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• Can JAXB Incrementally Marshall An Object?

  - by Intellectual Tortoise

  I've got a fairly simple, but potentially large structure to serialize. Basically the structure of the XML will be: <simple_wrapper> <main_object_type> <sub_objects> </main_object_type> ... main_object_type repeats up to 5,000 times </simple_wrapper> The main_object_type can have a significant amount of data. On my first 3,500 record extract, I had to give the JVM way more memory than it should need. So, I'd like to write out to disk after each (or a bunch of) main_object_type. I know that setting Marshaller.JAXB_FRAGMENT would allow it fragments, but I loose the outer xml document tags and the <simple_wrapper>. Any suggestions?

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• Trying to cause java.lang.OutOfMemoryException

  - by portoalet

  Hi, I am trying to reproduce java.lang.OutOfMemoryException in Jboss4, which one of our client got, presumably by running the J2EE applications over days/weeks. I am trying to find a way for the webapp to spitout java.lang.OutOfMemoryException in a matter of minutes (instead of days/weeks). One thing come into mind is to write a selenium script and has the script bombards the webapps. One other thing that we can do is to reduce JVM heap size, but we would prefer not to do this, as we want to see the limit of our system. Any suggestions? ps: I don't have access to the source code.

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• producing pixel-identical images of text between Sun Java and OpenJDK

  - by yuvi

  My release script produces images of the version number to save me the trouble of manually going into the MoinMoin wiki software and changing it by hand for each release. Unfortunately, since the fonts look a little different on each platform's JVM, the result is ugly. I solved the the font inconsistency by using Lucide Sans (comes with every Java system). (Loading Fonts from TTF files was another option, but was buggy on Mac Java). The result is much better, producing the exact same image on Mac/Windows (), but a slightly different one on OpenJDK (). I believe this is caused by OpenJDK having a different font rendering system (as opposed to different fonts). Is there any way I can get all three of my target platforms (Sun Windows, Mac, OpenJDK Linux) to produce images of text that look identical?

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• CPU and profiling not supported for remote jvisualvm session

  - by yawn

  When monitoring a remote app (using jstatd) I can neither profile nor monitor cpu consumption. Heap monitoring (provided I do not use G1) works. jvisualvm provides the message "Not supported for this JVM." in the CPU graph window. Is there anything missing in my setup? The google showed up next to no results. The local environment (Mac OS X 10.6): java version "1.6.0_15" Java(TM) SE Runtime Environment (build 1.6.0_15-b03-219) Java HotSpot(TM) 64-Bit Server VM (build 14.1-b02-90, mixed mode) The remote environment (Linux version 2.6.16.27-0.9-smp (gcc version 4.1.0 (SUSE Linux))): java version "1.6.0_16" Java(TM) SE Runtime Environment (build 1.6.0_16-b01) Java HotSpot(TM) 64-Bit Server VM (build 14.2-b01, mixed mode) Local monitoring works as advertised.

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• Google App Engine - Memcache - Java version of Python's client.add?

  - by Spines

  The python interface to the memcache has an add method: add(key, value, time=0, min_compress_len=0, namespace=None) Sets a key's value, if and only if the item is not already in memcache. ... The return value is True if added, False on error. So with this you can add an item if it doesn't exist, and see if it previously existed by the return value. The java memcache api equivalent for this doesn't let you know if there was a previous value or not: put(key, value, expiration, MemcacheService.SetPolicy.ADD_ONLY_IF_NOT_PRESENT); MemcacheService.SetPolicy.ADD_ONLY_IF_NOT_PRESENT: add the value if no value with the key, do nothing if the key exists Is there a way to know if a previous value existed or not with the java api? I can't just check with the contains method beforehand, because in between the call to contains and the call to put, another JVM instance could modify the memcache.

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• Using Java to retrieve the CPU Usage for Window's Processes

  - by stjowa

  Hello all, I am looking for a Java solution to finding the CPU usage for a running process in Windows. After looking around the web, there seems to be little information on a solution in Java. Keep in mind, I am not looking to find the CPU usage for the JVM, but any process running in Windows at the time. I am able to retrieve the memory usage in Java by using the exec("tasklist.exe ... ") to retrieve and parse process information. Although there is an aggregate CPU cycle timer for each process, I do not see a CPU usage column. Any help would be greatly appreciated. Also, if possible, I would like to stay away from C libraries; however, if there is no other alternative, a solution by that means would be appropriate. Thanks a lot, Steve

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• cast across classloader?

  - by IttayD

  How can I do this: class Foo { public static Foo get() throws Exception { ClassLoader cl = new URLClassLoader(new URL[]{"foo.jar"}, null); // Foo.class is in foo.jar return (Foo)cl.loadClass("Foo").newInstance(); // fails on class cast } } What I need is for the JVM to consider the Foo instance from cl as if it is an instance of Foo from the classloader of the executing code. I have seen these approaches, none of them good for me (the above example is a toy example): Load the class (or a separate interface) by a class loader that is a parent of both the calling code and created classloader Serialize and deserialize the object.

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• Socksifying a Java ServerSocket - how to approach

  - by Thorbjørn Ravn Andersen

  I would like to have a Java program running on network A have a ServerSocket living on another network B through a proxy. I have played with a SOCKS5 proxy (which works) but it appears that all the proxy facilities in Java only work with client connections, not with ServerSockets (no constructor taking a Proxy argument). Asking Google gives much hay and few needles. What is the approach I should take to get this running? If a specific client is better than a generic SOCKS or web proxy then fine, but it needs to be Java (that leaves sshd out). Target JVM is preferrably Java 5, and then Java 6.

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• Can somebody explain in a few sentences how these technologies relate: Flex, Flash, Air, ActionScrip

  - by SimpaCar

  I've read about each of these but I still don't understand how they all inter-operate, which are competing technologies, or even really what each of them is distinctly. Flash, Air, Flex... Are these all "containers"/JVM-like runtime environments, in which ActionScript code runs? SWF,FLV,AIR... Are these competing file formats which a Flash, Air or Flex runtime environment executes? ActionScript is a C-like language which compiles to SWF, FLV or AIR files? Sorry, with all the marketing around these terms, some of which are used interchangeably, I am quite lost. Suppose I wanted to write an AIR application... what would that entail? Writing ActionScript, compiling it to a SWF, and then installing the AIR runtime to execute it? How's that different than Flash? If I want to play AIR applications do I need a separate AIR runtime or does Flash execute AIR apps?

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• Problem with Apache Commons Id UUID Version 1 generation

  - by Pekka Mattila

  My problem is to generate version 1 UUIDs. We use Jetty 6.x, Maven (to start Jetty among other things) and Apache Commons ID (to generate UUID version 1 from the current time). Apache Commons ID requires a configuration file that is told to the JVM, using a parameter, e.g. 'org.apache.commons.id.uuid.config.resource.filename=commons-id-uuid.xml'. I checked the Apache Commons ID code and it tries to find the file from the classpath. Jetty's documentation states that WEB-INF/lib and WEB-INF/classes are in the classpath. The 'commons-id-uuid.xml' can be found from the deployed war file from the root of WEB-INF/classes directory but Jetty cannot load it: Message: java.lang.RuntimeException: java.lang.IllegalStateException: commons-id-uuid.xml loaded as system resource is null Jetty was started using the following command: mvn jetty:run -Dorg.apache.commons.id.uuid.config.resource.filename=commons-id-uuid.xml Any idea what is going wrong? We just need to generate UUID version 1 identifiers. Any suggestions?

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• [Java] Flood fill using a stack

  - by dafero

  Hello to everyone :), I am using the recursive Flood fill algorithm in Java to fill some areas of a image. With very small images it works fine, but when de image becomes larger the JVM gives me a Stack Over Flow Error. That's the reason why I have to reimplement the method using a Flood Fill with my own stack. (I read that's the best way to do it in these kind of cases) Can anyone explain me how to code it? (if you don't have the code at hand, with the pseudo-code of the algorithm will be fine) I've read a lot in the Internet but I haven't understood it very well. Thanks!

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• Java 'Prototype' pattern - new vs clone vs class.newInstance

  - by Guillaume

  In my project there are some 'Prototype' factories that create instances by cloning a final private instance. The author of those factories says that this pattern provides better performance than calling 'new' operator. Using google to get some clues about that, I've found nothing really relevant about that. Here is a small excerpt found in a javdoc from an unknown project javdoc from an unknown project Sadly, clone() is rather slower than calling new. However it is a lot faster than calling java.lang.Class.newInstance(), and somewhat faster than rolling our own "cloner" method. For me it's looking like an old best practice of the java 1.1 time. Does someone know more about this ? Is this a good practice to use that with 'modern' jvm ?

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• Looking for a .NET 3.5 / J2EE architecture concept comparison article/chart

  - by Edward Tanguay

  We are thinking about combining .NET technology with Java technology (WCF, JBoss/ESB, MOM, WPF, WF) and I need to have a high-level idea of what are the apples and oranges in the .NET 3.5 and Java worlds. Does anyone know of a good, clear article or better yet a simple chart which answers questions such as: WCF in the Java world is __ the equivalent of WPF in the Java world is _ the closes thing to JBoss in the .NET world is _ the JVM and CLR are essentially the same except for these differences: .... in the Java world you don't have the concept of WF/WCF/WPF, instead you have .... there is no "LINQ" in the Java world yet, but you can use ___ the closest you get to ADO.NET Data Services in the Java world is .... I'm not looking to debate this so I'm not looking for "fighting points", I just need a neutral what-is-what chart comparing the two worlds.

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• C++ to bytecode compiler for Silverlight CLR?

  - by paleozogt

  I'd like to be able to compile a C/C++ library so that it runs within a safe managed runtime in the Silverlight CLR. There are several tools for doing this with the JVM that allows C++ code to run within a CRT emulation layer (see NestedVM, LLJVM, etc), which effectively allows C++ code to be run within a Java Applet. There's even a tool for this for the Adobe Flash VM (see Alchemy). However, I can't seem to find any tools like this for the CLR. fyi, the MSVC tools don't seem to allow for this: The /clr:pure flag will create C++ code that runs in the CLR, but it isn't safe (because the CRT isn't safe) and /clr:safe requires massive code changes (no native types, etc).

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• Is java HashMap.clear() and remove() memory effective?

  - by Shaman

  Consider the follwing HashMap.clear() code: /** * Removes all of the mappings from this map. * The map will be empty after this call returns. */ public void clear() { modCount++; Entry[] tab = table; for (int i = 0; i < tab.length; i++) tab[i] = null; size = 0; } It seems, that the internal array (table) of Entrys is never shrinked. So, when I add 10000 elements to a map, and after that call map.clear(), it will keep 10000 nulls in it's internal array. So, my question is, how does JVM handle this array of nothing, and thus, is HashMap memory effective?

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• using BOSH/similar technique for existing application/system

  - by SnapConfig.com

  We've an existing system which connects to the the back end via http (apache/ssl) and polls the server for new messages, needless to say we have scalability issues. I'm researching on removing this polling and have come across BOSH/XMPP but I'm not sure how we should take the BOSH technique (using long lived http connection). I've seen there are few libraries available but the entire thing seems bloaty since we do not need buddy lists etc and simply want to notify the clients of available messages. The client is written in C/C++ and works across most OS so that is an important factor. The server is in Java. does bosh result in huge number of httpd processes? since it has to keep all the clients connected, what would be the limit on that. we are also planning to move to 64 bit JVM/apache what would be the max limit of clients in that case. any hints?

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• Limiting the size of the managed heap in a C# application

  - by Assaf Lavie

  Can I configure my C# application to limit its memory consumption to, say, 200MB? IOW, I don't want to wait for the automatic GC (which seems to allow the heap to grow much more than actually needed by this application). I know that in Java there's a command line switch you can pass to the JVM that achieves this.. is there an equivalent in C#? p.s. I know that I can invoke the GC from code, but that's something I would rather not have to do periodically. I'd rather set it once upon startup somehow and forget it.

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• How to catch printf from a dll?

  - by Xarx

  I've got a C++ console application that uses a third-party dll (jvm.dll, indirectly) that uses printf to print various error messages (Java stacktrace). I need to catch these stacktraces to a string in order to process them further, or at least to see them printed on the console. The thing is that I see the stacktrace only when debugging my application in VisualStudio (VS 2010). When I run my application in the "normal way", i.e. from the command line, nothing is printed on the console. So VS is able to somehow interfere the java output and display it. I need to be able to do the same thing. I've already tried freopen(), but without success. Also, I've found this question on the same problem, but without a clear answer.

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• Is there a possibility to run applets on Android or Blackberry?

  - by Maxood

  This is what the Java site www.java.com says: "KVM, the virtual machine for mobile devices, is the counterpart of JVM (Java virtual machine). It is used to run applets and applications written with Java technology on mobile devices. KVM must be installed by the manufacturer. It is NOT available for download or installation by consumers". Now Android has a customized virtual machine called DVM (Dalvik Virtual Machine). Can we compare it with KVM? Wonder if we can further reprogram DVM to incorporate features of KVM to run applets on Android? Same goes for Blacberry, is there a possibility?

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• How to indefinitely pause a thread in Java and later resume it?

  - by Carlos Torres

  Maybe this question has been asked many times before, but I never found a satisfying answer. The problem: I have to simulate a process scheduler, using the round robin strategy. I'm using threads to simulate processes and multiprogramming; everything works fine with the JVM managing the threads. But the thing is that now I want to have control of all the threads so that I can run each thread alone by a certain quantum (or time), just like real OS processes schedulers. What I'm thinking to do: I want have a list of all threads, as I iterate the list I want to execute each thread for their corresponding quantum, but as soon the time's up I want to pause that thread indefinitely until all threads in the list are executed and then when I reach the same thread again resume it and so on. The question: So is their a way, without using deprecated methods stop(), suspend(), or resume(), to have this control over threads?

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• What causes "java.lang.IncompatibleClassChangeError: vtable stub"?

  - by JimN

  What causes "java.lang.IncompatibleClassChangeError: vtable stub"? In our application, we have seen this error pop up randomly and very seldom (just twice so far, and we run it a lot). It is not readily reproducible, even when restarting the app, using the same jvm/jars without rebuilding. As for our build process, we clean all classes/jars and rebuild them, so it's not the same problem as others have encountered where they made a change in one class and didn't recompile some other dependent classes. This is unlike some of the other questions related to IncompatibleClassChangeError -- none of them mention "vtable stub". In fact, there are surprisingly few google results when searching for "IncompatibleClassChangeError "vtable stub"".

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• Anyone up to creating a tomcat based alternative for GAE?

  - by bach

  Hi, If we had the possibility to run GAE app without any code change on our servlet engine that would be great because: in case that google changes their billing policy we can just jump to our own server or in case their current policy doesn't fit our app needs we can do stuff which is not allowed in the GAE, compromising a 1 JVM, 1 DB We don't actually need a distributed system but more of a realtime system with synchronize, true locking mechanisms, other servers/software installed on the server machine, socket interface etc... Such a package should include at least: TomCat (or equivalent) DataNucleus Access Platform (Task Queue service) Any idea if it's easy to get such a thing or if it's already exist somewhere? Thanks

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• What is cached on a client machine when using https.

  - by TroyP

  I have an application that is working on https for everybody and on http for all but two users. The two users get a JavaScript error when trying to "edit" a page while on http but can edit the page on https. The problem is for occurs for both IE6 and FF3.6 for one of these users. Others have no problem using any browser. I have used Charles Proxy to look at the server response and no request is being made to https when on http and all browser requests return successfully. I have cleared all caches known to me on the clients (browser, jvm). Are http and https caches stored in different locations on the clients computers. Could a cached encrypted file be being read on the unencrypted port.

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• Problem with starting OpenOffice service (soffice) from Java (command working in commandline, but no

  - by Shervin

  I want to exceute a simple command which works from the shell but doesn't work from Java. This is the command I want to execute, which works fine: soffice -headless "-accept=socket,host=localhost,port=8100;urp;" This is the code I am excecuting from Java trying to run this command: String[] commands = new String[] {"soffice","-headless","\"-accept=socket,host=localhost,port=8100;urp;\""}; Process process = Runtime.getRuntime().exec(commands) int code = process.waitFor(); if(code == 0) System.out.println("Commands executed successfully"); When I run this program I get "Commands executed successfully". However the process is not running when the program finishes. Is it possible that the JVM kills the program after it has run? Why doesn't this work?

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• HPC (mainly on Java)

  - by Insectatorious

  I'm looking for some way of using the number-crunching ability of a GPU (with Java perhaps?) in addition to using the multiple cores that the target machine has. I will be working on implementing (at present) the A* Algorithm but in the future I hope to replace it with a Genetic Algorithm of sorts. I've looked at Project Fortress but as I'm building my GUI in JavaFX, I'd prefer not to stray too far from a JVM. Of course, should no feasible solution be available, I will migrate to the easiest solution to implement.

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