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  • Why do sockets not die when server dies? Why does a socket die when server is alive?

    - by Roman
    I try to play with sockets a bit. For that I wrote very simple "client" and "server" applications. Client: import java.net.*; public class client { public static void main(String[] args) throws Exception { InetAddress localhost = InetAddress.getLocalHost(); System.out.println("before"); Socket clientSideSocket = null; try { clientSideSocket = new Socket(localhost,12345,localhost,54321); } catch (ConnectException e) { System.out.println("Connection Refused"); } System.out.println("after"); if (clientSideSocket != null) { clientSideSocket.close(); } } } Server: import java.net.*; public class server { public static void main(String[] args) throws Exception { ServerSocket listener = new ServerSocket(12345); while (true) { Socket serverSideSocket = listener.accept(); System.out.println("A client-request is accepted."); } } } And I found a behavior that I cannot explain: I start a server, than I start a client. Connection is successfully established (client stops running and server is running). Then I close the server and start it again in a second. After that I start a client and it writes "Connection Refused". It seems to me that the server "remember" the old connection and does not want to open the second connection twice. But I do not understand how it is possible. Because I killed the previous server and started a new one! I do not start the server immediately after the previous one was killed (I wait like 20 seconds). In this case the server "forget" the socket from the previous server and accepts the request from the client. I start the server and then I start the client. Connection is established (server writes: "A client-request is accepted"). Then I wait a minute and start the client again. And server (which was running the whole time) accept the request again! Why? The server should not accept the request from the same client-IP and client-port but it does!

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  • Printing user specified column from JTable

    - by technomage
    I have an application, and I would like to print a JTable, but since it has many columns, I would like user to select/limit which columns to print so it can fit in regular printer paper. I'm using JTable.print() function to print. (http://java.sun.com/docs/books/tutorial/uiswing/misc/printtable.html) Right now, my solution, is to create another JTable with the columns that user selected, then repopulate the table with the data, then send it to printer. Is there a better way to do it?

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  • A question about GC

    - by chun
    This is a quesiton taken from a java exam, How many objects are eligible for gabage collection at #1 ? public class Main { Integer x = 32768; public static void main(String[] args) { Main m = new Main(); m = null; // #1 } } I thought it just collect Integer x, does GC even collect the Main object m?

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  • I am faceing problem with this error of struts application.

    - by Sanjeev
    I am using My-eclipse and doing a struts project there is no syntax error but on starting tomcat server the following error appear in console. java.lang.ClassNotFoundException: org.apache.commons.logging.LogFactory and javax.servlet.UnavailableException: Parsing error processing resource path jndi:/localhost/strutspro/WEB-INF/struts-config.xml any idea whats the problem.

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  • What is the best way to organize object oriented code?

    - by Adam
    I haven't coded in java for a long time, and after coding in C, I'm having issued organizing my code for OOP. More specifically I'm not sure when to create a new method, and when to create a new class, and when to just lump everything together. Are there some general rules or guidelines on how it should be done?

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  • Ternary operator in if-statement?

    - by Pindatjuh
    I've written the following if-statement in Java: if(methodName.equals("set" + this.name) || isBoolean() ? methodName.equals("is" + this.name) : methodName.equals("get" + this.name)) { ... } Is this a good practice to write such expressions in if, to separate state from condition? And can this expression be simplified?

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  • Create all directories up to a point?

    - by Stefan Kendall
    I need to be able to build all directories up to and including the directory specified by my File object. For example, suppose I have something like this: File file = new File( "/var/a/b/c/d/" ); But only /var/ exists. I need a method that builds up to d, and I was wondering if there was a method in a java io library somewhere that does this already.

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  • Sessions not persisting between requests

    - by klonq
    My session objects are only stored within the request scope on google app engine and I can't figure out how to persist objects between requests. The docs are next to useless on this matter and I can't find anyone who's experienced a similar problem. Please help. When I store session objects in the servlet and forward the request to a JSP using: getServletContext().getRequestDispatcher("/example.jsp").forward(request,response); Everything works like it should. But when I store objects to the session and redirect the request using: response.sendRedirect("/example/url"); The session objects are lost to the ether. In fact when I dump session key/value pairs on new requests there is absolutely nothing, session objects only appear within the request scope of servlets which create session objects. It appears to me that the objects are not being written to Memcache or Datastore. In terms of configuring sessions for my application I have set <sessions-enabled>true</sessions-enabled> In appengine-web.xml. Is there anything else I am missing? The single paragraph of documentation on sessions also notes that only objects which implement Serializable can be stored in the session between requests. I have included an example of the code which is not working below. The obvious solution is to not use redirects, and this might be ok for the example given below but some application data does need to be stored in the session between requests so I need to find a solution to this problem. EXAMPLE: The class FlashMessage gives feedback to the user from server-side operations. if (email.send()) { FlashMessage flash = new FlashMessage(FlashMessage.SUCCESS, "Your message has been sent."); session.setAttribute(FlashMessage.SESSION_KEY, flash); // The flash message will not be available in the session object in the next request response.sendRedirect(URL.HOME); } else { FlashMessage flash = new FlashMessage(FlashMessage.ERROR, FlashMessage.INVALID_FORM_DATA); session.setAttribute(FlashMessage.SESSION_KEY, flash); // The flash message is displayed without problem getServletContext().getRequestDispatcher(Templates.CONTACT_FORM).forward(request,response); } FlashMessage.java import java.io.Serializable; public class FlashMessage implements Serializable { private static final long serialVersionUID = 8109520737272565760L; // I have tried using different, default and no serialVersionUID public static final String SESSION_KEY = "flashMessage"; public static final String ERROR = "error"; public static final String SUCCESS = "success"; public static final String INVALID_FORM_DATA = "Your request failed to validate."; private String message; private String type; public FlashMessage (String type, String message) { this.type = type; this.message = message; } public String display(){ return "<div id='flash' class='" + type + "'>" + message + "</div>"; } }

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  • UnsupportedOperationException on Collection

    - by Duke Vador
    While studying the Collection API, we find that some methods (add, remove,...) may throw a java.lang.UnsupportedOperationException if the current implementation of the Collection does not support those functionalities. Is there,actually, in the JDK, a concrete Collection that does not support those methods ? Thanks a lot for your answers.

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  • Is MobiForms for Android worth investigating ?

    - by Alan B
    I'm working my way through the NotePad tutorial, and that's all fine - I'm not a Java programmer but it's close enough to C# (or vice versa) to make it easy to pick up. I'm surprised that there aren't any RAD tools for Android apart from Mobiforms. Is there anyone out there with experience of Mobiforms ?

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  • How does JVM handles dynamic allocation

    - by Nile
    I want to understand how JVM manages heap for the dynamic allocations. Since every java program is invoked as a thread, when does JVM's garbage collector come into play. Also, how things work for javascript's dynamic allocation ?

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  • will php/apache ever support multi threading?

    - by fayer
    i mainly focus on the web, i think i will never create desktop applications. so i think it's better for me to focus on typical web languages like php. i know an advantage java has over php is multi threading though. will php ever support this feature in the future? thanks

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  • Where can i find exercises for familiarising OOPS

    - by CrazyBoy123
    Now that i have learned the theory of OOPS in good number of books , and practised a little. Still i am not comfortable when i look into OOPS being applied in some of the Open Source projs. Can someone suggest any problem / solution kind of book , or any resources , that covers OOPS end - end. (C# , Java preferably)

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  • Is there a good NumPy clone for Jython?

    - by jbrogdon
    I'm a relatively new convert to Python. I've written some code to grab/graph data from various sources to automate some weekly reports and forecasts. I've been intrigued by the Jython concept, and would like to port some Python code that I've written to Jython. In order to do this quickly, I need a NumPy clone for Jython (or Java). Is there anything like this out there?

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  • Reading POM's with it's children

    - by khmarbaise
    Based on the post it is mentioned (By Brett Porter) that a POM can be read. What i need is to read not only a single pom. I need to read the whole tree of pom's in a multimodule build. Starting with the root pom and it should read automatically the child pom's if it's possible? I need to do this in separate Java Code not in relationship with Maven itself.

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