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  • Java - JPA - Generators - @SequenceGenerator

    - by Yatendra Goel
    I am learning JPA and have confusion in the @SequenceGenerator annotation. Upto my understanding, it automatically assigns a value to numeric identity fields/properties of an entity. Q1. Does this sequence generator make use of the database's increasing numeric value generating capability or generates the number on his own? Q2. If JPA uses database auto increement feauture, then will it work with datastores that don't have auto increement feature? Q3. If JPA generate numeric value on his own, then how the JPA implementation knows which value to generate next? Does it consult with the database first to see what value was stored last so as to generate the value (last + 1). ====================================================================================== Q4. Please also throw some light on sequenceName and allocationSize properties of @SequenceGenerator annotation.

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  • [java] Returning the element number of the longest string in an array

    - by JohnRoberts
    Hoookay, so. I'm trying to get the longestS method to take the user-inputted array of strings, then return the element number of the longest string in that array. I got it to the point where I was able to return the number of chars in the longest string, but I don't believe that will work for what I need. My problem is that I keep getting incompatible type errors when trying to figure this out. I don't understand the whole data type thing with strings yet. It's confusing me how I go about return a number of the array yet the array is of strings. The main method is fine, I got stuck on the ???? part. { public static void main(String [] args) { Scanner inp = new Scanner( System.in ); String [] responseArr= new String[4]; for (int i=0; i<4; i++) { System.out.println("Enter string "+(i+1)); responseArr[i] = inp.nextLine(); } int highest=longestS(responseArr); } public static int longestS(String[] values) { int largest=0 for( int i = 1; i < values.length; i++ ) { if ( ????? ) } return largest; } }

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  • Fastest way to pad a number in Java to a certain number of digits

    - by Martin
    Am trying to create a well-optimised bit of code to create number of X-digits in length (where X is read from a runtime properties file), based on a DB-generated sequence number (Y), which is then used a folder-name when saving a file. I've come up with three ideas so far, the fastest of which is the last one, but I'd appreciate any advice people may have on this... 1) Instantiate a StringBuilder with initial capacity X. Append Y. While length < X, insert a zero at pos zero. 2) Instantiate a StringBuilder with initial capacity X. While length < X, append a zero. Create a DecimalFormat based on StringBuilder value, and then format the number when it's needed. 3) Create a new int of Math.pow( 10, X ) and add Y. Use String.valueOf() on the new number and then substring(1) it. The second one can obviously be split into outside-loop and inside-loop sections. So, any tips? Using a for-loop of 10,000 iterations, I'm getting similar timings from the first two, and the third method is approximately ten-times faster. Does this seem correct? Full test-method code below... // Setup test variables int numDigits = 9; int testNumber = 724; int numIterations = 10000; String folderHolder = null; DecimalFormat outputFormat = new DecimalFormat( "#,##0" ); // StringBuilder test long before = System.nanoTime(); for ( int i = 0; i < numIterations; i++ ) { StringBuilder sb = new StringBuilder( numDigits ); sb.append( testNumber ); while ( sb.length() < numDigits ) { sb.insert( 0, 0 ); } folderHolder = sb.toString(); } long after = System.nanoTime(); System.out.println( "01: " + outputFormat.format( after - before ) + " nanoseconds" ); System.out.println( "Sanity check: Folder = \"" + folderHolder + "\"" ); // DecimalFormat test before = System.nanoTime(); StringBuilder sb = new StringBuilder( numDigits ); while ( sb.length() < numDigits ) { sb.append( 0 ); } DecimalFormat formatter = new DecimalFormat( sb.toString() ); for ( int i = 0; i < numIterations; i++ ) { folderHolder = formatter.format( testNumber ); } after = System.nanoTime(); System.out.println( "02: " + outputFormat.format( after - before ) + " nanoseconds" ); System.out.println( "Sanity check: Folder = \"" + folderHolder + "\"" ); // Substring test before = System.nanoTime(); int baseNum = (int)Math.pow( 10, numDigits ); for ( int i = 0; i < numIterations; i++ ) { int newNum = baseNum + testNumber; folderHolder = String.valueOf( newNum ).substring( 1 ); } after = System.nanoTime(); System.out.println( "03: " + outputFormat.format( after - before ) + " nanoseconds" ); System.out.println( "Sanity check: Folder = \"" + folderHolder + "\"" );

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  • Java consistent synchronization

    - by ring0
    We are facing the following problem in a Spring service, in a multi-threaded environment: three lists are freely and independently accessed for Read once in a while (every 5 minutes), they are all updated to new values. There are some dependencies between the lists, making that, for instance, the third one should not be read while the second one is being updated and the first one already has new values ; that would break the three lists consistency. My initial idea is to make a container object having the three lists as properties. Then the synchronization would be first on that object, then one by one on each of the three lists. Some code is worth a thousands words... so here is a draft private class Sync { final List<Something> a = Collections.synchronizedList(new ArrayList<Something>()); final List<Something> b = Collections.synchronizedList(new ArrayList<Something>()); final List<Something> c = Collections.synchronizedList(new ArrayList<Something>()); } private Sync _sync = new Sync(); ... void updateRunOnceEveryFiveMinutes() { final List<Something> newa = new ArrayList<Something>(); final List<Something> newb = new ArrayList<Something>(); final List<Something> newc = new ArrayList<Something>(); ...building newa, newb and newc... synchronized(_sync) { synchronized(_sync.a) { _synch.a.clear(); _synch.a.addAll(newa); } synchronized(_sync.b) { ...same with newb... } synchronized(_sync.c) { ...same with newc... } } // Next is accessed by clients public List<Something> getListA() { return _sync.a; } public List<Something> getListB() { ...same with b... } public List<Something> getListC() { ...same with c... } The question would be, is this draft safe (no deadlock, data consistency)? would you have a better implementation suggestion for that specific problem? update Changed the order of _sync synchronization and newa... building. Thanks

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  • java protected method accessibility

    - by JavaUser
    In the below code the Consumer class can access the protected method of Parent class.How is it possible since there is no relation between Parent and Consumer class.Please explain class Parent { public void method1(){ System.out.println("PUBLIC METHOD"); } private void method2(){ System.out.println("PRIVATE METHOD"); } protected void method3(){ System.out.println("PROTECTED METHOD"); } } public class Consumer { public static void main(String[] args){ Parent parentObj = new Parent(); parentObj.method1(); //parentObj.method2(); parentObj.method3(); } } Thanks

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  • How to remove namespace in saop using java?

    - by atknatk
    I have imported a WSDL and use it to send a SOAP request. It looks like this: <Envelope xmlns="http://schemas.xmlsoap.org/soap/envelope/"> <Body> <version xmlns="http://www.tempuri.org"> <parRequest xmlns=""> <faturaUUID>[string?]</faturaUUID> <faturaNo>[string?]</faturaNo> <faturaReferansNo>[string?]</faturaReferansNo> <durumKodu>[int]</durumKodu> <durumAciklamasi>[string?]</durumAciklamasi> </parRequest> </version> </Body> </Envelope> But I want to remove xmlns="" such as <Envelope xmlns="http://schemas.xmlsoap.org/soap/envelope/"> <Body> <acceptResponse xmlns="http://tempuri.org/"> <responseRes> <faturaUUID>[string?]</faturaUUID> <faturaNo>[string?]</faturaNo> <faturaReferansNo>[string?]</faturaReferansNo> <durumKodu>1</durumKodu> <durumAciklamasi>[string?]</durumAciklamasi> </responseRes> </acceptResponse> </Body> </Envelope> My web service code: @WebService(serviceName = "test", targetNamespace = "http://www.tempuri.org") public class ErpEntServ { @WebMethod(operationName = "version") public String version(@WebParam(name = "parRequest") acceptResponse acceptResponse) { return "0"; } how to remove it? I try to @WebParam(name = "parRequest",targetNamespace = "http://www.tempuri.org") acceptResponse acceptResponse but it did not. Thank you for helping

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  • Adding file names to an array list in java

    - by Chris G
    Hi I am currently needing to load the contents of a folders filenames to an arraylist I have but I am unsure as how to do this. To put it into perspective I have a folder with One.txt, Two.txt, Three.txt etc. I want to be able to load this list into an arraylist so that if I was to check the arraylist its contents would be : arraylist[0] = One arraylist[1] = Two arraylist[3] = Three If anyone could give me any insight into this it would be much appreciated.

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  • Java file searching problem

    - by Infinity
    Hello guys! I need to search a file for a word and return the whole line and the line number with this word, then edit the line and write back to the file. Maybe the line number isn't necesary to edit a line in a file. I `was reading after seraching with regexp and opening the filechannel of the file, but I can't get the line number. Maybe there are other better ways to do this. Can you help me how to start this?

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  • how to display a image in java application after downloading the image

    - by Nubkadiya
    i want to display a image after downloading that image from a web-server i have wrote the code for downloading the image. but i cant set it up to a label or any thing other than jframe (because i want to add more buttons and labels to the GUI). here is the code to download the image from the webserver. now i want to set it to a label. please help me URL url = new URL("http://www.personal.psu.edu/acr117/blogs/audrey/images/image-2.jpg"); image = ImageIO.read(url);

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  • java alternative for phpMyAdmin

    - by rcourtna
    I find myself working in an environment where all I have access to is Tomcat + MySQL. No Apache, no PHP. I'm looking for a web interface to MySQL that will run under Tomcat (can't be a desktop interface, as the mysql port is not accessible). I'm tried jMyAdmin and javaMyAdmin. I can't get either to work, and both lack documentation and community support. Can anyone make a recommendation please?

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  • PLEASE HELP JAVA/SQL question

    - by fred-ghosn
    Hello everyone, well I'm new here and I really need some help.. I want to create a table and this table's name will be inserted from a textfield. However when I run the query it's giving me an error, any help on this one? Ill paste the code here: public boolean CreateTable() { TableNumber=jTextField4.getText(); try { String password = null; String s = "CREATE TABLE '"+TableNumber+'" (Item char(50),Price char(50))"; ConnectionForOrders(); stmt = conn.createStatement(); stmt.executeUpdate(s); boolean f=false; ConnectionForOrdersclose();

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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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  • Java: Tracking a user login session - Session EJBs vs HTTPSession

    - by bguiz
    If I want to keep track of a conversational state with each client using my web application, which is the better alternative - a Session Bean or a HTTP Session - to use? Using HTTP Session: //request is a variable of the class javax.servlet.http.HttpServletRequest //UserState is a POJO HttpSession session = request.getSession(true); UserState state = (UserState)(session.getAttribute("UserState")); if (state == null) { //create default value .. } String uid = state.getUID(); //now do things with the user id Using Session EJB: In the implementation of ServletContextListener registered as a Web Application Listener in WEB-INF/web.xml: //UserState NOT a POJO this this time, it is //the interface of the UserStateBean Stateful Session EJB @EJB private UserState userStateBean; public void contextInitialized(ServletContextEvent sce) { ServletContext servletContext = sce.getServletContext(); servletContext.setAttribute("UserState", userStateBean); ... In a JSP: public void jspInit() { UserState state = (UserState)(getServletContext().getAttribute("UserState")); ... } Elsewhere in the body of the same JSP: String uid = state.getUID(); //now do things with the user id It seems to me that the they are almost the same, with the main difference being that the UserState instance is being transported in the HttpRequest.HttpSession in the former, and in a ServletContext in the case of the latter. Which of the two methods is more robust, and why?

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  • Can I avoid repeating myself in this situation (Java)

    - by UltimateGuy
    if (openFile == null) { new AppFileDialog().chooseFile("Save", appFrame); } if (openFile == null) { return; } Here I need to check to see if the user has already chosen a file. If not, they are given a prompt to. If the file is still null, the function returns without saving. The problem is the two identical if statements, can I avoid it? I take DRY very seriously, but at the same time KISS. Ideally the two go hand in hand, but in a situation like this, it seems they are mutually exclusive.

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  • java memory usage

    - by xdevel2000
    I know I always post a similar question about array memory usage but now I want post the question more specific. After I read this article: http://www.javamex.com/tutorials/memory/object_memory_usage.shtml I didn't understand some things: the size of a data type is always the same also on different platform (Linux / Windows 32 / 64 bit)??? so an int will be always 32 bit?; when I compute the memory usage I must put also the reference value itself? If I have an object to a class that has an int field its memory will be 12 (object header) + 4 reference + 4 (the int field) + 3 (padding) = 24 bytes??

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  • Changing Color with LinearLayout and TextView in Java (Android)

    - by Rob S.
    I'm a relatively new Android developer and I noticed what seems like an oddity to me that I'm hoping someone can explain. I have LinearLayout ll. This line of code fails for me when executed: ll.setBackgroundColor(R.color.white); However this line of code works: ll.setBackgroundResource(R.color.white); I assume its simply because I have white defined in my resources. However, I've also tried passing 0xFFFFFF in setBackgroundColor() and that doesn't work either. Similarly with my TextView text this line of code fails when executed: text.setTextColor(R.color.white); I can see my TextView so I know I initialized it correctly (like my LinearLayout which I can also see). So I guess my question boils down to: How do I properly use LinearLayout.setBackgroundColor() and TextView.setTextColor() ? Thanks a ton in advance. I've read through the docs and tried to find information online via googling and haven't come up with anything.

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  • Java, Massive message processing with queue manager (trading)

    - by Ronny
    Hello, I would like to design a simple application (without j2ee and jms) that can process massive amount of messages (like in trading systems) I have created a service that can receive messages and place them in a queue to so that the system won't stuck when overloaded. Then I created a service (QueueService) that wraps the queue and has a pop method that pops out a message from the queue and if there is no messages returns null, this method is marked as "synchronized" for the next step. I have created a class that knows how process the message (MessageHandler) and another class that can "listen" for messages in a new thread (MessageListener). The thread has a "while(true)" and all the time tries to pop a message. If a message was returned, the thread calls the MessageHandler class and when it's done, he will ask for another message. Now, I have configured the application to open 10 MessageListener to allow multi message processing. I have now 10 threads that all time are in a loop. Is that a good design?? Can anyone reference me to some books or sites how to handle such scenario?? Thanks, Ronny

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  • Java Logger only to file, no screen output!

    - by Tom Taylor
    Hello there SO'ers, I got a quite simple problem but cant find a solution for it. I have a logger with a file handler added, but it still spams to hell out of my console. How could I get the logger to solely route all output to a file, with NO console outputs? Thanks a lot, cru

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  • Statically checking a Java app for link errors

    - by monorailkitty
    I have a scenario where I have code written against version 1 of a library but I want to ship version 2 of the library instead. The code has shipped and is therefore not changeable. I'm concerned that it might try to access classes or members of the library that existed in v1 but have been removed in v2. I figured it would be possible to write a tool to do a simple check to see if the code will link against the newer version of the library. I appreciate that the code may still be very broken even if the code links. I am thinking about this from the other side - if the code won't link then I can be sure there is a problem. As far as I can see, I need to run through the bytecode checking for references, method calls and field accesses to library classes then use reflection to check whether the class/member exists. I have three-fold question: (1) Does such a tool exist already? (2) I have a niggling feeling it is much more complicated that I imagine and that I have missed something major - is that the case? (3) Do you know of a handy library that would allow me to inspect the bytecode such that I can find the method calls, references etc.? Thanks!

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