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• Is lock returned by ReentrantReadWriteLock equivalent to it's read and write locks?

  - by Todd

  Hello, I have been looking around for the answer to this, but no joy. In Java, is using the lock created by ReentrantReadWriteLock equivalent to getting the read and write locks as returned by readLock.lock() and writeLock.lock()? In other words, can I expect the read and write locks associated with the ReentrantReadWriteLock to be requested and held by synchronizing on the ReentrantReadWriteLock? My gut says "no" since any object can be used for synchronization. I wouldn't think that there would be special behavior for ReentrantReadWriteLock. However, special behavior is the corner case of which I may not be aware. Thanks, Todd

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• Batch and the for loop

  - by Farid

  Hi everyone, I have a java application launched by a .cmd file. I want to set the classpath of the application through this batch, all the needed jars are into a lib folder. Here is what I tried : set _classpath=. for %%i in (%1/lib/*.*) do ( set _classpath=%_classpath%;%%i ) Surprisingly, it seems that it does not act as expected. Let's say there is 3 jar in the lib folder : pikachu.jar sonic.jar mario.jar Here is what happens : set _classpath=. set _classpath=.;pikachu.jar set _classpath=.;sonic.jar set _classpath=.;mario.jar Obviously, what I am looking to get is set _classpath=.;pikachu.jar;sonic.jar;mario.jar Any idea ? Thanks and regards,

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• Type-safe, generic, empty Collections with static generics

  - by Droo

  I return empty collections vs. null whenever possible. I switch between two methods for doing so using java.util.Collections: return Collections.EMPTY_LIST; return Collections.emptyList(); where emptyList() is supposed to be type-safe. But I recently discovered: return Collections.<ComplexObject> emptyList(); return Collections.<ComplexObject> singletonList(new ComplexObject()); etc. I see this method in Eclipse Package Explorer: <clinit> () : void but I don't see how this is done in the source code (1.5). How is this magic tomfoolerie happening!!

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• Are there any tools to help the user to design a State Machine to be consumed by my application?

  - by kolrie

  When reading this question I remembered there was something I have been researching for a while now and I though Stackoverflow could be of help. I have created a framework that handles applications as state machines. Currently all the state business logic and transactions are handled via Java code. I was looking for some UI implementation that would allow the user to draw the state machines and transactions and generate a file that can later on be consumed by my framework to "run" the workflow according to one or more defined state machines. Ideally I would like to use an open standard like SCXML. The goal as the UI would be to have something like this plugin IBM have for Rational Software Architect: Do you know any editor, plugin or library that would have something similar or at least serve as a good starting point?

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• Seam cache provider with ehcache null

  - by Cateno Viglio

  Hi every one, I'm trying to configure seam/ehcache following the tutorial from jboss page: http://docs.jboss.org/seam/2.1.2/reference/en-US/html/cache.html I put the ehcache.1.2.3.jar in project.ear/lib and injected CacheProvider as especified, but the CacheProvider always return null. The documentation doesn't show any aditional configuration for ehcache, just for jboss cache. I am probably doing something wrong, it's impossible be so easy :). besides put the jar in /lib, i created the following seam component to test: @Scope(ScopeType.SESSION) @Name("cacheBean") public class CacheSeamBean implements java.io.Serializable { @In(required=false, create=true) private EntityManager em; @Logger private Log log; @In private Events events; @In CacheProvider cacheProvider; Boolean blLoaded = Boolean.FALSE; @Create public void buscar() { if (!blLoaded){ List<Parametro> lstParametro = em.createQuery("select p from Parametro p").getResultList(); for (Parametro parametro : lstParametro){ cacheProvider.put(parametro.getCodigo(), parametro.getValor()); } blLoaded= Boolean.TRUE; } } } Thanks

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• How to center align background image in JPanel

  - by Jaguar

  I wanted to add background image to my JFrame. Background image means I can later add Components on the JFrame or JPanel Although I coudn't find how to add background image to a JFrame, I found out how to add background image to a JPanel from here: How to set background image in Java? This solved my problem, but now since my JFrame is resizable I want to keep the image in center. The code I found uses this method public void paintComponent(Graphics g) { //Draw the previously loaded image to Component. g.drawImage(img, 0, 0, null); //Draw image } Can anyone say how to align the image to center of the JPanel. As g.drawImage(img, 0, 0, null); provides x=0 and y=0 Also if there is a method to add background image to a JFrame then I would like to know. Thanks.

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• Rotate a 2d matrix to the right

  - by adam

  I want a 2d matrix to rotate to the right, it compiles fine but when I try to the run it freezes. For example I want {{10,20,30},{40,50,60}} to rotate into {{40,10},{50,20},{60,30}} import java.util.*; public class Rotate{ public static int[][] rotate(int[][] m) { int [][] rotateM = new int[m[0].length][m.length]; for (int i= 0; i< m.length; i= i++){ for (int j= 0; j< m[0].length; j= j++){ rotateM[i][j] = m[j][m.length-i-1]; } } return rotateM; } public static void main(String[]args){ int[][]m = {{10,20,30}, {40,50,60}}; System.out.println(Arrays.toString(rotate(m))); } }

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• Ant ignores attempt to override the LANG environment variable

  - by Steen

  We need to test a java build with the languages set to different values. I can manually (i.e. via export LANG=en_DK.UTF-8 and export LANG=en_DK) test that the unit tests run with the ant build script behaves differently, but I need to set the environment variable from ant. I have tried setting it using these methods (with the shell $LANG set to en_DK.UTF-8): using -D on the command line: ant -DLANG=en_DK using a build.properties file with the line LANG=en_DK in it using the following statements in the build.xml file (sorry for the formatting, I can't get SO to display it otherwise): : <property environment="ANTENV"/> <property name="ANTENV.LANG" value="en_DK"/> Using any of the three possibilities, and when run with -debug, ant reports that: Override ignored for property "LANG" What can I do to set the LANG environment variable from within ant?

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• Multiple complete HTTP requests stuck in TCP CLOSE_WAIT state

  - by Sean Owen

  I have a Java and Tomcat-based server application which initiates many outbound HTTP requests to other web sites. We use Jakarta's HTTP Core/Client libraries, very latest versions. The server locks up at some point since all its worker threads are stuck trying to close completed HTTP connections. Using 'lsof' reveals a bunch of sockets stuck in TCP CLOSE_WAIT state. This doesn't happen for all, or even most connections. In fact, I saw it before and resolved it by making sure to set the Connection: Close response header. So that makes me think it may be bad behavior of remote servers. It may have come up again since I moved the app to a totally new service provider -- different OS, network situation. But, I am still at a loss as to what I could do, if anything, to work around this. Some poking around on the internet didn't turn up anything I'm not already doing. Just thought I'd ask if anyone has seen and solved this?

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• How to compare two maps by their values

  - by lewap

  How to compare two maps by their values? I have two maps containing equal values and want to compare them by their values. Here is an example: Map a = new HashMap(); a.put("f"+"oo", "bar"+"bar"); a.put("fo"+"o", "bar"+"bar"); Map b = new HashMap(); a.put("f"+"oo", "bar"+"bar"); a.put("fo"+"o", "bar"+"bar"); System.out.println("equals: " + a.equals(b)); // obviously false .... what to call to obtain a true? Obviously, to implement a comparison it not difficult, it is enough to compare all keys and their associated values. I don't believe I'm the first one to do this, so there must be already a library functions either in java or in one of the jakarta.commons libraries. Thanks

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• h:commandButton not working within PrimeFaces p:dataTable

  - by JamesB

  I have a PrimeFaces datatable. For each row in this table, I want to allow the user to update/delete the row entry (a user). <html xmlns="http://www.w3.org/1999/xhtml" xmlns:f="http://java.sun.com/jsf/core" xmlns:h="http://java.sun.com/jsf/html" xmlns:p="http://primefaces.prime.com.tr/ui"> <h:head> <link type="text/css" rel="stylesheet" href="themes/bluesky/skin.css" /> </h:head> <h:body> <center> <h:form> <p:panel id="viewUsersPanel" header="View Users"> <p:dataTable var="user" value="#{uController.users}" emptyMessage="No Users Found."> <p:column style="text-align: center;"> <f:facet name="header"> <h:outputText value="Name" /> </f:facet> <h:outputText value="#{user.name}" /> </p:column> <p:column style="text-align: center;"> <f:facet name="header"> <h:outputText value="Postal Address" /> </f:facet> <h:outputText value="#{user.address}" /> </p:column> <p:column style="text-align: center;"> <f:facet name="header"> <h:outputText value="Phone Number" /> </f:facet> <h:outputText value="#{user.phone}" /> </p:column> <p:column style="text-align: center;"> <f:facet name="header"> <h:outputText value="Email Address" /> </f:facet> <h:outputText value="#{user.email}" /> </p:column> <p:column style="text-align: center;"> <f:facet name="header"> <h:outputText value="DOB" /> </f:facet> <h:outputText value="#{user.dob}"> <f:convertDateTime pattern="dd-MMM-yyyy" /> </h:outputText> </p:column> <p:column style="text-align: center;"> <f:facet name="header"> <h:outputText value="No. Memberships" /> </f:facet> <h:outputText value="#{user.numberOfMemberships}" /> </p:column> <p:column style="text-align: center;"> <f:facet name="header"> <h:outputText value="Actions" /> </f:facet> <h:commandButton value="Update" action="#{uController.update}" /> <h:commandButton value="Delete" action="#{uController.delete}" /> </p:column> </p:dataTable> <h:panelGrid columns="2" cellpadding="2" id="footerPanelGrid" border="0"> <h:commandButton action="#{uController.home}" value="Home Page" /> </h:panelGrid> </p:panel> </h:form> </center> </h:body> </html> However, neither of the buttons work. Instead they appear to simply refresh the view page. I have ran the app in debug and neither update or delete method is hit. I suspect this may be due to using h:commandButton within a p:dataTable. However, I have also tried p:commandButton but to no avail. For reference, here is a snippet of the UserController class: @ManagedBean(name="uController") public class UserController extends AbstractController { private Collection<User> users; ... public String update() { System.out.println("Ready for update"); return "update-user"; } public String delete() { System.out.println("Ready for delete"); return "delete-user"; } ... }

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• Estimate serialization size of objects?

  - by Stefan K.

  In my thesis, I woud like to enhance messaging in a cluster. It's important to log runtime information about how big a message is (should I prefer processing local or remote). I could just find frameoworks about estimating the object memory size based on java instrumentation. I've tested classmexer, which didn't come close to the serialization size and sourceforge SizeOf. In a small testcase, SizeOf was around 10% wrong and 10x faster than serialization. (Still transient breaks the estimation completely and since e.g. ArrayList is transient but is serialized as an Array, it's not easy to patch SizeOf. But I could live with that) On the other hand, 10x faster with 10% error doesn't seem very good. Any ideas how I could do better?

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• Techniques to avoid DeadlineExceededException in GAE/J?

  - by Tahir Akram

  I am developing an Twitter4J web application in Google App Engine/Java. I need to show two lists. One is Twitter friends and other is followers. With photo and screen name. It is working fine for people who have 20-30 followers and friends. But it gave me DeadlineExceededException when I try a user who has 150+ followers and friends. GAE throws this exception if web request take time more than 30 seconds. So what techniques I can adopt to avoid this exception. Should I generate two AJAX calls for each of my list. After page loads. So that every call will have its own 30 secs limit? Or what else you think? I am gone make it. Please help.

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• Maven eclipse does not add a dependency

  - by Calm Storm

  I have the following snippet in my pom.xml <dependency> <groupId>aspectj</groupId> <artifactId>aspectjrt</artifactId> <version>1.5.3</version> </dependency> and in one of my Java files I refer a class org.aspectj.lang.ProceedingJoinPoint. When I do a "mvn clean install" it compiles and builds fine but when I do an eclipse:eclipse, and import the project in eclipse it gives me an error The import org.aspectj cannot be resolved. I checked the .classpath file that was generated and it does not have an entry to this file. I tried a "mvn dependency:tree" and it lists this fine. Can someone tell me what is going wrong here?

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• What would be the use of accepting itself as type arguments in generics

  - by Newtopian

  I saw some code on an unrelated question but it got me curious as I never saw such construct with Java Generics. What would be the use of creating a generic class that can take as type argument itself or descendants of itself. Here is example : abstract class A<E extends A> { abstract void foo(E x); } the first thing that came to mind would be a list that takes a list as parameter. Using this code feels strange, how do you declare a variable of type A ? Recursive declaration !? Does this even work ? If so did any of you see that in code ? How was it used ?

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• Lazy loading in Hibernate

  - by Steve

  My Java Web application uses Hibernate to perform ORM. In some of my objects, I use lazy loading to avoid getting data until I absolutely need it. The problem is that I load the initial object in a session, and then that session is destroyed. When I later attempt to resolve the lazy-loaded collections in my object I get the following error: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: common.model.impl.User.groups, no session or session was closed I tried associating a new session with the collection and then resolving, but this gives the same results. Does anyone know how I can resolve the lazy collections once the original session is gone? Thanks... --Steve

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• How to display characters in http get response correctly with the right encoding

  - by DixieFlatline

  Hello! Does anyone know how to read c,š,ž characters in http get response properly? When i make my request in browser the browser displays all characters correctly. But in java program with apache jars i don't know how to set the encoding right. I tried with client.getParams().setParameter(CoreProtocolPNames.HTTP_CONTENT_CHARSET, "UTF-8"); but it's not working. My code: HttpClient client = new DefaultHttpClient(); String getURL = "http://www.google.com"; HttpGet get = new HttpGet(getURL); HttpResponse responseGet = client.execute(get); HttpEntity resEntityGet = responseGet.getEntity(); if (resEntityGet != null) { Log.i("GET RESPONSE",EntityUtils.toString(resEntityGet)); } } catch (Exception e) { e.printStackTrace(); }

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• How can I further optimize this color difference function?

  - by aLfa

  I have made this function to calculate color differences in the CIE Lab colorspace, but it lacks speed. Since I'm not a Java expert, I wonder if any Java guru around has some tips that can improve the speed here. The code is based on the matlab function mentioned in the comment block. /** * Compute the CIEDE2000 color-difference between the sample color with * CIELab coordinates 'sample' and a standard color with CIELab coordinates * 'std' * * Based on the article: * "The CIEDE2000 Color-Difference Formula: Implementation Notes, * Supplementary Test Data, and Mathematical Observations,", G. Sharma, * W. Wu, E. N. Dalal, submitted to Color Research and Application, * January 2004. * available at http://www.ece.rochester.edu/~gsharma/ciede2000/ */ public static double deltaE2000(double[] lab1, double[] lab2) { double L1 = lab1[0]; double a1 = lab1[1]; double b1 = lab1[2]; double L2 = lab2[0]; double a2 = lab2[1]; double b2 = lab2[2]; // Cab = sqrt(a^2 + b^2) double Cab1 = Math.sqrt(a1 * a1 + b1 * b1); double Cab2 = Math.sqrt(a2 * a2 + b2 * b2); // CabAvg = (Cab1 + Cab2) / 2 double CabAvg = (Cab1 + Cab2) / 2; // G = 1 + (1 - sqrt((CabAvg^7) / (CabAvg^7 + 25^7))) / 2 double CabAvg7 = Math.pow(CabAvg, 7); double G = 1 + (1 - Math.sqrt(CabAvg7 / (CabAvg7 + 6103515625.0))) / 2; // ap = G * a double ap1 = G * a1; double ap2 = G * a2; // Cp = sqrt(ap^2 + b^2) double Cp1 = Math.sqrt(ap1 * ap1 + b1 * b1); double Cp2 = Math.sqrt(ap2 * ap2 + b2 * b2); // CpProd = (Cp1 * Cp2) double CpProd = Cp1 * Cp2; // hp1 = atan2(b1, ap1) double hp1 = Math.atan2(b1, ap1); // ensure hue is between 0 and 2pi if (hp1 < 0) { // hp1 = hp1 + 2pi hp1 += 6.283185307179586476925286766559; } // hp2 = atan2(b2, ap2) double hp2 = Math.atan2(b2, ap2); // ensure hue is between 0 and 2pi if (hp2 < 0) { // hp2 = hp2 + 2pi hp2 += 6.283185307179586476925286766559; } // dL = L2 - L1 double dL = L2 - L1; // dC = Cp2 - Cp1 double dC = Cp2 - Cp1; // computation of hue difference double dhp = 0.0; // set hue difference to zero if the product of chromas is zero if (CpProd != 0) { // dhp = hp2 - hp1 dhp = hp2 - hp1; if (dhp > Math.PI) { // dhp = dhp - 2pi dhp -= 6.283185307179586476925286766559; } else if (dhp < -Math.PI) { // dhp = dhp + 2pi dhp += 6.283185307179586476925286766559; } } // dH = 2 * sqrt(CpProd) * sin(dhp / 2) double dH = 2 * Math.sqrt(CpProd) * Math.sin(dhp / 2); // weighting functions // Lp = (L1 + L2) / 2 - 50 double Lp = (L1 + L2) / 2 - 50; // Cp = (Cp1 + Cp2) / 2 double Cp = (Cp1 + Cp2) / 2; // average hue computation // hp = (hp1 + hp2) / 2 double hp = (hp1 + hp2) / 2; // identify positions for which abs hue diff exceeds 180 degrees if (Math.abs(hp1 - hp2) > Math.PI) { // hp = hp - pi hp -= Math.PI; } // ensure hue is between 0 and 2pi if (hp < 0) { // hp = hp + 2pi hp += 6.283185307179586476925286766559; } // LpSqr = Lp^2 double LpSqr = Lp * Lp; // Sl = 1 + 0.015 * LpSqr / sqrt(20 + LpSqr) double Sl = 1 + 0.015 * LpSqr / Math.sqrt(20 + LpSqr); // Sc = 1 + 0.045 * Cp double Sc = 1 + 0.045 * Cp; // T = 1 - 0.17 * cos(hp - pi / 6) + // + 0.24 * cos(2 * hp) + // + 0.32 * cos(3 * hp + pi / 30) - // - 0.20 * cos(4 * hp - 63 * pi / 180) double hphp = hp + hp; double T = 1 - 0.17 * Math.cos(hp - 0.52359877559829887307710723054658) + 0.24 * Math.cos(hphp) + 0.32 * Math.cos(hphp + hp + 0.10471975511965977461542144610932) - 0.20 * Math.cos(hphp + hphp - 1.0995574287564276334619251841478); // Sh = 1 + 0.015 * Cp * T double Sh = 1 + 0.015 * Cp * T; // deltaThetaRad = (pi / 3) * e^-(36 / (5 * pi) * hp - 11)^2 double powerBase = hp - 4.799655442984406; double deltaThetaRad = 1.0471975511965977461542144610932 * Math.exp(-5.25249016001879 * powerBase * powerBase); // Rc = 2 * sqrt((Cp^7) / (Cp^7 + 25^7)) double Cp7 = Math.pow(Cp, 7); double Rc = 2 * Math.sqrt(Cp7 / (Cp7 + 6103515625.0)); // RT = -sin(delthetarad) * Rc double RT = -Math.sin(deltaThetaRad) * Rc; // de00 = sqrt((dL / Sl)^2 + (dC / Sc)^2 + (dH / Sh)^2 + RT * (dC / Sc) * (dH / Sh)) double dLSl = dL / Sl; double dCSc = dC / Sc; double dHSh = dH / Sh; return Math.sqrt(dLSl * dLSl + dCSc * dCSc + dHSh * dHSh + RT * dCSc * dHSh); }

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• How to force javax xslt transformer to encode entities in utf-8?

  - by calavera.info

  I'm working on filter that should transform an output with some stylesheet. Important sections of code looks like this: PrintWriter out = response.getWriter(); ... StringReader sr = new StringReader(content); Source xmlSource = new StreamSource(sr, requestSystemId); transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8"); transformer.setParameter("encoding", "UTF-8"); //same result when using ByteArrayOutputStream xo = new java.io.ByteArrayOutputStream(); StringWriter xo = new StringWriter(); StreamResult result = new StreamResult(xo); transformer.transform(xmlSource, result); out.write(xo.toString()); The problem is that national characters are encoded as html entities and not by using UTF. Is there any way to force transformer to use UTF-8 instead of entities?

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• Verify mail server connection programmatically

  - by Sergii

  I'm using custom SMTP servers and would like to verify the connection when user enters his own server credentials. Exactly the same type of check as Adobe CF and Railo allow to do when adding mail server. Sure, this does not guarantee that delivery will be working, but at least to check that entered server/username/pass are valid. I can see one tricky way: try to send the email with cfmail and check the mail log. But I believe that it can be done with more elegant. Is there any Java library available with standard ACF/Railo distro to help me? How would I use them? Examples are highly appreciated. Thanks in advance.

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• Does ImageIO read imply anti-aliased scaling?

  - by tigger

  I've replaced the Java internal ImageFetcher with an own implementation using ImageIO. Some image renderers of our software, which use these images, now draw anti-aliased scaled images instead of non anti-aliased. The only change is the source of the image, which are now BufferedImages instead of Toolkit-Images. The question now is, where is the difference? Which property causes the images to scale anti-aliased? I've always thought that the anti-alias key ONLY depends on the graphics I paint on - but this is obviously wrong. By the way: unfortunately I cannot change the renderers.

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• Riddle: Spot the serious bug in this bubble sort implementation

  - by ripper234

  (No, this isn't a homework assignment, I just found the bug and thought it might be useful to share it here) import java.util.List; public class BubbleSorter { public <T extends Comparable<T>> void sort(List<T> list) { while (true) { boolean didWork = false; for (int i = 0; i < list.size() - 1; ++i) { if (list.get(i).compareTo(list.get(i + 1)) > 0) { swap(list, i, i + 1); didWork = true; break; } } if (!didWork) return; } } private static <T> void swap(List<T> list, int i, int j) { T tmp = list.get(i); list.set(i, list.get(j)); list.set(j, tmp); } }

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• Escaping ampersands in URLs for HttpClient requests

  - by jpatokal

  So I've got some Java code that uses Jakarta HttpClient like this: URI aURI = new URI( "http://host/index.php?title=" + title + "&action=edit" ); GetMethod aRequest = new GetMethod( aURI.getEscapedPathQuery()); The problem is that if title includes any ampersands (&), they're considered parameter delimiters and the request goes screwy... and if I replace them with the URL-escaped equivalent %26, then this gets double-escaped by getEscapedPathQuery() into %2526. I'm currently working around this by basically repairing the damage afterward: URI aURI = new URI( "http://host/index.php?title=" + title.replace("&", "%26") + "&action=edit" ); GetMethod aRequest = new GetMethod( aURI.getEscapedPathQuery().replace("%2526", "%26")); But there has to be a nicer way to do this, right? Note that the title can contain any number of unpredictable UTF-8 chars etc, so escaping everything else is a requirement.

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• Why does Spring Security's BindAuthenticator require read permissions for users?

  - by Thomas

  Hi all, I'm currently implementing/configuring the LDAP authentication of a Java web application using Spring Security 3.0. I'm using Microsoft AD LDS as LDAP server and chose the Spring's BindAuthenticator. I found out that the authentication only works if the authenticated user is a member of the partition's Readers role. The BindAuthenticator tries to read the user's attributes after the authentication, which seems reasonable in scenarios where authorities are retrieved from the directory service. Being new to LDAP and AD, is this an acceptable practise when the application is integrated in an existing AD structure? Can fine-tune an give the user dns only read permissions for their own attributes rather than adding them to the Reader group? Thanks Thomas

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• Simple cross platform GUI app

  - by Joe Cannatti

  I would like to know if there is any way that I could build a very simple GUI app (it doesn't even have to look good) that will run on a fresh install of Windows Vista and OS X with no other installations needed by the user. I would perfer not to use Java (just out of personal programming preference). I will use it though, if it is the only way. Specically, I am wondering if I can write a swing app with Scala or Groovy and run in on windows without them having to install anything. Sorry if this is a silly question, I am a Obj-C developer by trade.

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