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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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • In Java, is there a gain in using interfaces for complex models?

    - by Gnoupi
    The title is hardly understandable, but I'm not sure how to summarize that another way. Any edit to clarify is welcome. I have been told, and recommended to use interfaces to improve performances, even in a case which doesn't especially call for the regular "interface" role. In this case, the objects are big models (in a MVC meaning), with many methods and fields. The "good use" that has been recommended to me is to create an interface, with its unique implementation. There won't be any other class implementing this interface, for sure. I have been told that this is better to do so, because it "exposes less" (or something close) to the other classes which will use methods from this class, as these objects are referring to the object from its interface (all public method from the implementation being reproduced in the interface). This seems quite strange to me, as it seems like a C++ use to me (with header files). There I see the point, but in Java? Is there really a point in making an interface for such unique implementation? I would really appreciate some clarifications on the topic, so I could justify not following such kind of behavior, and the hassle it creates from duplicating all declarations.

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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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  • How to call Java code from Javascript and assign a value to a JSP page?

    - by Frank
    I have the following "form.jsp" program, it generates a drop down list, below the list is a textarea to show the display_name of a selected item, now when user selected a item, it shows the selected item id in the textarea, how to call the DB from my code and get the display_name in the javascript so the result display_name will be shown in the textarea ? <%@ taglib prefix="s" uri="/struts-tags"%> <script type="text/javascript"> function callme(Display_Name) { alert('callme : Display_Name = '+Display_Name); var v=document.getElementById('hiddenValue').value; alert('hiddenValue : v = '+v); document.getElementById('defaultDisplayName').value=Display_Name; } </script> <s:hidden id="pricelist.id" name="pricelist.id" value="%{pricelist.id}"/> <div class="dialog"> <table> <tbody> <s:if test="%{enableProductList}"> <tr class="prop"> <td valign="top" class="name required"><label for="description">Product:</label></td> <td valign="top"> <s:select id="productPrice.product" name="productPrice.product" headerKey="0" headerValue="-- Select Product --" list="products" listKey="id" listValue="name" value="productPrice.product.id" theme="simple" displayName1='value' onchange="callme(value)" /> <s:hidden id="hiddenValue" name="hiddenValue" value="123"/> </td> </tr> </s:if> <tr class="prop"> <td valign="top" class="name"><label for="description">Default Display Name:</label></td> <td valign="top"><s:textarea id="defaultDisplayName" name="defaultDisplayName" theme="simple" readonly="true"/></td> </tr> See attached image for details, in the DB, a product table has the product Id and display_name, I know the Id, how to use Java to get the display_name and plug it into the jsp ?

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  • In Java, is there a performance gain in using interfaces for complex models?

    - by Gnoupi
    The title is hardly understandable, but I'm not sure how to summarize that another way. Any edit to clarify is welcome. I have been told, and recommended to use interfaces to improve performances, even in a case which doesn't especially call for the regular "interface" role. In this case, the objects are big models (in a MVC meaning), with many methods and fields. The "good use" that has been recommended to me is to create an interface, with its unique implementation. There won't be any other class implementing this interface, for sure. I have been told that this is better to do so, because it "exposes less" (or something close) to the other classes which will use methods from this class, as these objects are referring to the object from its interface (all public methods from the implementation being reproduced in the interface). This seems quite strange to me, as it seems like a C++ use to me (with header files). There I see the point, but in Java? Is there really a point in making an interface for such unique implementation? I would really appreciate some clarifications on the topic, so I could justify not following such kind of behavior, and the hassle it creates from duplicating all declarations. Edit: Plenty of valid points in most answers, I'm wondering if I won't switch this question for a community wiki, so we can regroup these points in more structured answers.

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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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  • Best (Java) book for understanding 'under the bonnet' for programming?

    - by Ben
    What would you say is the best book to buy to understand exactly how programming works under the hood in order to increase performance? I've coded in assembly at university, I studied computer architecture and I obviously did high level programming, but what I really dont understand is things like: -what is happening when I perform a cast -whats the difference in performance if I declare something global as opposed to local? -How does the memory layout for an ArrayList compare with a Vector or LinkedList? -Whats the overhead with pointers? -Are locks more efficient than using synchronized? -Would creating my own array using int[] be faster than using ArrayList -Advantages/disadvantages of declaring a variable volatile I have got a copy of Java Performance Tuning but it doesnt go down very low and it contains rather obvious things like suggesting a hashmap instead of using an ArrayList as you can map the keys to memory addresses etc. I want something a bit more Computer Sciencey, linking the programming language to what happens with the assembler/hardware. The reason im asking is that I have an interview coming up for a job in High Frequency Trading and everything has to be as efficient as possible, yet I cant remember every single possible efficiency saving so i'd just like to learn the fundamentals. Thanks in advance

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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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  • How do I bind HTML table data to a java object in a spring controller?

    - by predhme
    I have a spring MVC application using JSP as my view technologies with Jquery for AJAX. I have a table such as the following: <table> <tr> <td>name1</td> <td>value1</td> <td>setting1</td> </tr> <tr> <td>name2</td> <td>value2</td> <td>setting2</td> </tr> </table> I need to serialize this table so that it can later be bound to an object in my controller. However the jquery serialize() method only works on form fields. What would be the best approach to get the table data into the HTTP request so that I can later bind it to a java object?

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  • Which options do I have for Java process communication?

    - by Dmitriy Matveev
    We have a place in a code of such form: void processParam(Object param) { wrapperForComplexNativeObject result = jniCallWhichMayCrash(param); processResult(result); } processParam - method which is called with many different arguments. jniCallWhichMayCrash - a native method which is intended to do some complex processing of it's parameter and to create some complex object. It can crash in some cases. wrapperForComplexNativeObject - wrapper type generated by SWIG processResult - a method written in pure Java which processes it's parameter by creation of several kinds (by the kinds I'm not meaning classes, maybe some like hierarchies) of objects: 1 - Some non-unique objects which are referencing each other (from the same hierarchy), these objects can have duplicates created from the invocations of processParam() method with different parameter values. Since it's costly to keep all the duplicates it's necessary to cache them. 2 - Some unique objects which are referencing each other (from the same hierarchy) and some of the objects of 1st kind. After processParam is executed for each of the arguments from some set the data created in processResult will be processed together. The problem is in fact that jniCallWhichMayCrash method may crash the entire JVM and this will be very bad. The reason of crash may be such that it can happen for one argument value and not for the other. We've decided that it's better to ignore crashes inside of JVM and just skip some chunks of data when such crashes occur. In order to do this we should run processParam function inside of separate process and pass the result somehow (HOW? HOW?! This is a question) to the main process and in case of any crashes we will only lose some part of data (It's ok) without lose of everything else. So for now the main problem is implementation of transport between different processes. Which options do I have? I can think about serialization and transmitting of binary data by the streams, but serialization may be not very fast due to object complexity. Maybe I have some other options of implementing this?

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