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• How to create new account using servlets

  - by Alvin

  I want to know how can I create new account using servlets in post method? I'm currently following MVC design pattern, and I want to know if I pass the required data to register new account from JSP page, then how can I get that data in post method? As request.getParameter() method returning me null. How can I know that post method is calling to create new account? How can I pass all the relevant user information from servlets to model class for registering data to the database table?

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• how to get access to private members of nested class?

  - by macias

  Background: I have enclosed (parent) class E with nested class N with several instances of N in E. In the enclosed (parent) class I am doing some calculations and I am setting the values for each instance of nested class. Something like this: n1.field1 = ...; n1.field2 = ...; n1.field3 = ...; n2.field1 = ...; ... It is one big eval method (in parent class). My intention is -- since all calculations are in parent class (they cannot be done per nested instance because it would make code more complicated) -- make the setters only available to parent class and getters public. And now there is a problem: when I make the setters private, parent class cannot acces them when I make them public, everybody can change the values and C# does not have friend concept I cannot pass values in constructor because lazy evaluation mechanism is used (so the instances have to be created when referencing them -- I create all objects and the calculation is triggered on demand) I am stuck -- how to do this (limit access up to parent class, no more, no less)? I suspect I'll get answer-question first -- "but why you don't split the evaluation per each field" -- so I answer this by example: how do you calculate min and max value of a collection? In a fast way? The answer is -- in one pass. This is why I have one eval function which does calculations and sets all fields at once.

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• MVC and conditional formatting - strategies for implementation

  - by Extrakun

  Right now I am writing a simulation program which output is formatted according to certain factors. The question is in a MVC architecture, where is the conditional formatting to be taken place? What are some strategies for implement this feature? FYI, The platform I am using is rather bare-bone in its GUI/front-end execution. To change color and formatting, it requires a change to the formatting state (much like OpenGL).

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• What are the responsibilities of the data layer?

  - by alimac83

  I'm working on a project where I had to add a data layer to my application. I've always thought that the data layer is purely responsible for CRUD functions ie. shouldn't really contain any logic but should simply retrieve data for the business layer to manipulate. However I'm a little confused with my project because I'm not sure whether I've structured my app correctly for this scenario. Basically I'm trying to retrieve a list of products from the database that fall within a certain pricing threshold. At the moment I have a function in my data layer that basically returns all products where price min threshold and price < max threshold. But it got me thinking that maybe this is incorrect. Should the data layer simply return a list of ALL products and then the business logic do the filtering? I'm pretty confused over whether the data layer should simply provide methods that allow the business layer to get raw data or whether it should be responsible for getting filtered data too? If anyone has an article or something explaining this in detail it'd be very helpful. Thanks

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• Objective-c design advice for use of different data sources, swapping between test and live

  - by user200341

  I'm in the process of designing an application that is part of a larger piece of work, depending on other people to build an API that the app can make use of to retrieve data. While I was thinking about how to setup this project and design the architecture around it, something occurred to me, and I'm sure many people have been in similar situations. Since my work is depending on other people to complete their tasks, and a test server, this slows work down at my end. So the question is: What's the best practice for creating test repositories and classes, implementing them, and not having to depend on altering several places in the code to swap between the test classes and the actual repositories / proper api calls. Contemplate the following scenario: GetDataFromApiCommand *getDataCommand = [[GetDataFromApiCommand alloc]init]; getDataCommand.delegate = self; [getDataCommand getData]; Once the data is available via the API, "GetDataFromApiCommand" could use the actual API, but until then a set of mock data could be returned upon the call of [getDataCommand getData] There might be multiple instances of this, in various places in the code, so replacing all of them wherever they are, is a slow and painful process which inevitably leads to one or two being overlooked. In strongly typed languages we could use dependency injection and just alter one place. In objective-c a factory pattern could be implemented, but is that the best route to go for this? GetDataFromApiCommand *getDataCommand = [GetDataFromApiCommandFactory buildGetDataFromApiCommand]; getDataCommand.delegate = self; [getDataCommand getData]; What is the best practices to achieve this result? Since this would be most useful, even if you have the actual API available, to run tests, or work off-line, the ApiCommands would not necessarily have to be replaced permanently, but the option to select "Do I want to use TestApiCommand or ApiCommand". It is more interesting to have the option to switch between: All commands are test and All command use the live API, rather than selecting them one by one, however that would also be useful to do for testing one or two actual API commands, mixing them with test data. EDIT The way I have chosen to go with this is to use the factory pattern. I set up the factory as follows: @implementation ApiCommandFactory + (ApiCommand *)newApiCommand { // return [[ApiCommand alloc]init]; return [[ApiCommandMock alloc]init]; } @end And anywhere I want to use the ApiCommand class: GetDataFromApiCommand *getDataCommand = [ApiCommandFactory newApiCommand]; When the actual API call is required, the comments can be removed and the mock can be commented out. Using new in the message name implies that who ever uses the factory to get an object, is responsible for releasing it (since we want to avoid autorelease on the iPhone). If additional parameters are required, the factory needs to take these into consideration i.e: [ApiCommandFactory newSecondApiCommand:@"param1"]; This will work quite well with repositories as well.

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• C++ interpreter conceptual problem

  - by Jan Wilkins

  I've built an interpreter in C++ for a language created by me. One main problem in the design was that I had two different types in the language: number and string. So I have to pass around a struct like: class myInterpreterValue { myInterpreterType type; int intValue; string strValue; } Objects of this class are passed around million times a second during e.g.: a countdown loop in my language. Profiling pointed out: 85% of the performance is eaten by the allocation function of the string template. This is pretty clear to me: My interpreter has bad design and doesn't use pointers enough. Yet, I don't have an option: I can't use pointers in most cases as I just have to make copies. How to do something against this? Is a class like this a better idea? vector<string> strTable; vector<int> intTable; class myInterpreterValue { myInterpreterType type; int locationInTable; } So the class only knows what type it represents and the position in the table This however again has disadvantages: I'd have to add temporary values to the string/int vector table and then remove them again, this would eat a lot of performance again. Help, how do interpreters of languages like Python or Ruby do that? They somehow need a struct that represents a value in the language like something that can either be int or string.

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• Dependency Injection: I don't get where to start!

  - by Andy

  I have several articles about Dependency Injection, and I can see the benefits, especially when it comes to unit testing. The units can me loosely coupled, and mocking of dependencies can be made. The trouble is - I just don't get where to start. Consider this snippet below of (much edited for the purpose of this post) code that I have. I am instantiating a Plc object from the main form, and passing in a communications mode via the Connect method. In it's present form it becomes hard to test, because I can't isolate the Plc from the CommsChannel to unit test it. (Can I?) The class depends on using a CommsChannel object, but I am only passing in a mode that is used to create this channel within the Plc itself. To use dependancy injection, I should really pass in an already created CommsChannel (via an 'ICommsChannel' interface perhaps) to the Connect method, or maybe via the Plc constructor. Is that right? But then that would mean creating the CommsChannel in my main form first, and this doesn't seem right either, because it feels like everything will come back to the base layer of the main form, where everything begins. Somehow it feels like I am missing a crucial piece of the puzzle. Where do you start? You have to create an instance of something somewhere, but I'm struggling to understand where that should be. public class Plc() { public bool Connect(CommsMode commsMode) { bool success = false; // Create new comms channel. this._commsChannel = this.GetCommsChannel(commsMode); // Attempt connection success = this._commsChannel.Connect(); return this._connected; } private CommsChannel GetCommsChannel(CommsMode mode) { CommsChannel channel; switch (mode) { case CommsMode.RS232: channel = new SerialCommsChannel( SerialCommsSettings.Default.ComPort, SerialCommsSettings.Default.BaudRate, SerialCommsSettings.Default.DataBits, SerialCommsSettings.Default.Parity, SerialCommsSettings.Default.StopBits); break; case CommsMode.Tcp: channel = new TcpCommsChannel( TCPCommsSettings.Default.IP_Address, TCPCommsSettings.Default.Port); break; default: // Throw unknown comms channel exception. } return channel; } }

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• Appropriate programming design questions.

  - by Edward

  I have a few questions on good programming design. I'm going to first describe the project I'm building so you are better equipped to help me out. I am coding a Remote Assistance Tool similar to TeamViewer, Microsoft Remote Desktop, CrossLoop. It will incorporate concepts like UDP networking (using Lidgren networking library), NAT traversal (since many computers are invisible behind routers nowadays), Mirror Drivers (using DFMirage's Mirror Driver (http://www.demoforge.com/dfmirage.htm) for realtime screen grabbing on the remote computer). That being said, this program has a concept of being a client-server architecture, but I made only one program with both the functionality of client and server. That way, when the user runs my program, they can switch between giving assistance and receiving assistance without having to download a separate client or server module. I have a Windows Form that allows the user to choose between giving assistance and receiving assistance. I have another Windows Form for a file explorer module. I have another Windows Form for a chat module. I have another Windows Form form for a registry editor module. I have another Windows Form for the live control module. So I've got a Form for each module, which raises the first question: 1. Should I process module-specific commands inside the code of the respective Windows Form? Meaning, let's say I get a command with some data that enumerates the remote user's files for a specific directory. Obviously, I would have to update this on the File Explorer Windows Form and add the entries to the ListView. Should I be processing this code inside the Windows Form though? Or should I be handling this in another class (although I have to eventually pass the data to the Form to draw, of course). Or is it like a hybrid in which I process most of the data in another class and pass the final result to the Form to draw? So I've got like 5-6 forms, one for each module. The user starts up my program, enters the remote machine's ID (not IP, ID, because we are registering with an intermediary server to enable NAT traversal), their password, and connects. Now let's suppose the connection is successful. Then the user is presented with a form with all the different modules. So he can open up a File Explorer, or he can mess with the Registry Editor, or he can choose to Chat with his buddy. So now the program is sort of idle, just waiting for the user to do something. If the user opens up Live Control, then the program will be spending most of it's time receiving packets from the remote machine and drawing them to the form to provide a 'live' view. 2. Second design question. A spin off question #1. How would I pass module-specific commands to their respective Windows Forms? What I mean is, I have a class like "NetworkHandler.cs" that checks for messages from the remote machine. NetworkHandler.cs is a static class globally accessible. So let's say I get a command that enumerates the remote user's files for a specific directory. How would I "give" that command to the File Explorer Form. I was thinking of making an OnCommandReceivedEvent inside NetworkHandler, and having each form register to that event. When the NetworkHandler received a command, it would raise the event, all forms would check it to see if it was relevant, and the appropriate form would take action. Is this an appropriate/the best solution available? 3. The networking library I'm using, Lidgren, provides two options for checking networking messages. One can either poll ReadMessage() to return null or a message, or one can use an AutoResetEvent OnMessageReceived (I'm guessing this is like an event). Which one is more appropriate?

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• Parent child class relationship design pattern

  - by Jeremy

  I have a class which has a list of child items. Is there a design pattern I can copy that I can apply to these classes so that I can access the parent instance from the child, and it enforces rules such as not being able to add the child to multiple parents, etc?

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• Designing a class in such a way that it doesn't become a "God object"

  - by devoured elysium

  I'm designing an application that will allow me to draw some functions on a graphic. Each function will be drawn from a set of points that I will pass to this graphic class. There are different kinds of points, all inheriting from a MyPoint class. For some kind of points it will be just printing them on the screen as they are, others can be ignored, others added, so there is some kind of logic associated to them that can get complex. How to actually draw the graphic is not the main issue here. What bothers me is how to make the code logic such that this GraphicMaker class doesn't become the so called God-Object. It would be easy to make something like this: class GraphicMaker { ArrayList<Point> points = new ArrayList<Point>(); public void AddPoint(Point point) { points.add(point); } public void DoDrawing() { foreach (Point point in points) { if (point is PointA) { //some logic here else if (point is PointXYZ) { //...etc } } } } How would you do something like this? I have a feeling the correct way would be to put the drawing logic on each Point object (so each child class from Point would know how to draw itself) but two problems arise: There will be kinds of points that need to know all the other points that exist in the GraphicObject class to know how to draw themselves. I can make a lot of the methods/properties from the Graphic class public, so that all the points have a reference to the Graphic class and can make all their logic as they want, but isn't that a big price to pay for not wanting to have a God class?

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• strategy for observer pattern?

  - by fayer

  I want to use observer pattern for a logging system. We have got logObservers and logObservables. The class that will have to log something will implement iLogObservable and include these methods: private $logObservers = array(); public function addLogObserver($logObserver) { $this->logObservers[] = $logObserver; } public function removeLogObserver($logObserver) { $this->logObservers[] = $logObserver; } public function write($type, $message) { foreach($this->logObservers as $logObserver) { $logObserver->log($level, $message); ; } } Then I noticed, that a lot of classes that will use logging will have these methods and I have to copy paste. So isn't it better to have these methods in a class I call LogObservable or just Log and then use strategy (instantiate this class inside all classes that will have to log). When I change the methods in Log, all logObservables will be affected. However, I have not seen anyone use observer pattern with strategy pattern yet, but it seems to be very efficient and remove the duplications. What do you think?

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• How can I make a family of singletons?

  - by Jay

  I want to create a set of classes that share a lot of common behavior. Of course in OOP when you think that you automatically think "abstract class with subclasses". But among the things I want these classes to do is to each have a static list of instances of the class. The list should function as sort of a singleton within the class. I mean each of the sub-classes has a singleton, not that they share one. "Singleton" to that subclass, not a true singleton. But if it's a static, how can I inherit it? Of course code like this won't work: public abstract A { static List<A> myList; public static List getList() { if (myList==null) myList=new ArrayList<A>(10); return myList; } public static A getSomethingFromList() { List listInstance=getList(); ... do stuff with list ... } public int getSomethingFromA() { ... regular code acting against current instance ... } } public class A1 extends A { ... } public class A2 extends A { ... } A1 somethingfromA1List=(A1) A1.getSomethingFromList(); A2 somethingfromA2List=(A2) A2.getSomethingFromList(); The contents of the list for each subclass would be different, but all the code to work on the lists would be the same. The problem with the above code is that I'd only have one list for all the subclasses, and I want one for each. Yes, I could replicate the code to declare the static list in each of the subclasses, but then I'd also have to replicate all the code that adds to the lists and searches the list, etc, which rather defeats the purpose of subclassing. Any ideas on how to do this without replicating code?

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• Design for a Debate club assignment application

  - by Amir Rachum

  Hi all, For my university's debate club, I was asked to create an application to assign debate sessions and I'm having some difficulties as to come up with a good design for it. I will do it in Java. Here's what's needed: What you need to know about BP debates: There are four teams of 2 debaters each and a judge. The four groups are assigned a specific position: gov1, gov2, op1, op2. There is no significance to the order within a team. The goal of the application is to get as input the debaters who are present (for example, if there are 20 people, we will hold 2 debates) and assign them to teams and roles with regards to the history of each debater so that: Each debater should debate with (be on the same team) as many people as possible. Each debater should uniformly debate in different positions. The debate should be fair - debaters have different levels of experience and this should be as even as possible - i.e., there shouldn't be a team of two very experienced debaters and a team of junior debaters. There should be an option for the user to restrict the assignment in various ways, such as: Specifying that two people should debate together, in a specific position or not. Specifying that a single debater should be in a specific position, regardless of the partner. etc... If anyone can try to give me some pointers for a design for this application, I'll be so thankful! Also, I've never implemented a GUI before, so I'd appreciate some pointers on that as well, but it's not the major issue right now.

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• Service Layer Pattern - Could we avoid the service layer on a specific case?

  - by lidermin

  Hi, we are trying to implement an application using the Service Layer Pattern cause our application needs to connect to other multiple applications too, and googling on the web, we found this link of a demonstrative graphic for the "right" way of apply the pattern: martinfowler.com - Service Layer Pattern But now we have a question: what if our system needs to implement some business logic, only for our application (like some maintenance data for the system itself) that we don't need to share with other systems. Based on this graphic: As it seems, it will be unnecesary to implement a service layer just for that; it will be more practical to avoid the service layer, and just go from User Interface to the Business Layer (for example). What should be the right way in this case to implement the Service Layer Pattern? What do you suggest us for a scenario like the one I told you? Thanks in advance.

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• Best approach to design a service oriented system

  - by Gustavo Paulillo

  Thinking about service orientation, our team are involved on new application designs. We consist in a group of 4 developers and a manager (that knows something about programming and distributed systems). Each one, having own opinion on service design. It consists in a distributed system: a user interface (web app) accessing the services in a dedicated server (inside the firewall), to obtain the business logic operations. So we got 2 main approachs that I list above : Modular services Having many modules, each one consisting of a service (WCF). Example: namespaces SystemX.DebtService, SystemX.CreditService, SystemX.SimulatorService Unique service All the business logic is centralized in a unique service. Example: SystemX.OperationService. The web app calls the same service for all operations. In your opinion, whats the best? Or having another approach is better for this scenario?

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• maya "export all" window blocks my plugins script UI

  - by Hinchy

  I'm writing a custom File Translator for Maya which can export only (I have only declared the writer function). Currently having a problem with the MEL script which defines the plugin's options as a GUI. Currently I have a blank Maya scene, go to "file-export all". This creates the "File Export All" dialog, I then select my plugin exporter which runs my MEL script to create the bespoke options window. This new window is created behind the "File Export All" dialog and is not selectable! Do I have to place my export plugin specific options within the export all dialog rather than placing them in a separate window? Thanks for any links, tips or pointers you can provide.

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• Should I use the Model-View-ViewModel (MVVM) pattern in Silverlight projects?

  - by Jon Galloway

  One challenge with Silverlight controls is that when properties are bound to code, they're no longer really editable in Blend. For example, if you've got a ListView that's populated from a data feed, there are no elements visible when you edit the control in Blend. I've heard that the MVVM pattern, originated by the WPF development community, can also help with keeping Silverlight controls "blendable". I'm still wrapping my head around it, but here are some explanations: http://www.nikhilk.net/Silverlight-ViewModel-Pattern.aspx http://mark-dot-net.blogspot.com/2008/11/model-view-view-model-mvvm-in.html http://www.ryankeeter.com/silverlight/silverlight-mvvm-pt-1-hello-world-style/ http://jonas.follesoe.no/YouCardRevisitedImplementingTheViewModelPattern.aspx One potential downside is that the pattern requires additional classes, although not necessarily more code (as shown by the second link above). Thoughts?

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• Getting UI button's event in Windows Phone 7

  - by kite

  Hello. I'm currently making a game in XNA4 for Windows phone 7, and I'd like to know if it were possible to get the event of the return button, or even the windows button that are basically present on the phone's interface. If so, how can i do that? thanks, KiTe

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• Lackadaisical One-to-One between Char and Byte Streams

  - by Vaibhav Bajpai

  I expected to have a one-to-one correspondence between the character streams and byte streams in terms of how the classes are organized in their hierarchy. FilterReader and FilterWriter (character streams) correspond back to FilterInputStream and FilterOutputStream (byte stream) classes. However I noticed few changes as - BufferedInputStream extends FilterInputStream, but BufferedReader does NOT extend FilterReader. BufferedOutputStream and PrintStream both extend FilterOutputStream, but BufferedWriter and PrintWriter does NOT extend FilterWriter. FilterInputStream and FilterOutputStream are not abstract classes, but FilterReader and FilterWriter are. I am not sure if I am being too paranoid to point out such differences, but was just curious to know if there was design reasoning behind such decision.

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• asp.mvc model design

  - by Radu D

  Hi, I am pretty new to MVC and I am looking for a way to design my models. I have the MVC web site project and another class library that takes care of data access and constructing the business objects. If I have in that assembly a class named Project that is a business object and I need to display all projects in a view ... should I make another model class Project? In this case the classes will be identical. Do I gain something from doing a new model class? I don't like having in views references to objects from another dll ... but i don't like duplicating the code neither. Did you encounter the same problem?

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• Naming remote proxy classes

  - by Tobbe

  What are some good names for the client and server side classes that communicate over the network when implementing a remote proxy? The classes are often called stub and skelleton but I don't find those names very "intention revealing". Are there any other (better) alternatives?

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• what happens to running/blocked runnables when executorservice is shutdown()

  - by prmatta

  I posted a question about a thread pattern today, and almost everyone suggested that I look into the ExecutorService. While I was looking into the ExecutorService, I think I am missing something. What happens if the service has a running or blocked threads, and someone calls ExecutorService.shutdown(). What happens to threads that are running or blocked? Does the ExecutorService wait for those threads to complete before it terminates? The reason I ask this is because a long time ago when I used to dabble in Java, they deprecated Thread.stop(), and I remember the right way of stopping a thread was to use sempahores and extend Thread when necessary: public void run () { while (!this.exit) { try { block(); //do something } catch (InterruptedException ie) { } } } public void stop () { this.exit = true; if (this.thread != null) { this.thread.interrupt(); this.thread = null; } } How does ExecutorService handle running threads?

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• Simple but good pattern for EJB

  - by Sara

  What would you suggest as a good and practical but simple pattern for a soloution with: HTML + JSP (as a view/presentation) SERVLETS (controller, request, session-handling) EJB (persistence, businesslogic) MySQL DB And is it necessary to use an own layer of DAO for persistence? I use JPA to persist objects to my DB. Should I withdraw business logic from my EJB? Sources online all tell me different things and confuses me...

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• Java interface and abstract class issue

  - by George2

  Hello everyone, I am reading the book -- Hadoop: The Definitive Guide, http://www.amazon.com/Hadoop-Definitive-Guide-Tom-White/dp/0596521979/ref=sr_1_1?ie=UTF8&s=books&qid=1273932107&sr=8-1 In chapter 2 (Page 25), it is mentioned "The new API favors abstract class over interfaces, since these are easier to evolve. For example, you can add a method (with a default implementation) to an abstract class without breaking old implementations of the class". What does it mean (especially what means "breaking old implementations of the class")? Appreciate if anyone could show me a sample why from this perspective abstract class is better than interface? thanks in advance, George

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• Meta Search Engine Architecture

  - by Loki

  The question wasn't clear enough, I think; here's an updated straight to the point question: What are the common architectures used in building a meta search engine and is there any libraries available to build that type of search engine? I'm looking at building an "enterprise" type of search engine where the indexed data could be coming from proprietary (like Autonomy or a Google Box) or public search engines (like Google Web or Yahoo Web).

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