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  • Hibernate: how to maintain insertion order

    - by jwaddell
    I have a list of entities where creation order is important, but they do not contain a timestamp to use for sorting. Entities are added to the end of the list as they are created so they will be ordered correctly in the list itself. After persisting the list using Hibernate the entities appear in the database table in the order that they were created. However when retrieving the list using a new Hibernate session the list is now in reverse order of insertion/creation. Is this expected behaviour? Is there any way to retrieve the list in the same order as it appears in the table? The primary key is a UUID, and the list of entities should always have been created on the same IP address and JVM. This mean sorting by UUID is a possibility but I'd rather not make assumptions. Another possibility is if the list is guaranteed to always come out in reverse order I could always just work through it backwards.

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  • Do I need to enable DRS to use Dynacache in Websphere Application Server Cluster

    - by rabs
    We are running a websphere commerce application with several websphere application servers configured in a cluster. We are using dynacache, so each server in the cluster will have its own cached objects in its own JVM. We are using CACHEIVL with database triggers for all cache invalidations. I was reading http://www.ibm.com/developerworks/websphere/library/techarticles/0603_crick/0603_crick.html and found an interesting sentence: "Furthermore, cache replication is necessary to ensure that invalidation messages are shared between the servers in a cluster." After thinking about this it would make sense that for the invalidation to work it would need to be triggered on all the servers in the cluster, but I couldn't find confirmation of this in the mountains of IBM doco. Does anyone know if you can use trigger based cache invalidation (through CACHEIVL) when you have several application servers clustered each with their own cache without DRS turned on? or do I need to use DRS for this to work?

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  • How do I enable automatic reloading of view files in development mode in JRuby on Rails?

    - by thekingoftruth
    I am developing an app in JRuby on Rails. For some reason, when I edit the view files, the development JRuby Mongrel server doesn't reload them. The perplexing thing is that after editing the controller files, the server reloads them just fine on the next request. This would be annoying even when using MRI Ruby, however starting up JRuby Mongrel after every view edit is much slower, and much more annoying. (Note that once it starts up it's quite fast, the only issue is startup--the JVM has to load up every time I start JRuby Mongrel.) I'm running JRuby 1.5.0, Rails 2.3.5, and Java 6.

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  • Java: How to test methods that call System.exit()?

    - by Chris Conway
    I've got a few methods that should call System.exit() on certain inputs. Unfortunately, testing these cases causes JUnit to terminate! Putting the method calls in a new Thread doesn't seem to help, since System.exit() terminates the JVM, not just the current thread. Are there any common patterns for dealing with this? For example, can I subsitute a stub for System.exit()? [EDIT] The class in question is actually a command-line tool which I'm attempting to test inside JUnit. Maybe JUnit is simply not the right tool for the job? Suggestions for complementary regression testing tools are welcome (preferably something that integrates well with JUnit and EclEmma).

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  • Template engine recommendations

    - by alex
    I'm looking for a template engine. Requirements: Runs on a JVM. Java is good; Jython, JRuby and the like, too... Can be used outside of servlets (unlike JSP) Is flexible wrt. to where the templates are stored (JSP and a lot of people require the templates to be stored in the FS). It should provide a template loading interface which one can implement or something like that Easy inclusion of parameterized templates- I really like JSP's tag fragments Good docs, nice code, etc., the usual suspects I've looked at JSP- it's nearly perfect except for the servlet and filesystem coupling, Stringtemplate- I love the template syntax, but it fails on the filesystem coupling, the documentation is lacking and template groups and stuff are confusing, GXP, TAL, etc. Ideas, thoughts? Alex

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  • Generics Type issue

    - by JohnJohnGa
    ArrayList<Integer> arrI = new ArrayList<Integer>(); ArrayList arrO = arrI; // Warning /* It is ok to add a String as it is an ArrayList of Objects but the JVM will know the real type, arrO is an arrayList of Integer... */ arrO.add("Hello"); /* How I can get a String in an ArrayList<Integer> ?? Even if the compiler told me that I will get an Integer! */ System.out.println(arrI.get(0)); Anybody can explain what's happening here?

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  • ANTLR - Embedding Java code, evaluate before or after?

    - by wvd
    Hello all, I'm writing a simple scripting language on top of Java/JVM, where you can also embed Java code using the {} brackets. The problem is, how do I parse this in the grammar? I have two options: 1] Allow everything to be in it, such as: [a-z|a-Z|0-9|_|$], and go on 2] Get an extra java grammar and use that grammar to parse that small code (is it actually possible and efficient?) Since option 2] is basically a double-check since when evaluating java code it's also being checked. Now my last question is -- is way that can dynamically execute java code also with objects which have been created at runtime? Thanks, William van Doorn

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  • Java - Could not find the main class?

    - by asmo
    I'm having a hard-time with a Java error. I'm getting this when double-clicking on my compiled project Jar file in order to run it: Could not find the main class: testPackage.testFrame. Program will exit. However, my main class is cleary defined in the project properties. Furthermore, everything works fine when I run the project directly from NetBeans. I'm using the ip2c.jar third-party library to determine countries from IP addresses. If I comment the class that is using the ip2c.jar file, I don't get the error. How can a third-party library be preventing the JVM from finding my main class?

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  • Is it possible to find out what FlashBuilder is doing during compilation?

    - by justkevin
    I've found that Flash Builder 4 (formerly Flex Builder) has trouble working with large projects. After a certain point, builds seem to take longer and longer. I've tried many different ways of improving build time including: Moving embedded resources into externally linked projects. Using -incremental. Tweaking the .ini jvm settings including memory and -server. Turning off automatic build (I'd prefer not to have to do this, because one of the main reasons for using an IDE is to be told about errors as you make them). Deleting the project and re-checking out from the repository. While some of these may help a bit, the performance is still annoyingly slow. I feel if I knew what was taking so long I could refactor my projects to build faster. Is there some setting that tells FlashBuilder to let me see what parts of the build process take so much time?

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  • Why is run() not immediately called when start() called on a thread object in java

    - by pi
    Or is it? I have a thread object from: Thread myThread = new Thread(pObject); Where pObject is an object of a class implementing the Runnable interface and then I have the start method called on the thread object like so: myThread.start(); Now, my understanding is that when start() is called, the JVM implicitly (and immediately) calls the run() method which may be overridden (as it is in my case) However, in my case, it appears that the start() method is not called immediately (as desired) but until the other statements/methods are completed from the calling block i.e. if I had a method after the start() call like so: myThread.start(); doSomethingElse(); doSomthingElse() gets executed before the run() method is run at all. Perhaps I am wrong with the initial premise that run() is always called right after the start() is called. Please help! The desired again is making executing run() right after start(). Thanks.

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  • OpenSSL compatible API for Scala?

    - by pfleidi
    Hello, I'm working on a project with a friend. He's implementing his software in Ruby and I'm doing my stuff in Scala (with Lift). We're using some asynchronous encryption and he is using the ruby OpenSSL bindings for that: key = OpenSSL::PKey::RSA.generate(4096) self.public_key = key.public_key self.private_key = key What I'm looking for is a simple API which is compatible to OpenSSL and runs on the JVM. I need it to create key-pairs and to encrypt and sign our payload. Do you have any suggestions?

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  • Why is an anonymous inner class containing nothing generated from this code?

    - by Andrew Westberg
    When run through javac on the cmd line Sun JVM 1.6.0_20, this code produces 6 .class files OuterClass.class OuterClass$1.class OuterClass$InnerClass.class OuterClass$InnerClass2.class OuterClass$InnerClass$InnerInnerClass.class OuterClass$PrivateInnerClass.class When run through JDT in eclipse, it produces only 5 classes. OuterClass.class OuterClass$1.class OuterClass$InnerClass.class OuterClass$InnerClass2.class OuterClass$InnerClass$InnerInnerClass.class OuterClass$PrivateInnerClass.class When decompiled, OuterClass$1.class contains nothing. Where is this extra class coming from and why is it created? package com.test; public class OuterClass { public class InnerClass { public class InnerInnerClass { } } public class InnerClass2 { } //this class should not exist in OuterClass after dummifying private class PrivateInnerClass { private String getString() { return "hello PrivateInnerClass"; } } public String getStringFromPrivateInner() { return new PrivateInnerClass().getString(); } }

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  • Jboss failover testing

    - by Sam
    Hi All, I have a peculiar situation here. I have installed JBoss 5.1.0 as a service in Wintel box. The service will restart itself if the JBoss instance fails. However I could not find a way to test this scenario. I killed the JVM that was running the JBoss, but it did not restart the service. I need to make the JBoss service end abnormally so that I can ensure it is restarts again. In a nutsehll, I need a way to make JBoss end abnormally. Please help.

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  • How to synchronize static method in java.

    - by Summer_More_More_Tea
    Hi there: I come up with this question when implementing singleton pattern in Java. Even though the example listed blow is not my real code, yet very similar to the original one. public class ConnectionFactory{ private static ConnectionFactory instance; public static synchronized ConnectionFactory getInstance(){ if( instance == null ){ instance = new ConnectionFactory(); } return instance; } private ConnectionFactory(){ // private constructor implementation } } Because I'm not quite sure about the behavior of a static synchronized method, I get some suggestion from google -- do not have (or as less as possible) multiple static synchronized methods in the same class. I guess when implementing static synchronized method, a lock belongs to Class object is used so that multiple static synchronized methods may degrade performance of the system. Am I right? or JVM use other mechanism to implement static synchronized method? What's the best practice if I have to implement multiple static synchronized methods in a class? Thank you all! Kind regards!

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  • Multimap Space Issue: Guava

    - by Arpssss
    In my Java code, I am using Guavas Multimap (com.google.common.collect.Multimap) by using this: Multimap< Integer, Integer Index = HashMultimap.create() Here, Multimap key is some portion of URL and value is another portion of URL (converted into integer). Now, I assign my JVM 2560 Mb (2.5 GB) heap space (by using Xmx and Xms). However, it can only store 9 millions of such (key,value) pairs of integers (approx 10 million). But, theoretically (according to memory occupied by int) it should store more. Can anybody help me, 1) Why is this happening (means Multimap is taking lots of space) ? I checked my code with out inserting pairs in Multimap, it takes only 1/2 MB space. 2) Is there any other way or home-baked solution to solve this space issue ? More clearly, how to solve this memory issue ? Thanks in advance and any idea is perfectly OK for me.

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  • Java application failing on special characters.

    - by Scottm
    An application I am working on reads information from files to populate a database. Some of the characters in the files are non-English, for example accented French characters. The application is working fine in Windows but on our Solaris machine it is failing to recognise the special characters and is throwing an exception. For example when it encounters the accented e in "Gérer" it says :- Encountered: "\u0161" (353), after : "\'G\u00c3\u00a9rer les mod\u00c3" (an exception which is thrown from our application) I suspect that in order to stop this from happening I need to change the file.encoding property of the JVM. I tried to do this via System.setProperty() but it has not stopped the error from occurring. Are there any suggestions for what I could do? I was thinking about setting the basic locale of the solaris platform in /etc/default/init to be UTF-8. Does anyone think this might help? Any thoughts are much appreciated.

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  • in java, which is better - three arrays of booleans or 1 array of bytes?

    - by joe_shmoe
    I know the question sounds silly, but consider this: I have an array of items and a labelling algorithm. at any point the item is in one of three states. The current version holds these states in a byte array, where 0, 1 and 2 represent the three states. alternatively, I could have three arrays of boolean - one for each state. which is better (consumes less memory) depends on how jvm (sun's version) stores the arrays - is a boolean represented by 1 bit? (p.s. don't start with all that "this is not the way OO/Java works" - I know, but here performance comes in front. plus the algorithm is simple and perfectly readable even in such form). Thanks a lot

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  • Best and safest Java Profiler for production use?

    - by Pete
    I'm looking for a Java Profiler for use in a very high demand production environment, either commercial or free, that meets all of the following requirements: Lightweight integration with code (no recompile with special options, no code hooks, etc). Dropping some profiler specific .jars alongside the application code is ok. Should be able to connect/disconnect to the JVM without restarting the application. When profiling is not active, no impact to performance When profiling is active, negligible impact to performance. Very slight degradation is acceptable. Must do all the 'expected' stuff a profiler does - time spent in each method to find hotspots, object allocation/memory profiling, etc. Essentially I need something that can sit dormant in production when everything is fine without anyone knowing or caring that it is there, but then be able to connect to it hassle (and performance degradation) free to pinpoint the hard to find problems like hotspots and synchronization issues.

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  • Ways to optimize Android App code based on function call stack?

    - by K-RAN
    I've been told that Android OS stores all function calls in a stack. This can lead to many problems and cause the 'hiccups' during runtime, even if a program is functionalized properly, correct? So the question is, how can we prevent this from happening? The obvious solution is to functionalize less, along with other sensible acts such as refraining from excessively/needlessly creating objects, performing static calls to functions that don't access fields, etc... Is there another way though? Or can this only be done through careful code writing on the programmers' part? Does the JVM/JIT automatically optimize the bytecode during compile time to account for this?? Thanks a lot for your responses!!

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  • How to trigger code on two different servers in a WAS cluster?

    - by Dean J
    I have an administrative page in a web application that resets the cache, but it only resets the cache on the current JVM. The web application is deployed as a cluster to two WAS servers. Any way that I can elegantly have the "clear cache" button on each server trigger the method on both JVMs? Edit: The original developer just wrote a singleton holding a HashMap to be the cache in question. Lightweight and (previously) worked just fine for the requirements. It caches content pulled from six or seven web services for specified amounts of time. Edit: The entire application in question is three pages, so the elegant solution might well be the lightest solution.

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  • java increase xmx dynamically at runtime

    - by Tomer
    Hi, I have a jvm server in my machine, now I want to have 2 apservers of mine sitting in same machine, however I want the standby one to have a really low amount of memory allocated with xmx because its passive, one the main server (active) goes down I want to allocate more memory to my passive server which is already up without restarting it (I have have them both having too much xmx - note they would consume memory at startup and I cant allow possibility of outOfMemory). So I want passive - low xmx once active goes down I want my passive to receive much more xmx. is there a way for me to achieve that. Thanks

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  • How to change code settings in eclipse

    - by Maven
    Sorry if the question title is confusing. Let me explain further. I am building a Java project with Eclipse. In my Java product I have conditionals that determine what code is included in the product and relies on static final constants for dead stripping. class BuildFlags { public static final boolean SOME_FLAG = true; // Need to set this programmatically } class SomeOtherClass { public void someMethod() { if (BuildFlags.SOME_FLAG) { // flag specific code } } } My question is how can I change BuildFlags.SOME_FLAG (above) so that I can run a special build without changing the source? Is there some way I can pass flags to the jvm (from eclipse) which I can then access to set this flag programatically?

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  • I know the big picture but can't put it in place

    - by Simbilim
    Hi, I'm interested in web development and by that I mean the bigger projects like facebook or twitter. I know the basics of java, css, php and mysql. I know there is a lot more out there. I read about it. But I don't know what the purpose is and how to put in place. Things like: Scribe, thrift, casandra, Unix/Linux, shell/perl/python scripting, PostgreSQL, MongoDB, non-relational NoSQL datastores, JVM, nginx I want to know why they need it, how they use it and what te purpose is. What I need is a book like technical background of facebook for dummies or so. Are there any books or websites that explain this from scratch? Thank you!

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  • JNI AttachCurrentThread NULLs the jenv

    - by Damg
    Hello all, I'm currently in the process of adding JNI functionality into a legacy delphi app. In a single-threaded environment everything works fine, but as soon as I move into multi-threaded environment, things start to become hairy. My problem is that calling JavaVM^.AttachCurrentThread( JavaVM, @JEnv, nil ); returns 0, but puts the JEnv pointer to nil. I have no idea why jvm.dll should return a NULL pointer. Is there anything I am missing? Thank you in advance -- damg PS: * Environment: WinXP + JDK 1.6 * Using JNI.pas from http://www.pacifier.com/~mmead/jni/delphi/

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  • Getter/Setter from separate class file in Java

    - by Crystal
    I'm new to Java and for a HW assignment, we had to create a Person class that has a constructor, getter/setter for the attributes of firstName, lastName, phone. That is in a separate file from an old HW assignment (Person.java). Now we have to use that Person class in our new HW assignment (LoanApplication.java). So if one of the attributes is private Person client do I need to create getter/setters or a constructor again? Otherwise, how does each LoanApplicaiton instance know which Person attribute it is to go with? How does the JVM know that it can use the Person.class even though my LoanApplicaiton.class does not extend Person.class? Thanks.

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