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  • How to fire off a asych thread in a web application, and gaurantee only 1 thread fires?

    - by Blankman
    I want to cache a object in memory. Regenerating the object when the cache expires is fairly expensive, so I want to do the following: When the cache is "about" to expire, I want to fire off a asychronous thread that will go and rebuild the object and then reset the cache. One thing I am worry about is multiple threads firing to fetch the object to cache, I only want a single thread doing this, realizing many people will be hitting the website. This might not be the best use case to do this, but I want to know how to do this sort of thing.

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  • how to selectively filter items in a collection

    - by Samuel
    I use the following snippet to filter the list of selected users, where isSelected is a boolean variable. Is there a simpler way (helper function) to populate the selectedUsers collection instead of writing the following lines of code. List<User> selectedUsers = new ArrayList<User>(0); for (User user : this.getUsers()) { if (user.isSelected()) { selectedUsers.add(user.getId()); } }

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  • how should i load a bitmap for an android game?

    - by Heysus Escobar
    i been working on a game with no bitmaps or anything, I'm using rectangles as objects and changing their color for their purpose like a red rectangles for player and gray rectangles for walls. My question is what is the right way to replace the rectangles with bitmaps/images? I know to load Bitmaps you can just do this : Bitmap randomBitmap = BitmapFactory.decodeResource(getResources(), com.example.android4gametest.R.drawable.ic_launcher); Should i load all my Bitmaps and pass them to their Classes or should i load the bitmap inside their class instead of passing it ? and how would i do that because i cannot use the BitmapFactory because i have no access to the getResources()! or should i load my bitmaps/images from my assets folder which i know i wont have the same "tools" you can say to mess with the bitmap.

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  • Proper structure for dependency injection (using Guice)

    - by David B.
    I would like some suggestions and feedback on the best way to structure dependency injection for a system with the structure described below. I'm using Guice and thus would prefer solutions centered around it's annotation-based declarations, not XML-heavy Spring-style configuration. Consider a set of similar objects, Ball, Box, and Tube, each dependent on a Logger, supplied via the constructor. (This might not be important, but all four classes happen to be singletons --- of the application, not Gang-of-Four, variety.) A ToyChest class is responsible for creating and managing the three shape objects. ToyChest itself is not dependent on Logger, aside from creating the shape objects which are. The ToyChest class is instantiated as an application singleton in a Main class. I'm confused about the best way to construct the shapes in ToyChest. I either (1) need access to a Guice Injector instance already attached to a Module binding Logger to an implementation or (2) need to create a new Injector attached to the right Module. (1) is accomplished by adding an @Inject Injector injectorfield to ToyChest, but this feels weird because ToyChest doesn't actually have any direct dependencies --- only those of the children it instantiates. For (2), I'm not sure how to pass in the appropriate Module. Am I on the right track? Is there a better way to structure this? The answers to this question mention passing in a Provider instead of using the Injector directly, but I'm not sure how that is supposed to work. EDIT: Perhaps a more simple question is: when using Guice, where is the proper place to construct the shapes objects? ToyChest will do some configuration with them, but I suppose they could be constructed elsewhere. ToyChest (as the container managing them), and not Main, just seems to me like the appropriate place to construct them.

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  • J2SE Client Server App: Client calls RMI method. Server handles RMI method and returns, but Client

    - by Mike
    J2SE Client Server App: Client calls RMI message. Server handles RMI method and returns, but Client never receives it. Any ideas how this could happen? Our attempted solution is to set client read timeouts and come up with a framework for resending requests or otherwise handling those failures gracefully. But really, I'd like to know any root causes for how this might happen rather than addressing the symptoms.

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  • inter servlet communication

    - by mithun1538
    Hello everyone, I have two servlets: LoginServlet and MailServlet. LoginServlet queries a mysql table using jdbc to get a string(eMail). What I want is to forward this string to MailServlet which in turn will send an email to that e-mail ID sent by LoginServlet. My question is how do I call and send the variable eMail to MailServlet, from LoginServlet? I thought of creating an instance of the MailServlet as : MailServlet servlet = new MailServlet(); And then use the servlet object to call the function doGet() in MailServlet. But I am feeling that there is some error in this as this is not the right way to call a servlet. So how do I call and pass a variable to MailServlet?

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  • How to detect if a form input element of type file is empty

    - by Ankur
    I have some code which reads a file through a form field of type file <input type="file" ... /> I want to give the user another option of providing a url to a file rather than having to upload it as many are already online. How can I detect when this field is empty on the server side. I am using Apache Commons FileUpload FileItemStream item = iter.next(); name = item.getFieldName(); stream = item.openStream(); if(!item.isFormField()){ if(item.toString()!=""){ .... I need to detect when item is empty. The above code doesn't work, nor does using: if(item.equals(null)){ ....

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  • Validation of method parameters

    - by Anton Tsivarev
    I have a RESTful web service. For implementation using JAX-RS (Jersey). Have the following method: public void foo (@PathParam ("name") String uuid) { ... } I need to do validation of input parameters. And if data invalid throw WebApplicationException. I added my custom annotation CheckUuid (extends ): public void foo (@PathParam ("name") @CheckUuid String uuid) { ... } Is it possible to do validation using annotations on a stage when the method chosen, but not yet called? For example using PreProcessInterceptor?

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  • Android - save/restore state of custom class

    - by user1209216
    I have some class for ssh support - it uses jsch internally. I use this class on main activity, this way: public class MainActivity extends Activity { SshSupport ssh = new SshSupport(); ..... @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); //Handle events for ssh ssh.eventHandler = new ISshEvents() { @Override public void SshCommandExecuted(SshCommandsEnum commandType, String result) { } //other overrides here } //Ssh operations on gui item click @Override public void onItemClick(AdapterView<?> arg0, View v, int position, long arg3) { if (ssh.IsConnected() == false) { try { ssh.ConnectAsync(/*parameters*/); } catch (Exception e) { e.printStackTrace(); } } try { ssh.ExecuteCommandAsync(SshCommandsEnum.values()[position]); } catch (Exception e) { e.printStackTrace(); } } }); } It works very well. My application connects to ssh, performs all needed operation in background thread and results are reported to gui, via events as shown above. But nothing works after user change device orientation. It's clear for me - activity is re-created and all state is lost. Unfortunately, my SshSupport class object is lost as well. It's pretty easy to store gui state for dynamically changed/added objects (using put/get serializable etc methods). But I have no idea how to prevent my ssh object, ssh connected session being lost. Since my class is not serializable, I can't save it to bundle. Also, even if I make my SshSupport class serializable, jsch objects it uses still are not serializable. So what is the best way to solve this?

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  • Can Spring understand @Inject replacing Weld as a JSR-299 implementation?

    - by Thorbjørn Ravn Andersen
    I have noticed from several web pages that apparently Spring 3.0 supports @Inject from JSR-330. As we would really like to use JSR-299 syntax for dependency injection in our libraries for both web apps and stand-alone applications, and have alternatives to Weld, it would be nice if Spring could do this. Being a novice to Spring, I tried downloading the Spring Framework distribution and put all jars on the Eclipse build path. No Inject annotation so my existing test project using Weld did not compile. Can this be done with Spring? What do I need to do to get it running? (I am aware that Guice eventually will support this too. It is only in SVN for now, and if there is an official Spring release which can, that would be better.)

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  • "No row with the given identifier exists" although it DOES exist!

    - by roesslerj
    Hello all! I am using Hibernate and getting Exception in thread "main" org.hibernate.ObjectNotFoundException: No row with the given identifier exists: [<MyDbObject>#271] What is pretty weird about this error is, that the object with the given id exists in the database. I inserted the problematic record in another run of the application. If I access it in the same run (i.e. same hibernate session) there seem to be no problems retrieving the data. Just because it could be a fault of the mapping: public class ProblemClass { @ManyToOne(optional = false) private MyDbObject myDbObject; } public class MyDbObject { @OneToMany(mappedBy = "myDbObject") private List<ProblemClass> problemClasses; } I have absolutely no clue even where to look at. Any hints highly appreciated!

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  • Problem formatting in Eclipse

    - by fastcodejava
    I have a method in Eclipse as below. public String toString() { return "HouseVo [ " + "Name : " + this.name == null ? "" : this.name + "Address : " + this.address == null ? "" : this.address; } When I format it becomes: return "HouseVo [ " + "Name : " + this.name == null ? "" : this.name + "Address : " + this.address == null ? "" : this.address; Any way to fix it so it correctly formats?

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  • Maven profile for single module

    - by c0mrade
    I have a multi module maven project, which builds successfully, I'd like to build just one of the modules I have. How would I do that with profiles ? I could do it from console in two ways, one way is go to the child module and mvn package or I could use reactor to build just one module. Can I do the same thing with profiles? By modifying POM? Thank you EDIT If is impossible from POM, can I do it from settings.xml ?

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  • Set reference = null in finally block?

    - by deamon
    A colleague of mine sets reference to null in finally blocks. I think this is nonsense. public Something getSomething() { JDBCConnection jdbc=null; try { jdbc=JDBCManager.getConnection(JDBCTypes.MYSQL); } finally { JDBCManager.free(jdbc); jdbc=null; // <-- Useful or not? } } What do you think of it?

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  • Failing faster when URL content is not found, howto

    - by Jam
    I have a thread pool that loops over a bunch of pages and checks to see if some string is there or not. If String is found, or not found response is near instant, however if server is offline or application is not running getting a rejection seems to take seconds How can I change my code to fail faster? for (Thread thread : pool) { thread.start(); } for (Thread thread : pool) { try { thread.join(); } catch (InterruptedException e) { e.printStackTrace(); } } Here is my run method @Override public void run() { for (Box b : boxes) { try { connection = new URL(b.getUrl()).openConnection(); scanner = new Scanner(connection.getInputStream()); scanner.useDelimiter("\\Z"); content = scanner.next(); if (content.equals("YES")) { } else { System.out.println("\tFAILED ON " + b.getName() + " BAD APPLICATION STATE"); } } catch (Exception ex) { System.out.println("\tFAILED ON " + b.getName() + " BAD APPLICATION STATE"); } } }

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  • How to embed revision information using mercurial and maven (and svn)

    - by Zwei Steinen
    Our project had a nice hack (although I'm guessing there are better ways to do it) to embed revision information into the artifacts (jar etc.) when we used svn. Now we have migrated to mercurial, and we want to have a similar thing, but before I start working on a similar hack with mercurial, I wanted to know if there are better ways to do this. Thanks for your answers! <plugin> <groupId>org.codehaus.mojo</groupId> <artifactId>exec-maven-plugin</artifactId> <executions> <execution> <phase>process-classes</phase> <id>svninfo</id> <goals> <goal>exec</goal> </goals> <configuration> <executable>svn</executable> <arguments> <argument>info</argument> <argument>../</argument> <argument>></argument> <argument>target/some-project/META-INF/svninfo.txt</argument> </arguments> </configuration> </execution> </executions> </plugin>

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  • Making an efficient algorithm

    - by James P.
    Here's my recent submission for the FB programming contest (qualifying round only requires to upload program output so source code doesn't matter). The objective is to find two squares that add up to a given value. I've left it as it is as an example. It does the job but is too slow for my liking. Here's the points that are obviously eating up time: List of squares is being recalculated for each call of getNumOfDoubleSquares(). This could be precalculated or extended when needed. Both squares are being checked for when it is only necessary to check for one (complements). There might be a more efficient way than a double-nested loop to find pairs. Other suggestions? Besides this particular problem, what do you look for when optimizing an algorithm? public static int getNumOfDoubleSquares( Integer target ){ int num = 0; ArrayList<Integer> squares = new ArrayList<Integer>(); ArrayList<Integer> found = new ArrayList<Integer>(); int squareValue = 0; for( int j=0; squareValue<=target; j++ ){ squares.add(j, squareValue); squareValue = (int)Math.pow(j+1,2); } int squareSum = 0; System.out.println( "Target=" + target ); for( int i = 0; i < squares.size(); i++ ){ int square1 = squares.get(i); for( int j = 0; j < squares.size(); j++ ){ int square2 = squares.get(j); squareSum = square1 + square2; if( squareSum == target && !found.contains( square1 ) && !found.contains( square2 ) ){ found.add(square1); found.add(square2); System.out.println( "Found !" + square1 +"+"+ square2 +"="+ squareSum); num++; } } } return num; }

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  • problem with update the counter value

    - by Edan
    Hello, I having problem to update the counter (integer value). this is the definitions of the class: public class Item_Actions { private final int MAX_ITEMS = 100; private Item myItem[]; private int counter; public Item_Actions() { myItem = new Item[MAX_ITEMS]; counter++; } //Constructor add item into the menu (Description, type & price of Item) public void addItem(Item itm) { myItem[counter] = itm; counter++; }....... Now everytime I call the addItem constructor from another class, the counter always stays on zero. What causing it and how do I save the data inside? thanks

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  • Why do I have to explicitly cast sometimes for varargs?

    - by Daniel Lew
    I've got a Class that uses reflection a lot, so I wrote a method to help out: private <T> T callMethod(String methodName, Class[] parameterTypes, Object[] args) { try { Class c = mVar.getClass(); Method m = c.getMethod(methodName, (Class[]) parameterTypes); return (T) m.invoke(mVar, args); } // Insert exception catching here [...] } This worked well for any method that had parameters, however I had to explicitly cast parameterTypes to Class[] in order for this to work for methods with no parameters (e.g., callMethod('funName', null, null);). I've been trying to figure out why this is the case. It seems to me that if parameterTypes, when null, had no concept of what type it is (Class[]), then I'd need to cast it for getMethod(). But if that's the case, why is getMethod() able to tell the difference between null, and (Class[]) null when the method is invoked?

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