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  • interfacing: simplified

    - by code wombat
    i've been doing some research on interfaces and a simple layman's explanation for what it truly is. For some reason people love using overly complex explanations and jargon to explain truly simple concepts (guess it makes them feel big) and i have a gut feeling it's the same in this case. so from what i could grasp, it seems like interfaces are nothing more than a way to reserve method names, their return type if any, and the type and amount of arguments they accept. so when a class implements an interface (or interfaces) it is forced to define the body of each method from the interface(s). Am i on the nose with this one or do i need to keep digging? p.s. i know javascript doesn't have support for interfaces, but i still need to understand the concept because there are quite a few places where it's shown how to emulate to an extent.

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  • Pointers, links, object and reference count

    - by EugeneP
    String a = "a"; // allocate memory and write address of a memory block to a variable String b = "b"; // in a and b hold addresses b = a; // copy a address into b. // Now what? b value is completely lost and will be garbage collected //* next step a = null; // now a does not hold a valid address to any data, // still data of a object exist somewhere, yet we cannot get access to it. Correct me if there's a mistake somewhere in my reflexions. My question is: suppose anInstance object of type Instance has a property ' surname ' anInstance.getSurname() returns "MySurname". now String s = anInstance.getSurname(); anInstance = null; question is - is it true that getSurname value, namely MySurname will not be garbage collected because and only because it has active reference counter 0, and if other properties of anInstance have a zero reference counter, they'll be garbage collected?

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  • Using HSQLDB in production environments

    - by lewap
    I want to use HSQLDB in a production environment for stroring some data in memory and for data export using files. Does anybody have experience with using hsqldb in production environments? Is hsqldb treating server resources gracefully and does it cleanup unused resources properly?

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  • ExecutorSerrvice memory leak on exception

    - by TofuBeer
    I am having a hard time tracking this down since the profiler keeps crashing (hotspot error). Before I go too deep into figuring it out I'd like to know if I really have a problem or not :-) I have a few thread pools created via: Executors.newFixedThreadPool(10); The threads connect to different web sites and, on occasion, I get connection refused and wind up throwing an exception. When I later on call Future.get() to get the result it will then catch the ExecutionException that wraps the exception that was thrown when the connection could not be made. The program uses a fairly constant amount of memory up until the point in time that the exceptions get thrown (they tend to happen in batches when a particular site is overloaded). After that point the memory again remains constant but at a higher level. So my question is along the lines of is the memory behaviour (reported by "top" on Unix) expected because the exceptions just triggered something or do I probably have an actual leak that I'll need to track down? Additionally when Future.get() throws an exception is there anything else I need to do besides catch the exception (such as call Future.cancel() on it)?

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  • Keeping messages in queue in case of receiver crash

    - by John Doe
    Hi, We've a Spring JMS message listener container for receiving messages asynchronously. Using DefaultMessageListenerContainer and in sessionTransacted mode. I understand being in sessionTransacted mode means in case of an exception the message will be put back into the queue. But how can I make sure the message won't be deleted from the queue even if the receiver (which is picked the message) crashes or just the machine running it looses power? At first I thought CLIENT_ACKNOWLEDGE acknowledge mode should save me, but apparently it's not the case, Spring calls .acknowledge() no matter what. So here's my question, how can I guarantee the delivery? Using a custom MessageListenerContainer? Using a transaction manager?

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  • Question about factory classes

    - by devoured elysium
    Currently I have created a ABCFactory class that has a single method creating ABC objects. Now that I think of it, maybe instead of having a factory, I could just make a static method in my ABC Method. What are the pro's and con's on making this change? Will it not lead to the same? I don't foresee having other classes inherit ABC, but one never knows! Thanks

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  • Android HTTP Connection

    - by Ubersoldat
    Can anybody tell my why this doesn't work in the Android emulator? From the browser I have access and the server is internal. All I can think of is that I'm missing some configuration on my app so it can access the network layer. try { InetAddress server = Inet4Address.getByName("thehost"); //Doesn't work either //or InetAddress server2 = Inet4Address.getByAddress(new String("192.168.1.30").getBytes()); if(server.isReachable(5000)){ Log.d(TAG, "Ping!"); } Socket clientsocket = new Socket(server, 8080); } catch (UnknownHostException e) { Log.e(TAG, "Server Not Found"); } catch (IOException e) { Log.e(TAG, "Couldn't open socket"); } Throws an UnknownHostException Thanks

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  • business object and codelist

    - by feiroox
    Hi How to design a business object? I have a library which returns me an Object which have ten lists of other different objects. I need to store it into database all. List of objects are often like: class Item { private int id; private String name; private double point; } But the name is often the same. Like basic title of the product or code. Containing from 3 characters up to 70characters. Should I make conversion for every Object to: (or something similar) class ConvertedItem { private int id; private int code; private double point; } And have a separated table of codes ( I guess around 60). Or do not bother with duplicated stuff? It's not mission critical app. What would you do in my case? thanks in advance

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  • Two pass JSP page rendering

    - by dotsid
    Suppose an example. I have following interface: public interface DataSource<T> { Future<T> fetch(); } This datasource can do asynchronous data fetching. And we have following tag for using datasource in JSP: <html> <d:fetch from="${orderDS}" var="orders"> <c:foreach in="${orders}" var="order"> <div class="order"> <c:out value="${order.title}" /> </div> </c:foreach> </d:fetch> </html> So, what I want? I want JSP rendering engine to call my custom tag (FetchTag in this example) twice. On first call FetchTag will do DataSource.fetch() call and save Future locally as a object field. On second call FetchTag do Future.get() call and will be blocked until data becomes available. Is there any way to do such a thing?

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  • Extracting startup errors from Spring contexts

    - by sehugg
    Consider the following output from a Tomcat server under Eclipse: INFO: Initializing Coyote HTTP/1.1 on http-8080 INFO: Initialization processed in 634 ms INFO: Starting service Catalina INFO: Starting Servlet Engine: Apache Tomcat/6.0.20 SEVERE: Error listenerStart SEVERE: Context [/MyServlet] startup failed due to previous errors I would like to figure out what exception caused "Error listenerStart", but Spring seems to be preventing me from finding the error via Eclipse. I'd love to start Catalina manually, but that doesn't seem to do anything. What's the best way to find the hidden exception? I'm not afraid to use torture methods.

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  • Disposing a dialog in touch devices in lwuit

    - by MANISH
    I am displaying a dialog when a user touches the screen and want the dialog to dispose when the user touches anywhere outside the dialog.i have set setDisposeWhenPointerOutOfBounds() to true though by default it is...n hav written the following code in pointerReleased() event but whenever the user touches the screen outside of dialog the dialog disposes but not without executing the code that shud be executed only wen the x,y are within the dialog....plz help me out....ne1... public void pointerReleased(int x, int y) { dispose(); if (contains(x, y)) { actionCommand((cmds[l.getSelectedIndex()])); } }

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  • http_access.log on WebSphere 6.1.0.29

    - by DavidG
    I am running WebSphere 6.1.0.29 and I need to track the requests being made to an Enterprise Application. Previously I did this by routing the requests through a proxy server, but I need to repeat the exercise and I figure there must be a simpler way. Does anyone know how to enable HTTP access logging? I have been through the console an thought I had enabled http_access.log and http_error.log via: Application servers server1 HTTP error and NCSA access logging (where 'server1' is the application server) I've enabled the service at startup, and ticked the boxes to enable access logging and error logging - however... nothing has happened. I have restarted the server, restarted the Enterprise apps and even did a "find . -name" for the log files - but they don't seem to be anywhere on the system. I saw on a JavaRanch thread someone suggested writing a custom filter for requests in an application, but this seems like wild overkill - plus I am doing the logs to test a pre-built binary, so I don't want to mess with the code. Anyone have any ideas/suggestions? Help! :-)

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  • Is there any difference in which order I createCriteria and beginTransaction using Hibernate?

    - by user2519543
    Just wondering is there any difference when I beginTransaction [org.hibernate] before or after creating Criteria/Query etc.? example 1: ... Transaction tx= session.beginTransaction(); Criteria c = session.createCriteria(class); result = c.uniqueResult(); tx.commit(); ... example 2: ... Criteria c = session.createCriteria(class); Transaction tx= session.beginTransaction(); result = c.uniqueResult(); tx.commit(); ... Thanks.

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  • stop thread that does not get interrupted

    - by prmatta
    I have a thread that sits and reads objects off of an ObjectInputStream: public void run() { try { ois = new ObjectInputStream(clientSocket.getInputStream()); Object o; while ((o = ois.readObject()) != null) { //do something with object } } catch (Exception ex) { //Log exception } } readObject does not throw InterruptedException and as far as I can tell, no exception is thrown when this thread is interrupted. How do I stop this thread?

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  • Long running method causing race condition

    - by keeleyt83
    Hi, I'm relatively new with hibernate so please be gentle. I'm having an issue with a long running method (~2 min long) and changing the value of a status field on an object stored in the DB. The pseudo-code below should help explain my issue. public foo(thing) { if (thing.getStatus() == "ready") { thing.setStatus("finished"); doSomethingAndTakeALongTime(); } else { // Thing already has a status of finished. Send the user back a message. } } The pseudo-code shouldn't take much explanation. I want doSomethingAndTakeALongTime() to run, but only if it has a status of "ready". My issue arises whenever it takes 2 minutes for doSomethingAndTakeALongTime() to finish and the change to thing's status field doesn't get persisted to the database until it leaves foo(). So another user can put in a request during those 2 minutes and the if statement will evaluate to true. I've already tried updating the field and flushing the session manually, but it didn't seem to work. I'm not sure what to do from here and would appreciate any help. PS: My hibernate session is managed by spring.

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  • Does Hibernate support one-to-one associations as pkeys?

    - by Andrzej Doyle
    Hi all, Can anyone tell me whether Hibernate supports associations as the pkey of an entity? I thought that this would be supported but I am having a lot of trouble getting any kind of mapping that represents this to work. In particular, with the straight mapping below: @Entity public class EntityBar { @Id @OneToOne(optional = false, mappedBy = "bar") EntityFoo foo // other stuff } I get an org.hibernate.MappingException: "Could not determine type for: EntityFoo, at table: ENTITY_BAR, for columns: [org.hibernate.mapping.Column(foo)]" Diving into the code it seems the ID is always considered a Value type; i.e. "anything that is persisted by value, instead of by reference. It is essentially a Hibernate Type, together with zero or more columns." I could make my EntityFoo a value type by declaring it serializable, but I wouldn't expect this would lead to the right outcome either. I would have thought that Hibernate would consider the type of the column to be integer (or whatever the actual type of the parent's ID is), just like it would with a normal one-to-one link, but this doesn't appear to kick in when I also declare it an ID. Am I going beyond what is possible by trying to combine @OneToOne with @Id? And if so, how could one model this relationship sensibly?

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  • how to share a variable between two threads

    - by prmatta
    I just inherited some code, two threads within this code need to perform a system task. One thread should do the system task before the other thread. They should not be performing the system task together. The two threads do not have references to each other. Now, I know I can use some sort of a semaphore to achieve this. But my question is what is the right way to get both threads to access this semaphore. I could create a static variable/method a new class : public class SharedSemaphore { private static Semaphore s = new Semaphore (1, true); public static void performSystemTask () { s.acquire(); } public static void donePerformingSystemTask() { s.release(); } } This would work (right?) but this doesn't seem like the right thing to do. Because, the threads now have access to a semaphore, without ever having a reference to it. This sort of thing doesn't seem like a good programming practice. Am I wrong?

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  • How to retrieve the ordered list of best articles having a minimum number of votes by using HSQL ?

    - by fabien7474
    I have a Vote domain class from my grails application containing properties like article_id and note I want to HQL query the Vote domain class in order to retrieve the 5 best rated articles having at least 10 votes. I tried : SELECT v.article_id, avg(v.note), count(*) FROM vote v where count(*) >= 10 group by v.article_id order by avg(v.note) desc limit 5; But unfortunately the insertion of where count(*) >= 10 throws an error. How can I do that in a simple way? Thank you for your help.

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  • Just need someone familiar with HTTPClient to check over a piece of code

    - by jax
    here are two little helper methods I have made for downloading files. I have had to mix and match different tutorials of the web to get what I have here. Now is there anything that I have done blatantly wrong here? public static InputStream simplePostRequest(URL url, List<NameValuePair> postData) throws ClientProtocolException, IOException { DefaultHttpClient httpclient = new DefaultHttpClient(); HttpPost postMethod=new HttpPost(url.toExternalForm()); postMethod.setEntity(new UrlEncodedFormEntity(postData, HTTP.UTF_8)); HttpResponse response = httpclient.execute(postMethod); HttpEntity entity = response.getEntity(); return entity.getContent(); } public static InputStream simpleGetRequest(URL url, List<NameValuePair> queryString) throws ClientProtocolException, IOException { Uri.Builder uri = new Uri.Builder(); uri.path(url.getPath()); for(NameValuePair nvp: queryString) { uri.appendQueryParameter(nvp.getName(), nvp.getValue()); } DefaultHttpClient httpClient = new DefaultHttpClient(); HttpHost host = new HttpHost(url.getHost()); HttpResponse response = httpClient.execute(host, new HttpGet(uri.build().toString())); HttpEntity entity = response.getEntity(); return entity.getContent(); }

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  • How to properly encode "[" and "]" in queries using Apache HttpClient?

    - by Jason Nichols
    I've got a GET method that looks like the following: GetMethod method = new GetMethod("http://host/path/?key=[\"item\",\"item\"]"); Such a path works just fine when typed directly into a browser, but the above line when run causes an IllegalArgumentException : Invalid URI. I've looked at using the URIUtils class, but without success. Is there a way to automatically encode this (or to add a query string onto the URL without causing HttpClient to barf?).

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  • Servlet Security question about j_security_check, j_username and j_password

    - by Nitesh Panchal
    Hello, I used jdbcRealm in my web application and it's working fine. I defined all constraints also in my web.xml. Like all pages of url pattern /Admin/* should be accessed by only admin. I have a login form with uses standard j_security_check, j_username and j_password. Now, when i type Admin/home.jsf it rightly redirects me login.jsf and there when i type the password i am redirected to home.jsf. This works alright but problem comes i directly go to login.jsf and then type password and username. This time it again redirects me to login.jsf. Is there any way through which i can specify which page to go when successful login is there? I need to specify different different pages for different roles. For Admin, it is /Admin/home.jsf for general users it is /General/home.jsf because login form is shared between different type of users. Where do i specify all these things? Secondly, i want to have a remember me checkbox at the end of login form. How do i do this? By default, it is submitted to j_security_check servlet and i have no control over its execution. Please help. This doesn't seem so hard but looks like i am missing something.

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