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  • Does Socket open another thread? Does it return something?

    - by Roman
    In the client application I call new Socket(serverIP,serverPort). As a result the client application sends a request to the server application to open a socket. Does it start a new thread? I mean which of the following is true? Client application sends a request and immediately starts to execute following commands (not weighting for the answer). Client sends the request and weights for the answer. As soon as the answer is obtained, the client application continues to execute following commands. The second case seems to be more realistic and logical for me. However, I do not understand what happens if the server does not open a socket and it does not say that it does not "want" to open the second (it can happen if the server does not exist or network is broken). What will happen in this case? Will server weight forever? In general it would be nice for the client to know what is the result of its request for the socket. For example I can imagine the following situations: The socket is opened by the server. The server refuses to open a socket. So, server exists, it got the request from the client but it says "no". There is no response from the server. I know that new Socket(serverIP,serverPort) does not "return" this kind of information. But it throws exceptions. One of them is "UnkownHostException". When it is thrown? When the server is not responding for a while (for how long)? ADDED: I just found out that UnknownHostException is thrown to indicate that the IP address of a host could not be determined. So, it is unrelated with the above described situations (server is not responding, server refuses to open a socket).

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  • A beginner's log4J question

    - by Nitesh Panchal
    Hello, i configured log4j for basic purpose usin the conversion pattern :- log4j.appender.rollingFile.layout.ConversionPattern=%p %t %c - %m%n But now i want to log the class name from which the error came as well as the username(available in session object) as well as the date and time when that event occurs. How do i do this? What changes do i need to make in format string? Thanks in advance :)

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  • JUnit 4 test suite problems

    - by Hypnus
    Hi, i have a problem with some JUnit 4 tests that i run with a test suite. If i run the tests individually they work with no problems but when run in a suite most of them, 90% of the test methods, fail with errors. What i noticed is that always the first tests works fine but the rest are failing. Another thing is that a few of the tests the methods are not executed in the right order (the reflection does not work as aspected - or it does because the retrieval of the methods is not necessarily in the created order). This usually happens if there is more than one test with methods that have the same name. I tried to debug some of the tests and it seems that from a line to the next the value of some attributes gets null. Does anyone know what is the problem, or if the behavior is "normal"? Thanks in advance.

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  • prefix and postfix increments while comparing variables

    - by miatech
    could someone explain why this code output is not equals not equals 2 in the first if statement it seems that a = 0 b/c is a postfix increment; therefore a will not increase untile next line; however, the two a's are not equal why? and in the second if when I run the debugger the value of a is 2, but the test is false, why? public static void main (String[] args) { int a = 0; if (a++ == a++) { System.out.println("equals"); } else { System.out.println("not equals"); } if (++a == 2) { System.out.println("equals 2"); } else { System.out.println("not equals 2"); } }

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  • Image creation performance / image caching

    - by Kilnr
    Hello, I'm writing an application that has a scrollable image (used to display a map). The map background consists of several tiles (premade from a big JPG file), that I draw on a Graphics object. I also use a cache (Hashtable), to prevent from having to create every image when I need it. I don't keep everything in memory, because that would be too much. The problem is that when I'm scrolling through the map, and I need an image that wasn't cached, it takes about 60-80 ms to create it. Depending on screen resolution, tile size and scroll direction, this can occur multiple times in one scroll operation (for different tiles). In my case, it often happens that this needs to be done 4 times, which introduces a delay of more than 300 ms, which is extremely noticeable. The easiest thing for me would be that there's some way to speed up the creation of Images, but I guess that's just wishful thinking... Besides that, I suppose the most obvious thing to do is to load the tiles predictively (e.g. when scrolling to the right, precache the tiles to the right), but then I'm faced with the rather difficult task of thinking up a halfway decent algorithm for this. My actual question then is: how can I best do this predictive loading? Maybe I could offload the creation of images to a separate thread? Other things to consider? Thanks in advance.

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  • multiple search fields

    - by user234194
    What will be the best approach if I have search fields for 20 or more and any combination should be valid. Is there any special way to do it in openJPA or native SQL is better. Any idea would be helpful.Thanks.

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  • multiple search fields

    - by user234194
    What will be the best approach if I have search fields for 20 or more and any combination should be valid. Is there any special way to do it in openJPA or native SQL is better. Any idea would be helpful.Thanks.

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  • How to calculate "holes" in timetable

    - by genesiss
    I've got a 2-dimensional array like this (it represents a timetable): http://www.shrani.si/f/28/L6/37YvFye/timetable.png Orange cells are lectures and whites are free time. How could I calculate number of free hours between lectures in the same day? (columns are days and rows are hours) For example, in this table the result should be: 2 for first column 0 for second colum -- The function returns 2 (because 2+0=2)

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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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  • What does the exception "javax.servlet.jsp.JspException: Broken pipe" signify?

    - by Ruepen
    I'm getting the following error: javax.servlet.jsp.JspException: Broken pipe Now I have seen questions/answers with respects to the socket exception, but this error is coming from a different package. Any help is greatly appreciated. BTW, I am seeing quite a lot of these errors in a struts web app Weblogic Node logs and I am thinking that it has to do with end users closing their web browser before the page reloads/executes the next step (database transaction which takes quite a bit of time to execute, anywhere from 30 seconds to 4 mins).

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  • Modular Inverse and BigInteger division

    - by dano82
    I've been working on the problem of calculating the modular inverse of an large integer i.e. a^-1 mod n. and have been using BigInteger's built in function modInverse to check my work. I've coded the algorithm as shown in The Handbook of Applied Cryptography by Menezes, et al. Unfortunately for me, I do not get the correct outcome for all integers. My thinking is that the line q = a.divide(b) is my problem as the divide function is not well documented (IMO)(my code suffers similarly). Does BigInteger.divide(val) round or truncate? My assumption is truncation since the docs say that it mimics int's behavior. Any other insights are appreciated. This is the code that I have been working with: private static BigInteger modInverse(BigInteger a, BigInteger b) throws ArithmeticException { //make sure a >= b if (a.compareTo(b) < 0) { BigInteger temp = a; a = b; b = temp; } //trivial case: b = 0 => a^-1 = 1 if (b.equals(BigInteger.ZERO)) { return BigInteger.ONE; } //all other cases BigInteger x2 = BigInteger.ONE; BigInteger x1 = BigInteger.ZERO; BigInteger y2 = BigInteger.ZERO; BigInteger y1 = BigInteger.ONE; BigInteger x, y, q, r; while (b.compareTo(BigInteger.ZERO) == 1) { q = a.divide(b); r = a.subtract(q.multiply(b)); x = x2.subtract(q.multiply(x1)); y = y2.subtract(q.multiply(y1)); a = b; b = r; x2 = x1; x1 = x; y2 = y1; y1 = y; } if (!a.equals(BigInteger.ONE)) throw new ArithmeticException("a and n are not coprime"); return x2; }

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  • I love programming but i also want to learn hardware. [closed]

    - by user167082
    I like programming so much, i did it since i was 10, and i believe that studying computer science will make a lot of money as well as i love it. However I also want to learn hardware. I don't only want to do programming all the time without knowing the architecture of device that i program. I asked my teacher, and she said that if I get into computer science, i won't learn anything about hardware, is it true?(She graduated from u-dub) In the other hand, my math teacher told me to get into electrical engineering, since it also contain programming. The thing is that i want to emphasize my study to programming while learning some about hardware. What is major that suits me the best? Can i take some hardware courses if I get into computer science major? Thanks a lot.

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  • utf-8 convertion doesn't work always

    - by Marco Piccinni
    I searched into other stack before to type here and I didn't find anythong similar. I have to scrape different utf-8 webpages which contain text like "Oggi è una bellissima giornata" the problem is on the characther "è" I extract this text with jtidy and xpath query expression and I convert it with byte[] content = filteredEncodedString.getBytes("utf-8"); String result = new String(content,"utf-8"); where filteredEncodedString contains the text "Oggi è una bellissima giornata". This procedures works on the most webpages analyzed so far but in some case it doesn't extract a utf-8 string. Page encoding is always the same as the text is similar. Any ideas about the problem? thanks Marco

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  • Is there a better way than a sequence of if's to handle events?

    - by Matt
    I recently ran across several objects implemented to handle events with a hard coded mapping using this pattern: public void handleEvent(Event event) { if(event.getCode() == SOME_STATIC_EVENT) doSomething(event); if(event.getCode() == ANOTHER_STATIC_EVENT) doSomethingElse(event); } where doSomething functions are implemented as methods of the same class. In hopes of striving for looser coupling, how would you suggest abstracting out this pattern? Also, what's the best approach for mapping 0..N functions to a fired event?

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  • user access management in j2ee web application

    - by kawtousse
    Hi everyone, I am working with jsp/servlet project and i have to complete the module of access management to my jsps since I have more than one user with different profile. I defined a table in my database wich resume the profil and the url permitted like that: id_profil :1 url : http://localhost/...xyz.jsp id page 1 Now I am trying to let the menu modified appropriately to the id_profil of the logged user. So there are pages allowed in one profile but must be hidden to others. I have no idea since now how to realize this and it is so important for me. thanks for your help.

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  • Can Spring access-denied-handler refer to popup?

    - by Rens Groenveld
    I am working with Spring Security 3.1.x and have implemented method annotation securities. As I want, when I perform a certain action while being logged in as a used that doesn't have the rights, I get a 403 acces is denied in my console! Perfect! Now I would like to catch this 403, and give the user a popup with a custom message. I don't want to redirect users to a page saying that they have no rights. Is there any way the access-denied-handler of Spring can take care of a popup? Or can it only redirect to another page? Maybe there are other options for me? Thanks in advance!

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  • Can I write a module/filter that gets fired before the web app get's run in Tomcat?

    - by Blankman
    Can I write a module/filter that gets put into the processing pipleline in Tomcat BEFORE the web application even gets run? Something that I could turn on/off for each web application that tomcat is handling. is this possible? So basically it would be a re-usable filter that hooks into the web pipeline that could alter the requests behavior or perform/modify the requests. One example would be to log all ip's, or redirect based on the url, block the request, etc.

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  • What does assert do?

    - by peiska
    What does assert do? for example in the function? private static int charAt(String s, int d) { assert d >= 0 && d <= s.length(); if (d == s.length()) return -1; return s.charAt(d); }

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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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  • How to handle injecting dependencies into rich domain models?

    - by Arne
    In a web server project with a rich domain model (application logic is in the model, not in the services) how do you handle injecting the dependencies into the model objects? What are your experiences? Do you use some form of AOP? Like Springs @Configurable annotation? Load time or build time weawing? Problems you encountered? Do you use manual injection? Then how do you handle different instantiation scenarios (creating of the objects through an library [like Hibernate], creating objects with "new" ...)? Or do you use some other way of injecting the dependencies?

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  • How to calculate Centered Moving Average of a set of data in Hadoop Map-Reduce?

    - by 100gods
    I want to calculate Centered Moving average of a set of Data . Example Input format : quarter | sales Q1'11 | 9 Q2'11 | 8 Q3'11 | 9 Q4'11 | 12 Q1'12 | 9 Q2'12 | 12 Q3'12 | 9 Q4'12 | 10 Mathematical Representation of data and calculation of Moving average and then centered moving average Period Value MA Centered 1 9 1.5 2 8 2.5 9.5 3 9 9.5 3.5 9.5 4 12 10.0 4.5 10.5 5 9 10.750 5.5 11.0 6 12 6.5 7 9 I am stuck with the implementation of RecordReader which will provide mapper sales value of a year i.e. of four quarter. The RecordReader Problem Question Thread Thanks

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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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