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• What is the best practice for including third party jar files in a Java program?

  - by ZoFreX

  I have a program that needs several third-party libraries, and at the moment it is packaged like so: zerobot.jar (my file) libs/pircbot.jar libs/mysql-connector-java-5.1.10-bin.jar libs/c3p0-0.9.1.2.jar As far as I know the "best" way to handle third-party libs is to put them on the classpath in the manifest of my jar file, which will work cross-platform, won't slow down launch (which bundling them might) and doesn't run into legal issues (which repackaging might). The problem is for users who supply the third party libraries themselves (example use case, upgrading them to fix a bug). Two of the libraries have the version number in the file, which adds hassle. My current solution is that my program has a bootstrapping process which makes a new classloader and instantiates the program proper using it. This custom classloader adds all .jar files in lib/ to its classpath. My current way works fine, but I now have two custom classloaders in my application and a recent change to the code has caused issues that are difficult to debug, so if there is a better way I'd like to remove this complexity. It also seems like over-engineering for what I'm sure is a very common situation. So my question is, how should I be doing this?

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• Java - Call to start method on thread : how does it route to Runnable interface's run () ?

  - by Bhaskar

  Ok , I know the two standard ways to create a new thread and run it in Java : 1 Implement Runnable in a class , define run method ,and pass an instance of the class to a new Thread. When the start method on the thread instance is called , the run method of the class instance will be invoked. 2 Let the class derive from Thread, so it can to override the method run() and then when a new instance's start method is called , the call is routed to overridden method. In both methods , basically a new Thread object is created and its start method invoked. However , while in the second method , the mechanism of the call being routed to the user defined run() method is very clear ,( its a simple runtime polymorphism in play ), I dont understand how the call to start method on the Thread object gets routed to run() method of the class implementing Runnable interface. Does the Thread class have an private field of Type Runnable which it checks first , and if it is set then invokes the run method if it set to an object ? that would be a strange mechanism IMO. How does the call to start() on a thread get routed to the run method of the Runnable interface implemented by the class whose object is passed as a parameter when contructing the thread ?

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• Would an immutable keyword in Java be a good idea?

  - by berry120

  Generally speaking, the more I use immutable objects in Java the more I'm thinking they're a great idea. They've got lots of advantages from automatically being thread-safe to not needing to worry about cloning or copy constructors. This has got me thinking, would an "immutable" keyword go amiss? Obviously there's the disadvantages with adding another reserved word to the language, and I doubt it will actually happen primarily for the above reason - but ignoring that I can't really see many disadvantages. At present great care has to be taken to make sure objects are immutable, and even then a dodgy javadoc comment claiming a component object is immutable when it's in fact not can wreck the whole thing. There's also the argument that even basic objects like string aren't truly immutable because they're easily vunerable to reflection attacks. If we had an immutable keyword the compiler could surely recursively check and give an iron clad guarantee that all instances of a class were immutable, something that can't presently be done. Especially with concurrency becoming more and more used, I personally think it'd be good to add a keyword to this effect. But are there any disadvantages or implementation details I'm missing that makes this a bad idea?

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• Java abstract visitor - guarantueed to succeed? If so, why?

  - by disown

  I was dealing with hibernate, trying to figure out the run-time class behind proxied instances by using the visitor pattern. I then came up with an AbstractVisitable approach, but I wonder if it will always produce correct results. Consider the following code: interface Visitable { public void accept(Visitor v); } interface Visitor { public void visit(Visitable visitorHost); } abstract class AbstractVisitable implements Visitable { @Override public void accept(Visitor v) { v.visit(this); } } class ConcreteVisitable extends AbstractVisitable { public static void main(String[] args) { final Visitable visitable = new ConcreteVisitable(); final Visitable proxyVisitable = (Visitable) Proxy.newProxyInstance( Thread.currentThread().getContextClassLoader(), new Class<?>[] { Visitable.class }, new InvocationHandler() { @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { return method.invoke(visitable, args); } }); proxyVisitable.accept(new Visitor() { @Override public void visit(Visitable visitorHost) { System.out.println(visitorHost.getClass()); } }); } } This makes a ConcreteVisitable which inherits the accept method from AbstractVisitable. In c++, I would consider this risky, since this in AbstractVisitable could be referencing to AbstractVisitable::this, and not ConcreteVisitable::this. I was worried that the code under certain circumstances would print class AbstractVisible. Yet the code above outputs class ConcreteVisitable, even though I hid the real type behind a dynamic proxy (the most difficult case I could come up with). Is the abstract visitor approach above guaranteed to work, or are there some pitfalls with this approach? What guarantees are given in Java with respect to the this pointer?

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• How to create and display a list in Java?

  - by lox

  i have to create a list of ,let's say 50 people, (in Java) and display the list, and i don't really know how to do that. so this is what i have tried to do so far . please correct and complete some of my code . public class Person { String name; String stuff; } public class CreatePerson { public static void ang() { ArrayList<Person> thing=new ArrayList<Person>(); Scanner diskScanner = new Scanner(in); for(int i=0; i<50; i++){ Person pers = new Person(); out.print("name: "); pers.name=diskScanner.nextLine(); out.print("stuff: "); pers.stuff=diskScanner.nextLine(); thing.add(pers); break; } // Display people for (int i=0; i<50; i++) { out.println(??);{ } } }}

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• Which is better Java programming practice: stacking enums and enum constructors, or subclassing?

  - by Arvanem

  Hi folks, Given a finite number of items which differ in kind, is it better to represent them with stacked enums and enum constructors, or to subclass them? Or is there a better approach altogether? To give you some context, in my small RPG program (which ironically is supposed to be simple), a character has different kinds of items in his or her inventory. Items differ based on their type and use and effect. For example, one item of inventory is a spell scroll called Gremlin that adjusts the Utility attribute. Another item might be a sword called Mort that is used in combat and inflicts damage. In my RPG code, I now have tried two ways of representing inventory items. One way was subclassing (for example, InventoryItem - Spell - AdjustingAttributes; InventoryItem - Weapon - Sword) and instantiating each subclass when needed, and assigning values such as names like Gremlin and Mort. The other way was by stacking enums and enum constructors. For example, I created enums for itemCategory and itemSpellTypes and itemWeaponTypes, and the InventoryItem enum was like this: public enum InventoryItem { GREMLIN(itemType.SPELL, itemSpellTypes.ATTRIBUTE, Attribute.UTILITY), MORT(itemType.WEAPON, itemWeaponTypes.SWORD, 30); InventoryItem(itemType typeOfItem, itemSpellTypes spellType, Attribute attAdjusted) { // snip, enum logic here } InventoryItem(itemType typeOfItem, itemWeaponTypes weaponType, int dmg) { // snip, enum logic here } // and so on, for all the permutations of items. } Is there a better Java programming practice than these two approaches? Or if these are the only ways, which of the two is better? Thanks in advance for your suggestions.

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• Java - How to find the redirected url of a url?

  - by Yatendra Goel

  I am accessing web pages through java as follows: URLConnection con = url.openConnection(); But in some cases, a url redirects to another url. So I want to know the url to which the previous url redirected. Below are the header fields that I got as a response: null-->[HTTP/1.1 200 OK] Cache-control-->[public,max-age=3600] last-modified-->[Sat, 17 Apr 2010 13:45:35 GMT] Transfer-Encoding-->[chunked] Date-->[Sat, 17 Apr 2010 13:45:35 GMT] Vary-->[Accept-Encoding] Expires-->[Sat, 17 Apr 2010 14:45:35 GMT] Set-Cookie-->[cl_def_hp=copenhagen; domain=.craigslist.org; path=/; expires=Sun, 17 Apr 2011 13:45:35 GMT, cl_def_lang=en; domain=.craigslist.org; path=/; expires=Sun, 17 Apr 2011 13:45:35 GMT] Connection-->[close] Content-Type-->[text/html; charset=iso-8859-1;] Server-->[Apache] So at present, I am constructing the redirected url from the value of the Set-Cookie header field. In the above case, the redirected url is copenhagen.craigslist.org Is there any standard way through which I can determine which url the particular url is going to redirect. I know that when a url redirects to other url, the server sends an intermediate response containing a header field that tells the url which it is going to redirect but I am not receiving that intermediate response through the url.openConnection(); method.

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• What does it mean to say "Instance variables are not over-rided" in java?

  - by Ankit

  I am aware of the concept called field hiding in java. But still I am having a confusion in relation to instance variable being not over-ridden. According to my present knowledge, overriding a method of super-class means that the JVM will call the sub-class's over-ridden method though the super-class's method is available to the sub-class. And I read the similar thing for field hiding via the link:- Hiding Fields So, in any case we are over-ridding the instance if we change the values of the inherited instance variable in the sub-class. I am confused please help. I am using the following super-class:- public class Animal{ File picture; String food; int hunger; int width, height; int xcoord, ycoord; public void makeNoise(){ ......... } public void eat(){ ............. } public void sleep(){ .......... } public void roam(){ ............. } } It has sub-classes like Tiger, cat, dog,hippo etc. The sub-classes over-ride the makeNoise(), eat and roam() method. But each sub-class also uses a different set of values for instance variables. So as per my confusion, I am kind-of overriding all the instance variables and 3 methods of the super-class Animal; and I still have the super-class instance variables available to the sub-class with the use of the super keyword.

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• Help with Java Generics: Cannot use "Object" as argument for "? extends Object"

  - by AniDev

  Hello, I have the following code: import java.util.*; public class SellTransaction extends Transaction { private Map<String,? extends Object> origValueMap; public SellTransaction(Map<String,? extends Object> valueMap) { super(Transaction.Type.Sell); assignValues(valueMap); this.origValueMap=valueMap; } public SellTransaction[] splitTransaction(double splitAtQuantity) { Map<String,? extends Object> valueMapPart1=origValueMap; valueMapPart1.put(nameMappings[3],(Object)new Double(splitAtQuantity)); Map<String,? extends Object> valueMapPart2=origValueMap; valueMapPart2.put(nameMappings[3],((Double)origValueMap.get(nameMappings[3]))-splitAtQuantity); return new SellTransaction[] {new SellTransaction(valueMapPart1),new SellTransaction(valueMapPart2)}; } } The code fails to compile when I call valueMapPart1.put and valueMapPart2.put, with the error: The method put(String, capture#5-of ? extends Object) in the type Map is not applicable for the arguments (String, Object) I have read on the Internet about generics and wildcards and captures, but I still don't understand what is going wrong. My understanding is that the value of the Map's can be any class that extends Object, which I think might be redundant, because all classes extend Object. And I cannot change the generics to something like ? super Object, because the Map is supplied by some library. So why is this not compiling? Also, if I try to cast valueMap to Map<String,Object>, the compiler gives me that 'Unchecked conversion' warning. Thanks!

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• Where are the network boundaries in the Java Connector Architecture (JCA)?

  - by Laird Nelson

  I am writing a JCA resource adapter. I'm also, as I go, trying to fully understand the connection management portion of the JCA specification. As a thought experiment, pretend that the only client of this adapter will be a Swing Java Application Client located on a different machine. Also assume that the resource adapter will communicate with its "enterprise information system" (EIS) over the network as well. As I understand the JCA specification, the .rar file is deployed to the application server. The application server creates the .rar file's implementation of the ManagedConnectionFactory interface. It then asks it to produce a connection factory, which is the opaque object that is deployed to JNDI for the user to use to obtain a connection to the resource. (In the case of JDBC, the connection factory is a javax.sql.DataSource.) It is a requirement that the connection factory retain a reference to the application-server-supplied ConnectionManager, which, in turn, is required to be Serializable. This makes sense--in order for the connection factory to be stored in JNDI, it must be serializable, and in order for it to keep a reference to the ConnectionManager, the ConnectionManager must also be serializable. So fine, this little object graph gets installed in the application client's JNDI tree. This is where I start to get queasy. Is the ConnectionManager--the piece supplied by the application server that is supposed to handle connection management, sharing, pooling, etc.--wholly present on the client at this point? One of its jobs is to create ManagedConnection instances, and a ManagedConnection is not required to be Serializable, and the user connection handles it vends are also not required to be Serializable. That suggests to me that the whole connection pooling machinery is shipped wholesale to the application client and stuffed into its JNDI tree. Does this all mean that JCA interactions from the client side bypass the server-side componentry of the application server? Where are the network boundaries in the JCA API?

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• Is it possible to Kick off a java process under Windows Service with C#?

  - by Wing C. Chen

  I would like to wrap a java program into a windows service with C# using System.ServiceProcess.ServiceBase. So I came up with the following code: /// <summary> /// The main entry point for the application. /// </summary> static void Main() { System.ServiceProcess.ServiceBase.Run(new JavaLauncher()); } protected override void OnStart(string[] args) { Thread _thread; _thread = new Thread(StartService); _thread.Start(); base.OnStart(args); } protected override void OnStop() { Thread _thread; _thread = new Thread(StopService); _thread.Start(); base.OnStop(); } static public void StartService() { System.Diagnostics.Process proc = new System.Diagnostics.Process(); proc.EnableRaisingEvents = false; proc.StartInfo.FileName = "javaw"; proc.StartInfo.Arguments = config.generateLaunchCommand(); proc.Start(); } static public void StopService() { System.Diagnostics.Process proc = new System.Diagnostics.Process(); proc.EnableRaisingEvents = false; proc.StartInfo.FileName = "javaw"; proc.StartInfo.Arguments = "-jar stop.jar"; proc.Start(); } Firstly I had to use Threads in OnStart and OnStop. If not, an exception occurs complaining that the service is terminated because of doing nothing. Secondly, the service can be hooked up to windows smoothly. However, the service terminates a short while after it is started. I looked into the process monitor, only the service process stays alive for that short while, the javaw process never showed up, however. Is there anyone who knows how this can be fixed? It works fine in an ordinary console environment. I think it has something to do with Windows service.

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• Can someone explain the declaration of these java generic methods?

  - by Tony Giaccone

  I'm reading "Generics in the Java Programming Language" by Gilad Bracha and I'm confused about a style of declaration. The following code is found on page 8: interface Collection<E> { public boolean containsAll(Collection<?> c); public boolean addAll(Collection<? extends E> c); } interface Collection<E> { public <T> boolean containsAll(Collection<T> c); public <T extends E> boolean addAll(Collection<T> c); // hey, type variables can have bounds too! } My point of confusion comes from the second declaration. It's not clear to me what the purpose the <T> declaration serves in the following line: public <T> boolean containsAll(Collection<T> c); The method already has a type (boolean) associated with it. Why would you use the <T> and what does it tell the complier? I think my question needs to be a bit more specific. Why would you write: public <T> boolean containsAll(Collection<T> c); vs public boolean containsAll(Collection<T> c); It's not clear to me, what the purpose of <T> is, in the first declaration of containsAll.

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• Java sockets: multiple client threads on same port on same machine?

  - by espcorrupt

  I am new to Socket programming in Java and was trying to understand if the below code is not a wrong thing to do. My question is: Can I have multiple clients on each thread trying to connect to a server instance in the same program and expect the server to read and write data with isolation between clients" public class Client extends Thread { ... void run() { Socket socket = new Socket("localhost", 1234); doIO(socket); } } public class Server extends Thread { ... void run() { // serverSocket on "localhost", 1234 Socket clientSock = serverSocket.accept(); executor.execute(new ClientWorker(clientSock)); } } Now can I have multiple Client instances on different threads trying to connect on the same port of the current machine? For example, Server s = new Server("localhost", 1234); s.start(); Client[] c = new Client[10]; for (int i = 0; i < c.length; ++i) { c.start(); }

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• How i can convert client for Axis 1.4 to Axis2 in JAVA ?

  - by dahevos

  Hello, First of all i success to programming a client for an Axis 1.2 web service, but for Axis2 i don't know how i can do, and the tutorial in Apache don't really help me. Here my code : import java.net.URL; import javax.xml.namespace.QName; import org.apache.axis.client.Call; import org.apache.axis.client.Service; public class EmployeClient { public static void main(String [] args) throws Exception { Service service = new Service(); Call call = (Call)service.createCall(); String endpoint = "http://localhost:8080/axis/services/EmployeService"; call.setTargetEndpointAddress(new URL(endpoint)); call.setOperationName(new QName("getCurrentID")); String dept = "marketing"; String name = "sacha"; String position = (String)call.invoke(new Object [] {new String(dept), new String(name)}); System.out.println("Résultat de la recherche : " + position ); } } So how can i do for convert this code in Axis2 ? Thanks you very much. ps : i'm french, sorry for my bad english !

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• How do i integrate paypal in my website? Java

  - by Nitesh Panchal

  Hello, I want to integrate paypal in my java web application. I saw that they offer many methods to accomplish this. But i want my visitors to remain on my site only. My friend told me that Paypal offers webservice. But i can't seem to find any documentation on Paypal site. If anybody could help me with this, i would be really very grateful. Please offer me the relevant links on Paypal where i could read and get my things done. Secondly, my friend also told me that we need to give location to paypal where my visitors would be redirected once paypal payment is complete. But i am confused. I am working on localhost. How would Paypal know about my localhost? I have already created my sandbox testing account. What should be my next step. Please explain me in detail. I don't know anything about Paypal. Once i created a demo application of Express checkout where they give a simple button of Pay Now and on clicking on it shopping cart etc appears. But now i want my visitors to stay on same website. Thanks in advance :)

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• Performance Comparison of Shell Scripts vs high level interpreted langs (C#/Java/etc.)

  - by dferraro

  Hi all, First - This is not meant to be a 'which is better, ignorant nonionic war thread'... But rather, I generally need help in making an architecture decision / argument to put forward to my boss. Skipping the details - I simply just would love to know and find the results of anyone who has done some performance comparisons of Shell vs [Insert General Purpose Programming Language (interpreted) here), such as C# or Java... Surprisingly, I have spent some time on Google on searching here to not find any of this data. Has anyone ever done these comparisons, in different use-cases; hitting a database like in a XYX # of loops doing different types of SQL (Oracle pref, but MSSQL would do) queries such as any of the CRUD ops - and also not hitting database and just regular 50k loop type comparison doing different types of calculations, and things of that nature? In particular - for right now, I need to a comparison of hitting an Oracle DB from a shell script vs, lets say C# (again, any GPPL thats interpreted would be fine, even the higher level ones like Python). But I also need to know about standard programming calculations / instructions/etc... Before you ask 'why not just write a quick test yourself? The answer is: I've been a Windows developer my whole life/career and have very limited knowledge of Shell scripting - not to mention *nix as a whole.... So asking the question on here from the more experienced guys would be grealty beneficial, not to mention time saving as we are in near perputual deadline crunch as it is ;). Thanks so much in advance,

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• Java - Reading a csv file line by line - stuck with weird non-existent characters being read!

  - by rockit

  hello fellow java developers. I'm having a very strange issue. I'm trying to read a csv file line by line. Im at the point where Im just testing out the reading of the lines. ONly each time that I read a line, the line contains square characters between each character of text. I even saved the file as a txt file in wordpad and notepad with no change. Thus I must be doing something stupid... I have a csv file, standard csv file, yes a text file with commas in it. I try to read a line of text, but the text is all f-ed up and cannot find the phrase within the text. Any advice? code below. //open csv File filReadMe = new File(strRoot + "data2.csv"); BufferedReader brReadMe = new BufferedReader(new InputStreamReader(new FileInputStream(filReadMe))); String strLine = brReadMe.readLine(); //for all lines while (strLine != null){ //if line contains "(see also" if (strLine.toLowerCase().contains("(see also")){ //write line from "(see also" to ")" int iBegin = strLine.toLowerCase().indexOf("(see also"); String strTemp = strLine.substring(iBegin); int iLittleEnd = strTemp.indexOf(")"); System.out.println(strLine.substring(iBegin, iBegin + iLittleEnd)); } //update line strLine = brReadMe.readLine(); } //end for brReadMe.close();

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• Multiple Exception Handling in one if statement [closed]

  - by JA3N

  I am having trouble with throwing and catching exceptions. Here is the code for assignSeat(), assignSeat is called in a try block in another class. void assignSeat(String passengerName, int x, int y) throws SeatOccupiedException, InvalidPassengerNameException { Seat tSeat = airplane.getSeat(x,y); if (tSeat!=null) { if (passengerName.isEmpty() || !passengerName.matches("[a-zA-Z]+")) { throw new InvalidPassengerNameException(); } //excluded else if else if (foundPassenger(passengerName)) { airplane.seatList.get(airplane.seatNumber(passengerName)).unOccupy(); tSeat.occupy(); for (int i = 0; i<passengers.size();i++) if (passengers.get(i).getName().equals(passengerName)) passengers.get(i).changeSeat(tSeat.getSeatName()); } else if (!tSeat.occupied) { tSeat.occupy(); addPassenger(passengerName, tSeat.getSeatName()); } else if (tSeat.occupied) { throw new SeatOccupiedException(); } } and here is the code that calls assignSeat() and is in another class (I won't copy the whole class to make it look clearer) if (afComp.currentAF != null) { try { afComp.currentAF.assignSeat(nameField.getText(), x, y); //<-Problem here, "Unhandled exception type SeatOccupiedException" } catch (SeatOccupiedException exception) //<-Problem here, "Unreachable catch block, This exception is never thrown from the try statement body" { } catch(InvalidPassengerNameException exception) //<-No problems. { } } Whats wrong with the try block? why won't it throw the SeatOccupiedException? Exception classes: SeatOccupied: package a2; public class SeatOccupiedException extends Exception { public SeatOccupiedException(){} } InvalidPassengerName: package a2; public class InvalidPassengerNameException extends Exception { public InvalidPassengerNameException() {} } Every class I have is in package a2 imports for class that calls assignSeat package a2; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.awt.event.MouseListener; import java.awt.event.MouseMotionListener; import java.awt.event.MouseEvent; import java.awt.BorderLayout; import javax.swing.*; import javax.swing.event.*; imports for class that has assignSeat package a2; import java.util.ArrayList;

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• Java extends classes - Share the extended class fields within the super class.

  - by Bastan

  Straight to the point... I have a class public class P_Gen{ protected String s; protected Object oP_Gen; public P_Gen(String str){ s = str; oP_Gen = new Myclass(this); } } Extended class: public class P extends P_Gen{ protected Object oP; public P(String str){ oP = new aClass(str); super(str); } } MyClass: public class MyClass{ protected Object oMC; public MyClass(P extendedObject){ oMc = oP.getSomething(); } } I came to realize that MyClass can only be instantiated with (P_Gen thisObject) as opposed to (P extendedObject). The situation is that I have code generated a bunch of classes like P_Gen. For each of them I have generated a class P which would contains my P specific custom methods and fields. When I'll regenerate my code in the future, P would not be overwritten as P_Gen would. ** So what happened in my case???!!!... I realized that MyClass would beneficiate from the info stored in P in addition to only P_Gen. Would that possible? I know it's not JAVA "realistic" since another class that extends P_Gen might not have the same fields... BY DESIGN, P_Gen will not be extended by anything but P.... And that's where it kinda make sens. :-) at least in other programming language ;-) In other programming language, it seems like P_Gen.this === P.this, in other word, "this" becomes a combination of P and P_Gen. Is there a way to achieve this knowing that P_Gen won't be extended by anything than P?

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• Is this a safe way to release resources in Java?

  - by palto

  Usually when code needs some resource that needs to be released I see it done like this: InputStream in = null; try{ in = new FileInputStream("myfile.txt"); doSomethingWithStream(in); }finally{ if(in != null){ in.close(); } } What I don't like is that you have to initialize the variable to null and after that set it to another value and in the finally block check if the resource was initialized by checking if it is null. If it is not null, it needs to be released. I know I'm nitpicking, but I feel like this could be done cleaner. What I would like to do is this: InputStream in = new FileInputStream("myfile.txt"); try{ doSomethingWithStream(in); }finally{ in.close(); } To my eyes this looks almost as safe as the previous one. If resource initialization fails and it throws an exception, there's nothing to be done(since I didn't get the resource) so it doesn't have to be inside the try block. The only thing I'm worried is if there is some way(I'm not Java certified) that an exception or error can be thrown between operations? Even simpler example: Inputstream in = new FileInputStream("myfile.txt"); in.close(); Is there any way the stream would be left open that a try-finally block would prevent?

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• i have this code but when i run it i get an exception:

  - by nisnis84

  i have this code but when i run it i get an exception: java.security.AccessControlException: access denied (java.net.SocketPermission 127.0.0.1:8081 connect,resolve) this is the code, the server running good but the client dont work <OBJECT classid="clsid:8AD9C840-044E-11D1-B3E9-00805F499D93" width="615" height="360" codebase="http://java.sun.com/products/plugin/autodl/jinstall-1_4-windows-i586.cab#Version=1,4,0,mn"> <PARAM name="code" value="client/LlamaChat.class"> <PARAM name="archive" value="LlamaChat.jar"> <PARAM name="type" value="application/x-java-applet;version=1.4"> <PARAM name="scriptable" value="true"> <PARAM name="username" value="[replace with username]"> <PARAM name="port" value="[replace with port]"> <COMMENT> <EMBED type="application/x-java-applet;version=1.4" width="615" height="360" code="client/LlamaChat.class" archive="LlamaChat.jar" pluginspage="http://java.sun.com/j2se/1.4.1/download.html" username="nis" port="8081" <NOEMBED> No Java 1.4 plugin </NOEMBED></EMBED> </COMMENT> </OBJECT>

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• SWIG: From Plain C++ to working Wrapper

  - by duckworthd

  Hi everyone. I've been trying to create a SWIG wrapper for this tiny little C++ class for the better part of 3 hours with no success, so I was hoping one of you out there could lend me a small hand. I have the following class: #include <stdio.h> class Example { public: Example(); ~Example(); int test(); }; #include "example.h" Along with the implementation: Example::Example() { printf("Example constructor called\n"); } Example::~Example() { printf("Example destructor called\n"); } int Example::test() { printf("Holy shit, I work!\n"); return 42; } I've read through the introduction page ( www.swig.org/Doc1.3/Java.html ) a few times without gaining a whole lot of insight into the situation. My steps were Create an example.i file Compile original alongside example_wrap.cxx (no linking) link resulting object files together Create a little java test file (see below) javac all .java files there and run Well steps 4 and 5 have created a host of problems for me, starting with the basic ( library 'example' not found due to not being in java's path ) to the weird ( library not found even unless LD_LIBRARY_PATH is set to something, even if it's nothing at all). I've included my little testing code below public class test2 { static { String libpath = System.getProperty("java.library.path"); String currentDir = System.getProperty("user.dir"); System.setProperty("java.library.path", currentDir + ":" + libpath); System.out.println(System.getProperty("java.library.path")); System.loadLibrary("example"); } public static void main(String[] args){ System.out.println("It loads!"); } } Well, if anyone has navigated these murky waters of wrapping, I could not be happier than if you could light the way, particularly if you could provide the example.i and bash commands to go along with it.

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• Error running web project in eclipse

  - by DarkKnight

  I am a newbie to servlets. I created a dynamic web project in eclipse. I have following files in my project home.html validateServlet.java I have defined validated servlet as an action in home.html form. However when I run it, I get http status 404. Below is the hierarchy of my project Project Java Resources src com.servlets ValidateServlet.java build WebContent META-INF WEB-INF web.xml hello.html Contents of my web.xml are as follows: <?xml version="1.0" encoding="UTF-8"?> <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web- app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0"> <display-name>Website</display-name> <servlet> <description></description> <display-name>ValidateServlet</display-name> <servlet-name>validate</servlet-name> <servlet-class>com.oracle.coen235.servlets.ValidateServlet</servlet-class> </servlet> </web-app> In my hello.html, action is specified as , What might be the issue? I guess I am not able to generate the class file for my servlet. Can anyone guide me through this problem?

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• How to deal with a Java serialized object whose package changed?

  - by Alex

  I have a Java class that is stored in an HttpSession object that's serialized and transfered between servers in a cluster environment. For the purpose of this explanation, lets call this class "Person". While in the process of improving the code, this class was moved from "com.acme.Person" to "com.acme.entity.Person". Internally, the class remains exactly the same (same fields, same methods, same everything). The problem is that we have two sets of servers running the old code and the new code at the same time. The servers with the old code have serialized HttpSession object and when the new code unserializes it, it throws a ClassNotFoundException because it can't find the old reference to com.acme.Person. At this point, it's easy to deal with this because we can just recreate the object using the new package. The problem then becomes that the HttpSession in the new servers, will serialize the object with the new reference to com.acme.entity.Person, and when this is unserialized in the servers running the old code, another exception will be thrown. At this point, we can't deal with this exception anymore. What's the best strategy to follow for this kind of cases? Is there a way to tell the new servers to serialize the object with the reference to the old package and unserialize references to the old package to the new one? How would we transition to using the new package and forgetting about the old one once all servers run the new code?

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• Do the 'up to date' guarantees provided by final field in Java's memory model extend to indirect ref

  - by mattbh

  The Java language spec defines semantics of final fields in section 17.5: The usage model for final fields is a simple one. Set the final fields for an object in that object's constructor. Do not write a reference to the object being constructed in a place where another thread can see it before the object's constructor is finished. If this is followed, then when the object is seen by another thread, that thread will always see the correctly constructed version of that object's final fields. It will also see versions of any object or array referenced by those final fields that are at least as up-to-date as the final fields are. My question is - does the 'up-to-date' guarantee extend to the contents of nested arrays, and nested objects? An example scenario: Thread A constructs a HashMap of ArrayLists, then assigns the HashMap to final field 'myFinal' in an instance of class 'MyClass' Thread B sees a (non-synchronized) reference to the MyClass instance and reads 'myFinal', and accesses and reads the contents of one of the ArrayLists In this scenario, are the members of the ArrayList as seen by Thread B guaranteed to be at least as up to date as they were when MyClass's constructor completed?

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