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  • How to drop/restart a client connection to a flaky socket server

    - by Steve Prior
    I've got Java code which makes requests via sockets from a server written in C++. The communication is simply that the java code writes a line for a request and the server then writes a line in response, but sometimes it seems that the server doesn't respond, so I've implemented an ExecutorService based timeout which tries to drop and restart the connection. To work with the connection I keep: Socket server; PrintWriter out; BufferedReader in; so setting up the connection is a matter of: server = new Socket(hostname, port); out = new PrintWriter(new OutputStreamWriter(server.getOutputStream())); in = new BufferedReader(new InputStreamReader(socket.getInputStream())); If it weren't for the timeout code the request/receive steps are simply: String request="some request"; out.println(request); out.flush(); String response = in.readLine(); When I received a timeout I was trying to close the connection with: in.close(); out.close(); socket.close(); but one of these closes seems to block and never return. Can anyone give me a clue why one of these would block and what would be the proper way to abandon the connection and not end up with resource leak issues?

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  • Is there a way to make sure classes implementing an Interface implement static methods?

    - by Tobias Kienzler
    Frist of all, I read erickson's usefull reply to "Why can’t I define a static method in a Java interface?". This question is not about the "why" but about the "how then?". So basically I want one Interface to provide both usual methods and e.g. a getSimilarObject method. For (a made up) example public interface ParametricFunction { /** @return f(x) using the parameters */ static abstract public double getValue(double x, double[] parameters); /** @return The function's name */ static abstract public String getName(); } and then public class Parabola implements ParametricFunction { /** @return f(x) = parameters[0] * x² + parameters[1] * x + parameters[2] */ static public double getValue(double x, double[] parameters) { return ( parameters[2] + x*(parameters[1] + x*parameters[0])); } static public String getName() { return "Parabola"; } } Since this is not allowed in the current Java standard, what is the closest thing to this? The idea behind this is putting several ParametricFunction's in a package and use Reflection to list them all, allowing the user to pick e.g. which one to plot. Obviously one could provide a loader class containing an array of the available ParametricFunction's, but every time a new one is implemented one has to remember adding it there, too.

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  • Hibernate not loading associated object

    - by Noor
    Hi, i am trying to load a hibernate object ForumMessage but in it contain another object Users and the Users object is not being loaded. My ForumMessage Mapping File: <?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <!-- Generated Jan 4, 2011 10:10:29 AM by Hibernate Tools 3.4.0.Beta1 --> <hibernate-mapping> <class name="com.BiddingSystem.Models.ForumMessage" table="FORUMMESSAGE"> <id name="ForumMessageId" type="long"> <column name="FORUMMESSAGEID" /> <generator class="native" /> </id> <property name="ForumMessage" type="java.lang.String"> <column name="FORUMMESSAGE" /> </property> <many-to-one name="User" class="com.BiddingSystem.Models.Users" fetch="join"> <column name="UserId" /> </many-to-one> <property name="DatePosted" type="java.util.Date"> <column name="DATEPOSTED" /> </property> <many-to-one name="Topic" class="com.BiddingSystem.Models.ForumTopic" fetch="join"> <column name="TopicId" /> </many-to-one> </class> </hibernate-mapping> and I am using the follwing code: Session session = gileadHibernateUtil.getSessionFactory().openSession(); SQL="from ForumMessage"; System.out.println(SQL); Query query=session.createQuery(SQL); System.out.println(query.list().size()); return new LinkedList <ForumMessage>(query.list());

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  • Detecting TCP dropout over an unreliable network

    - by yx
    I am doing some experimentation over an unreliable radio network (home brewed) using very rudimentary java socket programming to transfer messages back and forth between the end nodes. The setup is as follows: Node A --- Relay Node --- Node B One problem I am constantly running into is that somehow the connection drops out and neither Node A or B knows that the link is dead, and yet continues to transmit data. The TCP connection does not time out either. I have added in a heartbeat message that causes a timeout after a while, but I still would like to know what is the underlying cause of why TCP does not time out. Here are the options I am enabling when setting up a socket: channel.socket().setKeepAlive(false); channel.socket().setTrafficClass(0x08); // for max throughput This behavior is strange since it is totally different than when I have a wired network. On a wired network, I can simulate a disconnected connection by pulling out the ethernet cord, however, once I plug the cord back in, the connection becomes restablished and messages begin to be passed through once more. On the radio network, the connection is never reestablished and once it silently dies, the messages never resume. Is there some other unknown java implentation or setting for a socket that I can use, also, why am I seeing this behavior in the first place? And yes, before anyone says anything, I know TCP is not the preffered choice over an unreliable network, but in this case I wanted to ensure no packet loss.

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  • JMS message. Model to include data or pointers to data?

    - by John
    I am trying to resolve a design difference of opinion where neither of us has experience with JMS. We want to use JMS to communicate between a j2ee application and the stand-alone application when a new event occurs. We would be using a single point-to-point queue. Both sides are Java-based. The question is whether to send the event data itself in the JMS message body or to send a pointer to the data so that the stand-alone program can retrieve it. Details below. I have a j2ee application that supports data entry of new and updated persons and related events. The person records and associated events are written to an Oracle database. There are also stand-alone, separate programs that contribute new person and event records to the database. When a new event occurs through any of 5-10 different application functions, I need to notify remote systems through an outbound interface using an industry-specific standard messaging protocol. The outbound interface has been designed as a stand-alone application to support scalability through asynchronous operation and by moving it to a separate server. The j2ee application currently has most of the data in memory at the time the event is entered. The data would consist of approximately 6 different objects; a person object and some with multiple instances for an average size in the range of 3000 to 20,000 bytes. Some special cases could be many times this amount. From a performance and reliability perspective, should I model the JMS message to pass all the data needed to create the interface message, or model the JMS message to contain record keys for the data and have the stand-alone Java application retrieve the data to create the interface message?

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  • Experiences wanted: producing a jar artifact in IntelliJ

    - by skiaddict1
    Developing with IntelliJ 9.0.2 Community Edition, on the Mac. This is a follow-up to this post about including jar files in an artifact, which has not received any replies. I'm hoping that the reason is that somehow, in creating my artifact (or setting my project settings), I unwittingly did something which people don't tend to do, and which is causing my problem, and that by asking people here to share how they create jar artifacts and set up projects, I will discover what it is. To recap: I have a Java project which depends on two library files. I need to package up the entire thing, with the jars inlined (such that on doing jar -tfv <filename> I see ALL the classes listed, including the ones in the two libraries), into a single jar file. I can make an artifact, I can add the library files to the Output Layout pane, but I CANNOT, no matter what I do, I cannot get the "Inline Artifact" item in the context menu to be selectable (i.e. non-grey) when I right-click on one or other library file. The thing is, making a jar which contains library files as well as the project code is NOT an unusual situation in the Java world! So I figure there are lots of IntelliJ folks out there who have done what I need to do. And I would really like to hear from you folks. What project settings do you use? (be specific, please :-) And exactly how do you set up your jar artifacts? (again, as many specific details as possible, please :-) Clearly, I'd be particularly interested to hear from folks with similar setups to mine (above) who are successfully doing what I need to do. Grateful thanks in advance, folks.

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  • date() returning wrong day although the timestamp is correct!

    - by Spiros
    I have a bizzare problem with php date function. code: $numDays = 8; $date = strtotime('2010-11-06'); for ($i=1; $i<=$numDays; $i++) { $thisDay = date("D, d M Y", $date); print ($thisDay.'<br>'); $date+=86400; // add one day to timestamp } result on my server (local host, windows): Sat, 06 Nov 2010 Sun, 07 Nov 2010 Mon, 08 Nov 2010 Tue, 09 Nov 2010 Wed, 10 Nov 2010 Thu, 11 Nov 2010 Fri, 12 Nov 2010 Sat, 13 Nov 2010 Result on my web server (linux) Sat, 06 Nov 2010 *Sun, 07 Nov 2010 Sun, 07 Nov 2010* Mon, 08 Nov 2010 Tue, 09 Nov 2010 Wed, 10 Nov 2010 Thu, 11 Nov 2010 Fri, 12 Nov 2010 Notice how Sun, 07 Nov 2010 appears twice on the remote server?? Why is this happening? can anyone explain this Behavior?

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  • Using enum values to represent binary operators (or functions)

    - by Bears will eat you
    I'm looking for an elegant way to use values in a Java enum to represent operations or functions. My guess is, since this is Java, there just isn't going to be a nice way to do it, but here goes anyway. My enum looks something like this: public enum Operator { LT, LTEQ, EQEQ, GT, GTEQ, NEQ; ... } where LT means < (less than), LTEQ means <= (less than or equal to), etc - you get the idea. Now I want to actually use these enum values to apply an operator. I know I could do this just using a whole bunch of if-statements, but that's the ugly, OO way, e.g.: int a = ..., b = ...; Operator foo = ...; // one of the enum values if (foo == Operator.LT) { return a < b; } else if (foo == Operator.LTEQ) { return a <= b; } else if ... // etc What I'd like to be able to do is cut out this structure and use some sort of first-class function or even polymorphism, but I'm not really sure how. Something like: int a = ..., b = ...; Operator foo = ...; return foo.apply(a, b); or even int a = ..., b = ...; Operator foo = ...; return a foo.convertToOperator() b; But as far as I've seen, I don't think it's possible to return an operator or function (at least, not without using some 3rd-party library). Any suggestions?

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  • How do I find all the datetimes that happen on a particular date in ruby?

    - by Angela
    I have a method which goes through each day of the week: def dates_week(d, delim) "<tr>" + (d.beginning_of_week...(d.beginning_of_week+5)).map do |day| "<#{delim}> #{yield(day)} </#{delim}>" end.join + "</tr>" end For each day of the week, I plug that as an arg into a method (or maybe a named_scope, haven't figured out which), that will then output the .count for :all the emails that have a :date_sent on that date. However, :date_sent is a date-timestamp, so I can't use == as I have below. def sent_emails_by_date(date) ContactEmail.find(:all, :conditions => "date_sent = '#{date}'" " ).count end How do I find all the emails that fall on the day for the date passed through from the method which loops through a week as shown above?

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  • How can you remove a Criterion from a criteria?

    - by ChuckM
    Hello, For instance if I do something like: Criteria c = session.createCriteria(Book.class) .add(Expression.ge("release",reDate); .add(Expression.ge("price",price); .addOrder( Order.asc("date") ) .setFirstResult(0) .setMaxResults(10); c.list(); How can I use the same criteria instance, but remove (for example) the second criterion? I'm trying to build a dynamic query in which I'd like to let the user remove a filter, without the backend having to reconstruct the criteria from scratch. Thank you

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  • why this code not works?

    - by badgirl
    Hello. I want to create new node of BeanTreeView, and when I add some node in constructor, then run the app, and then I try to view the window with tree, it throws this error java.lang.AssertionError: Component cannot be created for {component=null, displayName=Exploirer, instanceCreate=AlwaysEnabledAction[Exploirer]} at org.openide.windows.OpenComponentAction.getTopComponent(OpenComponentAction.java:71) Why? And how to add node there? See the code. private ProjectsChildren projectsChildren; private ProjectNode projectNode = new ProjectNode(new MainProject("ggg"), projectsChildren); public ExploirerTopComponent() { initComponents(); setName(NbBundle.getMessage(ExploirerTopComponent.class, "CTL_ExploirerTopComponent")); setToolTipText(NbBundle.getMessage(ExploirerTopComponent.class, "HINT_ExploirerTopComponent")); // setIcon(ImageUtilities.loadImage(ICON_PATH, true)); //map.put("delete", ExplorerUtils.actionDelete(mgr, true)); associateLookup (ExplorerUtils.createLookup(mgr, getActionMap())); //projectsChildren.createProject("demence"); /* somewhere here is the problem*/ mgr.setRootContext(projectNode); ProjectNode[] pr = null; pr[0] = projectNode; mgr.getRootContext().getChildren().add(pr); }

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  • when to use Hibernate vs. Simple ResultSets for small application

    - by luke
    I just started working on upgrading a small component in a distributed java application. The main application is a rather complicated applet/servlet combo running on JBoss and it extensively uses Hibernate for its DataAccess. The component i am working on however is very a very straightforward data importing service. Basically the workflow is Listen for a network event Parse the data packet, extract a set of identifiers Map the identifier set to a primary key in our database Parse the rest of the packet and insert items in a related table using the foreign key found in step 3 Repeat in the previous version of this component it used a hibernate based DAL, that is no longer usable for a variety of reasons (in particular it is EOL), so I am in charge of replacing the Data Access layer for this component. So on the one hand I think i should use Hibernate because that's what the rest of the application does, but on the other i think i should just use regular java.sql.* classes because my requirements are really straightforward and aren't expected to change any time soon. So my question is (and i understand it is subjective) at what point do you think that the added complexity of using an ORM tool (in terms of configuration, dependencies...) is worth it? UPDATE due to the way the DataAccesLayer for the main application was written (weird dependencies) i cannot easily use it, i would have to implement it myself.

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  • Suitable web framework for the following scenario

    - by Paralife
    I have the following scenario: I have a view in an Oracle server and all Iwant is to show that view in a web browser, along with an input field or two for basic filtering. No users, no authentication, just this view maybe with a column or two linking to a second page for master detail viewing. The children are just string descriptions of the columns of the master that contain IDs. No inserts or updates. The question is which is the JAVA based web framework of choice that can accomplish the above in the minimum amount of code lines code time(subjective but also kind of objective if someone has expirience with more than one or two frameworks) configuration effort deployment effort and requirements. dependencies and mem footprint Also: 6. Oracle APEX is not an option. 3,4 and 5 are maybe the same in the sense that they are everything except the functionality coding. I want something that I can compile, deploy by just FTPing to the database host, run and forget. (e.g. For the deployment aspect, Hudson way comes in mind (java -jar hudson.war and that's all)). Also: 3,4 have priority over 1 and 2. (Explanation with a rant: I dont mind coding a lot as long as it is application code and not "why the fuck do we still use javascript over http for everything" code) Thanks.

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  • Calling an Overridden Method from a Parent-Class Constructor

    - by Vaibhav Bajpai
    I tried calling an overridden method from a constructor of a parent class and noticed different behavior across languages. C++ - echoes A.foo() class A{ public: A(){foo();} virtual void foo(){cout<<"A.foo()";} }; class B : public A{ public: B(){} void foo(){cout<<"B.foo()";} }; int main(){ B *b = new B(); } Java - echoes B.foo() class A{ public A(){foo();} public void foo(){System.out.println("A.foo()");} } class B extends A{ public void foo(){System.out.println("B.foo()");} } class Demo{ public static void main(String args[]){ B b = new B(); } } C# - echoes B.foo() class A{ public A(){foo();} public virtual void foo(){Console.WriteLine("A.foo()");} } class B : A{ public override void foo(){Console.WriteLine("B.foo()");} } class MainClass { public static void Main (string[] args) { B b = new B(); } } I realize that in C++ objects are created from top-most parent going down the hierarchy, so when the constructor calls the overridden method, B does not even exist, so it calls the A' version of the method. However, I am not sure why I am getting different behavior in Java and C#.

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  • Identify words with ascending characters from text file

    - by user2914000
    I am having a fair amount of trouble trying to write a program that counts the amount of ascending words (words in which each character is larger than the previous character) in a text file. I have tried a few different methods to solve this but cannot seem to get it working. If anyone could help me revise the code to work properly it would be appreciated. The code will print about 5 of the words from the list of nearly 20000, but none considered are ascending (the file does have many ascending words) and it sometimes prints the same word twice. I am printing theWord to the console simply to see if the code works. import java.util.Scanner; import java.io.*; public class { public static void main (String [] args) throws FileNotFoundException{ String theWord; Scanner inputFile = new Scanner(new File("file.txt")); boolean ascending = true; int i = 1; while(inputFile.hasNextLine()){ theWord = inputFile.nextLine(); if(theWord.length() >= 2){ while(i < theWord.length() - 1){ if(theWord.charAt(i) <= theWord.charAt(i + 1)){ ascending = true; System.out.println("+ " + theWord); totalNum = totalNum + 1; } else{ ascending = false; System.out.println("= " + theWord); } i++; } } }

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  • Quantifying the Performance of Garbage Collection vs. Explicit Memory Management

    - by EmbeddedProg
    I found this article here: Quantifying the Performance of Garbage Collection vs. Explicit Memory Management http://www.cs.umass.edu/~emery/pubs/gcvsmalloc.pdf In the conclusion section, it reads: Comparing runtime, space consumption, and virtual memory footprints over a range of benchmarks, we show that the runtime performance of the best-performing garbage collector is competitive with explicit memory management when given enough memory. In particular, when garbage collection has five times as much memory as required, its runtime performance matches or slightly exceeds that of explicit memory management. However, garbage collection’s performance degrades substantially when it must use smaller heaps. With three times as much memory, it runs 17% slower on average, and with twice as much memory, it runs 70% slower. Garbage collection also is more susceptible to paging when physical memory is scarce. In such conditions, all of the garbage collectors we examine here suffer order-of-magnitude performance penalties relative to explicit memory management. So, if my understanding is correct: if I have an app written in native C++ requiring 100 MB of memory, to achieve the same performance with a "managed" (i.e. garbage collector based) language (e.g. Java, C#), the app should require 5*100 MB = 500 MB? (And with 2*100 MB = 200 MB, the managed app would run 70% slower than the native app?) Do you know if current (i.e. latest Java VM's and .NET 4.0's) garbage collectors suffer the same problems described in the aforementioned article? Has the performance of modern garbage collectors improved? Thanks.

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  • For each loop not reading in the last item

    - by Gandalf StormCrow
    I'm trying to read in a multi line string then split it then print it .. here is the string : 1T1b5T!1T2b1T1b2T!1T1b1T2b2T!1T3b1T1b1T!3T3b1T!1T3b1T1b1T!5T1*1T 11X21b1X 4X1b1X When I split the string with ! I get this without the last line string : 1T1b5T 1T1b5T1T2b1T1b2T 1T2b1T1b2T1T1b1T2b2T 1T1b1T2b2T1T3b1T1b1T 1T3b1T1b1T3T3b1T 3T3b1T1T3b1T1b1T 1T3b1T1b1T5T1*1T 5T1*1T11X21b1X 11X21b1X Here is my code : import java.io.BufferedInputStream; import java.util.Scanner; public class Main { public static void main(String args[]) { Scanner stdin = new Scanner(new BufferedInputStream(System.in)); while (stdin.hasNext()) { for (String line : stdin.next().split("!")) { System.out.println(line); for (int i = 0; i < line.length(); i++) { System.out.print(line.charAt(i)); } } } } } Where did I make the mistake, why is not reading in the last line? After I read in all lines properly I should go trough each line if I encounter number I should print the next char the n times the number I just read, but that is long way ahead first I need help with this. Thank you

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  • Looking forward to a programming future but confused where to start.

    - by Kraivyne
    Hi there, I am very new to this site and to programming. I started doing some basic programming with python a few weeks ago and recently, messing around with Java basics. My main problem is that I am completely overwhelmed and haven't got the slightest clue where I should be starting. I want to learn programming because I really enjoy doing it, the simple applications that I have managed to conjure up put a smile on my face. My plan is to eventually (by eventually I'm talking about 6 years+) go into games programming. I have been informed that C++ is the best way to go about this but haven't got the slightest clue what book/sight is optimal for someone who is still learning the very basics. These are my questions: I have been to the Definitive C++ Book Guide but am still unsure which book is best to start of with. Should I stick with Python or Java instead of moving on to C++? Is there any advice you would give to a beginner programmer? Thanks again for all your help.

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  • Question about singleton property

    - by Jack
    I'm reading the java tutorial for enums located here and have a question: http://java.sun.com/j2se/1.5.0/docs/guide/language/enums.html#Card The part i'm confused about is as follows: "The Card class, above, contains a static factory that returns a deck, but there is no way to get an individual card from its rank and suit. Merely exposing the constructor would destroy the singleton property (that only a single instance of each card is allowed to exist). Here is how to write a static factory that preserves the singleton property, using a nested EnumMap: " Now as I understand, changing the original private "Card" constructor to public would allow us to instantiate an unlimited number of copies of a "Card" object with a given suit+rank. The solution as proposed was to create an EnumMap which would store four Maps (one for each suit), which themselves contained 13 Card objects with the rank as their keys. And so now if you wanted to retrieve a specific Card object from the deck, you would just call the "valueOf" method. My question now is, what's the prevent you with calling the valueOf method as many times as you like? Wouldn't that lead to the same problem as making the original private constructor public? Thanks.

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  • Netbeans platform tutorials

    - by James P.
    I mostly use Eclipse but have mentionned Netbeans on my cv. Are there any good concise and up-to-date tutorials apart from the official ones that could bring me up to speed on how to use the platform efficiently (shortcuts, debugging, views ...)? This excludes programming tutorials as I don't really need them unless there's a special manipulation involved.

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  • Multiple Rectangle Generation

    - by user1610541
    In my code i wrote a method that creates a rectangle at mouseX, mouseY. but all it does is update the position of that rectangle so it follows the mouse, i want it to create a new one at the mouse every time the method runs, can someone please help? this is my method public void drawParticle(float x, float y){ g.drawRect(x, y, 4, 4); } The main class Control call the drawParticle method; import java.awt.Point; import java.awt.geom.Point2D; import org.newdawn.slick.GameContainer; import org.newdawn.slick.Graphics; import org.newdawn.slick.SlickException; import org.newdawn.slick.state.BasicGameState; import org.newdawn.slick.state.StateBasedGame; public class Control extends BasicGameState { public static final int ID = 1; public Methods m = new Methods(); public Graphics g = new Graphics(); int mouseX; int mouseY; public void init(GameContainer container, StateBasedGame game) throws SlickException{ } public void render(GameContainer container, StateBasedGame game, Graphics g) throws SlickException { m.drawParticle(mouseX, mouseY); } public void update(GameContainer container, StateBasedGame game, int delta) { } public void mousePressed(int button, int x, int y) { mouseX = x; mouseY = y; } public int getID() { return ID; } } Thanks - Shamus

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