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  • When should EntityManagerFactory instance be created/opened ?

    - by masato-san
    Ok, I read bunch of articles/examples how to write Entity Manager Factory in singleton. One of them easiest for me to understand a bit: http://javanotepad.blogspot.com/2007/05/jpa-entitymanagerfactory-in-web.html I learned that EntityManagerFactory (EMF) should only be created once preferably in application scope. And also make sure to close the EMF once it's used (?) So I wrote EMF helper class for business methods to use: public class EmProvider { private static final String DB_PU = "KogaAlphaPU"; public static final boolean DEBUG = true; private static final EmProvider singleton = new EmProvider(); private EntityManagerFactory emf; private EmProvider() {} public static EmProvider getInstance() { return singleton; } public EntityManagerFactory getEntityManagerFactory() { if(emf == null) { emf = Persistence.createEntityManagerFactory(DB_PU); } if(DEBUG) { System.out.println("factory created on: " + new Date()); } return emf; } public void closeEmf() { if(emf.isOpen() || emf != null) { emf.close(); } emf = null; if(DEBUG) { System.out.println("EMF closed at: " + new Date()); } } }//end class And my method using EmProvider: public String foo() { EntityManager em = null; List<Object[]> out = null; try { em = EmProvider.getInstance().getEntityManagerFactory().createEntityManager(); Query query = em.createNativeQuery(JPQL_JOIN); //just some random query out = query.getResultList(); } catch(Exception e) { //handle error.... } finally { if(em != null) { em.close(); //make sure to close EntityManager } } I made sure to close EntityManager (em) within method level as suggested. But when should EntityManagerFactory be closed then? And why EMF has to be singleton so bad??? I read about concurrency issues but as I am not experienced multi-thread-grammer, I can't really be clear on this idea.

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  • Why is an anonymous inner class containing nothing generated from this code?

    - by Andrew Westberg
    When run through javac on the cmd line Sun JVM 1.6.0_20, this code produces 6 .class files OuterClass.class OuterClass$1.class OuterClass$InnerClass.class OuterClass$InnerClass2.class OuterClass$InnerClass$InnerInnerClass.class OuterClass$PrivateInnerClass.class When run through JDT in eclipse, it produces only 5 classes. OuterClass.class OuterClass$1.class OuterClass$InnerClass.class OuterClass$InnerClass2.class OuterClass$InnerClass$InnerInnerClass.class OuterClass$PrivateInnerClass.class When decompiled, OuterClass$1.class contains nothing. Where is this extra class coming from and why is it created? package com.test; public class OuterClass { public class InnerClass { public class InnerInnerClass { } } public class InnerClass2 { } //this class should not exist in OuterClass after dummifying private class PrivateInnerClass { private String getString() { return "hello PrivateInnerClass"; } } public String getStringFromPrivateInner() { return new PrivateInnerClass().getString(); } }

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  • JPQL: What kind of objects contains a result list when querying multiple columns?

    - by Bunkerbewohner
    Hello! I'm trying to do something which is easy as pie in PHP & Co: SELECT COUNT(x) as numItems, AVG(y) as average, ... FROM Z In PHP I would get a simple array like [{ numItems: 0, average: 0 }] which I could use like this: echo "Number of Items: " . $result[0]['numItems']; Usually in JPQL you only query single objects or single columns and get Lists types, for example List or List. But what do you get, when querying multiple columns?

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  • Concept of creating static Map

    - by chetan
    I want to create a Map object that can lose value only if we explicitly delete it from map. I have created Map object like public static Map<Long,String> listUser =new HasMap<Long,String>(); but every time class object is created new instance of Map is also created that contain null value. I want to create a Map instance that contain value we stored before.

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  • Are there some good and modern alternatives to Javadoc?

    - by ivan_ivanovich_ivanoff
    Let's face it: You don't need to be a designer to see that default Javadoc looks ugly. There are some resources on the web which offer re-styled Javadoc. But the default behaviour represents the product and should be as reasonably good-looking. Another problem is the fact that the usability of Javadoc is not up-to-date compared to other similar resources. Especially huge projects are hard to navigate using Firefox's quick search. Practical question: Are there any standalone (desktop) applications which are able to browse existing Javadoc in a more usable way than a browser would? I'm thinking about something like Mono's documentation browser. Theoretical question: Does anyone know, if there some plans to evolve Javadoc, in a somehow-standardized way? EDIT: A useful link to Sun' wiki on this topic.

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  • Is there a faster method then StringBuilder for a max 9-10 step string concatenation?

    - by Pentium10
    I have this code to concate some array elements: StringBuilder sb = new StringBuilder(); private RatedMessage joinMessage(int step, boolean isresult) { sb.delete(0, sb.length()); for (int i = 0; i <= step; i++) { if (mStack[i] == null) continue; rm = mStack[i].getCurrentMsg(); if (rm == null || rm.msg.length() == 0) continue; if (sb.length() != 0) { sb.append(", "); } sb.append(rm.msg); } return sb.toString(); } Important the array holds max 10 items, so it's not quite much. My trace output tells me this method is called 18864 times, 16% of the runtime was spent in this method. Can I optimize more?

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  • Inconsistent GWT behavior in IE 8

    - by Don Branson
    All, I have a web site that's built with GWT at https://penwag.com/penwag/. If you just hit the site and see the main page, there's supposed to be a login/registration area that displays, along with a teaser for the site. I've tried the site with most of the main browsers - FF 3 & 3.5, IE 6 & 8, Safari, and Chrome, and all appears well to me. However, I have a non-geek user that has visited the site from both work and home. The work computer can see the intro page fine, but the home computer shows only the static content, and non of the javascript-based portion, that is the login/registration and teaser. Both computers are using IE 8. He checked the computer where the site fails, and scripting is enabled. Can anyone else see the problem? (You don't have to register to see the problem, just hit the main page.) Anything else I should check or have him try? Thanks! Edit: The site is implemented using GWT 1.7.0. I'll have to find out about the OS versions. Edit: The one that works is running Windows XT, the failing one is running Windows Vista. (There's a shocker!) I myself have viewed it successfully with both OSs. Edit: I've since completely re-structured the site, and documented the changes here: http://penwag.blogspot.com/2010/04/april-penwag-update.html So, the site is no longer the same as when I asked this question.

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  • Why this cache doesn't work using final as modifier

    - by Pentium10
    I have this code to get the Cursor once for this instance, and the Log shows it is called many times although I marked as final. What I am missing? private Cursor getAllContactsCached() { final Cursor c=this.getList(); return c; } getAllContactsCached method should retrieve list once, and the 2nd time it should reuse the final object for return

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  • BufferedWriter overwriting itself

    - by Danson
    I want to read in a file and create a duplicate of the file but my code only write the last line in the file. How do I make so that whenever I call write(), it writes to a new line. I want to create a new file for the duplicate so I can't add true to FileWriter constructor. This is my code: //Create file reader BufferedReader iReader = new BufferedReader(new FileReader(args[1])); //Create file writer BufferedWriter oWriter = new BufferedWriter(new FileWriter(args[2], true)); String strLine; //reading file int iterate = 0; while((strLine = iReader.readLine()) != null) { instructions[iterate] = strLine; } //creating duplicate for(int i = 0; i < instructions.length; i++) { if(instructions[i] != null) { oWriter.write(instructions[i]); oWriter.newLine(); } else { break; } } try { iReader.close(); oWriter.close(); } catch (IOException e) { e.printStackTrace(); }

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  • how to retrive String from DatagramPacket

    - by sajith
    the following code prints [B@40545a60,[B@40545a60abc exp but i want to print abc,so that i can retrive the correct message from the receiving system public class Operation { InetAddress ip; DatagramSocket dsock; DatagramPacket pack1; byte[] bin,bout; WifyOperation(InetAddress Systemip) { ip=Systemip; try { dsock=new DatagramSocket(); } catch (SocketException e) { // TODO Auto-generated catch block e.printStackTrace(); } } void sendbyte() { String senddata="abc"+"123"; bout=senddata.getBytes(); pack1=new DatagramPacket(bout,bout.length,ip,3322); try { dsock.send(pack1); Log.d(pack1.getData().toString(),"abc exp"); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } } how i retrieve string instead of byte from the packet pack1

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  • Persistence store in blackberry

    - by arunabha
    i am trying to save a simple string value "1".If i go back from one screen to another,its saving,but when i exit the app,and start again,i dont see that value being saved.I am implementing persistable interface.Can anyone suggest me where i am getting wrong import net.rim.device.api.util.Persistable; import net.rim.device.api.system.PersistentObject; import net.rim.device.api.system.PersistentStore; public class Persist implements Persistable { public static PersistentObject abc; public static String b; static { abc = PersistentStore.getPersistentObject(0xb92c8fe20b256b82L); } public static void data(){ synchronized (abc) { abc.setContents(1+""); abc.commit(); } } public static String getCurrQuestionNumber() { synchronized (abc) { System.out.println("new title is"+b); b= (String)abc.getContents(); System.out.println("title is"+b); return b; } } }

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  • Eclipse: find resource on classpath

    - by seanizer
    Is there a way in eclipse to search the classpath for arbitrary resource file names (or patterns)? I know I can use either Navigate > Open Type (which will scan the classpath for classes) or Navigate > Open Resource, which will search for any resource type, but only in my project folders. Is there any way to achieve a combination ob both, to do a resource search (something like *.xsd) that searches all jars on the classpath?

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  • jpa-Primarykey relationship

    - by megala
    Hi created student entity in gogole app engine datastore using JPA. Student---Coding @Entity @Table(name="StudentPersonalDetails", schema="PUBLIC") public class StudentPersonalDetails { @Id @Column(name = "STUDENTNO") private Long stuno; @Basic @Column(name = "STUDENTNAME") private String stuname; public void setStuname(String stuname) { this.stuname = stuname; } public String getStuname() { return stuname; } public void setStuno(Longstuno) { this.stuno = stuno; } public Long getStuno() { return stuno; } public StudentPersonalDetails(Long stuno,String stuname) { this.stuno = stuno; this.stuname = stuname; } } I stored Property value as follows Stuno Stuname 1 a 2 b If i stored Again Stuno No 1 stuname z means it wont allow to insert the record But. It Overwrite the value Stuno Stuname 1 z 2 b How to solve this?

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  • Redeclaration of parameters

    - by Scott
    While looking through the Selenium source code I noticed the following in the PageFactory: public static <T> T initElements(WebDriver driver, Class<T> pageClassToProxy) { T page = instantiatePage(driver, pageClassToProxy); initElements(driver, page); return page; } public static void initElements(WebDriver driver, Object page) { final WebDriver driverRef = driver; initElements(new DefaultElementLocatorFactory(driverRef), page); } What is the benefit of having the following line? final WebDriver driverRef = driver; Wouldn't it have made sense to just make the parameter final, and then passing that along to the next method without declaring the new reference?

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  • How do I create a new AnyType[] array?

    - by cb
    Which is the best practice in this situation? I would like an un-initialized array of the same type and length as the original. public static <AnyType extends Comparable<? super AnyType>> void someFunction(AnyType[] someArray) { AnyType[] anotherArray = (AnyType[]) new Comparable[someArray.length]; ...or... AnyType[] anotherArray = (AnyType[]) new Object[someArray.length]; ...some other code... } Thanks, CB

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