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  • Is this use of PreparedStatements in a Thread in JAVA correct?

    - by Gormcito
    I'm still an undergrad just working part time and so I'm always trying to be aware of better ways to do things. Recently I had to write a program for work where the main thread of the program would spawn "task" threads (for each db "task" record) which would perform some operations and then update the record to say that it has finished. Therefore I needed a database connection object and PreparedStatement objects in or available to the ThreadedTask objects. This is roughly what I ended up writing, is creating a PreparedStatement object per thread a waste? I thought static PreparedStatments could create race conditions... Thread A stmt.setInt(); Thread B stmt.setInt(); Thread A stmt.execute(); Thread B stmt.execute(); A´s version never gets execed.. Is this thread safe? Is creating and destroying PreparedStatement objects that are always the same not a huge waste? public class ThreadedTask implements runnable { private final PreparedStatement taskCompleteStmt; public ThreadedTask() { //... taskCompleteStmt = Main.db.prepareStatement(...); } public run() { //... taskCompleteStmt.executeUpdate(); } } public class Main { public static final db = DriverManager.getConnection(...); }

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  • What is the purpose of Process class in Java?

    - by Nitesh Panchal
    Runtime objRuntime = Runtime.getRuntime(); String strBackupString = "mysqldump -u " + userName + " -p" + password + " " + dbName; Process objProcess = objRuntime.exec(strBackupString); This is used for backup of database. But what exactly happens? Can anybody make me explain, what is the purpose of Runtime and Process class? Is this class used to act as if we are typing command from command prompt? Then what should i pass to objRuntime.exec() if i want to open notepad? And is the command executed as soon as we call exec method? If yes, then what purpose does Process serve here? I really can't understand these two classes. Please make me understand. Thanks in advance :)

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  • Selenium : Handling Loading screens obscuring the web elements. (Java)

    - by Sheldon Cooper
    I'm writing an automated test case for a web page. Here's my scenario. I have to click and type on various web elements in an html form. But, sometimes while typing on a text field, an ajax loading image appears , fogging all elements i want to interact with. So, I'm using web-driver wait before clicking on the actual elements like below, WebdriverWait innerwait=new WebDriverWait(driver,30); innerwait.until(ExpectedConditions.elementToBeClickable(By.xpath(fieldID))); driver.findelement(By.xpath(fieldID)).click(); But the wait function returns the element even if it is fogged by another image and is not clickable. But the click() throws an exception as Element is not clickable at point (586.5, 278). Other element would receive the click: <div>Loading image</div> Do I have to check every time if the loading image appeared before interacting with any elements?.(I can't predict when the loading image will appear and fog all elements.) Is there any efficient way to handle this? Currently I'm using the following function to wait till the loading image disappears, public void wait_for_ajax_loading() throws Exception { try{ Thread.sleep(2000); if(selenium.isElementPresent("id=loadingPanel")) while(selenium.isElementPresent("id=loadingPanel")&&selenium.isVisible("id=loadingPanel"))//wait till the loading screen disappears { Thread.sleep(2000); System.out.println("Loading...."); }} catch(Exception e){ Logger.logPrint("Exception in wait_for_ajax_loading() "+e); Logger.failedReport(report, e); driver.quit(); System.exit(0); } } But I don't know exactly when to call the above function, calling it at a wrong time will fail. Is there any efficient way to check if an element is actually clickable? or the loading image is present? Thanks..

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  • Java: most efficient way to defensively copy an int[]?

    - by Jason S
    I have an interface DataSeries with a method int[] getRawData(); For various reasons (primarily because I'm using this with MATLAB, and MATLAB handles int[] well) I need to return an array rather than a List. I don't want my implementing classes to return the int[] array because it is mutable. What is the most efficient way to copy an int[] array (sizes in the 1000-1000000 length range) ? Is it clone()?

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  • benefit os having a factory for object creation?

    - by ajsie
    im trying to understand the factory design pattern. i dont understand why it's good to have a middleman between the client and the product (object that the client wants). example with no factory: $mac = new Mac(); example with a factory: $appleStore = new AppleStore(); $mac = $appleStore->getProduct('mac'); how does the factory pattern decouple the client from the product? could someone give an example of a future code change that will impact on example 1 negative, but positive in example 2 so i understand the importance of decoupling? thanks

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  • Can you tell on runtime if you're running java from within a jar?

    - by Dikla
    Hi, I have an application that some of my users run from Eclipse, and others run it by using a jar file. I want some actions to be done when running from within the jar, but I don't want them to be done when running from Eclipse. Is there a way to know on runtime whether the current application is running from within a jar? Thanks! Dikla

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  • Is it a good or bad practice to call instance methods from a java constructor?

    - by Steve
    There are several different ways I can initialize complex objects (with injected dependencies and required set-up of injected members), are all seem reasonable, but have various advantages and disadvantages. I'll give a concrete example: final class MyClass { private final Dependency dependency; @Inject public MyClass(Dependency dependency) { this.dependency = dependency; dependency.addHandler(new Handler() { @Override void handle(int foo) { MyClass.this.doSomething(foo); } }); doSomething(0); } private void doSomething(int foo) { dependency.doSomethingElse(foo+1); } } As you can see, the constructor does 3 things, including calling an instance method. I've been told that calling instance methods from a constructor is unsafe because it circumvents the compiler's checks for uninitialized members. I.e. I could have called doSomething(0) before setting this.dependency, which would have compiled but not worked. What is the best way to refactor this? Make doSomething static and pass in the dependency explicitly? In my actual case I have three instance methods and three member fields that all depend on one another, so this seems like a lot of extra boilerplate to make all three of these static. Move the addHandler and doSomething into an @Inject public void init() method. While use with Guice will be transparent, it requires any manual construction to be sure to call init() or else the object won't be fully-functional if someone forgets. Also, this exposes more of the API, both of which seem like bad ideas. Wrap a nested class to keep the dependency to make sure it behaves properly without exposing additional API:class DependencyManager { private final Dependency dependency; public DependecyManager(Dependency dependency) { ... } public doSomething(int foo) { ... } } @Inject public MyClass(Dependency dependency) { DependencyManager manager = new DependencyManager(dependency); manager.doSomething(0); } This pulls instance methods out of all constructors, but generates an extra layer of classes, and when I already had inner and anonymous classes (e.g. that handler) it can become confusing - when I tried this I was told to move the DependencyManager to a separate file, which is also distasteful because it's now multiple files to do a single thing. So what is the preferred way to deal with this sort of situation?

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  • How to set up a different context to point to an external directory outside webapps Tomcat/Java

    - by pinkb
    Hi Folks, I am successful to map an external directory by creating an xml file like : <Context path="/uploads" docBase="C:\uploads\photos" crossContext="true"/> And I named this xml file as uploads.xml and saved under "#Tomcat\conf\Catalina\localhost" here # = Directory where Tomcat has been installed. And when I start Tomcat(5) from cammand line (batch file) i.e. startup.bat The images can be accessed normally like "http://localhost:8080/uploads/user1.png" It works. Actually I am using IntelliJ Idea 8 for devevelopment. When I start Tomcat from IntelliJ Idea, I am not able to access the context i.e. the images. "http://localhost:8080/uploads/user1.png" It shows "HTTP 400 Bad Request" The context path for my project is "http://localhost:8080/spark/" Any help or suggestion is needed at the earliest time. Looking forward to as many appreciative responses as possible. Thanx Pink

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  • How should nested components interact with model in a GUI application?

    - by fig-gnuton
    Broad design/architecture question. If you have nested components in a GUI, what's the most common way for those components to interact with data? For example, let's say a component receives a click on one of its buttons to save data. Should the save request be delegated up that component's ancestors, with the uppermost ancestor ultimately passing the request to a controller? Or are models/datastores in a GUI application typically singletons, so that a component at any level of a hierarchy can directly get/set data? Or is a controller injected as a dependency down the hierarchy of components, so that any given component is only one intermediary away from the datastore/model?

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  • Java JIT compiler compiles at compile time or runtime ?

    - by Tony
    From wiki: In computing, just-in-time compilation (JIT), also known as dynamic translation, is a technique for improving the runtime performance of a computer program. So I guess JVM has another compiler, not javac, that only compiles bytecode to machine code at runtime, while javac compiles sources to bytecode,is that right?

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  • Is there a way to launch an aggressive and complete garbage collection in Java?

    - by Gnoupi
    For memory optimization reasons, I'm launching myself the garbage collector during profiling, to check if objects are correctly cleaned after disposing of them. The call to garbage collector is not enough, though, and it seems that there is no guarantee of what it will clean. Is there a way to call it, to be sure it will recover as much as it can, in profiling conditions (this would have no point in production, of course)? Or is "calling it several times" the only way to be "almost sure"? Or did I simply misunderstand something about the Garbage Collector?

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  • Sequencing ajax requests

    - by Scott Evernden
    I find I sometimes need to iterate some collection and make an ajax call for each element. I want each call to return before moving to the next element so that I don't blast the server with requests - which often leads to other issues. And I don't want to set async to false and freeze the browser. Usually this involves setting up some kind of iterator context that i step thru upon each success callback. I think there must be a cleaner simpler way? Does anyone have a clever design pattern for how to neatly work thru a collection making ajax calls for each item?

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  • Java Swing: How to add a CellRenderer for displaying a Date?

    - by HansDampf
    I have a Table: public class AppointmentTableModel extends AbstractTableModel { private int columns; private int rows; ArrayList<Appointment> appointments;... So each row of the table contains one Appointment. public class Appointment { private Date date; private Sample sample; private String comment; private ArrayList<Action> history; public Appointment(Date date, Sample sample, String comment) { this.date = date; this.sample = sample; this.comment = comment; this.history = new ArrayList<Action>(); } public Object getByColumn(int columnIndex) { switch (columnIndex) { case 0: return date;//Date: dd:mm:yyyy case 1: return date;//Time mm:hh case 2: return sample;//sample.getID() int (sampleID) case 3: return sample;//sample.getNumber string (telephone number) case 4: return sample;//sample.getName string (name of the person) case 5: return history;//newst element in history as a string case 6: return comment;//comment as string } return null; I added in comments what this one is going to mean. How would I create CellRenderers to display it like this. table.getColumnModel().getColumn(1).setCellRenderer(new DateRenderer()); I also want to add the whole row to be painted in red when the date is later then the current date. And then another column that holds a JButton to open up another screen with the corresponding Appointment as parameter.

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  • Multithreaded java cache for objects that are heavy to create ?

    - by krosenvold
    I need a cache some objects with fairly heavy creation times, and I need exactly-once creation semantics. It should be possible to create objects for different CacheKeys concurrently. I think I need something that (under the hood) does something like this: ConcurrentHashMap<CacheKey, Future<HeavyObject>> Are there any existing open-source implementations of this that I can re-use ?

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