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• Relationship DAO, Servlet, JSP and POJO

  - by John Hendrik

  I want to implement a JSP, POJO, DAO and Servlet in my J2EE program. However, I don't fully understand how the relationship between these elements should be. Is the following (MVC) setup the right way to do it? Main class creates servlet(controller) Servlet has a DAO defined in its class DAO has a POJO defined in its class Servlet communicates with the view (JSP page) Please give your feedback.

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• Access functions from user control without events?

  - by BornToCode

  I have an application made with usercontrols and a function on main form that removes the previous user controls and shows the desired usercontrol centered and tweaked: public void DisplayControl(UserControl uControl) I find it much easier to make this function static or access this function by reference from the user control, like this: MainForm mainform_functions = (MainForm)Parent; mainform_functions.DisplayControl(uc_a); You probably think it's a sin to access a function in mainform, from the usercontrol, however, raising an event seems much more complex in such case - I'll give a simple example - let's say I raise an event from usercontrol_A to show usercontrol_B on mainform, so I write this: uc_a.show_uc_b+= (s,e) => { usercontrol_B uc_b = new usercontrol_B(); DisplayControl(uc_b); }; Now what if I want usercontrol_B to also have an event to show usercontrol_C? now it would look like this: uc_a.show_uc_b+= (s,e) => { usercontrol_B uc_b = new usercontrol_B(); DisplayControl(uc_b); uc_b.show_uc_c += (s2,e2) => {usercontrol_C uc_c = new usercontrol_C(); DisplayControl(uc_c);} }; THIS LOOKS AWFUL! The code is much simpler and readable when you actually access the function from the usercontrol itself, therefore I came to the conclusion that in such case it's not so terrible if I break the rules and not use events for such general function, I also think that a readable usercontrol that you need to make small adjustments for another app is preferable than a 100% 'generic' one which makes my code look like a pile of mud. What is your opinion? Am I mistaken?

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• Dependency injection and IOC containers in a closed project

  - by Puckl

  Does it make sense to assemble my project with dependency injection containers if I am the only one who will use the code of that project? The question came up when I read this IOC Article http://martinfowler.com/articles/injection.html The justification for using dependency injection in this article is that friends can reuse a class, and replace depending classes with their own classes because they get injected and not instantiated in the class. I would only use it to inject objects where they are needed instead of passing them through layers to their target. (Which is not so bad I learned here: Is it bad practice to pass instances through several layers?) (Maybe I will reuse parts of the project, who knows, but I don´t know if that is a good justification)

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• Can you point me to a nontrivial strategy pattern implementation?

  - by Eugen Martynov

  We are faced implementing a registration workflow with many branches. There are three main flows which in some conditions lead to one another. Each flow has at least four different steps; some steps interact with the server, and every step adds more information to the state. Also the requirement is to have it persistent between sessions, so if the user closes the app (this is a mobile app), it will restore the process from the last completed step with the state from the previous session. I think this could benefit from the use of the strategy pattern, but I've never had to implement it for such a complex case. Does anyone know of any examples in open source or articles from which I could find inspiration? Preferably the examples would be from a live/working/stable application. I'm interested in Java implementation mostly; we are developing for Java mobile phones: android, blackberry and J2ME. We have an SDK which is quite well separated from platform specific implementations, but examples in C++, C#, Objective-C or Python would be acceptable.

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• Who should control navigation in an MVVM application?

  - by SonOfPirate

  Example #1: I have a view displayed in my MVVM application (let's use Silverlight for the purposes of the discussion) and I click on a button that should take me to a new page. Example #2: That same view has another button that, when clicked, should open up a details view in a child window (dialog). We know that there will be Command objects exposed by our ViewModel bound to the buttons with methods that respond to the user's click. But, what then? How do we complete the action? Even if we use a so-called NavigationService, what are we telling it? To be more specific, in a traditional View-first model (like URL-based navigation schemes such as on the web or the SL built-in navigation framework) the Command objects would have to know what View to display next. That seems to cross the line when it comes to the separation of concerns promoted by the pattern. On the other hand, if the button wasn't wired to a Command object and behaved like a hyperlink, the navigation rules could be defined in the markup. But do we want the Views to control application flow and isn't navigation just another type of business logic? (I can say yes in some cases and no in others.) To me, the utopian implementation of the MVVM pattern (and I've heard others profess this) would be to have the ViewModel wired in such a way that the application can run headless (i.e. no Views). This provides the most surface area for code-based testing and makes the Views a true skin on the application. And my ViewModel shouldn't care if it displayed in the main window, a floating panel or a child window, should it? According to this apprach, it is up to some other mechanism at runtime to 'bind' what View should be displayed for each ViewModel. But what if we want to share a View with multiple ViewModels or vice versa? So given the need to manage the View-ViewModel relationship so we know what to display when along with the need to navigate between views, including displaying child windows / dialogs, how do we truly accomplish this in the MVVM pattern?

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• Is there a Design Pattern for preventing dangling references?

  - by iFreilicht

  I was thinking about a design for custom handles. The thought is to prevent clients from copying around large objects. Now a regular handle class would probably suffice for that, but it doesn't solve the "dangling reference problem"; If a client has multiple handles of the same object and deletes the object via one of them, all the others would be invalid, but not know it, so the client could write or read parts of the memory he shouldn't have access to. Is there a design pattern to prevent this from happening? Two ideas: An observer-like pattern where the destructor of an object would notify all handles. "Handle handles" (does such a thing even exist?). All the handles don't really point to the object, but to another handle. When the object gets destroyed, this "master-handle" invalidates itself and therefore all that point to it.

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• Is is common to use the command pattern for property get/sets?

  - by k rey

  Suppose I have a controller class with a bunch of properties. Each time a property is changed, I would like to update the model. Now also suppose that I use the command pattern to perform model updates. Is it common to use command classes within property get and sets of the controller class or is there a better way? Here is an example of what I am currently using: class MyController { private int _myInt; public int MyInt { get { return _myInt; } set { MyCommand cmd = new MyCommand(); cmd.Argument = _myInt; cmd.Execute(); // Command object updates the model } } }

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• Designing a Business Rule Engine

  - by Nisha_Roy

  I have a requirement where there are 10 Rules to be applied on data in excel. If Rule 1 and Rule 2 fails rest of the rules are not checked. But if Rule 1 and Rule 2 passes the rest of all the Rules should be verified and if any errors found- they should be logged. Is there any design pattern which I can use to keep this Rule Engine flexible for adding these 10 rules and Closed for any additional chains in the Current Rule. I was thinking of something like a Decorator Pattern. Will this help me achieve that?

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• Designing web-based plugin systems correctly so they don't waste as many resources?

  - by Xeoncross

  Many CMS systems which rely on third parties for much of their code often build "plugin" or "hooks" systems to make it easy for developers to modify the codebase's actions without editing the core files. This usually means an Observer or Event design pattern. However, when you look at systems like wordpress you see that on every page they load some kind of bootstrap file from each of the plugin's folders to see if that plugin will need to run that request. Its this poor design that causes systems like wordpress to spend many extra MB's of memory loading and parsing unneeded items each page. Are there alternative ways to do this? I'm looking for ideas in building my own. For example, Is there a way to load all this once and then cache the results so that your system knows how to lazy-load plugins? In other words, the system loads a configuration file that specifies all the events that plugin wishes to tie into and then saves it for future requests? If that also performs poorly, then perhaps there is a special file-structure that could be used to make educated guesses about when certain plugins are unneeded to fullfil the request. Any ideas? If anyone wants an example of the "plugin" concept you can find one here.

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• Is there a name for the Builder Pattern where the Builder is implemented via interfaces so certain parameters are required?

  - by Zipper

  So we implemented the builder pattern for most of our domain to help in understandability of what actually being passed to a constructor, and for the normal advantages that a builder gives. The one twist was that we exposed the builder through interfaces so we could chain required functions and unrequired functions to make sure that the correct parameters were passed. I was curious if there was an existing pattern like this. Example below: public class Foo { private int someThing; private int someThing2; private DateTime someThing3; private Foo(Builder builder) { this.someThing = builder.someThing; this.someThing2 = builder.someThing2; this.someThing3 = builder.someThing3; } public static RequiredSomething getBuilder() { return new Builder(); } public interface RequiredSomething { public RequiredDateTime withSomething (int value); } public interface RequiredDateTime { public OptionalParamters withDateTime (DateTime value); } public interface OptionalParamters { public OptionalParamters withSeomthing2 (int value); public Foo Build ();} public static class Builder implements RequiredSomething, RequiredDateTime, OptionalParamters { private int someThing; private int someThing2; private DateTime someThing3; public RequiredDateTime withSomething (int value) {someThing = value; return this;} public OptionalParamters withDateTime (int value) {someThing = value; return this;} public OptionalParamters withSeomthing2 (int value) {someThing = value; return this;} public Foo build(){return new Foo(this);} } } Example of how it's called: Foo foo = Foo.getBuilder().withSomething(1).withDateTime(DateTime.now()).build(); Foo foo2 = Foo.getBuilder().withSomething(1).withDateTime(DateTime.now()).withSomething2(3).build();

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• Struggling with the Single Responsibility Principle

  - by AngryBird

  Consider this example: I have a website. It allows users to make posts (can be anything) and add tags that describe the post. In the code, I have two classes that represent the post and tags. Lets call these classes Post and Tag. Post takes care of creating posts, deleting posts, updating posts, etc. Tag takes care of creating tags, deleting tags, updating tags, etc. There is one operation that is missing. The linking of tags to posts. I am struggling with who should do this operation. It could fit equally well in either class. On one hand, the Post class could have a function that takes a Tag as a parameter, and then stores it in a list of tags. On the other hand, the Tag class could have a function that takes a Post as a parameter and links the Tag to the Post. The above is just an example of my problem. I am actually running into this with multiple classes that are all similar. It could fit equally well in both. Short of actually putting the functionality in both classes, what conventions or design styles exist to help me solve this problem. I am assuming there has to be something short of just picking one? Maybe putting it in both classes is the correct answer?

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• Strategies to Defeat Memory Editors for Cheating - Desktop Games

  - by ashes999

  I'm assuming we're talking about desktop games -- something the player downloads and runs on their local computer. Many are the memory editors that allow you to detect and freeze values, like your player's health. How do you prevent cheating? What strategies are effective to combat this kind of cheating? I'm looking for some good ones. Two I use that are mediocre are: Displaying values as a percentage instead of the number (eg. 46/50 = 92% health) A low-level class that holds values in an array and moves them with each change

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• What is the proper name for this design pattern in Python?

  - by James

  In Python, is the proper name for the PersonXXX class below PersonProxy, PersonInterface, etc? import rest class PersonXXX(object): def __init__(self,db_url): self.resource = rest.Resource(db_url) def create(self,person): self.resource.post(person.data()) def get(self): pass def update(self): pass def delete(self): pass class Person(object): def __init__(self,name, age): self.name = name self.age = age def data(self): return dict(name=self.name,age=self.age)

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• Resources about cross platform application development in ANSI C [closed]

  - by Anindya Chatterjee

  Where can I get good resources for learning cross platform application development in plain ISO/ANSI C? I have cygwin and eclipse cdt with me to start in my win7 pc. I just need a couple of good resources containing all the best practices and techniques to write good and robust and scalable cross platform application. I am totally new to this cross platform business, no prior idea. Want to learn it in a proper way from the very beginning. Please help me out here.

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• What are other ideologies to establish relationships between distinct users besides followers/following and friends?

  - by user784637

  Websites like myspace and facebook establish relationships between distinct users using the "friending" ideology, where one user sends a request to be accepted by another user in order for them to have the mutual permission to do stuff like post messages on each others walls. Less restrictive than the "friending" ideology, Twitter and instagram use the followers/following ideology where you can subscribe to the tweets or posts of another user without their permission. Less restrictive than the "followers/following" ideology, email and calling someone on the phone allows you to directly contact anyone. Are there other ideologies that have been successfully implemented either in social networking sites or other real world constructs to establish relations between users?

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• What is the simplest human readable configuration file format?

  - by Juha

  Current configuration file is as follows: mainwindow.title = 'test' mainwindow.position.x = 100 mainwindow.position.y = 200 mainwindow.button.label = 'apply' mainwindow.button.size.x = 100 mainwindow.button.size.y = 30 logger.datarate = 100 logger.enable = True logger.filename = './test.log' This is read with python to a nested dictionary: { 'mainwindow':{ 'button':{ 'label': {'value':'apply'}, ... }, 'logger':{ datarate: {'value': 100}, enable: {'value': True}, filename: {'value': './test.log'} }, ... } Is there a better way of doing this? The idea is to get XML type of behavior and avoid XML as long as possible. The end user is assumed almost totally computer illiterate and basically uses notepad and copy-paste. Thus the python standard "header + variables" type is considered too difficult. The dummy user edits the config file, able programmers handle the dictionaries. Nested dictionary is chosen for easy splitting (logger does not need or even cannot have/edit mainwindow parameters).

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• whats the name of this pattern?

  - by Wes

  I see this a lot in frameworks. You have a master class which other classes register with. The master class then decides which of the registered classes to delegate the request to. An example based passed in class may be something this. public interface Processor { public boolean canHandle(Object objectToHandle); public void handle(Object objectToHandle); } public class EvenNumberProcessor extends Processor { public boolean canHandle(Object objectToHandle) { if (!isNumeric(objectToHandle)){ return false } return isEven(objectToHandle); } public void handle(objectToHandle) { //Optionally call canHandleAgain to ensure the calling class is fufilling its contract doSomething(); } } public class OddNumberProcessor extends Processor { public boolean canHandle(Object objectToHandle) { if (!isNumeric(objectToHandle)){ return false } return isOdd(objectToHandle); } public void handle(objectToHandle) { //Optionally call canHandleAgain to ensure the calling class is fufilling its contract doSomething(); } } //Can optionally implement processor interface public class processorDelegator { private List processors; public void addProcessor(Processor processor) { processors.add(processor); } public void process(Object objectToProcess) { //Lookup relevant processor either by keeping a list of what they can process //Or query each one to see if it can process the object. chosenProcessor=chooseProcessor(objectToProcess); chosenProcessor.handle(objectToProcess); } } Note there are a few variations I see on this. In one variation the sub classes provide a list of things they can process which the ProcessorDelegator understands. The other variation which is listed above in fake code is where each is queried in turn. This is similar to chain of command but I don't think its the same as chain of command means that the processor needs to pass to other processors. The other variation is where the ProcessorDelegator itself implements the interface which means you can get trees of ProcessorDelegators which specialise further. In the above example you could have a numeric processor delegator which delegates to an even/odd processor and a string processordelegator which delegates to different strings. My question is does this pattern have a name.

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• Design for object with optional and modifiable attributtes?

  - by Ikuzen

  I've been using the Builder pattern to create objects with a large number of attributes, where most of them are optional. But up until now, I've defined them as final, as recommended by Joshua Block and other authors, and haven't needed to change their values. I am wondering what should I do though if I need a class with a substantial number of optional but non-final (mutable) attributes? My Builder pattern code looks like this: public class Example { //All possible parameters (optional or not) private final int param1; private final int param2; //Builder class public static class Builder { private final int param1; //Required parameters private int param2 = 0; //Optional parameters - initialized to default //Builder constructor public Builder (int param1) { this.param1 = param1; } //Setter-like methods for optional parameters public Builder param2(int value) { param2 = value; return this; } //build() method public Example build() { return new Example(this); } } //Private constructor private Example(Builder builder) { param1 = builder.param1; param2 = builder.param2; } } Can I just remove the final keyword from the declaration to be able to access the attributes externally (through normal setters, for example)? Or is there a creational pattern that allows optional but non-final attributes that would be better suited in this case?

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• Is it better to define all routes in the Global.asax than to define separately in the areas?

  - by Matthew Patrick Cashatt

  I am working on a MVC 4 project that will serve as an API layer of a larger application. The developers that came before me set up separate Areas to separate different API requests (i.e Search, Customers, Products, and so forth). I am noticing that each Area has separate Area registration classes that define routes for that area. However, the routes defined are not area-specific (i.e. {controller}/{action}/{id} might be defined redundantly in a couple of areas). My instinct would be to move all of these route definitions to a common place like the Global.asax to avoid redundancy and collisions, but I am not sure if I am correct about that.

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• Why is nesting or piggybacking errors within errors bad in general?

  - by dietbuddha

  Why is nesting or piggybacking errors within errors bad in general? To me it seems bad intuitively, but I'm suspicious in that I cannot adequately articulate why it is bad. This may be because it is not in general bad and that it is only bad in specific instances. Why is it detrimental to design error/exception handling in such a way. The specific instance is that of a REST service. There is a desire by some to use http errors (specifically the 500 response) as a way to indicate any problem with specific instances of a resource. An example of an instance resource in this case would be: http://server/ticket/80 # instance http://server/ticket # not an instance So this is the behavior that is being proposed. If ticket 80 does not exist return a http response code of 500. Within the body of the error return the "real" error as an additional error code and description. If the ticket resource doesn't exist return a response code of 404.

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• What is the difference between all-static-methods and applying a singleton pattern?

  - by shahensha

  I am making a database to store information about the users of my website (I am using stuts2 and hence Java EE technology). For the database I'll be making a DBManager. Should I apply singleton pattern here or rather make all it's methods static? I will be using this DBManager for basic things like adding, deleting and updating User profiles. Along with it, I'll use for all other querying purposes, for instance to find out whether a username already exists and to get all users for administrative purposes and stuff like that. My questions What is the benefit of singleton pattern? Which thing is most apt here? All static methods or a singleton pattern? Please compare both of them. regards shahensha P.S. The database is bigger than this. Here I am talking only about the tables which I'll be using for storing User Information.

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• Is there a way to prevent users from adjusting their gamma correction to 'cheat' their way out of a 'dark' area?

  - by Athix

  In almost every game I've come across that includes a dark situation designed to change the way a user interacts with the environment, there are always some players who turn up their monitor's gamma correction in order to negate the desired effect. Is there a way to prevent users from adjusting their gamma correction to 'cheat' their way out of a challenge? (the darkness) I'd imagine if you could reliably retrieve the current gamma correction of the user's monitor, you could use that to more or less prevent the advantage it would otherwise grant without causing the normal users any inconvenience.

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• What are cons of usage only non-member functions and POD?

  - by Miro

  I'm creating my own game engine. I've read these articles and this question about DOD and there was written to not use member functions and classes. I also heard some criticism to this idea. I can write it using member functions or non-member functions it would be similar. So what are benefits/cons of that approach or when project grows, does any of these approaches give clearer and better manageable code? With POD & non-member functions I don't have to make struct members public I can still use object id outside of engine like OpenGL does with all it's stuff, so It's not about encapsulation. POD - plain old data DOD - data oriented design

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• Authorization design-pattern / practice?

  - by Lawtonfogle

  On one end, you have users. On the other end, you have activities. I was wondering if there is a best practice to relate the two. The simplest way I can think of is to have every activity have a role, and assign every user every role they need. The problem is that this gets really messy in practice as soon as you go beyond a trivial system. A way I recently designed was to have users who have roles, and roles have privileges, and activities require some combinations of privileges. For the trivial case, this is more complex, but I think it will scale better. But after I implemented it, I felt like it was overkill for the system I had. Another option would be to have users, who have roles, and activities require you to have a certain role to perform with many activities sharing roles. A more complex variant of this would given activities many possible roles, which you only needed one of. And an even more complex variant would be to allow logical statements of role ownership to use an activity (i.e. Must have A and (B exclusive or C) and must not have D). I could continue to list more, but I think this already gives a picture. And many of these have trade offs. But in software design, there are oftentimes solutions, while perhaps not perfect in every possible case, are clearly top of the pack to an extent it isn't even considered opinion based (i.e. how to store passwords, plain text is worse, hashing better, hashing and salt even better, despite the increased complexity of each level) (i.e. 2, Smart UI designs for applications are bad, even if it is subjective as to what the best design is). So, is there a best practice for authorization design that is not purely opinion based/subjective?

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• Methodologies for Managing Users and Access?

  - by MadBurn

  This is something I'm having a hard time getting my head around. I think I might be making it more complicated than it is. What I'm trying to do is develop a method to store users in a database with varying levels of access, throughout different applications. I know this has been done before, but I don't know where to find how they did it. Here is an example of what I need to accomplish: UserA - Access to App1, App3, App4 & can add new users to App3, but not 4 or 1. UserB - Access to App2 only with ReadOnly access. UserC - Access to App1 & App4 and is able to access Admin settings of both apps. In the past I've just used user groups. However, I'm reaching a phase where I need a bit more control over each individual user's access to certain parts of the different applications. I wish this were as cut and dry as being able to give a user a role and let each role inherit from the last. Now, this is what I need to accomplish. But, I don't know any methods of doing this. I could easily just design something that works, but I know this has been done and I know this has been studied and I know this problem has been solved by much better minds than my own. This is for a web application and using sql server 2008. I don't need to store passwords (LDAP) and the information I need to store is actually very limited. Basically just username and access.

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