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• Java and .NET cost of use [on hold]

  - by 1110

  I work with .NET technology stack for about 4 years. I am learning and enjoy working with ASP MVC framework and I never did anything serious in other languages. This is not the question like what is better (I read all similar questions). What interest me is the cost of switching. For example: If you are about to start a start-up company today and you are in my situation not too much money, some good idea that you think others will use and have a knowledge of .NET. In my head I have a few questions that I can't answer and I know that somebody with experience can: 1) Java & .NET hosting. Suppose shared hosting is not good enough anymore, your site has grown and you need more resources. How much Java services is cheaper compared to .NET? 2) I didn't follow hype about ORACLE will kill java long time. Does oracle show interest in investing in java. I mean is is safe to bet on java as a technology when starting start-up (basically did oracle show some will to destroy java platform)? 3) I am not sure what I am asking here. When you use Java you can use JEEE stack or Java with third party stack (spring, hibernate, maven etc.). I saw a lot of project that work with second option if web application is not enterprise level but social networking site for example which stack is best pick? Summary of this question is is it safe to jump in to Java learn it and build product based on it. It's not too hard for me to learn it. But how much can I get from it.

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• Java: Why is this Subclass valid?

  - by incrediman

  Here, I have an abstract class: abstract class A<E extends A> { abstract void foo(E x); } Here's a class that extends A: class B extends A<B>{ void foo(B x){} } And here's another (E is B here on purpose): class C extends A<B>{ void foo(B x){} } Both of those classes are valid, and the reasoning for that makes sense to me. However what confuses me is how this could possibly be valid: class D extends A{ void foo(A x){} } Since when are generics optional like that? I thought the extending class (subclass) of A would be required to specify an E?

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• Autocomplete for generic types in Eclipse

  - by AvrDragon

  "Refer to objects by their interfaces" is a good practise, as mentioned in Effective Java. So for example i prefer List<String> al = new ArrayList<String>(); over ArrayList<String> al = new ArrayList<String>(); in my code. One annoying thing is that if i type ArrayList<String> al = new and then hit Ctrl+Space in Eclipse i get ArrayList<String>() as propostal. But if i type List al = new and then hit Ctrl+Space i will get only propostal to define anonymous inner class, but not propostals such as new ArrayList<String>(), what is 99% the case, or for example new Vector<String>(). Is there any way to get the subclasses as propostals for generic types?

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• Covariant return types in Java enums

  - by Kelvin Chung

  As mentioned in another question on this site, something like this is not legal: public enum MyEnum { FOO { public Integer doSomething() { return (Integer) super.doSomething(); } }, BAR { public String doSomething() { return (String) super.doSomething(); } }; public Object doSomething(); } This is due to covariant return types apparently not working on enum constants (again breaking the illusion that enum constants are singleton subclasses of the enum type...) So, how about we add a bit of generics: is this legal? public enum MyEnum2 { FOO { public Class<Integer> doSomething() { return Integer.class; } }, BAR { public Class<String> doSomething() { return String.class; } }; public Class<?> doSomething(); } Here, all three return Class objects, yet the individual constants are "more specific" than the enum type as a whole...

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• What's the purpuse behind wildcards and how are they different from generics?

  - by Nazgulled

  Hi, I never heard about wildcars until a few days ago and after reading my teacher's Java book, I'm still not sure about what's it for and wwhy would I need to use it. Let's say I have a super class Animal and few sub classes like Dog, Cat, Parrot, etc... Now I need to have a list of animals, my first thought would be something like: List<Animal> listAnimals Instead, my colleagues are recommending something like: List<? extends Animal> listAnimals Why should I use wildcards instead of simple generics? Let's say I need to have a get/set method, should I use the former or the later? How are they so different?

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• Passing a generic class to a java function?

  - by rodo

  Is it possible to use Generics when passing a class to a java function? I was hoping to do something like this: public static class DoStuff { public <T extends Class<List>> void doStuffToList(T className) { System.out.println(className); } public void test() { doStuffToList(List.class); // compiles doStuffToList(ArrayList.class); // compiler error (undesired behaviour) doStuffToList(Integer.class); // compiler error (desired behaviour) } } Ideally the List.class and ArrayList.class lines would work fine, but the Integer.class line would cause a compile error. I could use Class as my type instead of T extends Class<List> but then I won't catch the Integer.class case above.

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• DexFile.class error in eclipse

  - by ninjasense

  I get this weird error everytime I debug in eclipse. It just seemed to appear one day and I was wondering if anyone else was running int the same problem. It does not affect my app in anyway visibly and does not cause a crash but it is an annoyance while debugging. Here is the full error: // Compiled from DexFile.java (version 1.5 : 49.0, super bit) public final class dalvik.system.DexFile { // Method descriptor #8 (Ljava/io/File;)V // Stack: 3, Locals: 2 public DexFile(java.io.File file) throws java.io.IOException; 0 aload_0 [this] 1 invokespecial java.lang.Object() [1] 4 new java.lang.RuntimeException [2] 7 dup 8 ldc <String "Stub!"> [3] 10 invokespecial java.lang.RuntimeException(java.lang.String) [4] 13 athrow Line numbers: [pc: 0, line: 4] Local variable table: [pc: 0, pc: 14] local: this index: 0 type: dalvik.system.DexFile [pc: 0, pc: 14] local: file index: 1 type: java.io.File // Method descriptor #18 (Ljava/lang/String;)V // Stack: 3, Locals: 2 public DexFile(java.lang.String fileName) throws java.io.IOException; 0 aload_0 [this] 1 invokespecial java.lang.Object() [1] 4 new java.lang.RuntimeException [2] 7 dup 8 ldc <String "Stub!"> [3] 10 invokespecial java.lang.RuntimeException(java.lang.String) [4] 13 athrow Line numbers: [pc: 0, line: 5] Local variable table: [pc: 0, pc: 14] local: this index: 0 type: dalvik.system.DexFile [pc: 0, pc: 14] local: fileName index: 1 type: java.lang.String // Method descriptor #22 (Ljava/lang/String;Ljava/lang/String;I)Ldalvik/system/DexFile; // Stack: 3, Locals: 3 public static dalvik.system.DexFile loadDex(java.lang.String sourcePathName, java.lang.String outputPathName, int flags) throws java.io.IOException; 0 new java.lang.RuntimeException [2] 3 dup 4 ldc <String "Stub!"> [3] 6 invokespecial java.lang.RuntimeException(java.lang.String) [4] 9 athrow Line numbers: [pc: 0, line: 6] Local variable table: [pc: 0, pc: 10] local: sourcePathName index: 0 type: java.lang.String [pc: 0, pc: 10] local: outputPathName index: 1 type: java.lang.String [pc: 0, pc: 10] local: flags index: 2 type: int // Method descriptor #28 ()Ljava/lang/String; // Stack: 3, Locals: 1 public java.lang.String getName(); 0 new java.lang.RuntimeException [2] 3 dup 4 ldc <String "Stub!"> [3] 6 invokespecial java.lang.RuntimeException(java.lang.String) [4] 9 athrow Line numbers: [pc: 0, line: 7] Local variable table: [pc: 0, pc: 10] local: this index: 0 type: dalvik.system.DexFile // Method descriptor #30 ()V // Stack: 3, Locals: 1 public void close() throws java.io.IOException; 0 new java.lang.RuntimeException [2] 3 dup 4 ldc <String "Stub!"> [3] 6 invokespecial java.lang.RuntimeException(java.lang.String) [4] 9 athrow Line numbers: [pc: 0, line: 8] Local variable table: [pc: 0, pc: 10] local: this index: 0 type: dalvik.system.DexFile // Method descriptor #32 (Ljava/lang/String;Ljava/lang/ClassLoader;)Ljava/lang/Class; // Stack: 3, Locals: 3 public java.lang.Class loadClass(java.lang.String name, java.lang.ClassLoader loader); 0 new java.lang.RuntimeException [2] 3 dup 4 ldc <String "Stub!"> [3] 6 invokespecial java.lang.RuntimeException(java.lang.String) [4] 9 athrow Line numbers: [pc: 0, line: 9] Local variable table: [pc: 0, pc: 10] local: this index: 0 type: dalvik.system.DexFile [pc: 0, pc: 10] local: name index: 1 type: java.lang.String [pc: 0, pc: 10] local: loader index: 2 type: java.lang.ClassLoader // Method descriptor #37 ()Ljava/util/Enumeration; // Signature: ()Ljava/util/Enumeration<Ljava/lang/String;>; // Stack: 3, Locals: 1 public java.util.Enumeration entries(); 0 new java.lang.RuntimeException [2] 3 dup 4 ldc <String "Stub!"> [3] 6 invokespecial java.lang.RuntimeException(java.lang.String) [4] 9 athrow Line numbers: [pc: 0, line: 10] Local variable table: [pc: 0, pc: 10] local: this index: 0 type: dalvik.system.DexFile // Method descriptor #30 ()V // Stack: 3, Locals: 1 protected void finalize() throws java.io.IOException; 0 new java.lang.RuntimeException [2] 3 dup 4 ldc <String "Stub!"> [3] 6 invokespecial java.lang.RuntimeException(java.lang.String) [4] 9 athrow Line numbers: [pc: 0, line: 11] Local variable table: [pc: 0, pc: 10] local: this index: 0 type: dalvik.system.DexFile // Method descriptor #42 (Ljava/lang/String;)Z public static native boolean isDexOptNeeded(java.lang.String arg0) throws java.io.FileNotFoundException, java.io.IOException; } Thanks

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• Reusing OAuth request token when user refresh page - Twitter4j on GAE

  - by Tahir Akram

  Hi I am using Twitter4J API on GAE/J. I want to use the request token when user came to my page. (called back URL). And press refresh button. I write following code for that. But When user press refresh button. I got Authentication credentials error. Please see the stacktrance. It works fine when user first time used that token. HomeServlet.java code: HttpSession session = request.getSession(); twitter.setOAuthConsumer(FFConstants.CONSUMER_KEY, FFConstants.CONSUMER_SECRET); String token = (String) session.getAttribute("token"); String authorizedToken = (String)session.getAttribute("authorizedToken"); User user = null; if (!token.equals(authorizedToken)){ AccessToken accessToken = twitter.getOAuthAccessToken( token, (String) session .getAttribute("tokenSecret")); twitter.setOAuthAccessToken(accessToken); user = twitter.verifyCredentials(); session.setAttribute("authorizedToken", token); session.setAttribute("user", user); }else{ user = (User)session.getAttribute("user"); } TwitterUser twitterUser = new TwitterUser(); twitterUser.setFollowersCount(user.getFollowersCount()); twitterUser.setFriendsCount(user.getFriendsCount()); twitterUser.setFullName(user.getName()); twitterUser.setScreenName(user.getScreenName()); twitterUser.setLocation(user.getLocation()); Please suggest how I can do that. I have seen on many website. They retain the user with the same token. Even if user press browser refresh buttion again and again. Please help. Exception stacktrace: Reason: twitter4j.TwitterException: 401:Authentication credentials were missing or incorrect. /friends/ids.xml This method requires authentication. at twitter4j.http.HttpClient.httpRequest(HttpClient.java:469) at twitter4j.http.HttpClient.get(HttpClient.java:412) at twitter4j.Twitter.get(Twitter.java:276) at twitter4j.Twitter.get(Twitter.java:228) at twitter4j.Twitter.getFriendsIDs(Twitter.java:1819) at com.tff.servlet.HomeServlet.doGet(HomeServlet.java:86) at javax.servlet.http.HttpServlet.service(HttpServlet.java:693) at javax.servlet.http.HttpServlet.service(HttpServlet.java:806) at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487) at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1093) at com.google.apphosting.utils.servlet.ParseBlobUploadFilter.doFilter(ParseBlobUploadFilter.java:97) at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1084) at com.google.apphosting.runtime.jetty.SaveSessionFilter.doFilter(SaveSessionFilter.java:35) at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1084) at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43) at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1084) at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:360) at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216) at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181) at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:712) at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405) at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.handle(AppVersionHandlerMap.java:238) at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:139) at org.mortbay.jetty.Server.handle(Server.java:313) at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:506) at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:830) at com.google.apphosting.runtime.jetty.RpcRequestParser.parseAvailable(RpcRequestParser.java:76) at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:381) at com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:135) at com.google.apphosting.runtime.JavaRuntime.handleRequest(JavaRuntime.java:235) at com.google.apphosting.base.RuntimePb$EvaluationRuntime$6.handleBlockingRequest(RuntimePb.java:5235) at com.google.apphosting.base.RuntimePb$EvaluationRuntime$6.handleBlockingRequest(RuntimePb.java:5233) at com.google.net.rpc.impl.BlockingApplicationHandler.handleRequest(BlockingApplicationHandler.java:24) at com.google.net.rpc.impl.RpcUtil.runRpcInApplication(RpcUtil.java:363) at com.google.net.rpc.impl.Server$2.run(Server.java:838) at com.google.tracing.LocalTraceSpanRunnable.run(LocalTraceSpanRunnable.java:56) at com.google.tracing.LocalTraceSpanBuilder.internalContinueSpan(LocalTraceSpanBuilder.java:536) at com.google.net.rpc.impl.Server.startRpc(Server.java:793) at com.google.net.rpc.impl.Server.processRequest(Server.java:368) at com.google.net.rpc.impl.ServerConnection.messageReceived(ServerConnection.java:448) at com.google.net.rpc.impl.RpcConnection.parseMessages(RpcConnection.java:319) at com.google.net.rpc.impl.RpcConnection.dataReceived(RpcConnection.java:290) at com.google.net.async.Connection.handleReadEvent(Connection.java:466) at com.google.net.async.EventDispatcher.processNetworkEvents(EventDispatcher.java:759) at com.google.net.async.EventDispatcher.internalLoop(EventDispatcher.java:205) at com.google.net.async.EventDispatcher.loop(EventDispatcher.java:101) at com.google.net.rpc.RpcService.runUntilServerShutdown(RpcService.java:251) at com.google.apphosting.runtime.JavaRuntime$RpcRunnable.run(JavaRuntime.java:394) at java.lang.Thread.run(Unknown Source)

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• Hibernate+PostgreSQL throws JDBCConnectionException: Cannot open connection

  - by Omer Salmanoglu

  false true auto thread org.postgresql.Driver 1234 jdbc:postgresql://localhost/postgres postgres public org.hibernate.dialect.PostgreSQLDialect false true org.hibernate.transaction.JDBCTransactionFactory false false false false 100 When I press "Save" button I get the following exception: javax.servlet.ServletException: org.hibernate.exception.JDBCConnectionException: Cannot open connection javax.faces.webapp.FacesServlet.service(FacesServlet.java:325) root cause javax.faces.el.EvaluationException: org.hibernate.exception.JDBCConnectionException: Cannot open connection javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:102) com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102) javax.faces.component.UICommand.broadcast(UICommand.java:315) javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:775) javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1267) com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:82) com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101) com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118) javax.faces.webapp.FacesServlet.service(FacesServlet.java:312) root cause org.hibernate.exception.JDBCConnectionException: Cannot open connection org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:98) org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66) org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:52) org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:449) org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:167) org.hibernate.jdbc.JDBCContext.connection(JDBCContext.java:142) org.hibernate.transaction.JDBCTransaction.begin(JDBCTransaction.java:85) org.hibernate.impl.SessionImpl.beginTransaction(SessionImpl.java:1463) sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) java.lang.reflect.Method.invoke(Unknown Source) org.hibernate.context.ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:344) $Proxy108.beginTransaction(Unknown Source) com.yemex.beans.CompanyBean.saveOrUpdate(CompanyBean.java:52) sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) java.lang.reflect.Method.invoke(Unknown Source) org.apache.el.parser.AstValue.invoke(AstValue.java:196) org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:276) com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:98) javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:88) com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102) javax.faces.component.UICommand.broadcast(UICommand.java:315) javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:775) javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1267) com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:82) com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101) com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118) javax.faces.webapp.FacesServlet.service(FacesServlet.java:312) root cause java.sql.SQLException: No suitable driver found for jdbc:postgresql://localhost/postgres java.sql.DriverManager.getConnection(Unknown Source) java.sql.DriverManager.getConnection(Unknown Source) org.hibernate.connection.DriverManagerConnectionProvider.getConnection(DriverManagerConnectionProvider.java:133) org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:446) org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:167) org.hibernate.jdbc.JDBCContext.connection(JDBCContext.java:142) org.hibernate.transaction.JDBCTransaction.begin(JDBCTransaction.java:85) org.hibernate.impl.SessionImpl.beginTransaction(SessionImpl.java:1463) sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) java.lang.reflect.Method.invoke(Unknown Source) org.hibernate.context.ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:344) $Proxy108.beginTransaction(Unknown Source) com.yemex.beans.CompanyBean.saveOrUpdate(CompanyBean.java:52) sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) java.lang.reflect.Method.invoke(Unknown Source) org.apache.el.parser.AstValue.invoke(AstValue.java:196) org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:276) com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:98) javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:88) com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102) javax.faces.component.UICommand.broadcast(UICommand.java:315) javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:775) javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1267) com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:82) com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101) com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118) javax.faces.webapp.FacesServlet.service(FacesServlet.java:312)

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• JSF HIBERNATE POSTGRESQL

  - by user312619

  When I press "Save" button I get an exception like that ; javax.servlet.ServletException: org.hibernate.exception.JDBCConnectionException: Cannot open connection javax.faces.webapp.FacesServlet.service(FacesServlet.java:325) root cause javax.faces.el.EvaluationException: org.hibernate.exception.JDBCConnectionException: Cannot open connection javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:102) com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102) javax.faces.component.UICommand.broadcast(UICommand.java:315) javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:775) javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1267) com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:82) com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101) com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118) javax.faces.webapp.FacesServlet.service(FacesServlet.java:312) root cause org.hibernate.exception.JDBCConnectionException: Cannot open connection org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:98) org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66) org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:52) org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:449) org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:167) org.hibernate.jdbc.JDBCContext.connection(JDBCContext.java:142) org.hibernate.transaction.JDBCTransaction.begin(JDBCTransaction.java:85) org.hibernate.impl.SessionImpl.beginTransaction(SessionImpl.java:1463) sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) java.lang.reflect.Method.invoke(Unknown Source) org.hibernate.context.ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:344) $Proxy108.beginTransaction(Unknown Source) com.yemex.beans.CompanyBean.saveOrUpdate(CompanyBean.java:52) sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) java.lang.reflect.Method.invoke(Unknown Source) org.apache.el.parser.AstValue.invoke(AstValue.java:196) org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:276) com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:98) javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:88) com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102) javax.faces.component.UICommand.broadcast(UICommand.java:315) javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:775) javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1267) com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:82) com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101) com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118) javax.faces.webapp.FacesServlet.service(FacesServlet.java:312) root cause java.sql.SQLException: No suitable driver found for jdbc:postgresql://localhost/postgres java.sql.DriverManager.getConnection(Unknown Source) java.sql.DriverManager.getConnection(Unknown Source) org.hibernate.connection.DriverManagerConnectionProvider.getConnection(DriverManagerConnectionProvider.java:133) org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:446) org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:167) org.hibernate.jdbc.JDBCContext.connection(JDBCContext.java:142) org.hibernate.transaction.JDBCTransaction.begin(JDBCTransaction.java:85) org.hibernate.impl.SessionImpl.beginTransaction(SessionImpl.java:1463) sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) java.lang.reflect.Method.invoke(Unknown Source) org.hibernate.context.ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:344) $Proxy108.beginTransaction(Unknown Source) com.yemex.beans.CompanyBean.saveOrUpdate(CompanyBean.java:52) sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) java.lang.reflect.Method.invoke(Unknown Source) org.apache.el.parser.AstValue.invoke(AstValue.java:196) org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:276) com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:98) javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:88) com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102) javax.faces.component.UICommand.broadcast(UICommand.java:315) javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:775) javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1267) com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:82) com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101) com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118) javax.faces.webapp.FacesServlet.service(FacesServlet.java:312)

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• java.rmi.UnmarshalException: unable to pull client classes by server

  - by andrews

  Hi, I have an RMI client/server set-up on two machines that works fine in a simple situation when the server doesn't require a client-side defned class. However, when I need to use a class defined on the client side I am unable to have the server unmarshall those classes. I suspect this is an issue with my java.rmi.server.codebase property that I pass in as argument to the client app. I followed Sun's RMI Tutorial trail and I think I have followed the steps exactly except that I don't specify a classpath argument when executing client and server because they execute in the directory right above the root package directory (however I tried that too with no effect). The exceptions I get when attempting to execute the different client-side combinations described in detail below are all the same: RmiServer exception: java.rmi.ServerException: RemoteException occurred in server thread; nested exception is: java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is: java.lang.ClassNotFoundException: test.MyTask at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:353) at sun.rmi.transport.Transport$1.run(Transport.java:177) at java.security.AccessController.doPrivileged(Native Method) at sun.rmi.transport.Transport.serviceCall(Transport.java:173) at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:553) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:808) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:667) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) at java.lang.Thread.run(Thread.java:636) at sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(StreamRemoteCall.java:255) at sun.rmi.transport.StreamRemoteCall.executeCall(StreamRemoteCall.java:233) at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:142) at java.rmi.server.RemoteObjectInvocationHandler.invokeRemoteMethod(RemoteObjectInvocationHandler.java:178) at java.rmi.server.RemoteObjectInvocationHandler.invoke(RemoteObjectInvocationHandler.java:132) at $Proxy0.execute(Unknown Source) at test.myClient.main(myClient.java:32) The details are: My client/server rmi is set up over a home network behind a router. The router is assigned to a static ip address I will call myhostname. Appropriate port-mapping is set-up in the router that points to the right machines. role, machine, os, ip-address: server, venice, linux ubuntu 9.10, 10.0.1.2 client, naples, mac os x leopard, 10.0.1.4 I startup the server side as follows inside /home/andrews/workspace/epsilon/bin: 1 starting registry on the default port 1099: venice% rmiregistry & 2 starting web-server on port 2001 pointing to code base for common interfaces: venice% java webserver/ClassFileServer 2001 /home/andrew/workspace/epsilon/bin 3 starting server app (main class in test/myServer) which registers the server object: venice% java -Djava.rmi.server.codebase="http://myhostname:2001/" -Djava.security.policy=server.policy -Djava.rmi.server.hostname=myhostname test/myServer & Now the client side inside /Users/andrews/Development/Java/workspace/epsilon/bin: 1 start a local web server that can server client-side classes to the server (not sure if this is needed, but I added I tried it, and still no success; I have added port-mapping to the router for 2001 to venice, for 2002 to naples) naples$ java webserver/ClassFileServer 2002 /Users/andrews/Development/Java/workspace/epsilon/bin/ Trying to run the client (note: I don't specify the -cp argument because client executes right above the root package directory): 1 try #1 using an http hostname naples$ java -Djava.rmi.server.codebase=http://10.0.1.4:2002/ -Djava.security.policy=client.policy test.myClient myhostname Note 1: the myhostname argument at the end is passed-in to the client so that it resolves to server's rmi hostname. Note 2: I tried using localhost:2002 instead of 10.0.1.4:2002 too. Note 3: I tried using myhostname:2002 since myhostname is assigned to the router and I have proper port-mapping set-up, this address should resolve to naples and not venice 2 try #2: naples$ java -Djava.rmi.server.codebase=file:/Users/andrews/Development/Java/workspace/epsilon/bin/ -Djava.security.policy=client.policy test.myClient myhostname Note 1: the code base url format is correct, I created a small program to convert current file directory path into a url and used that. using file:///Users... has same effect. Other notes: 1 my server and client policy files correctly specify the path, as I've tested this setup with good and bad paths, and getting a security exception for bad path 2 this setup works if I don't use client-side defined objects, the client connects correctly to the server and the server executes. 3 when I place the client-side class on the server in the server's classpath, all executes fine. All help is appreciated.

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• How to learn high-level Java web development concepts

  - by titaniumdecoy

  I have some experience writing web applications in Java for class projects. My first project used Servlets and my second, the Stripes framework. However, I feel that I am missing the greater picture of Java web development. I don't really understand the web.xml and context.xml files. I'm not sure what constitutes a Java EE application as opposed to a generic Java web application. I can't figure out how a bean is different from an ordinary Java class (POJO?) and how that differs from an Enterprise Java Bean (EJB). These are just the first few questions I could think of, but there are many more. What is a good way to learn how Java web applications function from the top down rather than simply how to develop an application with a specific framework? (Is there a book for this sort of thing?) Ultimately, I would like to understand Java web applications well enough to write my own framework.

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• Error in java code.

  - by user243680

  I am getting the following error when i try to use a blue tooth dongle to transfer a video file from pc to mobile phone. does anyone know run: BlueCove log redirected to log4j log4j:WARN No appenders could be found for logger (com.intel.bluetooth). log4j:WARN Please initialize the log4j system properly. BlueCove version 2.1.0 on bluesoleil java.io.IOException: Device not discovered BlueCove stack shutdown completed at com.intel.bluetooth.BluetoothStackBlueSoleil.connectionRfOpenClientConnection(BluetoothStackBlueSoleil.java:361) at com.intel.bluetooth.BluetoothRFCommClientConnection.<init>(BluetoothRFCommClientConnection.java:37) at com.intel.bluetooth.MicroeditionConnector.openImpl(MicroeditionConnector.java:379) at com.intel.bluetooth.MicroeditionConnector.open(MicroeditionConnector.java:162) at javax.microedition.io.Connector.open(Connector.java:83) at de.avetana.obexsolo.OBEXConnector.open(OBEXConnector.java:103) at OBEXTest.main(OBEXTest.java:23)

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• casting a generic array in java

  - by liloboy

  The implementation is for a linked list in java : public AnyType[] toArr() { AnyType[] arr = (AnyType[]) new Object[size]; int i = 0; Node<AnyType> current = head.next; while (cur != head){ arr[i] = current.data;// fill the array i++; current = current.next; } return arr; } public static void main(String[] args) { System.out.println(ll.toArr().toString()); } The error that I get: Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.Integer; Thanks.

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• Java template classes using generator or similar?

  - by Hugh Perkins

  Is there some library or generator that I can use to generate multiple templated java classes from a single template? Obviously Java does have a generics implementation itself, but since it uses type-erasure, there are lots of situations where it is less than adequate. For example, if I want to make a self-growing array like this: class EasyArray { T[] backingarray; } (where T is a primitive type), then this isn't possible. This is true for anything which needs an array, for example high-performance templated matrix and vector classes. It should probably be possible to write a code generator which takes a templated class and generates multiple instantiations, for different types, eg for 'double' and 'float' and 'int' and 'String'. Is there something that already exists that does this? Edit: note that using an array of Object is not what I'm looking for, since it's no longer an array of primitives. An array of primitives is very fast, and uses only as much space a sizeof(primitive) * length-of-array. An array of object is an array of pointers/references, that points to Double objects, or similar, which could be scattered all over the place in memory, require garbage collection, allocation, and imply a double-indirection for access. Edit2: good god, voted down for asking for something that probably doesn't currently exist, but is technically possible and feasible? Does that mean that people looking for ways to improve things have already left the java community? Edit3: Here is code to show the difference in performance between primitive and boxed arrays: int N = 10*1000*1000; double[]primArray = new double[N]; for( int i = 0; i < N; i++ ) { primArray[i] = 123.0; } Object[] objArray = new Double[N]; for( int i = 0; i < N; i++ ) { objArray[i] = 123.0; } tic(); primArray = new double[N]; for( int i = 0; i < N; i++ ) { primArray[i] = 123.0; } toc(); tic(); objArray = new Double[N]; for( int i = 0; i < N; i++ ) { objArray[i] = 123.0; } toc(); Results: double[] array: 148 ms Double[] array: 4614 ms Not even close!

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• Could you please suggest any good books for Java EE

  - by attal

  Hi people, I am comfortable with Java SE 6 and I wanted to go deeper into Java by learning Java EE 6. However, I am confused and I don't know which book(s) should I read to master Java EE 6 (I have never learned Java EE previously). Could you please suggest any appropriate book(s) to help me master Java EE completely? Thank you for reading

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• Java-syntax for explicitly specifiying generic arguments in method calls

  - by hstoerr

  What is the syntax for explicitly giving the type parameters for a generic Java method?

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• Catch a generic exception in Java?

  - by Alex Baranosky

  We use JUnit 3 at work and there is no ExpectedException annotation. I wanted to add a utility to our code to wrap this: try { someCode(); fail("some error message"); } catch (SomeSpecificExceptionType ex) { } So I tried this: public static class ExpectedExceptionUtility { public static <T extends Exception> void checkForExpectedException(String message, ExpectedExceptionBlock<T> block) { try { block.exceptionThrowingCode(); fail(message); } catch (T ex) { } } } However, Java cannot use generic exception types in a catch block, I think. How can I do something like this, working around the Java limitation? Is there a way to check that the ex variable is of type T?

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• Boston: Free Java Developer Event March 3rd!

  - by Jacob Lehrbaum

  Attention Boston area developers!  Oracle has been running a series of free one-day Java Developer events in the US, Europe, and Asia since last November, and on March 3rd, this highly popular series is coming to the Westin Copley Place in Boston.  The Java Developer Day will include four tracks of sessions and hands-on-labs designed for developers interested in Server, Desktop, Embedded, and core Java SE platform topics.  Technologies covered include Java EE, Java ME and Java SE (including the JDK).  From the event page: Come to this free event if you are interested in:Evaluating the Java platformUsing other languages on the JVMBuilding server side JavaConstructing Rich Web or Desktop ApplicationsUnderstanding the JVM and its built in diagnosticsMaking Smart Devices even smarterCheck out the event page to read more and/or register.  The event is free, but space is limited so register today!

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• scalablity of Scala over Java

  - by Marcus

  I read an article that says Scala handles concurrency better than Java. http://www.theserverside.com/feature/Solving-the-Scalability-Paradox-with-Scala-Clojure-and-Groovy ...the scalability limitation is confined specifically to the Java programming language itself, but it is not a limitation of the Java platform as a whole... The scalability issues with Java aren't a new revelation. In fact, plenty of work has been done to address these very issues, with two of the most successful projects being the programming languages named Scala and Clojure... ...Scala is finding ways around the problematic thread and locking paradigm of the Java language... How is this possible? Doesn't Scala use Java's core libraries which brings all the threading and locking issues from Java to Scala?

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• Java - learning / migrating fast

  - by Yippie-Kai-Yay

  This is not one of those questions like "How do I learn Java extremely fast, I know nothing about programming, but I heard Java is cool, yo". I have an interview for a Java Software Developer in a couple of weeks and the thing is that I think that I know C++ really good and I am somewhat good at C# (like, here I can probably answer on a lot of questions related to these languages), but I have almost zero experience with Java. I have a lot of projects written in both languages, I participiated in several open-source projects (mostly C++, though). Now, what should I do (in your opinion) to prepare myself for this Java interview. I guess migrating from C# to Java should be kind of fast, especially when you know a lot about programming in global, patterns, modern techniques and have a lot of practical experience behind you. But still two weeks is obviously not enough to get Java in-depth - so what should I focus on to have the best chances to pass the interview? Thank you.

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• Java - learning / migrating fast

  - by Yippie-Kai-Yay

  Hello! This is not one of those questions like "How do I learn Java extremely fast, I know nothing about programming, but I heard Java is cool, yo". I have an interview for a Java Software Developer in a couple of weeks and the thing is that I think that I know C++ really good and I am somewhat good at C# (like, here I can probably answer on a lot of questions related to these languages), but I have almost zero experience with Java. I have a lot of projects written in both languages, I participiated in several open-source projects (mostly C++, though). Now, what should I do (in your opinion) to prepare myself for this Java interview. I guess migrating from C# to Java should be kind of fast, especially when you know a lot about programming in global, patterns, modern techniques and have a lot of practical experience behind you. But still two weeks is obviously not enough to get Java in-depth - so what should I focus on to have the best chances to pass the interview? Thank you.

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• Maker Faire 2012 Attendees build with Java Technology

  - by hinkmond

  Looks like Daniel Green, systems engineer from Oracle, and the panel of Java experts had a successful Java Technology booth at this year's Maker Faire 2012. See: Maker Faire 2012 adds Java Here's a quote: "We made a huge impact for Java and Oracle, creating positive perception, building brand awareness, and introducing fun and engaging ways for future technologists to learn Java programming," says Michelle Kovac, Oracle director, Java Marketing and Operations. Good stuff, considering all the future developers of exploding robots and fire-breathing dragon metal sculptures attend the Maker Faire. They can blow up stuff with Java technology just as effectively as other programming languages. Hinkmond

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• Java Plugin - Firefox

  - by Tomassino

  Having trouble getting Java to work with Firefox (22), I have followed the advice in this question and on the official Java site, but nothing seems to work. I have the latest Java (1.7.0_25) in /opt/java and have set a symlink in /usr/libs/mozilla/plugins for the libnpjp2.so file. I can see the file in the terminal and Java runs fine. However Firefox shows nothing in about:plugins. I have also run export JAVA_HOME="/opt/java/jre1.7.0_05/bin/java" to be on the safe side. I know there are multiple plugin directories such as /usr/lib/firefox/plugins and /usr/lib/firefox-addons/plugins, but all my current plugins show they are located in /usr/lib/mozilla/plugins when viewing the about:plugins page. A bit stuck on where to go next?

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• Understanding the Java Ecosystem

  - by syrion

  I have traditionally had the "luxury" of being a one-man development team. I've used Python extensively, have a reasonable command of Perl, PHP, and JavaScript. My problem is Java. I can write Java code. I'm not great at it--unlike Python, I rarely make use of anything unique to Java when I'm writing it. Furthermore, my experience is mostly in simple GUI/console programming. Unfortunately, I'm currently pursuing an IT degree where Java is the lingua franca. My database class is requiring that our projects be written in Java using servlets, and I just can't wrap my head around the ecosystem. Is there a good online overview of or tutorial on how the Java web ecosystem works? I have Thinking in Java, but it's mostly just the language itself (which I understand well enough to get by). I have looked at the Sun servlet tutorial, but it seems outdated.

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