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• What is design principle behind Servlets being Singleton

  - by Sandeep Jindal

  A servlet container "generally" create one instance of a servlet and different threads of the same instance to serve multiple requests. (I know this can be changed using deprecated SingleThreadModel and other features, but this is the usual way). I thought, the simple reason behind this is performance gain, as creating threads is better than creating instances. But it seems this is not the reason. On the other hand, creating instances have little advantage that developers never have to worry about thread safety. I am trying to understand the reason for this decision over the trade-off of thread-safety.

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• How do I sort an ArrayList lexicographically?

  - by Jake

  I am trying to sort an ArrayList of Strings that represent card values. So, some cards contain letters ("King") and some contain Strings containing only a number ("7"). I know to use Collections.sort, but it only sorts Strings that contain letters. How do I get the ArrayList to be sorted by number as well as alphabetically?

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• Running server-program from a .jar file

  - by skiwi

  I have created and am working on a server-application that monitors for specific folders and takes appropriate actions whenever files are being added. Now I come to the point where I want to be able to shutdown the program, for example for applying a patch. The server runs simply in a command prompt, how can I signal that I want to perform maintenance on it? I do not think reading System.In is feasible as I am also outputting text in the prompt. Regards.

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• Spring - Redirect after POST (even with validation errors)

  - by Taylor L

  I'm trying to figure out how to "preserve" the BindingResult so it can be used in a subsequent GET via the Spring <form:errors> tag. The reason I want to do this is because of Google App Engine's SSL limitations. I have a form which is displayed via HTTP and the post is to an HTTPS URL. If I only forward rather than redirect then the user would see the https://whatever.appspot.com/my/form URL. I'm trying to avoid this. Any ideas how to approach this? Below is what I'd like to do, but I only see validation errors when I use return "create". @RequestMapping(value = "/submit", method = RequestMethod.POST) public final String submit( @ModelAttribute("register") @Valid final Register register, final BindingResult binding) { if (binding.hasErrors()) { return "redirect:/register/create"; } return "redirect:/register/success"; }

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• Why a variable is seen in the loop and is not seen outside the loop?

  - by Roman

  I have the following code: String serviceType; ServiceBrowser tmpBrowser; for (String playerName: players) { serviceType = "_" + playerName + "._tcp"; tmpBrowser = BrowsersGenerator.getBrowser(serviceType); tmpBrowser.browse(); System.out.println(tmpBrowser.getStatus()); } System.out.println(tmpBrowser.getStatus()); The compiler complains about the last line. It writes "variable tmpBrowser might not been initialized". If I comment the last line the compile does not complain.

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• What is the best practice of using return keyword?

  - by Artic

  What is the best practice of using return keyword? If i need to return something from method which pattern is better to use? public boolean method(){ if (case1){ return true; } if (case 2){ return false; } return false; } or public boolean method(){ boolean result = false; if (case1){ result = true; } if (case 2){ result = false; } return result; }

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• Receiving a NullPointerException when calling a cursor in Android

  - by LordSnoutimus

  I am creating an application which tracks the users location using GPS, stores the longitude and latitude in a database using a content provider then output the first long and lat to a mapview. I am able to create the cursor using this line of code: Cursor c = getContentResolver().query(GPSContentProvider.CONTENT_URI, null, null, null, null); startManagingCursor(c); However, when I make a call to move to the first row in the database or even try to close the cursor using c.close(); I receive a NullPointerException.

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• How to encode special characters for a POST with Spring/Roo

  - by Nick

  I'm using Spring/Roo for an app server, and need to be able to post some special characters. Specifically, characters like the Yen symbol, or Euro symbol. When I receive these characters on my server, and display them in console, they appear as "?". How can they be properly encoded and received?

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• Caching Authentication Data

  - by PartlyCloudy

  Hi, I'm currently implementing a REST web service using CouchDB and RESTlet. The RESTlet layer is mainly for authentication and some minor filtering of the JSON data served by CouchDB: Clients <= HTTP = [ RESTlet <= HTTP = CouchDB ] I'm using CouchDB also to store user login data, because I don't want to add an additional database server for that purpose. Thus, each request to my service causes two CouchDB requests conducted by RESTlet (auth data + "real" request). In order to keep the service as efficent as possible, I want to reduce the number of requests, in this case redundant requests for login data. My idea now is to provide a cache (i.e.LRU-Cache via LinkedHashMap) within my RESTlet application that caches login data, because HTTP caching will probabily not be enough. But how do I invalidate the cache data, once a user changes the password, for instance. Thanks to REST, the application might run on several servers in parallel, and I don't want to create a central instance just to cache login data. Currently, I save requested auth data in the cache and try to auth new requests by using them. If a authentication fails or there is now entry available, I'll dispatch a GET request to my CouchDB storage in order to obtain the actual auth data. So in a worst case, users that have changed their data will perhaps still be able to login with their old credentials. How can I deal with that? Or what is a good strategy to keep the cache(s) up-to-date in general? Thanks in advance.

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• Why might RvdProxy.getServices() incorrectly return an empty Array?

  - by butterchicken

  The following code snippet attempts to create a Tib DaemonManager connecting to a particular rvd, and then query for that rvd's services. public static void main(String[] args) throws RuntimeException { DaemonManager daemonManager = new DaemonManager("http://foo.com:7580"); if(daemonManager.getDaemonType() == DaemonManager.RVD) { DaemonProxy daemonProxy = daemonManager.getDaemonProxy(); final RvdProxy rvdProxy = (RvdProxy) daemonProxy; Service[] services = rvdProxy.getServices(); System.out.println(services.length); //prints 0 for (Service service : services) { System.out.println(service.getNetwork()); } } } This prints zero, even though the web interface for this rvd lists multiple available services. Why might this happen? The daemon I am connecting to is running v 7.5.1 of the software, and the rvconfig.jar that I am using is from v 7.5.1 as well. Is there a gotcha when using Tibco's DaemonManager that is causing me to come unstuck?

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• Javax Swing Timer Help

  - by kap

  Hello Guys, I am having some problems concerning starting javax.swing.Timer after a mouse click. I want to start the timer to perform some animation after the user clicks on a button but it is not working. Here are the code snippets: public class ShowMe extends JPanel{ private javax.swing.Timer timer; public ShowMe(){ timer = new javax.swing.Timer(20, new MoveListener()); } // getters and setters here private class MoveListener implements ActionListener { public void actionPerformed(ActionEvent e) { // some code here to perform the animation } } } This is the class which contains a button so that when the user clicks on the button the timer starts to begin the animation public class Test{ // button declarations go here and registering listeners also here public void actionPerformed(ActionEvent e) { if(e.getSource() == this.btnConnect){ ShowMe vis = new ShowMe(); vis.getTimer().start(); } } } I want to start the timer to begin the animation but it is not working. Need help how to make a timer start after button click. Thanks.

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• Best practice for storage and retrieval of error messages.

  - by ferrari fan

  What is a best practice for storing user messages in a configuration file and then retrieving them for certain events throughout an application? I was thinking of having 1 single configuration file with entries such as REQUIRED_FIELD = {0} is a required field INVALID_FORMAT = The format for {0} is {1} etc. and then calling them from a class that would be something like this public class UIMessages { public static final String REQUIRED_FIELD = "REQUIRED_FIELD"; public static final String INVALID_FORMAT = "INVALID_FORMAT"; static { // load configuration file into a "Properties" object } public static String getMessage(String messageKey) { // return properties.getProperty(messageKey); } } Is this the right way to approach this problem or is there some de-facto standard already in place?

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• How to get fan list of Facebook page or can overwrite facebook social plugin css?

  - by Vaibhav Bhalke

  Hi, We are trying it with facebook social plugin. The HTML code for it as follow: <iframe border='0' src='http://www.facebook.com/plugins/likebox.php?id=1185611481&width=243&height=400&connections=15&stream=false&header=false' scrolling='yes' frameborder='0' allowTransparency='false' style='border:0px; overflow:hidden; width:243px; height:300px; background-color: #03869E; color: white;'> <iframe> As it replace inner HTML of frame on load. We want our own CSS to apply to this HTML. But as it replace whole HTML and it have its own CSS we are unable to set our CSS. We are doing this in GWT. Is there any way we can get the list of fans so we can display it as we want and can apply css? Or check given user is fan of page?

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• How to store some of the entity's values in another table using hibernate?

  - by nimcap

  Hi guys, is there a simple way to persist some of the fields in another class and table using hibernate. For example, I have a Person class with name, surname, email, address1, address2, city, country fields. I want my classes to be: public class Person { private String name; private String surname; private String email; private Address address; // .. } public class Address { private Person person; // to whom this belongs private String address1; private String address2; private String city; private Address country; // .. } and I want to store Address in another table. What is the best way to achieve this? Edit: I am using annotations. It does not have to be the way I described, I am looking for best practices. PS. If there is a way to make Address immutable (to use as a value object) that is even better, or maybe not because I thought everything from wrong perspective :)

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• Need a scrollable tomahawk table with fixed header

  - by Hari

  I have used t:commanSortHeader in my table and i need that table to have a fixed header and that table should be scrollable. suggest me a solution

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• Ant: foreach loop

  - by user305801

  I'm trying to use the foreach loop in an Ant script but I get the message: Problem: failed to create task or type foreach Cause: The name is undefined. I don't understand why this doesn't work. It is not a 3rd party library. It is a standard task that would be part of the latest version of Ant (1.8). <target name="parse"> <echo message="The first five letters of the alphabet are:"/> <foreach param="instance" list="a,b,c,d,e"> </foreach> </target>

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• Does HashMap provide a one to one correspondence?

  - by Roman

  I found the following statement: Map is an object that stores key/volume pairs. Given a key, you can find its value. Keys must be unique, but values may be duplicated. For example I have just one key/value pair (3,4). And now I put a new pair (3,5). It will remove the old pair. Right? But if I put (2,4) instead of (3,4) I will add a new pair of key/value to the HashMap. Right?

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• synchronized block vs synchronized method?

  - by Warrior

  Can any one tell me the advantage of synchronized method over synchronized block with an example?Thanks.

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• JTwitter OAuth with callback authorisation

  - by RenegadeAndy

  Hey guys. I am writing an App using JTwitter however I need to authenticate in order to not have the 150 requests per minute on the public api. Jtwitter seems to support OAuth however I have some questions. My app will be running behind a company firewall - so the URL wont be accessible outside of the company's network - will callback authorisation work, and does anybody have an example of using callback authorisation using OAuth in JTwitter - because I cannot work it out in order to try it. Cheers, Andy

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• Hibernate -using Table per subclass - how to link an existing superclass object to a sibclass object

  - by Chandni

  Hi, I have a User hibernate class, Clerk class and Consumer class. All these maps to their own tables in database. The User PK also acts as Clerk's and Consumer's PK. So now my problem is that if a user is initially a Clerk, he has a record in Users table and Clerks table. If that user wants to become a consumer, I want to link that User's record to the new Consumer's record. So even if I pass the userId to the consumer's record, it treats it as a new User to be persisted and gives a duplicate_key exception. How do I tell Hiernate to link the same user object with this new Consumer object. Thanks in advance, -Chandni

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• Is there a simpler way to convert a byte array to a 2-byte-size hexadecimal string?

  - by Tom Brito

  Is there a simpler way of implement this? Or a implemented method in JDK or other lib? /** * Convert a byte array to 2-byte-size hexadecimal String. */ public static String to2DigitsHex(byte[] bytes) { String hexData = ""; for (int i = 0; i < bytes.length; i++) { int intV = bytes[i] & 0xFF; // positive int String hexV = Integer.toHexString(intV); if (hexV.length() < 2) { hexV = "0" + hexV; } hexData += hexV; } return hexData; } public static void main(String[] args) { System.out.println(to2DigitsHex(new byte[] {8, 10, 12})); } the output is: "08 0A 0C" (without the spaces)

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• Variable length Blob in hibernate?

  - by Seth

  I have a byte[] member in one of my persistable classes. Normally, I'd just annotate it with @Lob and @Column(name="foo", size=). In this particular case, however, the length of the byte[] can vary a lot (from ~10KB all the way up to ~100MB). If I annotate the column with a size of 128MB, I feel like I'll be wasting a lot of space for the small and mid-sized objects. Is there a variable length blob type I can use? Will hibernate take care of all of this for me behind the scenes without wasting space? What's the best way to go about this? Thanks!

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• Get HTTP Get parameters from Restlet Request

  - by Holograham

  I am trying to figure out how to get the parameters from a Restlet request object. my request comes in as /customer?userId=1 and I want to grab the parameter to pass to my DAO for the query. @Get("xml") public Representation toXml() throws ResourceException, Exception { try { //get param from request //call DAO with parameter } catch(Exception e) { throw e; } }

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• What does this do and why does it require a transaction?

  - by S. Palin

  What does the following code example do and why does it require a transaction? // PersistenceManager pm = ...; Transaction tx = pm.currentTransaction(); User user = userService.currentUser(); List<Account> accounts = new ArrayList<Account>(); try { tx.begin(); Query query = pm.newQuery("select from Customer " + "where user == userParam " + "parameters User userParam"); List<Customer> customers = (List<Customer>) query.execute(user); query = pm.newQuery("select from Account " + "where parent-pk == keyParam " + "parameters Key keyParam"); for (Customer customer : customers) { accounts.addAll((List<Account>) query.execute(customer.key)); } } finally { if (tx.isActive()) { tx.rollback(); } }

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• Websphere 6.1, Datasource, two apps

  - by asrijaal

  Hi, I've got a webapp running on a Websphere 6.1 Server which JNDI lookups for a datasource. This webapp runs fine, the Websphere server recognizes the datasource ref in the web.xml etc.. Now we added a second webapp which should use this datasource with same configuration but I only getting a NULL Object when I invoke my JNDI lookup and a ClassCastException is thrown (which is correct). Maybe one of you has some suggestions?

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