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• How to initiate chatting between two clients and two clients only, using applets and servlets?

  - by mithun1538

  Hello everyone, I first need to apologize for my earlier questions. (You can check my profile for them)They seemed to ask more questions than give answers. Hence, I am laying down the actual question that started all them absurd questions. I am trying to design a chat applet. Till now, I have coded the applet, servlet and communication between the applet and the servlet. The code in the servlet side is such that I was able to establish chatting between clients using the applets, but the code was more like a broadcast all feature, i.e. all clients would be chatting with each other. That was my first objective when I started designing the chat applet. The second step is chatting between only two specific users, much like any other chat application we have. So this was my idea for it: I create an instance of the servlet that has the 'broadcast-all' code. I then pass the address of this instance to the respective clients. 2 client applets use the address to then chat. Technically the code is 'broadcast-all', but since only 2 clients are connected to it, it gives the chatting between two clients feature. Thus, groups of 2 clients have different instances of the same servlet, and each instance handles chatting between two clients at a max. However, as predicted, the idea didn't materialize! I tried to create an instance of the servlet but the only solution for that was using sessions on the servlet side, and I don't know how to use this session for later communications. I then tried to modify my broadcast-all code. In that code, I was using classes that implemented Observer and Observable interfaces. So the next idea that I got was: Create a new object of the Observable class(say class_1). This object be common to 2 clients. 2 clients that wish to chat will use same object of the class_1. 2 other clients will use a different object of class_1. But the problem here lies with the class that implements the Observer interface(say class_2). Since this has observers monitoring the same type of class, namely class_1, how do I establish an observer monitoring one object of class_1 and another observer monitoring another object of the same class class_1 (Because notifyObservers() would notify all the observers and I can't assign a particular observer to a particular object)? I first decided to ask individual problems, like how to create instances of servlets, using objects of observable and observer and so on in stackoverflow... but I got confused even more. Can anyone give me an idea how to establish chatting between two clients only?(I am using Http and not sockets or RMI). Regards, Mithun. P.S. Thanks to all who replied to my previous (absurd) queries. I should have stated the purpose earlier so that you guys could help me better.

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• Hibernate constraint ConstraintViolationException. Is there an easy way to ignore duplicate entries?

  - by vincent

  Basically I've got the below schema and I'm inserting records if they don't exists. However when it comes to inserting a duplicate it throws and error as I would expect. My question is whether there is an easy way to make Hibernate to just ignore inserts which would in effect insert duplicates? CREATE TABLE IF NOT EXISTS `method` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `name` varchar(10) DEFAULT NULL, PRIMARY KEY (`id`), UNIQUE KEY `name` (`name`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=2 ; SEVERE: Duplicate entry 'GET' for key 'name' Exception in thread "pool-11-thread-4" org.hibernate.exception.ConstraintViolationException: could not insert:

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• Printing is not working in tomcat, when i start server with services.msc(From client side we could not print )

  - by maya

  I am using JasperReports 1.3.1 to print the report. I am sing eclipse and tomcat for development purpose. In eclipse, when i run the application, the below code will show the listed printer devices and print button. If i click the print button, the report is printing by selected device. PrintRequestAttributeSet printRequestAttributeSet = new HashPrintRequestAttributeSet(); printRequestAttributeSet.add(MediaSizeName.ISO_A5); PrintServiceAttributeSet printServiceAttributeSet = new HashPrintServiceAttributeSet(); JRPrintServiceExporter exporter = new JRPrintServiceExporter(); exporter.setParameter(JRExporterParameter.JASPER_PRINT, jasperPrint); exporter.setParameter(JRPrintServiceExporterParameter.PRINT_REQUEST_ATTRIBUTE_SET, printRequestAttributeSet); exporter.setParameter(JRPrintServiceExporterParameter.PRINT_SERVICE_ATTRIBUTE_SET, printServiceAttributeSet); exporter.setParameter(JRPrintServiceExporterParameter.DISPLAY_PAGE_DIALOG, Boolean.FALSE); exporter.setParameter(JRPrintServiceExporterParameter.DISPLAY_PRINT_DIALOG, Boolean.TRUE); exporter.exportReport(); Here I am passing jasperPrint as a parameter which i manually construted.Its working good My problem is: I created war file and pasted in tomcat Apache Software Foundation\Tomcat 6.0\webapps directory and started the tomcat by using services.msc. At this point, its not displaying the listed printer details and also not printing. I put some logger, I found that, the code is hanging with exporter.exportReport(); after this line code is not executing . Please suggest me for how to print from client side using jasper

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• How can you write a function that accepts multiple types?

  - by matthy

  I have a function that should work on int[] and on String[] now i have made the same function with a int parameter and an String parameter however if it has to go this way its a bit copy paste work and doesn't look very organized is there a way to solve this and put these 4 functions in 2? static public void print(String s) { System.out.println(s); } static public void print(int s) { System.out.println(s); } static public void printArray(String[] s) { for (int i=0; i<s.length; i++) print(s[i]); } static public void printArray(int[] s) { for (int i=0; i<s.length; i++) print(s[i]); } Thanks Matthy

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• Do you have examples of un-helpful/Obscure error messages

  - by Wiretap

  Yesterday I got this error The processing instruction target matching "[xX][mM][lL]" is not allowed when I investigated, it was caused by whitespace at the very start of my XML document. Not difficult to solve, but I was struck with how unhelpful that particular error message was to identifying the actual problem. So what other examples of obscure errors do people have, and are you willing to admit to some of your own making.

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• JSF hiding exceptions?

  - by bshacklett

  I have a managed bean for a JSF page which is doing JPA calls in the constructor to populate fields in the bean. I'm having a bit of trouble with another call to persist an entity (to populate data for testing). I'm expecting it to throw some sort of exception since it's not working, but I'm not getting anything. Just of the heck of it I tried the following: Query newQuery = em.createQuery("Bad Syntax"); List newList = newQuery.getResultList(); I'd expect an IllegalArgumentException here since the query string is completely invalid, but the page still loads and I don't see any exceptions anywhere. Am I right in expecting this exception? If so, why am I not seeing it?

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• Can i use jmonkeyengine on android?

  - by Rafael

  Hi, i', trying to make a simple 3d game for android, and i want to use jmonkeyengine, Can i do this? How can i do it? Someboy can show me an example? thanks!!!

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• Constructor versus setter injection

  - by Chris

  Hi, I'm currently designing an API where I wish to allow configuration via a variety of methods. One method is via an XML configuration schema and another method is through an API that I wish to play nicely with Spring. My XML schema parsing code was previously hidden and therefore the only concern was for it to work but now I wish to build a public API and I'm quite concerned about best-practice. It seems that many favor javabean type PoJo's with default zero parameter constructors and then setter injection. The problem I am trying to tackle is that some setter methods implementations are dependent on other setter methods being called before them in sequence. I could write anal setters that will tolerate themselves being called in many orders but that will not solve the problem of a user forgetting to set the appropriate setter and therefore the bean being in an incomplete state. The only solution I can think of is to forget about the objects being 'beans' and enforce the required parameters via constructor injection. An example of this is in the default setting of the id of a component based on the id of the parent components. My Interface public interface IMyIdentityInterface { public String getId(); /* A null value should create a unique meaningful default */ public void setId(String id); public IMyIdentityInterface getParent(); public void setParent(IMyIdentityInterface parent); } Base Implementation of interface: public abstract class MyIdentityBaseClass implements IMyIdentityInterface { private String _id; private IMyIdentityInterface _parent; public MyIdentityBaseClass () {} @Override public String getId() { return _id; } /** * If the id is null, then use the id of the parent component * appended with a lower-cased simple name of the current impl * class along with a counter suffix to enforce uniqueness */ @Override public void setId(String id) { if (id == null) { IMyIdentityInterface parent = getParent(); if (parent == null) { // this may be the top level component or it may be that // the user called setId() before setParent(..) } else { _id = Helpers.makeIdFromParent(parent,getClass()); } } else { _id = id; } } @Override public IMyIdentityInterface getParent() { return _parent; } @Override public void setParent(IMyIdentityInterface parent) { _parent = parent; } } Every component in the framework will have a parent except for the top level component. Using the setter type of injection, then the setters will have different behavior based on the order of the calling of the setters. In this case, would you agree, that a constructor taking a reference to the parent is better and dropping the parent setter method from the interface entirely? Is it considered bad practice if I wish to be able to configure these components using an IoC container? Chris

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• How to override j_security_check in glassfish?

  - by Alex B

  I'm currently using FORM based authentication in glassfish v2.1 to log users in and it works fine. I want to switch to ProgrammaticLogin and I want to be able to get the initially requested URL (i.e. before redirecting to login page) and use it in my programmatic login code so that the user is redirected back to the requested page after authentication. I've seen the source code for j_security_check - in my case that's FormAuthenticator (catalina codebase) and it saves the initial request in a SavedRequest object in the session but that session is a StandardSession rather than HttpSession so there's no direct way to access it. Or should I change the authentication mechanism from FORM to something else? Thanks!

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• How can I find out if two arguments are instances of the same, but unknown class?

  - by Ingmar

  Let us say we have a method which accepts two arguments o1 and o2 of type Object and returns a boolean value. I want this method to return true only when the arguments are instances of the same class, e.g.: foo(new Integer(4),new Integer(5)); Should return true, however: foo(new SomeClass(), new SubtypeSomeClass()); should return false and also: foo(new Integer(3),"zoo"); should return false. I believe one way is to compare the fully qualified class names: public boolean foo(Object o1, Object o2){ Class<? extends Object> c1 = o1.getClass(); Class<? extends Object> c2 = o2.getClass(); if(c1.getName().equals(c2.getName()){ return true;} return false; } An alternative conditional statement would be : if (c1.isAssignableFrom(c2) && c2.isAssignableFrom(c1)){ return true; } The latter alternative is rather slow. Are there other alternatives to this problem?

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• Accelerometer Values from Android/iPhone device

  - by mrlinx

  I'm trying to map my movements with a android device into an OpenGL scene. I've recorded accelerometer values for a simples movement: Moving the phone (lies flat on a table) 10cm forward (+x), and then 10cm backward (-x). The problem is that this values when used to calculate velocity and position, makes only the opengl cube go forward. Seems like the negative acceleration recorded was not enough to reduce the speed and invert its movement. What can be the problem? This is my function that updates the velocity and position every time new data comes in: void updatePosition(double T2) { double T = 0.005; Vec3 old_pos = position.clone(), old_vel = velocity.clone(); velocity = old_vel.plus(acceleration.times(T)); position = old_pos.plus(old_vel.times(T).plus(acceleration.times(0.5 * Math.pow(T, 2)))); } This is the X,Y,Z accelerometer values over the entire captured time:

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• Using ControllerClassNameHandlerMapping with @Controller and extending AbstractController

  - by whiskerz

  Hey there, actually I thought I was trying something really simple. ControllerClassNameHandlerMapping sounded great to produce a small spring webapp using a very lean configuration. Just annotate the Controller with @Controller, have it extend AbstractController and the configuration shouldn't need more than this <context:component-scan base-package="test.mypackage.controller" /> <bean id="urlMapping" class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping" /> to resolve my requests and map them to my controllers. I've mapped the servlet to "*.spring", and calling <approot>/hello.spring All I ever get is an error stating that no mapping was found. If however I extend the MultiActionController, and do something like <approot>/hello/hello.spring it works. Which somehow irritates me, as I would have thought that if that is working, why didn't my first try? Does anyone have any idea? The two controllers I used looked like this @Controller public class HelloController extends AbstractController { @Override protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response) throws Exception { ModelAndView modelAndView = new ModelAndView("hello"); modelAndView.addObject("message", "Hello World!"); return modelAndView; } } and @Controller public class HelloController extends MultiActionController { public ModelAndView hello(HttpServletRequest request, HttpServletResponse response) throws Exception { ModelAndView modelAndView = new ModelAndView("hello"); modelAndView.addObject("message", "Hello World!"); return modelAndView; } }

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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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• Security when using GWT RPC

  - by gerdemb

  I have an POJO in Google Web Toolkit like this that I can retrieve from the server. class Person implements Serializable { String name; Date creationDate; } When the client makes changes, I save it back to the server using the GWT RemoteServiceServlet like this: rpcService.saveObject(myPerson,...) The problem is that the user shouldn't be able to change the creationDate. Since the RPC method is really just a HTTP POST to the server, it would be possible to modify the creationDate by changing the POST request. A simple solution would be to create a series of RPC functions like changeName(String newName), etc., but with a class with many fields would require many methods for each field, and would be inefficient to change many fields at once. I like the simplicity of having a single POJO that I can use on both the server and GWT client, but need a way to do it securely. Any ideas?

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• JPA getSingleResult() or null

  - by Eugene Ramirez

  Hi. I have an insertOrUpdate method which inserts an Entity when it doesn't exist or update it if it does. To enable this, I have to findByIdAndForeignKey, if it returned null insert if not then update. The problem is how do I check if it exists? So I tried getSingleResult. But it throws an exception if the public Profile findByUserNameAndPropertyName(String userName, String propertyName) { String namedQuery = Profile.class.getSimpleName() + ".findByUserNameAndPropertyName"; Query query = entityManager.createNamedQuery(namedQuery); query.setParameter("name", userName); query.setParameter("propName", propertyName); Object result = query.getSingleResult(); if(result==null)return null; return (Profile)result; } but "getSingleResult" throws an exception. Thanks

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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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• Any way of working with Eclipse WTP that does not mean redeploying the _WHOLE_ application when a J

  - by Thorbjørn Ravn Andersen

  I have migrated a Web Application from MyEclipse to Eclipse WTP, and I am now in the middle of the first major upgrade to the code base and web pages after the migration, and it is frankly driving me mad that saving a JSP page causes a redeployment of the WHOLE application, as it takes time and that my backend connection does not survive the serialization-deserialization of the session object (which is non-trivial to fix). In addition to that the JSP-editor is insanely slow so I frequently have to pause to let the editor catch up to be certain where my edits go in a small JSP using JavaServer Faces. Disabling validation did not help. The Eclipse Dynamic Web Project depends on several library eclipse projects so I cannot just tell e.g. Jetty to use the WebRoot folder, as several dependencies are then missing from the classpath. The question is: Is there a way of working - ANY way of working - with the Eclipse WTP system that does NOT imply redeploying everything every time any file is saved? I can use Tomcat 5.5 or Jetty 6 as servers.

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• A[i] * A[j] = k in O(nlog(n))

  - by gleb-pendler

  A is an Array of n positive int numbers k given int Algorithm should find if there is a pair of numbers which product gives the result a. A[i] * A[j] = k b. A[i] = A[j] + k if there is such a couple the algorithm should return thier index. thanks in advance.

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• Break a while loop without using If or Break

  - by Justin

  I need to create a program that uses while to find the volume of a cylinder. I need the while loop to break if the user inputs a negative value for the height. My code looks like this: double sentinel=1, h=1, v=0, r, count=0; // declares all variables needed final double PI=3.14159; boolean NotNegative=true; while(NotNegative){// && count==0){ // while both the height is positive AND the total times run is 0 System.out.print("Enter height (Use negative to exit): "); // has the user input the height h=Double.parseDouble(br.readLine()); sentinel=h; // save sentinel as the inputted height while(sentinel>0){ System.out.print("Enter radius: "); // have the user input the radius r=Double.parseDouble(br.readLine()); v=PI*(r*r)*h; // find the volume System.out.println("The volume is " + v); // print out the volume count++; // increase the count each time this runs NotNegative=true; sentinel=-1; } } Any help?

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• Traceroute comparison and statistics

  - by ben-casey

  I have a number of traceroutes that i need to compare against each other but i dont know the best way to do it, ive been told that hash maps are a good technique but i dont know how to implement them on my code. so far i have: FileInputStream fstream = new FileInputStream("traceroute.log"); // Get the object of DataInputStream DataInputStream in = new DataInputStream(fstream); BufferedReader br = new BufferedReader(new InputStreamReader(in)); String strLine; // reads lines in while ((strLine = br.readLine()) != null) { System.out.println(strLine); } and the output looks like this: Wed Mar 31 01:00:03 BST 2010 traceroute to www.bbc.co.uk (212.58.251.195), 30 hops max, 40 byte packets 1 139.222.0.1 (139.222.0.1) 0.873 ms 1.074 ms 1.162 ms 2 core-from-cmp.uea.ac.uk (10.0.0.1) 0.312 ms 0.350 ms 0.463 ms 3 ueaha1btm-from-uea1 (172.16.0.34) 0.791 ms 0.772 ms 1.238 ms 4 bound-from-ueahatop.uea.ac.uk (193.62.92.71) 5.094 ms 4.451 ms 4.441 ms 5 gi0-3.norw-rbr1.eastnet.ja.net (193.60.0.21) 4.426 ms 5.014 ms 4.389 ms 6 gi3-0-2.chel-rbr1.eastnet.ja.net (193.63.107.114) 6.055 ms 6.039 ms * 7 lond-sbr1.ja.net (146.97.40.45) 6.994 ms 7.493 ms 7.457 ms 8 so-6-0-0.lond-sbr4.ja.net (146.97.33.154) 8.206 ms 8.187 ms 8.234 ms 9 po1.lond-ban4.ja.net (146.97.35.110) 8.673 ms 6.294 ms 7.668 ms 10 bbc.lond-sbr4.ja.net (193.62.157.178) 6.303 ms 8.118 ms 8.107 ms 11 212.58.238.153 (212.58.238.153) 6.245 ms 8.066 ms 6.541 ms 12 212.58.239.62 (212.58.239.62) 7.023 ms 8.419 ms 7.068 ms what i need to do is compare this trace against another one just like it and look for the changes and time differences etc, then print a stats page.

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• how to access thread/busy thread counts within a jee filter under tomcat

  - by jeje

  Hi, I'd like to access my servlet container's thread/busy thread counts within a filter under tomcat. Is this a part of the jee standard? Or does it have to be tomcat specific? Is there a more general server load measurement?

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• Using Hibernate with Dynamic Eclipse Plug-ins

  - by AlbertoPL

  I have classes that are named exactly the same across different plug-ins that I use for my application, and I'd like to be able to configure them properly with Hibernate. The problem is that it looks like Hibernate dynamically generates a class' package name when trying to find a class when it's doing its mapping. With one plug-in this scheme works, but across multiple plug-ins it's not working. It looks like Hibernate gets confused when dealing with Hibernate configuration files across multiple plug-ins. Is this because each plug-in has its own class-loader? What is the best way to proceed to make this work with the existing plug-ins and Hibernate?

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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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• Delete files from blobstore using file serving URL

  - by Arturo

  In my app (GWT on GAE) we are storing on our database the serving URL that is stored on blobstore. When user selects one of these files and clicks "delete", we need to delete the file from blobstore. This is our code, but it is not deleting the file at all: public void remove(String fileURL) { BlobstoreService blobstoreService = BlobstoreServiceFactory.getBlobstoreService(); String key = getBlobKeyFromURL(box.getImageURL()); BlobKey blobKey = new BlobKey(key); blobstoreService.delete(blobKey); } Where fileURL looks like this: http://lh6.ggpht.com/d5VC0ywISACeJRiC3zkzaZug-tPsaI_LGt93-e_ATGTCwnGLao4yTWjLVppQ And getBlobKeyFromURL() would return what is after the last "/", in this example: d5VC0ywISACeJRiC3zkzaZug-tPsaI_LGt93-e_ATGTCwnGLao4yTWjLVppQ Could you please advice? Thanks

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• Disable automatic Date parsing in HtmlUnit

  - by submonoid

  Having just upgraded to a newer version of HtmlUnit (2.4), I've noticed certain tests are failing when comparing the output of asText. Looking into the differences, this is because dates (present on the page in the format 11/06/2010 00:00z) are being altered in the output to read 2010-06-11. Has anybody else encountered this, and can anybody advise how to turn off this (seemingly undocumented) feature of asText, which seems to go completely against the advised documentation.

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