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• How can I treat a sequence value like a generated key?

  - by Jeff Knecht

  Here is my situation and my constraints: I am using Java 5, JDBC, and DB2 9.5 My database table contains a BIGINT value which represents the primary key. For various reasons that are too complicated to go into here, the way I insert records into the table is by executing an insert against a VIEW; an INSTEAD OF trigger retrieves the NEXT_VAL from a SEQUENCE and performs the INSERT into the target table. I can change the triggers, but I cannot change the underlying table or the general approach of inserting through the view. I want to retrieve the sequence value from JDBC as if it were a generated key. Question: How can I get access to the value pulled from the SEQUENCE. Is there some message I can fire within DB2 to float this sequence value back to the JDBC driver?

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• JBoss 4.0.5 startup takes 15 minutes deploying a single war file

  - by dkblinux98

  This instance of JBoss deploys several war files. The rest of the JBoss startup takes about 5 minutes or less. But when it gets to one particular war file, startup just hangs with no further output to the jboss log. It waits there for about 15 minutes and then suddenly the war starts deploying. The rest of the JBoss startup is then fine. What I want to know is what steps do you recommend I take to diagnose the cause of this condition? It is not possible to upgrade this site to a newer version of JBoss nor java (currently 1.5.0.7). It is running on 32-bit CentOS 5.3 Linux on 3 xen-based virtual servers in a load balanced configuration. The code is common to all three servers via an nfs share. This same issue was seen, however, when the 3 servers were physical and the code was local to each server. The servers are each 2 cpu, 4GB RAM servers.

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• Refactoring if/else logic

  - by David

  I have a java class with a thousand line method of if/else logic like this: if (userType == "admin") { if (age > 12) { if (location == "USA") { // do stuff } else if (location == "Mexico") { // do something slightly different than the US case } } else if (age < 12 && age > 4) { if (location == "USA") { // do something slightly different than the age > 12 US case } else if (location == "Mexico") { // do something slightly different } } } else if (userType == "student") { if (age > 12) { if (location == "USA") { // do stuff } else if (location == "Mexico") { // do something slightly different than the US case } } else if (age < 12 && age > 4) { if (location == "USA") { // do something slightly different than the age > 12 US case } else if (location == "Mexico") { // do something slightly different } } How should I refactor this into something more managable?

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• No mapping for LONGVARCHAR in Hibernate 3.2

  - by jimbokun

  I am running Hibernate 3.2.0 with MySQL 5.1. After updating the group_concat_max_len in MySQL (because of a group_concat query that was exceeding the default value), I got the following exception when executing a SQLQuery with a group_concat clause: "No Dialect mapping for JDBC type: -1" -1 is the java.sql.Types value for LONGVARCHAR. Evidently, increasing the group_concat_max_len value causes calls to group_concat to return a LONGVARCHAR value. This appears to be an instance of this bug: http://opensource.atlassian.com/projects/hibernate/browse/HHH-3892 I guess there is a fix for this issue in Hibernate 3.5, but that is still a development version, so I am hesitant to put it into production, and don't know if it would cause issues for other parts of my code base. I could also just use JDBC queries, but then I have to replace every instance of a SQLQuery with a group_concat clause. Any other suggestions?

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• Concatinate integer arrays iteratively

  - by Ojtwist

  I have a methode in2.getImagesOneDim() which gives me an array of integers, to be more precise the pixel values of an image. Now i want to create one big array with all the pixel values of all the images. Therefore I have to call this method several times. Now I would like to concatenate the previous output to the current output until all images are read. In some kind of pseudo code, where the + is a concatination ... : for (int i = 1; i < 25; i++) { ConArray = ConArray + in2.getImagesOneDim("../images/"+i); } How would I do this in java ?

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• How to keep statefull web clients in sync, when multiple clients are looking at the same data?

  - by Hilbrand

  In a RIA web client, created with GWT, the state is maintained in the web client, while the server is (almost) stateless (this is the preferred technique to keep the site scalable). However, if multiple users looking at the same data in their browser and one user changes something, which is send to the server and stored in the database, the other users still have the old data in their browser state. For example a tree is shown and one of the users adds/removes an item from the tree. Since there can be a lot of state in the client, what is the best technique to keep the state in the clients in sync? Are there any java frameworks that take care of this?

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• Best way to access a sqlite database file in a web service.

  - by rogernorling

  First question from me on stack overflow. I have created a java web application containing a web service using netbeans (I hope a web application were the correct choice). I use the web application as is with no extra frameworks. This web service use a sqlite JDBC driver for accessing a sqlite database file. My problem is that the file path end up incorrect when I try to form the JDBC connection string. Also, the working directory is different when deploying and when running JUnit tests. I read somewhere about including the file as a resource, but examples of this were nowhere to be seen. In any case, what is the best way to open the sqlite database, both when the web service is deployed and when I test it "localy"? I don't know much about web services, I just need it to work, so please, help me with the technicalities.

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• Do fields need to be explicitly final to have a "proper" immutable object?

  - by Yishai

  You often read about immutable objects requiring final fields to be immutable in Java. Is this in fact the case, or is it simply enough to have no public mutability and not actually mutate the state? For example, if you have an immutable object built by the builder pattern, you could do it by having the builder assign the individual fields as it builds, or having the builder hold the fields itself and ultimately return the immutable object by passing the values to its (private) constructor. Having the fields final has the obvious advantage of preventing implementation errors (such as allowing code to retain a reference to the builder and "building" the object multiple times while in fact mutating an existing object), but having the Builder store its data inside the object as it is built would seem to be DRYer. So the question is: Assuming the Builder does not leak the Object early and stops itself from modifying the object once built (say by setting its reference to the object as null) is there actually anything gained (such as improved thread safety) in the "immutability" of the object if the object's fields were made final instead?

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• Tomcat + Struts + OpenID raising ServletExceptions

  - by Rocjoe

  I am working with Tomcat 5.5.x with Struts 1.2 to run a rather large website (large w.r.t. source code). I'm looking to add OpenID to my website, mostly to access attribute exchange to help accelerate the registration process. Every Java implementation for OpenID I have attempted to use will cause a ServletException. Tracing this has been very difficult, but it seems merely instancing any class that makes use of Apache HttpClient will cause the crash. Is this a configuration problem I can address in the JVM, or is it positively wrong to try to initiate an outbound Http request from within an inbound Http request?

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• Mixing synchronized() with ReentrantLock.lock()

  - by yarvin

  In Java, do ReentrantLock.lock() and ReetrantLock.unlock() use the same locking mechanism as synchronized()? My guess is "No," but I'm hoping to be wrong. Example: Imagine that Thread 1 and Thread 2 both have access to: ReentrantLock lock = new ReentrantLock(); Thread 1 runs: synchronized (lock) { // blah } Thread 2 runs: lock.lock(); try { // blah } finally { lock.unlock(); } Assume Thread 1 reaches its part first, then Thread 2 before Thread 1 is finished: will Thread 2 wait for Thread 1 to leave the synchronized() block, or will it go ahead and run?

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• Servlet container; What is it and do I need it in my case?

  - by Camran

  I have just ordered a VPS from my provider. I have some Q however... My website uses Solr, which requires the following according to their website: "Solr requires Java 1.5 and an Application server (such as Tomcat) which supports the Servlet 2.4 standard" I also need php 5, MySql, and the usual javascript etc... The OS is Ubuntu 9.10 1- So what do I need to install then? 2- What is a servlet container? 3- The solr I have downloaded came with Jetty. Is Jetty a Servlet container? Thanks

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• Write file in sub-directory in Android

  - by Davide Vosti

  I'm trying to save a file in a subdirectory in Android 1.5. I can successfully create a directory using _context.GetFileStreamPath("foo").mkdir(); (_context is the Activity where I start the execution of saving the file) but then if I try to create a file in foo/ by _context.GetFileStreamPath("foo/bar.txt"); I get a exception saying I can't have directory separator in a file name ("/"). I'm missing something of working with files in Android... I thought I could use the standard Java classes but they don't seem to work... I searched the Android documentation but I couldn't fine example and google is not helping me too... I'm asking the wrong question (to google)... Can you help me out with this? Thank you!

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• Can't get jQuery and IE to be friends

  - by Matthew

  Using jQuery and the Cycle plugin. Runs flawless in Safari, Chrome, Firefox, and the latest version of Opera. Won't run in older versions of Opera, and of course, IE. I know its running Java, because its picking up the rollovers. This is driving me batty. Hopefully its something simple. Here's the code... $(document).ready(function() { $("#slideshow").css("overflow", "hidden"); $("div#slides").cycle({ fx: 'scrollHorz', speed: 'slow', timeout: 0, prev: '#prev', next: '#next' }); Really appreciate the help guys.

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• When is BIG, big enough for a database?

  - by David ???

  I'm developing a Java application that has performance at its core. I have a list of some 40,000 "final" objects, i.e., I have an initialization input data of 40,000 vectors. This data is unchanged throughout the program's run. I am always preforming lookups against a single ID property to retrieve the proper vectors. Currently I am using a HashMap over a sub-sample of a 1,000 vectors, but I'm not sure it will scale to production. When is BIG, actually big enough for a use of DB? One more thing, an SQLite DB is a viable option as no concurrency is involved, so I guess the "threshold" for db use, is perhaps lower.

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• Waiting for ServerSocket accept() to put socket into "listen" mode

  - by inazaruk

  I need a simple client-server communication in order to implement unit-test. My steps: Create server thread Wait for server thread to put server socket into listen mode ( serverSocket.accept() ) Create client Make some request, verify responses Basically, I have a problem with step #2. I can't find a way to signal me when server socket is put to "listen" state. An asynchronous call to "accept" will do in this case, but java doesn't support this (it seems to support only asynchronous channels and those are incompatible with "accept()" method according to documentation). Of cause I can put a simple "sleep", but that is not really a solution for production code. So, to summarize, I need to detect when ServerSocket has been put into listen mode without using sleeps and/or polling.

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• how to achieve Inter-Widget communication

  - by bakore

  I was looking for a platform where widgets developed using various technologies like Java can communicate with each other. In other words When I add widgets to an interface I need them to talk to each other. For example A Click event in one widget should trigger an event in some other widget. I have been looking into the web for solutions and ways to do it, but couldnt find anything concrete. Any pointers or information on this would be great. Something like this http://blogs.sun.com/pdblog/entry/inter_widget_communication_in_cross

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• NullPointerException when accessing image files in a .jar file

  - by user548240

  Hi, I have pretty much tried everything but still have this same problem. I have the following setup: I have a images.jar containing a folder called 'images' in which there are multiple image files. I add images.jar to the java build path of the project in eclipse, and i've been trying to use the following code to access the individual images in the jar: URL url = this.getClass().getResource("images/a.png"); ImageIcon icon = new ImageIcon (url); Unfortunately, the URL object is always NULL. I don't think this has anything to do with where I put images.jar file as it is added to the classpath in eclipse. I have also tried using the path '/images/a.png', but still the same problem. Any suggestion would be extremely welcome! Thanks.

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• How to Get the Method/Function Call Trace for a Specific Run?

  - by JackWM

  Given a Java or JavaScript program, after its execution, print out a sequence of calls. The calls are in invocation order. E.g. main() { A(); } A() { B(); C(); } Then the call trace should be: main -> A() -> B() -> C() Is there any tool that can profile and output this kind of information? It seems this is common a need for debugging or performance tuning. I noticed that some profilers can do this, but I prefer a simpler/easy-to-use one. Thanks!

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• Web applet game design

  - by Vlad

  I making web games in java and having troubles each time when getting to the GUI design, usually I'm looking at others codes and copy most of the design, and I can't decide which design should I use. I used Applet, Canvas, JFrame. What i need is the main loop and draw function that changing between different games. So what class should I use and what design, which is better, why, maybe links to useful tutorials and examples... Please explain. Thanks.

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• Jython project in Eclipse can't find the xml module, but works in an identical project

  - by Rob Lourens

  I have two projects in Eclipse with Java and Python code, using Jython. Also I'm using PyDev. One project can import and use the xml module just fine, and the other gives the error ImportError: No module named xml. As far as I can tell, all the project properties are set identically. The working project was created from scratch and the other comes from code checked out of an svn repository and put into a new project. What could be the difference? edit- Same for os, btw. It's just missing some path somewhere...

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• What is the most efficient way to pass data (list of pairs of [Integer + Double]) between two Google App Engine instances?

  - by ruslan

  What is the most efficient way to pass data (list of pairs of [Integer, Double]) between two Google App Engine instances ? Currently I use Java binary serialization. Frontend servlet receives data from the client in JSON format. I convert it to byte[] using ObjectOutput.writeObject and then send it to backend servlet via HTTP POST. It's not in production yet. Should I just pass client's JSON as it is to backend? It seems more logical. But it's bigger in size. Or should I use Google Protocol Buffers as stated in this benchmark article ? Thank you!!!

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• Decoding MIME (HTML+Attachments)

  - by MH

  I'm planning to write an application that should handle incoming mails. Basically it will act more like a ticketing system than a webmail, so I'm only interested in receiving emails, and not sending them. I have made a simple prototype that downloads mails and displays the text with downloadable attachments in a web page, but handling mails from Outlook and others is more complicated. I have looked at some of the open source ticketing systems out there, but most of the code is tied to the system and is hard to separate. Is there a library that understands "rich" mail and makes this job simpler? Preferably in Python, Java, Ruby or Perl. I'm also open to suggestions for any command line mail clients that can be used for this, since the system will not receive large amounts of mail and can afford to launch external processes.

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• Generate service layer with Hibernate

  - by gmate

  Hi all! I generate *.hbm.xml mapping files and *.java file from the DB schema, with Hibernate tools. My question is, that is there any option, to generate service classes also? These are the classes where I implement the store(), find(), delete(), etc... methods. I know that for C# there are many solutions to generate almost everything. I'm looking for the same, but with Hibernate. Is there any? Thanks for every reply in advance!

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• Program not running from expected directory?

  - by twpc

  I am working on a web-based program, using Java. I am not sure exactly how to phrase this, but I expect the program to be running from within the c:/Resin/webapps/apps directory. However, when I reference a file in the program like this: "../files/randomfile.pdf", it cannot find that file. It works when I reference it like this: "c:/Resin/webapps/files/randomfile.pdf". How to I change the "running location"? (And what is the technical term for this?)

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• Count The Amount Of Data In An Array Including SOME Null

  - by Josephine

  I'm coding in java and I need to create a function that returns the number of Data objects that are currently in an ArrayList. At the moment I have this: int count = 0; for (int i = 0; i < data.length; i++) { if (data[i] != null) { count ++; } } return count; But the problem is that an array list that includes null data is acceptable, and I have to count their null data towards this counter. How do I include the null data that's in the middle of this array, and not the null data that's not supposed to be counted for? For example, I have some tester code that adds (8),null,null,(23),(25) to the array, and this function should return 5 when the initial array size is 10. Thank you so much

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