. I am wondering why is there need for us to set it's value as false even when we know the code is gonna run without it too !?? I am wondering what the coder had in mind ..I mean what could be the possible future use and motive behind doing this ? I am sorry if it's a dumb question. I just wanna know why or why not to include that particular statement ? It's not like there's a loop or something that we need to come out of. Why is that statement there ?

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• java partial classes

  - by Dewfy

  Hello colleagues, Small preamble. I was good java developer on 1.4 jdk. After it I have switched to another platforms, but here I come with problem so question is strongly about jdk 1.6 (or higher :) ). I have 3 coupled class, the nature of coupling concerned with native methods. Bellow is example of this 3 class public interface A { public void method(); } final class AOperations { static native method(. . .); } public class AImpl implements A { @Override public void method(){ AOperations.method( . . . ); } } So there is interface A, that is implemented in native way by AOperations, and AImpl just delegates method call to native methods. These relations are auto-generated. Everything ok, but I have stand before problem. Sometime interface like A need expose iterator capability. I can affect interface, but cannot change implementation (AImpl). Saying in C# I could be able resolve problem by simple partial: (C# sample) partial class AImpl{ ... //here comes auto generated code } partial class AImpl{ ... //here comes MY implementation of ... //Iterator } So, has java analogue of partial or something like.

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• Can't download pdf with java

  - by gedemagt

  I'm trying to download a file from http://aula.au.dk/main/document/document.php?action=download&id=%2F%D8velsesvejledning+2012.pdf but it dosen't appear to be a pdf, when i try downloading it with this code import java.io.*; import java.net.*; public class DownloadFile { public static void download(String address, String localFileName) throws IOException { URL url1 = new URL(address); byte[] ba1 = new byte[1024]; int baLength; FileOutputStream fos1 = new FileOutputStream(localFileName); try { // Contacting the URL System.out.print("Connecting to " + url1.toString() + " ... "); URLConnection urlConn = url1.openConnection(); // Checking whether the URL contains a PDF if (!urlConn.getContentType().equalsIgnoreCase("application/pdf")) { System.out.println("FAILED.\n[Sorry. This is not a PDF.]"); } else { try { // Read the PDF from the URL and save to a local file InputStream is1 = url1.openStream(); while ((baLength = is1.read(ba1)) != -1) { fos1.write(ba1, 0, baLength); } fos1.flush(); fos1.close(); is1.close(); } catch (ConnectException ce) { System.out.println("FAILED.\n[" + ce.getMessage() + "]\n"); } } } catch (NullPointerException npe) { System.out.println("FAILED.\n[" + npe.getMessage() + "]\n"); } } } Can you help me out here?

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