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  • J2EE and alternatives

    - by Ilya K
    Hello, I am J2SE developer but I have rich web-background (php, perl/cgi and so on) and now I am starting new project. It will have web interface, spaghetti business logic, relational database as storage and connections to other services. I do it from the scratch. My colleagues told me to use spring, spring security and struts. I look briefly at J2EE spec and found that it covers almost all aspects of enterprise application. I asked my colleagues why do they need spring and struts, but looks like they use technologies simply because they are familiar with them and not familiar with classic J2EE stack. So, my question is: what is bad about J2EE? Why do I need spring if there are JNDI lookups? It will take a day or two to create fake InitialContext for unit-tests. And that is all: I stand with out of external tools like spring. Why do I need spring-security if there is a security built in Servlets spec? I can map any request to any servlet using web.xml, no struts.xml is needed. I can use servlet-filters instead of struts interceptors. There is RMI, so I do not need spring-remote. And so on.. Why should I bother my self with all that fancy stuff if there is J2EE? I really want to find situation when J2EE is not enough. Do you have any? Thanks!

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  • How can CopyOnWriteArrayList be thread-safe?

    - by Shooshpanchick
    I've taken a look into OpenJDK's sources of CopyOnWriteArrayList and it seems that all write operations are protected by the same lock and read operations are not protected at all. As I understand, under JMM all accesses to a variable (both read and write) should be protected by lock or reordering effects may occur. For example, set(int, E) method contains these lines (under lock): /* 1 */ int len = elements.length; /* 2 */ Object[] newElements = Arrays.copyOf(elements, len); /* 3 */ newElements[index] = element; /* 4 */ setArray(newElements); The get(int) method, on the other hand, only does return get(getArray(), index);. In my understanding of JMM, this means that get may observe the array in an inconsistent state if statements 1-4 are reordered like 1-2(new)-4-2(copyOf)-3. Do I understand JMM incorrectly or is there any other explanations on why CopyOnWriteArrayList is thread-safe?

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  • ArrayBlockingQueue exceeds given capacity

    - by Wojciech Reszelewski
    I've written program solving bounded producer & consumer problem. While constructing ArrayBlockingQueue I defined capacity 100. I'm using methods take and put inside threads. And I've noticed that sometimes I see put 102 times with any take's between them. Why does it happen? Producer run method: public void run() { Object e = new Object(); while(true) { try { queue.put(e); } catch (InterruptedException w) { System.out.println("Oj, nie wyszlo, nie bij"); } System.out.println("Element added"); } } Consumer run method: public void run() { while(true) { try { queue.take(); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("Element removed"); } } Part of uniq -c on file with output: 102 Element removed 102 Element added 102 Element removed 102 Element added 102 Element removed 102 Element added 102 Element removed 102 Element added 102 Element removed 102 Element added 102 Element removed 102 Element added 2 Element removed 2 Element added 102 Element removed 102 Element added

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  • biginteger calculation problem

    - by murali
    I am using the following code but the parameters are not passed to the methods. BigInteger p = BigInteger.valueOf(0); BigInteger u1 = obj.bigi_calc(g1, l); In this g1,l are long values. The method is private BigInteger bigi_calc(long g1, long l){ BigInteger cal = BigInteger.valueOf(g1); BigInteger cal1= BigInteger.valueOf(l); for(BigInteger f = BigInteger.ONE;f.compareTo(cal1)>0;f=f.add(BigInteger.ONE)){ //BigInteger p= BigInteger.valueOf(0); p = cal.multiply(cal1); System.out.println("check p"+p); } // System.out.println("check p"+p); return p; } The elipse shows that it may be out of sync, but the parameters are not passed to the functions. Can you please help me to solve this problem?

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  • Long primitive or AtomicLong for a counter?

    - by Rich
    Hi I have a need for a counter of type long with the following requirements/facts: Incrementing the counter should take as little time as possible. The counter will only be written to by one thread. Reading from the counter will be done in another thread. The counter will be incremented regularly (as much as a few thousand times per second), but will only be read once every five seconds. Precise accuracy isn't essential, only a rough idea of the size of the counter is good enough. The counter is never cleared, decremented. Based upon these requirements, how would you choose to implement your counter? As a simple long, as a volatile long or using an AtomicLong? Why? At the moment I have a volatile long but was wondering whether another approach would be better. I am also incrementing my long by doing ++counter as opposed to counter++. Is this really any more efficient (as I have been led to believe elsewhere) because there is no assignment being done? Thanks in advance Rich

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  • Why is 1942/4/3 00:00:00 an illegal date in java.util.Calendar?

    - by Aleksi
    Is there something special in the date 3rd of April 1942? For some reason the the hour of day 0 (12:00 am) is illegal for this specific date. The date is accepted when a lenient calendar is used but the hour of day is incremented to 1 (1:00 am). Relevant code java.util.Calendar calendar = java.util.Calendar.getInstance(); calendar.clear(); calendar.setLenient(false); calendar.set(1942, 3, 3, 0, 0, 0); calendar.getTimeInMillis(); Exception java.lang.IllegalArgumentException: HOUR_OF_DAY at java.util.GregorianCalendar.computeTime(Unknown Source) at java.util.Calendar.updateTime(Unknown Source) at java.util.Calendar.getTimeInMillis(Unknown Source) I'd really prefer is the dates were not lenient as I don't want to accept impossible dates.

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  • @Intertceptors does not work for web bean for JSF page.

    - by Drevlyanin
    @Named @ConversationScoped @Interceptors(MyInterceptor.class) public class BeanWeb implements Serializable { public String methodThrowException throws Exception() { throws new Exception(); } } public class MyInterceptor { @AroundInvoke public Object intercept(InvocationContext ic) throws Exception { try { return ic.proceed(); } catch (Exception e) { return null; } } } For @Stateless beans interceptor works, but for the BeanWeb interceptor does not work. And we have never entered into "intercept" method. Why is this happening? How could intercept method calls in BeanWeb? P.S.: All this spin under Glassfish 3.x.

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  • Third Party Libraries and Technologies very Java Programmer must be aware of?

    - by kunjaan
    I agree that this is a very subjective question but as a student of Java , I get suggested good libraries and technologies for Java by my mentors at work. For example, I was not aware of Google Guice for Dependency Injection, awesomeness of Java Reflection APIs, ORMs like Hibernate or stuffs you could do with libraries like Hadoop. I want to collect and share some of the libraries that exemplifies good java programming (so that beginners like me could code walk and emulate the coding practice), teach unique concepts to Java (for example Dependency Injections or ORM) and/or are really interesting libraries that a student like me would get to do interesting projects on (eg. Hadoop). I redited this question 3 times to make it more specific : ). I am sorry if I am really not clear in my intentions. But some kind of a list of good concepts and third party libraries for Java could really help some of my intern friends here at work. Thank you.

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  • afterTransactionCompletion not working

    - by Attilah
    I created an hibernate interceptor : public class MyInterceptor extends EmptyInterceptor { private boolean isCanal=false; public boolean onSave(Object entity, Serializable arg1, Object[] arg2, String[] arg3, Type[] arg4) throws CallbackException { for(int i=0;i<100;i++){ System.out.println("Inside MyInterceptor(onSave) : "+entity.toString()); } if(entity instanceof Canal){ isCanal=true; } return false; } public void afterTransactionCompletion(Transaction tx){ if(tx.wasCommitted()&&(isCanal)){ for(int i=0;i<100;i++){ System.out.println("Inside MyInterceptor(afterTransactionCompletion) : Canal was saved to DB."); } } } but the method afterTransactionCompletion doesn't get executed after a transaction is commited. I've tried all the ways I know of but I can't make it work. What's more surprising is that the onSave method works fine. Help ! Could this be due to this bug ? : http://opensource.atlassian.com/projects/hibernate/browse/HHH-1956 How can I circumvent this bug if it's the cause ?

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  • EJB3.1 logout doesn't work

    - by Kevin
    Hello, I've got a problem with the authentication features of EJB3.1: With this code in a Servlet v3: log.info(""+request.getUserPrincipal()); log.info(""+request.getAuthType()); log.info("===^==="); request.logout() ; log.info(""+request.getUserPrincipal()); log.info(""+request.getAuthType()); request.authenticate(response) ; log.info("===v==="); log.info(""+request.getUserPrincipal()); log.info(""+request.getAuthType()); I would always expect to see the Username/login windows, because of the logout() function. Instead, it seems to be a 'cache' mechanism which repopulate the credential and cancel my logout ... Admin BASIC ===^=== null null ===v=== Admin BASIC is it a problem with my firefox, or something I'm missing in the Servlet code? Thanks

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  • JPA @version - can it be used to calcualate version of a table entry

    - by OpenSource
    Hi, Please consider the following table (created using a corresponding entity) request ------- id requestor type version items 1 a t1 1 5 2 a t1 2 3 3 b t1 1 2 4 a t2 1 4 5 a t1 3 9 The above is what I want to achieve. The version field is a calculated field others are user provided. Basically the request's version needs to be calculated based on the combination of requestor and the type. The first occurance with a given combination will have a version 1 then version 2 and so on. I tried various things using @version on a different entity with just the three columns and joining the two entities using ManytoOne etc but I'm not able to get to the desired outcome. I dont want to confuse you with the things I tried. Since the objective is simple there should be an easier way I suppose? Can you please help? - any help greatly appreciated! thanks in advance

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  • How do I make defensive copy of an object?

    - by kunjaan
    How do I make defensive copies of a Mutable Object which contains a mutable field in an Immutable Object? class ImmutableObject { private final MutableObject immutable_field; ImmutableObject(MutableObject y) { this.immutable_field = y; } MutableObject return_immutable_field() { return immutable_field; } } class MutableObject { public int mutable_field; } The MutableObject does not have a constructor that lets me set the field. The MutableObject's current state should be captured in the Immutable Object and never changed.

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  • Third Party Libraries and Technologies every Java Programmer must be aware of?

    - by kunjaan
    I agree that this is a very subjective question but as a student of Java , I get suggested good libraries and technologies for Java by my mentors at work. For example, I was not aware of Google Guice for Dependency Injection, awesomeness of Java Reflection APIs, ORMs like Hibernate or stuffs you could do with libraries like Hadoop. I want to collect and share some of the libraries that exemplifies good java programming (so that beginners like me could code walk and emulate the coding practice), teach unique concepts to Java (for example Dependency Injections or ORM) and/or are really interesting libraries that a student like me would get to do interesting projects on (eg. Hadoop). I redited this question 3 times to make it more specific : ). I am sorry if I am really not clear in my intentions. But some kind of a list of good concepts and third party libraries for Java could really help some of my intern friends here at work. Thank you.

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  • Reference to an instance method of a particular object

    - by Andrey
    In the following code, if i try to pass method reference using the class name, works. But passing the reference variable compiler gives an error, i do not understand why? public class User { private String name; public User(String name) { this.name = name; } public void printName() { System.out.println(name); } } public class Main { public static void main(String[] args) { User u1 = new User("AAA"); User u2 = new User("BBB"); User u3 = new User("ZZZ"); List<User> userList = Arrays.asList(u1, u2, u3); userList.forEach(User::printName); // works userList.forEach(u1::printName); // compile error } } Thanks,

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  • Why did you stop using Tapestry?

    - by ntownsend
    This question goes out to those who have used Tapestry as a web framework and then either gave it up or switched to something else, or even ported their application from Tapestry to something else. The question is why? What led you to make this change? EDIT: Also, what framework (if any) did you change to?

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  • Filter---after setting attribute--->Servlet---after getting and setting the attribute---->Jsp How do I do this?

    - by Y.E.P
    This is what I want to do : A servlet is called.Before a servlet is called , the request is intercepted by a filter. Filter gets some details out from the request,sets them as an attribute and the forwards it to a servlet via chain.doFilter(request,response). Request finally reaches the servlet. Servlet gets the attribute set by the filter before and sets a new attribute by another name. Then it forwards it to some jsp page where the page gets the attribute and processes it. How do I do this ? I know how to write a filter and a servlet but how do I forward it to a jsp page from the servlet or is there any other way to achieve this ?

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  • JAAS : on Callback ( Interesting based on HTTP headers )

    - by VJS
    I am using NameCallback and PasswordCallback for username and password.For username and password, popup comes on browser and when i enter username ans password, JAAS authenticates my request. On the wireshark, I have seen that 401 Unauthorized message (WWW-Authenticate header)comes and when i enter username/password HTTP request with credentials generate ( with Authorization header) and goes to server. My requirement : I don't want pop up to come.My application on other server having username / password, so once it received 401 then based on some logic it will generate HTTP request with Authorization header / credentials and sent it back. FLow : User - Other Server - My Tomcat5.5 Here on Other Server, nobody is available to enter username/password manually.Application is deployed and it will only generate HTTP request with credential and sent it back to tomcat. Can we have any other callback which behave like this.Need your help.Please provide me feedback as well related to approach.

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  • How to maintain GridPane's fixed-size after adding elemnts dynamically

    - by Eviatar G.
    I need to create board game that can be dynamically change. Its size can be 5x5, 6x6, 7x7 or 8x8. I am jusing JavaFX with NetBeans and Scene builder for the GUI. When the user choose board size greater than 5x5 this is what happens: This is the template on the scene builder before adding cells dynamically: To every cell in the GridPane I am adding StackPane + label of the cell number: @FXML GridPane boardGame; public void CreateBoard() { int boardSize = m_Engine.GetBoard().GetBoardSize(); int num = boardSize * boardSize; int maxColumns = m_Engine.GetNumOfCols(); int maxRows = m_Engine.GetNumOfRows(); for(int row = 0; row < maxRows ; row++) { for(int col = maxColumns - 1; col >= 0 ; col--) { StackPane stackPane = new StackPane(); stackPane.setPrefSize(150.0, 200.0); stackPane.getChildren().add(new Label(String.valueOf(num))); boardGame.add(stackPane, col, row); num--; } } boardGame.setGridLinesVisible(true); boardGame.autosize(); } The problem is the stack panes's size on the GridPane are getting smaller. I tried to set them equal minimum and maximum size but it didn't help they are still getting smaller. I searched on the web but didn't realy find same problem as mine. The only similar problem to mine was found here: Dynamically add elements to a fixed-size GridPane in JavaFX But his suggestion is to use TilePane and I need to use GridPane because this is a board game and it more easier to use GridPane when I need to do tasks such as getting to cell on row = 1 and column = 2 for example. EDIT: I removed the GridPane from the FXML and created it manually on the Controller but now it print a blank board: @FXML GridPane boardGame; public void CreateBoard() { int boardSize = m_Engine.GetBoard().GetBoardSize(); int num = boardSize * boardSize; int maxColumns = m_Engine.GetNumOfCols(); int maxRows = m_Engine.GetNumOfRows(); boardGame = new GridPane(); boardGame.setAlignment(Pos.CENTER); Collection<StackPane> stackPanes = new ArrayList<StackPane>(); for(int row = 0; row < maxRows ; row++) { for(int col = maxColumns - 1; col >= 0 ; col--) { StackPane stackPane = new StackPane(); stackPane.setPrefSize(150.0, 200.0); stackPane.getChildren().add(new Label(String.valueOf(num))); boardGame.add(stackPane, col, row); stackPanes.add(stackPane); num--; } } this.buildGridPane(boardSize); boardGame.setGridLinesVisible(true); boardGame.autosize(); boardGamePane.getChildren().addAll(stackPanes); } public void buildGridPane(int i_NumOfRowsAndColumns) { RowConstraints rowConstraint; ColumnConstraints columnConstraint; for(int index = 0 ; index < i_NumOfRowsAndColumns; index++) { rowConstraint = new RowConstraints(3, Control.USE_COMPUTED_SIZE, Double.POSITIVE_INFINITY, Priority.ALWAYS, VPos.CENTER, true); boardGame.getRowConstraints().add(rowConstraint); columnConstraint = new ColumnConstraints(3, Control.USE_COMPUTED_SIZE, Double.POSITIVE_INFINITY, Priority.ALWAYS, HPos.CENTER, true); boardGame.getColumnConstraints().add(columnConstraint); } }

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  • JDBC Pagination

    - by Zeeshan
    Hi, I want to implement pagination using JDBC. The actual thing I want to know is "How can i get first 50 and then next 50 records from database for page 1 and 2 respectively" My Query is Select * from data [data table contains 20,000 rows] For page #1 I get 50 records and for page #2 I want to get next 50 records. How can I implement it efficiently in JDBC? I have searched and found that rs.absolute(row) is the way to skip first page records but it takes some amount of time on large result sets and I don't want to bear this amount of time. Also, I don't want to use rownum and limit + offset in query because these are not good to use in query, I dont know why, still I don't want to use it in query. Can anyone help me how to get limited ResultSet for pagination or is there any way JDBC is giving us?

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