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• Does the OS make a significant difference for Ruby Development ?

  - by Bragaadeesh

  Hi, I have been working in Java for the past 4 years and I am currently switching over to Ruby. I am so excited about it and I feel good to finally get a hands on experience on a scripting language first time. The task assigned to me is to first pick a OS of my choice and setup a Ruby in it and study for 2 weeks. I have been developing applications in windows and Linux is not my cup of tea. Some part of me wants to try out Linux but I want to first convince myself whether OS really matters for Ruby development. If Linux does matter, which distribution can I start looking at? Please advise.

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• Programatically convert complex Excel file into HTML format

  - by shuby_rocks

  Hello all, I have a set of complex Excel files (with figures in it) that I want to show in a web browser. So I need to convert them into HTML page first. Since the excel files are very complex, I can not just parse them and generate a HTML table with HTML tags. The current manual solution that works fine is when I use Microsoft Excel software to save the spreadsheet as a HTML page. I want to automate this task in some way since I want to do it progrmatically through Java. Is their any existing solution or a way to do it? Thanks.

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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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• 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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• 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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• Inferring type from method generics

  - by ng

  I am from a Java background and I am looking from the equivalent in c# for the following. public interface Reader { <T> T read(Class<? extends T> type); } Such that I can do the following, constraining the parameter and inferring the return type. Cat cat = reader.read(Cat.class); Dog dog = reader.read(Dog.class); I was hoping something like this would work in c# but I am not sure it will. public interface Reader { T Read<T>(); } And and do this. public class TypeReader : Reader { public T Read<T>() { Type type = T.GetType(); ... } } Is something like this even possible in c#?

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• Hashing and salting values

  - by Avanst

  I am developing a small web app that internally authenticates users. Once the user is authenticated my web app then passes some information such as userID and Person's name to a third party web application. The third party developer is suggesting that we hash and salt the values. Forgive my ignorance, but what exactly does that mean? I am writing the app in Java. So what I am planning on doing is hashing the userID, Person's name, and some Math.random() value as the salt with Apache Commons Digest Utils SHA512 and passing that hashed string along with the userID and person's name. Is that the standard practice? I should be passing the third party the salt as well correct?

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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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• 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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• 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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• How do I print the method body reflectively?

  - by kunjaan

  Right now I have private static void getMethods(Class<? extends Object> clazz) { Method[] declaredMethods = clazz.getDeclaredMethods(); for (Method aMethod : declaredMethods) { aMethod.setAccessible(true); // Print the declaration System.out.print(Modifier.toString(aMethod.getModifiers()) + " " + aMethod.getReturnType().getSimpleName() + " " + aMethod.getName()); // Get Parameter Types getParameters(aMethod); //Empty Body System.out.println("{}\n"); } } Which prints most information reflectively but creates an empty body. How do I add to the reflective nature of Java to print the method body?

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• Eclipse bug? Switching on a null with only default case

  - by polygenelubricants

  I was experimenting with enum, and I found that the following compiles and runs fine on Eclipse (Build id: 20090920-1017, not sure exact compiler version): public class SwitchingOnAnull { enum X { ,; } public static void main(String[] args) { X x = null; switch(x) { default: System.out.println("Hello world!"); } } } When compiled and run with Eclipse, this prints "Hello world!" and exits normally. With the javac compiler, this throws a NullPointerException as expected. So is there a bug in Eclipse Java compiler?

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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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• Obtain distances to nearest landmarks (Mall, Hospital, and Airport etc.) using google map

  - by user227290

  I am working on a project in which I have around 100000 addreses in major cities in India(it is a table in a database). I want to know if it is possible to obtain the distances to to nearest landmarks (Mall, Hospital, and Airport etc.). Ideally I want these distances to be mergeed to the parent table. We have Java and Php coders to get it done once we find out how to go about it. Any pointers will be of great help. Thank you.

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• Accessing and encoding of properties files

  - by NoozNooz42

  I'm used to work with properties files, for example from Ant. Where I can simply reference the property file doing something like that: <property file="webapp_DO_NOT_COMMIT.properties"/> (the file is so named because our DVCS is configured as to never commit files containing "DO_NOT_COMMIT" to prevent committing credentials/passwords/etc.) Here's a very simple .properties file example: passwd=brokencleartextpassword Now I want to put some configuration in another, similar, properties file that I need to access from my Java code. How should I go about it? I also have another related question: is the character encoding of .properties file defined by any spec?

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• What happens when a OSGi service using JNI is unregistered while in use?

  - by schngrg

  As I understand, OSGi services can be unregistered anytime, including when they are in use. Consider an OSGi service which internally makes a long-running JNI call. And while that JNI call is executing, the service is unregistered by OSGi. Will the JNI call be allowed to finish or terminated mid-way? What if it was just a normal non-jni long running Java call? Will that call be allowed to finish execution or will OSGi terminate everything immediately and unregister? What is the expected behavior in such a case? Does the expected behavior depend on if the service was loaded using a 'tracker' or not? SG

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• How do you make long SQL invoked from other code readable?

  - by Artem

  This is a very open question, but I think it can be very beneficial for SQL readability. So you have a Java program, and you are trying to call a monster SQL statement from it, with many subqueries and joins. The starting point for my question is a string constant like this: static string MONSTER_STATEMENT = "SELECT " + " fields" + "WHERE "+ " fieldA = (SELECT a FROM TableC) " + "AND fieldB IN (%s)" + "AND fieldC = %d " + "FROM " " tableA INNER JOIN tableB ON ..."; It later gets filled using String.format and executed. What are you tricks for making this kind of stuff readable? Do you separate your inner joins. Do you indent the SQL itself inside the string? Where do you put the comments? Please share all of the tricks in your arsenal.

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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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• 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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• 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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• 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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• 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 is a constructor executed?

  - by simion

  I am doing some reviison from the lecture slides and it says a constructor is executed in the following way; If the constructor starts with this, recursively execute the indicated constructor, then go to step 4. Invoke the explicitly or implicitly indicated superclass constructor (unless this class is java.lang.Object) Initialise the fields of the object in the order in which they were declared in this class Execute the rest of the body of this constructor. What i dont undertsand is that, a constructor can never "start" with this, because even if it forms no class heirarchy/relationship then super() is inserted by default. How would this fit in with the description above? Thanks

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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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