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  • Synchronize write to two collections

    - by glaz666
    I need to put some value to maps if it is not there yet. The key-value (if set) should always be in two collections (that is put should happen in two maps atomically). I have tried to implement this as follows: private final ConcurrentMap<String, Object> map1 = new ConcurrentHashMap<String, Object>(); private final ConcurrentMap<String, Object> map2 = new ConcurrentHashMap<String, Object>(); public Object putIfAbsent(String key) { Object retval = map1.get(key); if (retval == null) { synchronized (map1) { retval = map1.get(key); if (retval == null) { Object value = new Object(); //or get it somewhere synchronized (map2) { map1.put(key, value); map2.put(key, new Object()); } retval = value; } } } return retval; } public void doSomething(String key) { Object obj1 = map1.get(key); Object obj2 = map2.get(key); //do smth } Will that work fine in all cases? Thanks

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  • How to avoid StaleObjectStateException when transaction updates thousands of entities?

    - by ThinkFloyd
    We are using Hibernate 3.6.0.Final with JPA 2 and Spring 3.0.5 for a large scale enterprise application running on tomcat 7 and MySQL 5.5. Most of the transactions in application, lives for less than a second and update 5-10 entities but in some use cases we need to update more than 10-20K entities in single transaction, which takes few minutes and hence more than 70% of times such transaction fails with StaleObjectStateException because some of those entities got updated by some other transaction. We generally maintain version column in all tables and in case of StaleObjectStateException we generally retry but since these longs transactions are anyways very long so if we keep on retrying then also I am not very sure that we'll be able to escape StaleObjectStateException. Also lot of activities keep updating these entities in busy hours so we cannot go with pessimistic approach because it can potentially halt many activities in system. Please suggest how to fix such long transaction issue because we cannot spawn thousands of independent and small transactions because we cannot afford messed up data in case of some failed & some successful transactions.

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  • How does Object Oriented Programming work?

    - by venom
    Hello, I am not sure about some things in OOP. If I have Class1, which has some private field, for example private Field field1, and make getField1 () { return field1; } then I have some class with constructor public Class2 (Field field) { someMethod(field); } And then I call constructor of Class2 in Class3 like: Class2 cl = new Class2(instanceOfClass1.getField1()); And now the question: Am I working with field1 of instanceOfClass1 in someMethod(field)?

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  • Chat client with GWT

    - by user284016
    What would be the best way to create a JS chat client with GWT? The bit that I'm having trouble with is the persistence and transfer of the messages. Should I store the messages in a DB and check the db for new messages? Is there a much better way to do this?

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  • CodeModel help needed for right-hand singleton.getinstance() assignment.

    - by antarti
    I've been able to generate 99% of what I need with the CodeModel API, but I am stumped here... Using the various "directXX" methods does not add import statements to the generated code, and I can work without the "directXXX" type of methods except for one place in a generated class. Suppose I desire a generated method like: /** * Copies data from this Value-Obj instance, to the returned PERSON instance. * * @return PERSON * */ public PERSON mapVOToPERSON() throws MappingException { Mapper mapper = (com.blah.util.MapperSingleton.getMapperInstance()); return mapper.map(this, PERSON.class); } You can see the right hand of the Mapper assignment in parens. Emitting the entire package+class was the only way I could find to just declare "SomeSingleton.someMethod()" on the right hand side and have the generated code compile. Without the MapperSingleton being added to the object model, there is no import generated... Questions: 1) Is there a way to force an import to be generated? 2) How to declare an expression that gives me the right side of the Mapper assignment within the object model (so that an import of MapperSingleton gets generated. Any help appreciated...

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  • LinkedList insert tied to inserted object

    - by wrongusername
    I have code that looks like this: public class Polynomial { List<Term> term = new LinkedList<Term>(); and it seems that whenever I do something like term.add(anotherTerm), with anotherTerm being... another Term object, it seems anotherTerm is referencing the same thing as what I've just inserted into term so that whenever I try to change anotherTerm, term.get(2) (let's say) get's changed too. How can I prevent this from happening?

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  • what does a tool like Jasper Reports give me?

    - by Itay Moav
    Ok, So I have to generate very complex reports from my DB. If I am to do it with SQL the query themselves will be complex, and I will have to do some more manipulation on the results later, code level. How do libraries like Jasper Reports/ Crystal Reports and friends save me time when developing such reports? What will they give me?

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  • Reusing an anonymous parameter in a prepared statement

    - by Chris Lieb
    I am customizing the insert SQL generated by hibernate and have hit an issue. When Hibernate generates the query by itself, it inserts data into the first two columns of the table, but this causes a database error since all four columns of the table are non-nullable. For the insert to be performed properly, it must insert the same data into two columns of the new record. This means that I need Hibernate to bind the same data to two different parameters in the query (prepared statement) that I am writing. Is there some SQL syntax that allows me to refer to anonymous parameters bound to a prepared statement in an order different from which they are bound? Details REF_USER_PAGE_XREF ---------------------------------------- PK FK1 | NETWORK_ID | VARCHAR2(100) PK FK1 | PAGE_PATH | VARCHAR2(1000) | USER_LAST_UPDT | VARCHAR2(100) | TMSP_LAST_UPDT | DATE insert into REF_USER_ROLE_XREF( NETWORK_ID, PAGE_PATH, TMSP_LAST_UPDT, USER_LAST_UPDT) values ( ?, /* want to insert the same data here */ ?, ?, /* and here */ (select to_char(sysdate, 'DD-MON-YY') from dual) I want to insert the same data into the first and third anonymous parameters.

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  • Is it possible to use maven only for running selenium plugin?

    - by tputkonen
    Our pom.xml currently contains both the build settings, as well as execution of selenium using selenium-maven-plugin. I would like to split it in to two pom files, one for the build and unit tests and the second one for executing selenium tests. (This way I could first build the project in Hudson, and after successful build execute Selenium tests using another project). Is it possible to configure maven to only execute the selenium-maven-plugin?

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  • Barcode reading method?

    - by Atlas
    I recently acquired a Metrologic Barcode scanner (USB port), as everyone already knows it works as a keyboard emulator out of the box. Now my question, how do I configure the scanner and my application, so that my app can process the barcode data directly. That is, I don't want the user to focus on a "Text field" and then process the data when the KeyPress event fires.

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  • Problem detaching entire object graph in GAE-J with JDO

    - by tempy
    I am trying to load the full object graph for User, which contains a collection of decks, which then contains a collection of cards, as such: User: @PersistenceCapable(detachable = "true") @Inheritance(strategy = InheritanceStrategy.SUBCLASS_TABLE) @FetchGroup(name = "decks", members = { @Persistent(name = "_Decks") }) public abstract class User { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) protected Key _ID; @Persistent protected String _UniqueIdentifier; @Persistent(mappedBy = "_Owner") @Element(dependent = "true") protected Set<Deck> _Decks; protected User() { } } Each Deck has a collection of Cards, as such: @PersistenceCapable(detachable = "true") @FetchGroup(name = "cards", members = { @Persistent(name = "_Cards") }) public class Deck { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Key _ID; @Persistent String _Name; @Persistent(mappedBy = "_Parent") @Element(dependent = "true") private Set<Card> _Cards = new HashSet<Card>(); @Persistent private Set<String> _Tags = new HashSet<String>(); @Persistent private User _Owner; } And finally, each card: @PersistenceCapable public class Card { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Key _ID; @Persistent private Text _Question; @Persistent private Text _Answer; @Persistent private Deck _Parent; } I am trying to retrieve and then detach the entire object graph. I can see in the debugger that it loads fine, but then when I get to detaching, I can't make anything beyond the User object load. (No Decks, no Cards). At first I tried without a transaction to simply "touch" all the fields on the attached object before detaching, but that didn't help. Then I tried adding everything to the default fetch group, but that just generated warnings about GAE not supporting joins. I tried setting the fetch plan's max fetch depth to -1, but that didn't do it. Finally, I tried using FetchGroups as you can see above, and then retrieving with the following code: PersistenceManager pm = _pmf.getPersistenceManager(); pm.setDetachAllOnCommit(true); pm.getFetchPlan().setGroup("decks"); pm.getFetchPlan().setGroup("cards"); Transaction tx = pm.currentTransaction(); Query query = null; try { tx.begin(); query = pm.newQuery(GoogleAccountsUser.class); //Subclass of User query.setFilter("_UniqueIdentifier == TheUser"); query.declareParameters("String TheUser"); List<User> results = (List<User>)query.execute(ID); //ID = Supplied parameter //TODO: Test for more than one result and throw if(results.size() == 0) { tx.commit(); return null; } else { User usr = (User)results.get(0); //usr = pm.detachCopy(usr); tx.commit(); return usr; } } finally { query.closeAll(); if (tx.isActive()) { tx.rollback(); } pm.close(); } This also doesn't work, and I'm running out of ideas...

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  • Login form to an a secured app in tomcat

    - by patricio
    I have a normal HTML page in a normal Apache http server (http://yyy.yyy.yyy.yyy/index.html ), with an authentication form, with that form I need to access with the credentials to an application located in other server with diferent IP , that server have a secured application with tomcat: here is the login form in the apache http server: <form method="POST" id="theForm" action="http://xxx.xxx.xxx.xxx:8080/securedapp/j_security_check"> <input name="j_username" type="text" class="tx_form" id="j_username" size="20" /> <input name="j_password" type="password" class="tx_form" id="textfield2" size="20" /> <input name="btn" type="submit" value="login" /> </form> the submit only works random in chrome and dont work in IE and FF. im doing something wrong?

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  • How do I connect StaticListableBeanFactory with ClassPathXmlApplicationContext?

    - by Aaron Digulla
    In the setup of my test cases, I have this code: ApplicationContext context = new ClassPathXmlApplicationContext( "spring/common.xml" ); StaticListableBeanFactory testBeanFactory = new StaticListableBeanFactory(); How do I connect the two in such a way that tests can register beans in the testBeanFactory during setup and the rest of the application uses them instead of the ones defined in common.xml? Note: I need to mix a static (common.xml) and a dynamic configuration. I can't use XML for the latter because that would mean to write 1000 XML files.

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  • Why is J2EE scalable?

    - by py213py
    I heard from various sources that J2EE is highly scalable, but to me it seems that you could never scale a J2EE application to the level of the google search engine or any other large website. I would like to hear the technical reasons why it is so scalable.

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  • How to Prevent an Applet from Unloading across web pages?

    - by Francis Shanahan
    I have a large applet that takes some 40 seconds to initialize (cabs are cached so ignore download time for this question). The issue is, if the user goes to Page A which launches the applet (single window) and then navigates to page B, the applet is unloaded. If the user goes back to Page A, they incur the 40 seconds init time once again. I'd like to be able to launch the applet, incurring the 40 seconds init time once and only once. The applet needs to reside inside a single browser window (the same window as my web application). In other words, I cannot launch the applet in a popup. Does anyone have any creative ideas around how to prevent the applet unloading?

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