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• Maintaining a pool of DAO Class instances vs doing new operator

  - by Fazal

  we have been trying to benchmark our application performance in multiple way for sometime now. I always believed that object creation in java using Class.newInstance() was not slow (at least after 1.4 version of java). But we anyways did a test to use newInstance method vs mainitain an object pool of 1000 objects. We did about 200K iterations of loading data from DB using JDBC and populating these objects. I was amazed (even shocked) to see that newInstance code compared to object pool code was almost 10 times slower. These objects represent tables with about 50 fields and all string type. Can someone share there thoughts on this issue as now I am more confused if object pooling of atleast some DAO instances is a better option. The pool size as I see right now should be large enough to meet size of average requests. There is a flip side as my memory footprint will go up but I am beginning to wonder if this kind of idea makes sense atleast for some of the DAO entities representing tables of about 50 or more columns Please share your ideas and let me know if this has been tried by someone or am I missing some point here

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• SecurityManager StackOverflowError

  - by Tom Brito

  Running the following code, I get a StackOverflowError at the getPackage() line. How can I grant permission just to classes inside package I want, if I can't access the getPackage() to check the package? package myPkg.security; import java.security.Permission; import javax.swing.JOptionPane; public class SimpleSecurityManager extends SecurityManager { @Override public void checkPermission(Permission perm) { Class<?>[] contextArray = getClassContext(); for (Class<?> c : contextArray) { checkPermission(perm, c); } } @Override public void checkPermission(Permission perm, Object context) { if (context instanceof Class) { Class clazz = (Class) context; Package pkg = clazz.getPackage(); // StackOverflowError String name = pkg.getName(); if (name.startsWith("java.")) { // permission granted return; } if (name.startsWith("sun.")) { // permission granted return; } if (name.startsWith("myPkg.")) { // permission granted return; } } // permission denied throw new SecurityException("Permission denied for " + context); } public static void main(String[] args) { System.setSecurityManager(new SimpleSecurityManager()); JOptionPane.showMessageDialog(null, "test"); } }

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• Rendering Swing Components to an Offscreen buffer

  - by Nick C

  I have a Java (Swing) application, running on a 32-bit Windows 2008 Server, which needs to render it's output to an off-screen image (which is then picked up by another C++ application for rendering elsewhere). Most of the components render correctly, except in the odd case where a component which has just lost focus is occluded by another component, for example where there are two JComboBoxes close to each other, if the user interacts with the lower one, then clicks on the upper one so it's pull-down overlaps the other box. In this situation, the component which has lost focus is rendered after the one occluding it, and so appears on top in the output. It renders correctly in the normal Java display (running full-screen on the primary display), and attempting to change the layers of the components in question does not help. I am using a custom RepaintManager to paint the components to the offscreen image, and I assume the problem lies with the order in which addDirtyRegion() is called for each of the components in question, but I can't think of a good way of identifying when this particular state occurs in order to prevent it. Hacking it so that the object which has just lost focus is not repainted stops the problem, but obviously causes the bigger problem that it is not repainted in all other, normal, circumstances. Is there any way of programmatically identifying this state, or of reordering things so that it does not occur? Many thanks, Nick

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• Raw types and subtyping

  - by Dmitrii

  We have generic class SomeClass<T>{ } We can write the line: SomeClass s= new SomeClass<String>(); It's ok, because raw type is supertype for generic type. But SomeClass<String> s= new SomeClass(); is correct to. Why is it correct? I thought that type erasure was before type checking, but it's wrong. From Hacker's Guide to Javac When the Java compiler is invoked with default compile policy it performs the following passes: parse: Reads a set of *.java source files and maps the resulting token sequence into AST-Nodes. enter: Enters symbols for the definitions into the symbol table. process annotations: If Requested, processes annotations found in the specified compilation units. attribute: Attributes the Syntax trees. This step includes name resolution, type checking and constant folding. flow: Performs data ow analysis on the trees from the previous step. This includes checks for assignments and reachability. desugar: Rewrites the AST and translates away some syntactic sugar. generate: Generates Source Files or Class Files. Generic is syntax sugar, hence type erasure invoked at 6 pass, after type checking, which invoked at 4 pass. I'm confused.

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• Axis2 Webservice -> php

  - by Peter Hagström

  Hi! If I have understood Axis2 correct i can construct a WebService and then access it with any SOAP compatible client. I have a java class with a couple of methods that I have written in Eclipse, and then automatically constructed a service with the Axis2 plugin from WTP. This is the methods of my class. public int test(int i){ return i+2; } public Car CarTest(int speed){ return new Car("Biltest", speed); } public CarFactoryAdapter getCarFactory(){ carFact.getCars().add(new Car("Bmw", 250)); carFact.getCars().add(new Car("seat", 350)); carFact.getCars().add(new Car("saab", 150)); carFact.getCars().add(new Car("volv", 50)); return new CarFactoryAdapter(carFact); } The code seems to work when I try it with soapUI and the Axis2-web interface has recognized the methods of my service. But when Iam trying the methods that receives parameters with PHP´s built in soapClient i get a Unknown exception. The getCarFactory methods works at least as expected, but it seems kind of crippled if I can´t send parameters. Example of non working method invocation. ini_set('soap.wsdl_cache_ttl',0); $client = new SoapClient("http://192.168.128.162:8080/ComplexWebService/services/CarService?wsdl", array('soap_version' => SOAP_1_2, 'trace' => 1)); $ar['i'] = (int)100; print_r($client->__soapCall("test",$ar)); I need to make sure that the SOA framework i choose will be able to comunicate with many platforms, there will be clients in at least PHP and Java, but it would be good if it will work in for example .NET to.

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• JPanel Appears Behind JMenuBar

  - by Matt H

  import javax.swing.JFrame; import javax.swing.JMenu; import javax.swing.JMenuBar; import javax.swing.JMenuItem; @SuppressWarnings("serial") public class Main extends JFrame { final int FRAME_HEIGHT = 400; final int FRAME_WIDTH = 400; public static void main(String args[]) { new Main(); } public Main() { super("Game"); GameCanvas canvas = new GameCanvas(); JMenuBar menuBar = new JMenuBar(); JMenu fileMenu = new JMenu("File"); JMenuItem startMenuItem = new JMenuItem("Pause"); menuBar.add(fileMenu); fileMenu.add(startMenuItem); super.setVisible(true); super.setSize(FRAME_WIDTH, FRAME_WIDTH); super.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); super.setJMenuBar(menuBar); } } import java.awt.Canvas; import java.awt.Graphics; import javax.swing.JPanel; @SuppressWarnings("serial") public class GameCanvas extends JPanel { public void paint(Graphics g) { g.drawString("hI", 0, 0); } } This code causes the string to appear behind the JMenuBar. To see the string, you must draw it at (0,10). I'm sure this must be something simple, so do you guys have any ideas?

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• Why can't I wrap the ServletRequest when trying to capture JSP Output

  - by Patrick Cornelissen

  I am trying to dispatch in a servlet request handler to the JSP processor and capture the content of it. I am providing wrapper instances for the ServletRequest and ServletResponse, they implement the corresponding HTTPServletRequest/-Response interfaces, so they should be drop-in replacements. All methods are currently passed to the original Servlet Request object (I am planning to modify some of them soon). Additionally I have introduced some new methods. (If you want to see the code: http://code.google.com/p/gloudy/source/browse/trunk/gloudyPortal/src/java/org/gloudy/gloudlet/impl/RenderResponseImpl.java) The HttpServletResponse uses it's own output streams to capture the output. When I try to call request.getRequestDispatcher("/WEB-INF/views/test.jsp").include(request, response); With my request and response wrappers the method returns and no content has been captured. When I tried to pass the original request object it worked! But that's not what I need in the long run... request.getRequestDispatcher("/WEB-INF/views/test.jsp").include(request.getServletRequest(), response); This works. getservletRequest() returns the original Request, given by the servlet container. Does anyone know why this is not working with my wrappers?

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• servlet resopnse data for autocomplete

  - by shams haque

  Hello experts, Following code is in php. i want to do same in java. Please tell me how do i generate this type of array or collection in java. I need this to response to json autocomplete. <?php $q = strtolower($_GET["q"]); if (!$q) return; $items = array( "Peter Pan"=>"[email protected]", "Molly"=>"[email protected]", "Forneria Marconi"=>"[email protected]", "Master Sync"=>"[email protected]", "Dr. Tech de Log"=>"[email protected]", "Don Corleone"=>"[email protected]", "Mc Chick"=>"[email protected]", "Donnie Darko"=>"[email protected]", "Quake The Net"=>"[email protected]", "Dr. Write"=>"[email protected]" ); $result = array(); foreach ($items as $key=>$value) { if (strpos(strtolower($key), $q) !== false) { array_push($result, array( "name" => $key, "to" => $value )); } } echo json_encode($result); ?>

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• Backreferences syntax in replacement strings (why dollar sign?)

  - by polygenelubricants

  In Java, and it seems in a few other languages, backreferences in the pattern is preceded by a slash (e.g. \1, \2, \3, etc), but in a replacement string it's preceded by a dollar sign (e.g. $1, $2, $3, and also $0). Here's a snippet to illustrate: System.out.println( "left-right".replaceAll("(.*)-(.*)", "\\2-\\1") // WRONG!!! ); // prints "2-1" System.out.println( "left-right".replaceAll("(.*)-(.*)", "$2-$1") // CORRECT! ); // prints "right-left" System.out.println( "You want million dollar?!?".replaceAll("(\\w*) dollar", "US\\$ $1") ); // prints "You want US$ million?!?" System.out.println( "You want million dollar?!?".replaceAll("(\\w*) dollar", "US$ \\1") ); // throws IllegalArgumentException: Illegal group reference Questions: Is the use of $ for backreferences in replacement strings unique to Java? If not, what language started it? What flavors use it and what don't? Why is this a good idea? Why not stick to the same pattern syntax? Wouldn't that lead to a more cohesive and an easier to learn language? Wouldn't the syntax be more streamlined if statements 1 and 4 in the above were the "correct" ones instead of 2 and 3?

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• Synchronizing screencasting (ffmpeg) and capturing from the webcam (OpenCV)

  - by lyuba

  As from my previous questions, I am trying to build a simple eye tracker. Decided to start from a Linux version (run Ubuntu). To complete this task one should organize screencasting and webcam capturing in such way that frames from both streams exactly match each other and there is the same number of frames in each of them totally. Screencasting fsp fully depends on the camera's fsp, so each time we get the image from the webcam we can potentially grab a screen frame and stay happy. However, all the tools for the fast screencasting, like ffmpeg, for example, return the .avi file as the result and require the fsp already known to be started. From the other side, tools like Java+Robot or ImageMagick seem to require around 20ms to return the .jpg screenshot, which is pretty slow for the task. But they may be requested right after each time the webcam frame is grabbed and provide the needed synchronization. So the sub-questions are: 1. Does the USD camera's frame rate vary during a single session? 2. Are there any tools which provide fast screencasting frame by frame? 3. Is there any way to make ffmpeg push a new frame to the .avi file only when program initiates this request? For my task I may either use C++ or Java. I am, actually, an interface designer, not the driver programmer, and this task seems to be pretty low-level. I would be grateful for any suggestion and tip!

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• Search and replace with sed

  - by Binoy Babu

  Last week I accidently externalized all my strings of my eclipse project. I need to revert this and my only hope is sed. I tried to create scripts but failed pathetically because I'm new with sed and this would be a very complicated operation. What I need to do is this: Strings in class.java file is currently in the following format(method) Messages.getString(<key>). Example : if (new File(DataSource.DEFAULT_VS_PATH).exists()) { for (int i = 1; i <= c; i++) { if (!new File(DataSource.DEFAULT_VS_PATH + Messages.getString("VSDataSource.89") + i).exists()) { //$NON-NLS-1$ getnewvfspath = DataSource.DEFAULT_VS_PATH + Messages.getString("VSDataSource.90") + i; //$NON-NLS-1$ break; } } } The key and matching Strings are in messages.properties file in the following format. VSDataSource.92=No of rows in db = VSDataSource.93=Verifying db entry : VSDataSource.94=DB is open VSDataSource.95=DB is closed VSDataSource.96=Invalid db entry for VSDataSource.97=\ removed. So I need the java file back in this format: if (new File(DataSource.DEFAULT_VS_PATH).exists()) { for (int i = 1; i <= c; i++) { if (!new File(DataSource.DEFAULT_VS_PATH + "String 2" + i).exists()) { //$NON-NLS-1$ getnewvfspath = DataSource.DEFAULT_VS_PATH + "String 1" + i; //$NON-NLS-1$ break; } } } How can I accomplish this with sed? Or is there an easier way?

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• Focus behavior in Applet-Javascript interaction

  - by Dan

  I have a web page with an applet that opens a popup window and also makes Javascript calls. When that Javascript call results in a focus() call on an HTML input, that causes the browser window to push itself in front of the applet window. But only on certain browsers, namely MSIE. On Firefox the applet window remains on top. How can I keep that behavior consistent in MSIE? Note that using the old Microsoft VM for Java also achieves the desired (applet window in front) result. HTML code: <html> <head> <script type="text/javascript"> function focusMe() { document.getElementById('mytext').focus(); } </script> </head> <body> <applet id="myapplet" mayscript code="Popup.class" ></applet> <form> <input type="text" id="mytext"> <input type="button" onclick="document.getElementById('myapplet').showPopup()" value="click"> </form> </body> </html> Java code: public class Popup extends Applet { Frame frame; public void start() { frame = new Frame("Test Frame"); frame.setLayout(new BorderLayout()); Button button = new Button("Push Me"); frame.add("Center", button); button.addActionListener(new ActionListener(){ public void actionPerformed(ActionEvent e) { frame.setVisible(false); } }); frame.pack(); } public void showPopup() { frame.setVisible(true); JSObject.getWindow(this).eval("focusMe()"); } }

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• JBoss Client-Cert Authentication: Hot to setup UsersRolesLoginModule in login-config.xml

  - by sixtyfootersdude

  I am looking that chapter 8 of the RedHat, JBoss documentation. I am trying to setup Certificate Authentication as described on this page . On the page it says that the login-config file should have this in it: <application-policy name="jmx-console"> <authentication> <login-module code="org.jboss.security.auth.spi.BaseCertLoginModule" flag="required"> <module-option name="password-stacking">useFirstPass</module-option> <module-option name="securityDomain">java:/jaas/jmx-console</module-option> </login-module> <login-module code="org.jboss.security.auth.spi.UsersRolesLoginModule" flag="required"> <module-option name="password-stacking">useFirstPass</module-option> <module-option name="usersProperties">jmx-console-users.properties</module-option> <module-option name="rolesProperties">jmx-console-roles.properties</module-option> </login-module> </authentication> </application-policy> I think that the BaseCertLoginModule chekcs the clients server and the UsersRolesloginModule assigns the client to role (using the file jmx-console-roles.properties). However I am completely bewildered as to what should be in this file: jmx-console-users.properties. Normally that file stores user/password pairs (source) but when using client-cert I don't think that there should be passwords in there. Right now I am leaving that file empty but I am getting this exception: [org.jboss.security.auth.spi.UsersRolesLoginModule.initialize:135] Failed to load users/passwords/role files java.io.IOException: No properties file: users.properties or defaults: defaultUsers.properties found ... What should be in that file? Thanks.

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• what is the point of heterogenous arrays?

  - by aharon

  I know that more-dynamic-than-Java languages, like Python and Ruby, often allow you to place objects of mixed types in arrays, like so: ["hello", 120, ["world"]] What I don't understand is why you would ever use a feature like this. If I want to store heterogenous data in Java, I'll usually create an object for it. For example, say a User has int ID and String name. While I see that in Python/Ruby/PHP you could do something like this: [["John Smith", 000], ["Smith John", 001], ...] this seems a bit less safe/OO than creating a class User with attributes ID and name and then having your array: [<User: name="John Smith", id=000>, <User: name="Smith John", id=001>, ...] where those <User ...> things represent User objects. Is there reason to use the former over the latter in languages that support it? Or is there some bigger reason to use heterogenous arrays? N.B. I am not talking about arrays that include different objects that all implement the same interface or inherit from the same parent, e.g.: class Square extends Shape class Triangle extends Shape [new Square(), new Triangle()] because that is, to the programmer at least, still a homogenous array as you'll be doing the same thing with each shape (e.g., calling the draw() method), only the methods commonly defined between the two.

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• How can I work around WinXP using ports 1025-5000 as ephemeral?

  - by Chris Dolan

  If you create a TCP client socket with port 0 instead of a non-zero port, then the operating system chooses any free ephemeral port for you. Most OSes choose ephemeral ports from the IANA dynamic port range of 49152-65535. However in Windows Server 2003 and earlier (including XP) Microsoft used ports 1025-5000 as the ephemeral range, according to their bind() documentation. I run multiple Java services on the same hardware. On rare occasions, this range collides with well-known ports that I use for other services (e.g. port 4160 for Jini discovery). While rare, this has caused real problems. Is there any easy way to tell Windows or Java to use a different port range for client sockets? Microsoft's docs indicate that I can change the high end of that range via the MaxUserPort TcpIP registry setting, but I see no way to change the low end. Update: I've made some progress on this. It looks like Microsoft has a concept of reserved ports that are exceptions to the ephemeral port range. There's a registry setting that lets you change this permanently and apparently there must be an API to do the same thing because there's a data structure that holds high/low values for reserved port ranges, but I can't find the actual function call anywhere... The registry solution may work, but now I'm fixated on this API.

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• Apache Tuscany 1.6 How do you set the JMS Binding Delivery Mode to NON_PERSISTENT?

  - by Robert Greiner

  I am using Tuscany 1.6 and am trying to set the Delivery Mode JMS Binding to NON_PERSISTENT. I've tried using uri="jms:MyService?deliveryMode=1" (which is what the spec (PDF) says to do) but, I ended up getting the following exception: Unknown token deliveryMode=1 I also tried <headers JMSDeliveryMode="NON_PERSISTENT"/>, although I did not get an exception the messages still got delivered as PERSISTENT. This is the format for the URI jms:<jms-dest>? connectionFactoryName=<Connection-Factory-Name> & destinationType={queue|topic} deliveryMode=<Delivery-Mode> & timeToLive=<Time-To-Live> & priority=<Priority> & <User-Property>=<User-Property-Value> & … This is the example I am using <composite xmlns="http://www.osoa.org/xmlns/sca/1.0" name="MyValueComposite"> <service name="MyValueService"> <interface.java interface="services.myvalue.MyValueService"/> <binding.jms uri="jms:MyValueServiceQueue?activationSpecName=MyValueServiceAS&... "/> </service> <reference name="StockQuoteService"> <interface.java interface="services.stockquote.StockQuoteService"/> <binding.jms uri="jms:StockQuoteServiceQueue?connectionFactoryName=StockQuoteServiceQCF&deliveryMode=1&... "/> </reference> </composite>

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• TreeMap sort by value

  - by vito huang

  I'm new to java, i want to write an comparator to that will let me sort TreeMap by value instead of the default natural sorting. i tried something like this, but can't find out what went wrong: import java.util.*; class treeMap { public static void main(String[] args) { System.out.println("the main"); byValue cmp = new byValue(); Map<String, Integer> map = new TreeMap<String, Integer>(cmp); map.put("de",10); map.put("ab", 20); map.put("a",5); for (Map.Entry<String,Integer> pair: map.entrySet()) { System.out.println(pair.getKey()+":"+pair.getValue()); } } } class byValue implements Comparator<Map.Entry<String,Integer>> { public int compare(Map.Entry<String,Integer> e1, Map.Entry<String,Integer> e2) { if (e1.getValue() < e2.getValue()){ return 1; } else if (e1.getValue() == e2.getValue()) { return 0; } else { return -1; } } } I guess what am i asking is what controls what get pass to comparator function, can i get an Map.Entry pass to comparator?

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• Default Button after dispose and setVisible

  - by DaDaDom

  Hi, given the following code: public class DialogTest implements ActionListener { public static void main(String[] args) {DialogTest g = new DialogTest();} public DialogTest() { JButton b1 = new JButton("Button A"); b1.addActionListener(this); JDialog d = new JDialog(); d.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE); JPanel p = new JPanel(); p.add(b1); d.add(p); d.getRootPane().setDefaultButton(b1); d.pack(); d.setVisible(true); d.dispose(); d.pack(); d.setVisible(true); } public void actionPerformed(ActionEvent e) {System.out.println("hello");} } Shouldn't pressing the Enter key write something to the console? According to the docs (http://java.sun.com/javase/7/docs/api/java/awt/Window.html#dispose()): The Window and its subcomponents can be made displayable again by rebuilding the native resources with a subsequent call to pack or show. The states of the recreated Window and its subcomponents will be identical to the states of these objects at the point where the Window was disposed Is this intended behaviour?

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• Why isn't componentHidden called for my JPopupMenu?

  - by heycam

  I want to be notified when my JPopupMenu is hidden — whether because an item was selected, the menu was dismissed, or setVisible(false) was called on it. Here is my test code: import javax.swing.*; import java.awt.*; import java.awt.event.*; public class A extends ComponentAdapter implements Runnable, ActionListener { private JButton b; public static void main(String[] args) { EventQueue.invokeLater(new A()); } public void run() { JFrame f = new JFrame("Test"); b = new JButton("Click me"); b.addActionListener(this); f.add(b); f.pack(); f.setVisible(true); } public void actionPerformed(ActionEvent e) { JPopupMenu pm = new JPopupMenu(); pm.addComponentListener(this); pm.add("Popup..."); pm.add("...menu!"); pm.show(b, 10, 10); } public void componentShown(ComponentEvent e) { System.out.println("componentShown"); } public void componentHidden(ComponentEvent e) { System.out.println("componentHidden"); } } Regardless of how I interact with the menu, neither of the two ComponentListener methods are being called. Why is that? Is there different/better/correct way of finding out when my JPopupMenu is hidden? Thanks, Cameron

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• Spring: Bean fails to read off values from external Properties file when using @Value annotation

  - by daydreamer

  XML Configuration <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:util="http://www.springframework.org/schema/util" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util.xsd"> <util:properties id="mongoProperties" location="file:///storage/local.properties" /> <bean id="mongoService" class="com.business.persist.MongoService"></bean> </beans> and MongoService looks like @Service public class MongoService { @Value("#{mongoProperties[host]}") private String host; @Value("#{mongoProperties[port]}") private int port; @Value("#{mongoProperties[database]}") private String database; private Mongo mongo; private static final Logger LOGGER = LoggerFactory.getLogger(MongoService.class); public MongoService() throws UnknownHostException { LOGGER.info("host=" + host + ", port=" + port + ", database=" + database); mongo = new Mongo(host, port); } public void putDocument(@Nonnull final DBObject document) { LOGGER.info("inserting document - " + document.toString()); mongo.getDB(database).getCollection(getCollectionName(document)).insert(document, WriteConcern.SAFE); } I write my MongoServiceTest as public class MongoServiceTest { @Autowired private MongoService mongoService; public MongoServiceTest() throws UnknownHostException { mongoRule = new MongoRule(); } @Test public void testMongoService() { final DBObject document = DBContract.getUniqueQuery("001"); document.put(DBContract.RVARIABLES, "values"); document.put(DBContract.PVARIABLES, "values"); mongoService.putDocument(document); } and I see failures in tests as 12:37:25.224 [main] INFO c.s.business.persist.MongoService - host=null, port=0, database=null java.lang.NullPointerException at com.business.persist.MongoServiceTest.testMongoService(MongoServiceTest.java:40) Which means bean was not able to read the values from local.properties local.properties ### === MongoDB interaction === ### host="127.0.0.1" port=27017 database=contract How do I fix this? update It doesn't seem to read off the values even after creating setters/getters for the fields. I am really clueless now. How can I even debug this issue? Thanks much!

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• volatile keyword seems to be useless?

  - by Finbarr

  import java.util.concurrent.CountDownLatch; import java.util.concurrent.atomic.AtomicInteger; public class Main implements Runnable { private final CountDownLatch cdl1 = new CountDownLatch(NUM_THREADS); private volatile int bar = 0; private AtomicInteger count = new AtomicInteger(0); private static final int NUM_THREADS = 25; public static void main(String[] args) { Main main = new Main(); for(int i = 0; i < NUM_THREADS; i++) new Thread(main).start(); } public void run() { int i = count.incrementAndGet(); cdl1.countDown(); try { cdl1.await(); } catch (InterruptedException e1) { e1.printStackTrace(); } bar = i; if(bar != i) System.out.println("Bar not equal to i"); else System.out.println("Bar equal to i"); } } Each Thread enters the run method and acquires a unique, thread confined, int variable i by getting a value from the AtomicInteger called count. Each Thread then awaits the CountDownLatch called cdl1 (when the last Thread reaches the latch, all Threads are released). When the latch is released each thread attempts to assign their confined i value to the shared, volatile, int called bar. I would expect every Thread except one to print out "Bar not equal to i", but every Thread prints "Bar equal to i". Eh, wtf does volatile actually do if not this?

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• non static method cannot be referenced from a static context.

  - by David

  First some code: import java.util.*; ... class TicTacToe { ... public static void main (String[]arg) { Random Random = new Random() ; toerunner () ; // this leads to a path of methods that eventualy gets us to the rest of the code } ... public void CompTurn (int type, boolean debug) { ... boolean done = true ; int a = 0 ; while (!done) { a = Random.nextInt(10) ; if (debug) { int i = 0 ; while (i<20) { System.out.print (a+", ") ; i++; }} if (possibles[a]==1) done = true ; } this.board[a] = 2 ; } ... } //to close the class Here is the error message: TicTacToe.java:85: non-static method nextInt(int) cannot be referenced from a static context a = Random.nextInt(10) ; ^ What exactly went wrong? What does that error message "non static method cannot be referenced from a static context" mean?

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• Long running transactions with Spring and Hibernate?

  - by jimbokun

  The underlying problem I want to solve is running a task that generates several temporary tables in MySQL, which need to stay around long enough to fetch results from Java after they are created. Because of the size of the data involved, the task must be completed in batches. Each batch is a call to a stored procedure called through JDBC. The entire process can take half an hour or more for a large data set. To ensure access to the temporary tables, I run the entire task, start to finish, in a single Spring transaction with a TransactionCallbackWithoutResult. Otherwise, I could get a different connection that does not have access to the temporary tables (this would happen occasionally before I wrapped everything in a transaction). This worked fine in my development environment. However, in production I got the following exception: java.sql.SQLException: Lock wait timeout exceeded; try restarting transaction This happened when a different task tried to access some of the same tables during the execution of my long running transaction. What confuses me is that the long running transaction only inserts or updates into temporary tables. All access to non-temporary tables are selects only. From what documentation I can find, the default Spring transaction isolation level should not cause MySQL to block in this case. So my first question, is this the right approach? Can I ensure that I repeatedly get the same connection through a Hibernate template without a long running transaction? If the long running transaction approach is the correct one, what should I check in terms of isolation levels? Is my understanding correct that the default isolation level in Spring/MySQL transactions should not lock tables that are only accessed through selects? What can I do to debug which tables are causing the conflict, and prevent those tables from being locked by the transaction?

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• Class initialization and synchronized class method

  - by nybon

  Hi there, In my application, there is a class like below: public class Client { public synchronized static print() { System.out.println("hello"); } static { doSomething(); // which will take some time to complete } } This class will be used in a multi thread environment, many threads may call the Client.print() method simultaneously. I wonder if there is any chance that thread-1 triggers the class initialization, and before the class initialization complete, thread-2 enters into print method and print out the "hello" string? I see this behavior in a production system (64 bit JVM + Windows 2008R2), however, I cannot reproduce this behavior with a simple program in any environments. In Java language spec, section 12.4.1 (http://java.sun.com/docs/books/jls/second_edition/html/execution.doc.html), it says: A class or interface type T will be initialized immediately before the first occurrence of any one of the following: T is a class and an instance of T is created. T is a class and a static method declared by T is invoked. A static field declared by T is assigned. A static field declared by T is used and the reference to the field is not a compile-time constant (§15.28). References to compile-time constants must be resolved at compile time to a copy of the compile-time constant value, so uses of such a field never cause initialization. According to this paragraph, the class initialization will take place before the invocation of the static method, however, it is not clear if the class initialization need to be completed before the invocation of the static method. JVM should mandate the completion of class initialization before entering its static method according to my intuition, and some of my experiment supports my guess. However, I did see the opposite behavior in another environment. Can someone shed me some light on this? Any help is appreciated, thanks.

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• Where is the taglib definition of PrimeFaces 4?

  - by Michael Wölm

  I am looking around how to define custom components in JSF. According to the Java EE tutorial, any custom component needs to be described in a taglib. When I take a look into the PrimeFaces source, I cannot find any taglib file or any hint where the namespace is bound and the available components are defined. I am adding primefaces jar to my dependencies, adding xmlns:p="http://primefaces.org/ui to the xml namespace, defining some primfaces components on my page and it works... Ok, but neither I can find the related taglib in the source or binary package nor my IDE (IntelliJ) is able to find where "xmlns:p="http://primefaces.org/ui" is pointing to. Therefore, code completion is also not possible. (all other mojarra taglibs are found.) Is it possible that PrimeFaces is defining the taglib via annotations directly in Java classes or is it generating it during runtime? I can easily find the UIComponents, primefaces defines in its source, but the configuration of the taglib seems to be missing. I am sure I just don't know how PrimeFaces is doing it, but the javaeetutorial is not describing any other opportunity than defining a ...-taglib.xml

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