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  • Asynchronous email processing in Java web application

    - by Denise
    Hi everyone, I would like to implement asynchronous email sending in my web application when users register for a new account. This is so that if there is a problem or delay in sending the email message (e.g. the mail server is down or the network connection to the mail server is slow) the user won't be kept waiting for the sending to complete. My web app is built using Spring and Hibernate's implementation of JPA. What would be the best and most reliable way for me to implement asynchronous email processing in this web application? I am thinking about persisting the email information in a database table which is then regularly polled by a Quartz (http://www.opensymphony.com/quartz/) scheduled job for updates and when it finds new unsent emails, it attempts to send them. Is this a reasonable way of implementing what I want? Thanks.

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  • Java App Engine - ranked counter

    - by Richard
    I understand the sharded counter, here: http://code.google.com/appengine/articles/sharding_counters.html The problem is that a simple counter will not work in my application. I am sorting my entities by a particular variable so I am returned not so much a count, but more of a rank. My current method is: SELECT COUNT(this) FROM Entity.class WHERE value <= ? Result + 1 is then the rank of the parameter in relation to the value variable in the persistent Entity objects. The limitation of this is the highest rank being returned is 1001 because count() can give a maximum of 1000. The reason I cannot store the rank on the Entity object is that the ranks are updated very often, and re-setting this rank variable would be much too costly. Any ideas on the best way to accomplish this?

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  • Java variadic function parameters

    - by Amir Rachum
    Hi, I have a function that accepts a variable number of parameters: foo (Class... types); In which I get a certain number of class types. Next, I want to have a function bar( ?? ) That will accepts a variable number of parameters as well, and be able to verify that the variables are the same number (that's easy) and of the same types (the hard part) as was specified in foo. How can I do that? Edit: to clarify, a call could be: foo (String.class, Int.class); bar ("aaa", 32); // OK! bar (3); // ERROR! bar ("aa" , "bb"); //ERROR! Also, foo and bar are methods of the same class.

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  • Java / Tomcat memory leak in RedHat Linux?

    - by black-rocky
    Hi, I've got a Red Hat box with 6G memory running Tomcat and I'm trying to figure out how much memory I have left on the box. Problem is, top & jconsole is showing one figure (around 200M), and system monitor is showing a different figure (around 2G). Does anybody know what the difference is? I'm not sure if there is a memory leak happenning here, but the highest memory consumer is a tomcat process that's taking 2.2G of memory. Screenshots below:

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  • change the class loading order google app engine java

    - by Shekhar
    I am trying to create an application on google app engine using struts2. Struts2 internally uses freemarker .One of the Freemarker framework classes suppose X internally uses a class javax.swing.Treenode which is not in google app engine jre white list. Now in order to run my application i created a new class X in the same package structure as it was in freemarker framework and copied the class to WEB-INF classes.Then When i run my application it run fine. The problem is that i want to take out the class X from my application sourcecode and move it to newly created jar and place it in WEB-INF/lib folder. So that i can reuse the code in multiple project and my code remains clean of the freemarker code. But when i run the application it picks the old class X from the original freemarker framework.As a result i get ClassNotFoundException. Can anyone provide any help such that i can change the ClassLoading order such that my jar containing X class loads first.

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  • Java - Regex problem

    - by Yatendra Goel
    I want a regex to find the following types of strings: http://anything.abc.tld http://anything.abc.tld/ where abc - abc always remains abc anything - it could be any string tld - it could be any tld (top-level-domain) like .com .net .co.in .co.uk etc.

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  • Java generic return type

    - by Colby77
    Hi, I'd like to write a method that can accept a type param (or whatever the method can figure out the type from) and return a value of this type so I don't have to cast the return type. Here is a method: public Object doIt(Object param){ if(param instanceof String){ return "string"; }else if(param instanceof Integer){ return 1; }else{ return null; } } When I call this method, and pass in it a String, even if I know the return type will be a String I have to cast the return Object. This is similar to the int param. How shall I write this method to accept a type param, and return this type?

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  • Java repaint is slow under certain conditions.

    - by Gabriel A. Zorrilla
    I'm doing a simple grid which each square is highlighted by the cursor: They are a couple of JPanels, mapgrid and overlay inside a JLayeredPane, with mapgrid on the bottom. Mapgrid just draws on initialization the grid, its paint metodh is: public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2d = (Graphics2D) g; g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); for (int i = 0; i < h; i++) { for (int j = 0; j < w; j++) { g2d.setColor(new Color(128, 128, 128, 255)); g2d.drawRect(tileSize * j, i * tileSize, tileSize, tileSize); } } In the overlay JPanel is where the highlighting occurs, this is what is repainted when the mouse is moved: public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2d = (Graphics2D) g; g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); g2d.setColor(new Color(255, 255, 128, 255)); g2d.drawRect((pointerX/tileSize)*tileSize,(pointerY/ tileSize)*tileSize, tileSize, tileSize); } I noticed that even though the base layer (mapgrid) is NOT repainted when the mouse moves, just the transparent overlay layer, the performance is lacking. If i give the overlay JPanel a background, its way faster. If i remove the mapgrid Antialiasing, its a bit faster too. I don't know why giving a background to the overlay layer (and thus, hiding the mapgrid) or disabling antialiasing in the mapgrid leads to much better performance. Is there a better way to do this? Why does this happen?

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  • Java Charset problem on linux

    - by scot
    Hi, problem: I have a string containing special characters which i convert to bytes and vice versa..the conversion works properly on windows but on linux the special character is not converted properly.the default charset on linux is UTF-8 as seen with Charset.defaultCharset.getdisplayName() however if i run on linux with option -Dfile.encoding=ISO-8859-1 it works properly.. how to make it work using the UTF-8 default charset and not setting the -D option in unix environment. edit: i use jdk1.6.13 edit:code snippet works with cs = "ISO-8859-1"; or cs="UTF-8"; on win but not in linux String x = "½"; System.out.println(x); byte[] ba = x.getBytes(Charset.forName(cs)); for (byte b : ba) { System.out.println(b); } String y = new String(ba, Charset.forName(cs)); System.out.println(y); ~regards daed

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  • Add Hexidecimal Header Info to JPEG File Using Java

    - by jboyd
    I need to add header info to a JPEG file in order to get it to work properly when shared on some websites, I've tracked down the correct info through a lot of Hex digging, but now I'm kind of stuck trying to get it into the file. I know where in the file it needs to go, and I know how long it is, my problem is that RandomAccessFile just overwrites existing data in the file and FileOutputStream appends the data to the end. I don't want either, I want to INSERT data starting at the third byte. My example code: File fileToChange = new File("someimage.jpg"); byte[] i = new byte[2]; i[0] = (byte)Integer.decode("0xcc"); i[1] = (byte)Integer.decode("0xcc"); RandomAccessFile f = new RandomAccessFile(new File("videothing.jpg"), "rw"); long aPositionWhereIWantToGo = 2; f.seek(aPositionWhereIWantToGo); // this basically reads n bytes in the file f.write((byte[])i); f.close(); So this doesn't work because it overwrites, and does not insert, I can't find any way to just insert data into a file

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  • using Java interfaces

    - by mike_hornbeck
    I need to create interface MultiLingual, that allows to display object's data in different languages (not data itself, but introduction like "Author", "Title" etc.). Printed data looks like this : 3 grudnia 1998 10th of June 1924 Autor: Tolkien Tytul: LoTR Wydawnictwo: Amazon 2010 Author: Mitch Albom Title: Tuesdays with Morrie Publishing House: Time Warner Books 2003 37 360,45 PLN 5,850.70 GBP 3rd of December 1998 10th of June 1924 Author: Tolkien Title: LoTR Publishing House: Amazon 2010 Author: Mitch Albom Title: Tuesdays with Morrie Publishing House: Time Warner Books 2003 37,360.45 GBP 5,850.70 GBP Test code looks like this : public class Main { public static void main(String[] args){ MultiLingual gatecrasher[]={ new Data(3,12,1998), new Data(10,6,1924,MultiLingual.ENG), new Book("LoTR", "Tolkien", "Amazon", 2010), new Book("Tuesdays with Morrie", "Mitch Albom", "Time Warner Books",2003, MultiLingual.ENG), new Money(1232895/33.0,MultiLingual.PL), new Money(134566/23.0,MultiLingual.ENG), }; for(int i=0;i < gatecrasher.length;i++) System.out.println(gatecrasher[i]+"\n"); for(int i=0;i < gatecrasher.length;i++) System.out.println(gatecrasher[i].get(MultiLingual.ENG)+"\n"); } } So i need to introduce constants ENG, PL in MultiLingual interface, as well as method get(int language) : public interface MultiLingual { int ENG = 0; int PL= 1; String get(int lang); } And then I have class Book. Problem starts with the constructors. One of them needs to take MultiLingual.ENG as argument, but how to achieve that ? Is this the proper way? : class Book implements MultiLingual { private String title; private String publisher; private String author; public Book(String t, String a, String p, int y, MultiLingual lang){ } Or should I treat this MultiLingual.ENG as int variable , that will just change automatically constants in interface? Second constructor for book doesn't take MultLingual as argument, but following implementation is somehow wrong : public Book(String t, String a, String p, int y){ Book someBook = new Book(t, a, p, y, MultiLingual m); } I could just send int m in place of MultiLingual m but then I will have no control if language is set to PL or ENG. And finally get() method for Boook but I think at least this should be working fine: public String get(int lang){ String data; if (lang == ENG){ data = "Author: "+this.author+"\n"+ "Title: "+this.title+"\n"+ "Publisher: "+this.publisher+"\n"; } else { data = "Autor: "+this.author+"\n"+ "Tytul: "+this.title+"\n"+ "Wydawca: "+this.publisher+"\n"; } return data; } @Override public String toString(){ return ""; } }

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  • Java - Get a list of all Classes loaded in the JVM

    - by Walter White
    Hi all, I would like to get a list of all the classes loaded in the JVM at a particular point in time. The classes are in a particular package and are accessible via /WEB-INF/classes and not through a jar file in /WEB-INF/lib. How would I get a list of classes? Would I simply get the classpath, list all the files, then look for the names? Walter

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  • Java Junit testing problem

    - by agazerboy
    Hi All, I am using Junit 4. My whole program is working fine. I am trying to write a test case. But there is one error... here is very basic sample test public class di extends TestCase{ private static Records testRec; public void testAbc() { Assert.assertTrue( "There should be some thing.", di.testRec.getEmployee() > 0); } } and when i run this it give me error that fName can not be null if i use super and do like this public TestAgnes() { super("testAbc"); } it work all fine. It wasn't this before with JUnit 3.X am I doing wrong or they changed it :( Sorry if I am not clear Is there any way to executre test without super? or calling functions etc. ?

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  • Java: Last access of 2D HashMap

    - by JamieFlowers
    I have the following structure: HashMap< String, HashMap< String, String Now i want to know the last accessed element in the 2nd dimension. I know there is TreeMap which makes sense in the 1rst dimension but after that it doesn't make any sense. How can I keep track of a 2D HashMap ordering? With access i mean: value = hashmap.get("a").get("1") value = hashmap.get("b").get("2") value = hashmap.get("c").get("3") hashmap.removeLast(); hashmap.removeLast(); hashmap.removeLast();

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  • Static initializer in Java

    - by Szere Dyeri
    My question is about one particular usage of static keyword. It is possible to use static keyword to cover a code block within a class which does not belong to any function. For example following code compiles: public class Test { private static final int a; static { a = 5; doSomething(a); } private static int doSomething(int x) { return (x+5); } } If you remove the static keyword it complains because the variable a is final. However it is possible to remove both final and static keywords and make it compile. It is confusing for me in both ways. How am I supposed to have a code section that does not belong to any method? How is it possible to invoke it? In general, what is the purpose of this usage? Or better, where can I find documentation about this?

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  • Write Java Method Signature with Annotated paramaters with JDT

    - by Scott
    Hi, I am writing an eclipse plug-in which generates code. I am leveraging eclipse jdt to gen out classes, fields, and methods. One of the requirements I have is to generate methods with annotated paramaters... public returnType foo(@someAnnotation int id) { ..... ..... } Does anybody know how to write out the @someAnnotation using JDT? To write out normal parameters in JDT you could do something like the following Signature.createTypeSignature("int", false)

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  • Java, LinkedList of Strings. Insert in alphabetical order

    - by user69514
    I have a simple linked list. The node contains a string (value) and an int (count). In the linkedlist when I insert I need to insert the new Node in alphabetical order. If there is a node with the same value in the list, then I simply increment the count of the node. I think I got my method really screwed up. public void addToList(Node node){ //check if list is empty, if so insert at head if(count == 0 ){ head = node; head.setNext(null); count++; } else{ Node temp = head; for(int i=0; i<count; i++){ //if value is greater, insert after if(node.getItem().getValue().compareTo(temp.getItem().getValue()) > 0){ node.setNext(temp.getNext()); temp.setNext(node); } //if value is equal just increment the counter else if(node.getItem().getValue().compareTo(temp.getItem().getValue()) == 0){ temp.getItem().setCount(temp.getItem().getCount() + 1); } //else insert before else{ node.setNext(temp); } } } }

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  • Sync between ms exchange calendar and Java app

    - by arkadiy
    Hi, we are developing a CRM app which holds customer meeting info. Users have requested that their Outlook calendars should reflect the activity they have booked in the CRM application and vice versa. Is there any solution to achieve this? Preferably not using any plugins or installs on the end user's PC?

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  • generate excel in java

    - by chetan
    I want to generate excel with enabling auto-filter option.For that I have create one template excel file by enabling auto-filter option but when I write something into that template excel file auto-filter option disabled again. Is there any solution to create excel file by enabling auto-filter option.

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  • Taking User Input in Java

    - by jdbeverly87
    I'm creating a program that checks if a word or phrase is a palindrome. I have the actual "palindrome tester" figured out. What I'm stuck with is where and what to place in my code to have the console read out "Enter palindrome..." and then text. I've tried with IO but it doesnt work out right. Also, how do I create a loop to keep going? This code only allows one at a time `public class Palindrome { public static void main(String args[]) { String s=""; int i; int n=s.length(); String str=""; for(i=n-1;i>=0;i--) str=str+s.charAt(i); if(str.equals(s)) System.out.println(s+ " is a palindrome"); else System.out.println(s+ " is not a palindrome"); } }

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  • Weird Java Math ,10 ^ 1 = 11?

    - by Simon
    For an exercise I was writing a loop that turns a string into an integer without using the built in functions by multiplying each individual value by its numerical position. 75 would be 7*(10 ^ 1) + 5*(10 ^ 0), for example. However, for some reason (10 ^ 1) keeps coming back as 11. Is there some mistake I have made or an explanation for this?

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  • Quick Java question about variables

    - by Spencer
    I'm declaring a variable: private static final String filename = "filename.txt"; First, does the order of private static final matter? If not, is there a standard excepted sequence or convention? Second, the filename in my application is fixed. Is this the best was to store it's value? Thanks, Spencer

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