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  • Hibernate 1:M relationship ,row order, constant values table and concurrency

    - by EugeneP
    table A and B need to have 1:M relationship a and b are added during application runtime, so A created, then say 4 B's created. Each B instance has to come in order, so that I could later extract them in the same order as I added them. The app will be a web-app running on Tomcat, so 10 instances may work simultaneously. So my question are: 1) How to preserve inserting order, so that I could extract B instances that A references in the same order as I persisted them. That's tricky, because we add to a Collection and then it gets saved (am I right?). So, it depends on how Hibernate saves it, what if it changes the order in what we added instances? I've seen something like LIST instead of SET when describing relationships, is that what I need? 2) How to add a 3-rd column to B so that I could differentiate the instances, something like SEX(M,F,U) in B table. Do I need a special table, or there's and easy way to describe constants in Hibernate. What do you recommend? 3) Talking about concurrency, what methods do you recommend to use? There should be no collisions in the db and as you see, there might easily be some if rows are not inserted (PK added) right where it is invoked without delays ?

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  • Spring @Transactional - Can I Override rollbackFor

    - by user475039
    Hi all, I am calling a service which has the following annotation: @Transactional(rollbackFor=ExceptionA.class) public void myMethodA(....) throws ExceptionA { . . } I am calling this method from an other method in another Spring Bean. @Transactional(rollbackFor=ExceptionB.class) public void mainEntryPointMethod(....) throws ExceptionB { . try { myMethodA() } catch (ExceptionA exp) { . } . } My problem is that if myMethodA throws an exception, my transaction (which is passed from mainEntryPointMethod - myMethodA by default propagation) will be marked for rollback. Is there a way in which the 'rollbackFor' for the inner method can be overriden? Thanks in advance Chris

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  • Best practice for an application with GUI

    - by chronosphenomena
    Hi, I'm about to start an application which will have both console and GUI interfaces. What I wan't to achieve is COMPLETE decoupling of application logic from interface. In future, I may also add web interface, and I don't want to change anything in my application. Is there a good example (perhaps some open source project) where I can learn how this should be done properly.... also I'd appreciate advices/guidelines on how to do this. Thanks

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  • One log4j.xml - many scripts

    - by psed
    One of my utility jar files is used by different nix scripts, located in different categories. Problem: unable to initialize log4j framework (unable to find log4j.xml). Solution, that allows to configure logger correctly while launching jar classes by different scripts - usage of env vars and force configuring using DOMConfigurtor.configure(pathToConfXml) method. is it possible to avoid path hardcoding and configure logger inside of a script? Appreciate all your help. Thanks.

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  • A typical lifecycle of a Hibernate object in a web app - ?

    - by EugeneP
    Describe please a typical lifecycle of a Hibernate object (that maps to a db table) in a web app. Suppose, you create a new instance of an object and persist in the db. But during the app lifetime you'll be working on a detached object and finally you need to update it in the database, for example on exit. How does it look like with hibernate and spring? p.s. Can transactions and sessions live between servlet transitions? So that we opened 1 session and use it in all servlets without a need to reopen it?

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  • Why is this removing all elements from my LinkedList?

    - by Brian
    Why is my remove method removing every element from my Doubly Linked List? If I take out that if/else statements then I can successfully remove middle elements, but elements at the head or tail of the list still remain. However, I added the if/else statements to take care of elements at the head and tail, unfortunately this method now removes every element in my list. What am I do wrong? public void remove(int n) { LinkEntry<E> remove_this = new LinkEntry<E>(); //if nothing comes before remove_this, set the head to equal the element after remove_this if (remove_this.previous == null) head = remove_this.next; //otherwise set the element before remove_this equal to the element after remove_this else remove_this.previous.next = remove_this.next; //if nothing comes after remove_this, set the tail equal to the element before remove_this if (remove_this.next == null) tail = remove_this.previous; //otherwise set the next element's previous pointer to the element before remove_this else remove_this.next.previous = remove_this.previous; //if remove_this is located in the middle of the list, enter this loop until it is //found, then remove it, closing the gap afterwards. int i = 0; for (remove_this = head; remove_this != null; remove_this = remove_this.next) { //if i == n, stop and delete 'remove_this' from the list if (i == n) { //set the previous element's next to the element that comes after remove_this remove_this.previous.next = remove_this.next; //set the element after remove_this' previous pointer to the element before remove_this remove_this.next.previous = remove_this.previous; break; } //if i != n, keep iterating through the list i++; } }

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  • Focussing multiple selected values

    - by sarah
    Hi All, I have the following code <%for(int x = 0; x < skuList.size(); x++) {% "<%= skuList.get(x)% <%} % and i have check if the skuList has the data from the following list aUserForm.getData() if yes i have to show them selected,How can i do this ? I am displaying data as a list in mulitple selection box,the scenario of focus is on edit where in i need to preselect the already selected values.So i have skuList having all data and aUserForm.getData() has only preselected data,i just need to focus this the multi select box

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  • What's an effective way to reuse ArrayLists in a for loop?

    - by Patrick
    hi, I'm reusing the same ArrayList in a for loop, and I use for loop results = new ArrayList<Integer>(); experts = new ArrayList<Integer>(); output = new ArrayList<String>(); .... to create new ones. I guess this is wrong, because I'm allocating new memory. Is this correct ? If yes, how can I empty them ? Added: another example I'm creating new variables each time I call this method. Is this good practice ? I mean to create new precision, relevantFound.. etc ? Or should I declare them in my class, outside the method to not allocate more and more memory ? public static void computeMAP(ArrayList<Integer> results, ArrayList<Integer> experts) { //compute MAP double precision = 0; int relevantFound = 0; double sumprecision = 0; thanks

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  • What to prefer in the following case?

    - by GK
    say suppose I have class as : public class Age { private int age; public int getAge() { return this.age; } } In my Main class I am calling the getAge() method many times. So I wanted to know is it advisable to call so many times or call once and assign it to some variable and use that variable. Which is best and why?

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  • servlet authentication and further reference to the credentials

    - by user553592
    What I got so far: It all begins with an HTML form which prompts the user for a username and password. From there it post the acquired user/pass to a servlet, GateKeeper. GateKeeper determines if the user/pass combination match any records in the MySQL database. Here is the sql I use: SELECT id FROM Users WHERE username='?' AND password=MD5('?') where the ? indicate information provided the previous HTML form. What I need now: I need some way to store the username and id of the record in the database. GateKeeper redirects the user to a control panel upon success. Therefore, I need a method to reference the username to display simple greetings, etc and also the id so it eliminates unnecessary calls to the database. The control panel may make AJAX calls to Servlets that preform some sort of task to the MySQL database.

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  • Ordered Data Structure that allows to efficiently remove duplicate items

    - by devoured elysium
    I need a data structure that Must be ordered (adding elements a, b and c to an empty structure, will make them be at positions 0, 1 and 2). Allows to add repeated items. This is, I can have a list with a, b, c, a, b. Allows removing all ocurrences of a given item (if I do something like delete(1), it will delete all ocurrences of 1 in the structure). I can't really pick what the best data structure could be in here. I thought at first about something like a List(the problem is having an O(n) operation when removing items), but maybe I'm missing something? What about trees/heaps? Hashtables/maps? I'll have to assume I'll do as much adding as removing with this data structure. Thanks

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  • Design classes/interface to support methods returning different types

    - by Nayn
    Hi, I have classes as below. public interface ITest <T> { public T MethodHere(); } public class test1 implements ITest<String> { String MethodHere(){ return "Bla"; } } public class test2 implements ITest<Integer> { Integer MethodHere(){ return Integer.valueOf(2); } } public class ITestFactory { public static ITest getInstance(int type) { if(type == 1) return new test1(); else if(type == 2) return new test2(); } } There is a warning in the factory class that ITest is used as raw type. What modification should I do to get rid of it? Thanks Nayn

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  • MVC architecture EJB funcionallity

    - by Ignacio
    HI would like to understand how do ejbs work in an MVC architecture, what i do not get is: When the web app starts, the system creates an ejb for each record in every table of db or an ejb with all the records of all tables? Thank you very much

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  • question on reverse array

    - by davit-datuashvili
    we know algorithm how reverse array of n integers for (int i=0;i<n/2;i++){ swap(a[i],a[n-1-i]): } is this method better according the speed of algorithm or not because swap using xor is more fast then in other method here is code public class swap { public static void main(String[]args){ int a[]=new int[]{2,4,5,7,8,11,13,12,14,24}; System.out.println(" array at the begining:"); for (int i=0;i<a.length;i++){ System.out.println(a[i]); } for (int j=0;j<a.length/2;j++){ a[j]^=a[a.length-1-j]; a[a.length-1-j]^=a[j]; a[j]^=a[a.length-1-j]; } System.out.println("reversed array:"); for (int j=0;j<a.length;j++){ System.out.println(a[j]); } } } Result: array at the begining: 2 4 5 7 8 11 13 12 14 24 reversed array: 24 14 12 13 11 8 7 5 4 2

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