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• Session serialization in JavaEE environment

  - by Ionut

  Please consider the following scenario: We are working on a JavaEE project for which the scalability starts to become an issue. Up until now, we were able to scale up but this is no longer an option. Therefore we need to consider scaling out and preparing the App for a clustered environment. Our main concern right now is serializing the user sessions. Sadly, we did not consider from the beginning the issue and we are encountering the following excetion: java.io.WriteAbortedException: writing aborted; java.io.NotSerializableException: org.apache.catalina.session.StandardSessionFacade I did some research and this exception is thrown because there are objects stored on the session which does not implement the Serializable interface. Considering that all over the app there are quite a few custom objects which are stored on the session without implementing this interface, it would require a lot of tedious work and dedication to fix all these classes declaration. We will fix all this declarations but the main concern is that, in the future, there may be a developer which will add a non Serializable object on the session and break the session serialization & replication over multiple nodes. As a quick overview of the project, we are developing using a home grown framework based on Struts 1 with the Servlet 3.0 API. This means that at this point, we are using the standard session.getAttribute() and session.setAttribute() to work with the session and the session handling is scattered all over the code base. Besides updating the classes of the objects stored on session and making sure that they implement the Serializable interface, what other measures of precaution should we take in order to ensure a reliable Session replication capability on the Application layer? I know it is a little bit late to consider this but what would be the best practice in this case? Furthermore, are there any other issues we should consider regarding this transition? Thank you in advance!

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• Difference between bug, defect and flaw

  - by Hossein

  I was reading "Software Security: Building Security In" and in the first chapter I faced with 3 terms: bug, defect and flaw. The author gave a definition for each of them but I couldn't completely understand these. Can someone give me some examples for each term? What is a defect and what is a flaw? I think I know what bug is, a bug is a malfunction of a part of system which produces undesirable result, be it crashing on a wrong input or miscalculating a series of computations. Can someone elaborate more and correct me if I am wrong in this? UPDATE To be more precise in the book I mentioned above, they (the words) are presented in a way to make a distinction, that's why I am asking to know more. In that book there are some examples denoting which sample belongs to what and which category. For example: Buffer overflow is said to be a bug and issues in method overriding (subclassing issues) is being related to flaw category. Again race condition handling issues are considered bugs and Error-handling problems (fails open) are told to be flaws! I want more elaboration on these regards.

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• Should a poll framework be closed sourced

  - by samquo

  I was having a chat with a coworker who is working on a polling app and framework. He was asking technical questions and I suggested he open source the application to get more quality opinions from developers who are interested in this problem and are willing to give it heavy though. He has a different point of view which I think is still valid so I want to open this question for discussion here. He says he believes something like a polling framework should not be open sourced because it will reduce its security and validity as people reveal loopholes through which they can cheat. Can't say I completely disagree. I see a somewhat valid point there, but I always believed that solutions by a group of people are almost always better than a solution thought by a single person asking a small number of coworkers, no matter how smart that person is. Again I'm willing to accept that maybe some types of applications are different. Does anyone have an argument in his favor? I'd really like to present your responses to him.

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• When to use identity comparison instead of equals?

  - by maaartinus

  I wonder why would anybody want to use identity comparison for fields in equals, like here (Java syntax): class C { private A a; public boolean equals(Object other) { // standard boring prelude if (other==this) return true; if (other==null) return false; if (other.getClass() != this.getClass()) return false; C c = (C) other; // the relevant part if (c.a != this.a) return false; // more tests... and then return true; } // getter, setters, hashCode, ... } Using == is a bit faster than equals and a bit shorter (due to no need for null tests), too, but in what cases (if any) you'd say it's really better to use == for fields inside equals?

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• Is it common practice to hire third parties to do code reviews for contractors?

  - by blueberryfields

  I recently observed some contract offers which included a "code review by third party" clause - the contract would not pay out fully until the code review was completed and it received a pass. I was surprised, especially considering that these were fairly simple, and small-scale contracts (churning out vanity apps for the iPhone). Is this kind of third-party code review a common thing to run into when contracting out as a programmer?

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• Finding the order of a set's elements

  - by Maciej Stachowski

  A little rephrased, in the form of a game, real-life problem: Suppose there is a set of elements {1, 2, ..., n}. Player A has chosen a single permutation of this set. Player B wants to find out the order of the elements by asking questions of form "Is X earlier in the permutation than Y?", where X and Y are elements of the set. Assuming B wants to minimize the amount of questions, how many times would he have to ask, and what would be the algorithm?

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• C# inherit from a class in a different DLL

  - by Onno

  I need to make an application that needs to be highly modular and that can easily be expanded with new functionality. I've thought up a design where I have a main window and a list of actions that are implemented using a strategy pattern. I'd like to implement the base classes/interfaces in a DLL and have the option of loading actions from DLL's which are loaded dynamically when the application starts. This way the main window can initiate actions without having to recompile or redistribute a new version. I just have to (re)distribute new DLL's which I can update dynamically at runtime. This should enable very easy modular updating from a central online source. The 'action' DLL's all inherit their structure from the code defined in the the DLL which defines the main strategy pattern structure and it's abstract factory. I'd like to know if C# /.Net will allow such a construction. I'd also like to know whether this construction has any major problems in terms of design.

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• Can this word search algorithm be made faster?

  - by Ashwin Singh

  Problem: Find a match of word S in text T Given: S and T are part of spoken and written English. Example: Match 'Math' in 'I love Mathematics' NOTE: Ignore CASES. My algorithm: STEP 1) Convert S, T to char[] STEP 2) for i=0, i < T.length , i++ STEP 3) for j=S.length-1, j>0 , j-- STEP 3 is the magic, instead of going about matching M,A,T,H, this matches M, H, T and finally A. This helps in eliminating a lot of possible partial matches. For example, if I go sequentially like M A as in Boyer Moore's method ... it can match Matter, Mass, Matchstick etc. using M _ _ H will bring down size of partial matches. STEP 4) if S[j]!=T[i] -> break; else if j==i -> PRINT MATCH

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• Can I migrate a clone of Google Code repository into Github?

  - by David Conde

  I want to create a clone of a Google Code repository, which I cannot download due to Country restrictions and I want to migrate that clone into Github, which I can use without any problem. The thing is I have a Github account and I can browse through GoogleCode but I cannot take my TortoiseHg and clone a repo just like that because I'm from Cuba and I get a lovely Google page saying that I cannot go into Google code. I'm guessing you know how I manage to browse :) I would like to import a mercurial repository into my Github repo, my questions: Is it possible? How can I do it?

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• What are the algorithms that are used for working with large data in popular web applications

  - by Moss Farmer

  I am looking for some well known algorithms that can be considered while handling very large amount of data.(Edit- By large amount of data I refer to records in a database excluding blobs). These algorithms if not in totality but in parts may be used in big web applications like Twitter, Last.fm , Amazon ,etc. Specifically, I'm looking for names or links to such algorithms. My primary interest lies in developing a very deep understanding on working with large database records and writing efficient code for working with the same.

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• Open source projects, how to choose?!

  - by Dhaivat Pandya

  I would like to join an open source project since I think I am good enough at programming to progress onto reading others code and to modify it. But the proble mis, how would I choose an open source project to work on? I know many languages and chief ones that I am good are python, C++ (not really very good at C, the lack of object orientation is difficult for me) and Java. For c++, I am proficient wit Qt. I would like to start with something that isn't huge, and hasn't reached a phase where the bugs are so complicated it would take me a month to understand what affects the bug. Any suggestions? At the current time, I don't use any libraries in either of the mentioned libraries that I would need to modify (AFAIK).

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• I'm hoping to start an online supermarket and needs advice on open source shopping cart software and applications..

  - by Betterman Simidi

  I have been researching on both open source software and off-the-shelf software for an online supermarket project in Africa. I have now narrowed by search to X-cart and the PHP based PrestaShop shopping carts. My plan is to acquire an open source shopping cart either by purchasing or as a free open source cart and hire a local developer to customize it to our local needs. I have been doing the demo for x-cart for three weeks now and had thought it might work best for us but after going through the 600 page manual and I'm concerned with how far it can be localized. Yesterday i was looking at the possible Prestashop free open source cart and i seem to like the back-end. Didn't like the back-end for Magento much but from reviews conducted by third-parties they seem to recommend it. I'm now wondering whether i should have a developer start the whole project from scratch, or use an open source software such us PrestaShop or get x-cart which can then be customized. Note that my store will have thousands of products and services including groceries and so i want something that can handle upto 500,000 products and over. Kindly advice. 93276

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• Business case for decentralized version control systems

  - by Keyo

  I searched and couldn't find any business reasons why git/mercurial/bazzr systems are better than centralized systems (subversion, perforce). If you were trying to sell a DVCS to a non-technical person what arguments would you provide for the DVCS increasing profit. I will shortly be pitching git to my manager, it will take some time converting out subversion repositories and some expense in buying smartgit licences.

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• Are there non-programming related activities akin to solving programming problems ?

  - by julien

  I'm talking about particular activities, for which you can draw parallels with the specific kind of reasonning needed when solving programming problems. Counter examples are activities that would help in almost any situation, like : take a shower or any other, somewhat passive activities, which are only helpful in triggering this sort of asynchronous problem solving our brain does exercise, because you brain simply works better when you're fit EDIT : It seems this question was quite misunderstood. I wasn't asking about what you can do when stuck on a problem but rather, what kind of activities you have in you spare time that you think help you, more or less directly, solving programing problems.

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• Naming methods that perform HTTP GET/POST calls?

  - by antonpug

  In the application I am currently working on, there are generally 3 types of HTTP calls: pure GETs pure POSTs (updating the model with new data) "GET" POSTs (posting down an object to get some data back, no updates to the model) In the integration service, generally we name methods that post "postSomething()", and methods that get, "getSomething()". So my question is, if we have a "GET" POST, should the method be called: getSomething - seeing as the purpose is to obtain data postSomething - since we are technically using POST performSomeAction - arbitrary name that's more relevant to the action What are everyone's thoughts?

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• The Singleton Pattern

  - by Darren Young

  Hi, I am a new programmer (4 months into my first job) and have recently taken an interest in design patterns. One that I have used recently is the Singleton. However, looking at some comments on this thread Overused or abused programming techniques .......it has some bad feedback. Come somebody explain why? I have found it useful in some places, however I could probably have achieved the same without it using a static class. Thanks.

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• Weeding out real agile from buzzword agile in an interview

  - by indyK1ng

  I've been interviewing for co-ops (paid internships) lately and a large number of the companies I've been interviewing with have been saying they use Scrum or some other agile methodology (scrum being the most popular). I know that there are real agile shops and there are places which say they use an agile methodology but are really doing something else and using agile as a buzzword. My question is, what are some questions I can ask in an interview which would separate these shops out?

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• Where can I find design exercises to work on?

  - by Oak

  I feel it's important to continue practicing my problem-solving skills. Writing my own mini-projects is one way, but another is to try and solve problems posted online. It's easy to find interesting programming quizzes online that require applying clever algorithms to solve - Project Euler is one well-known example. However, in a lot of real-life projects the design of the software - especially in the initial phases - has a large impact and at later stages it cannot be tweaked as easily as plain algorithms. In order to improve these skills, I'm looking for any collection of design problems. When I say "design", I mean the abstract design of a software solution - for example what modules will there be and what are the dependencies between them, how data will flow in the program, what sort of data needs to be saved in the database, etc. Design problems are those problems that are critical to solve in the early stages of any project, but their solution is a whiteboard diagram without a single line of code. Of course these sort of problems do not have a single correct solution, but I'll be especially happy with any place that also displays pros and cons of the typical solutions that might be used to approach the problem.

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• Should I be worried if I solve a lot of my problems the same way?

  - by Bryan Harrington

  I really enjoy programming games and puzzle creators/games. I find myself engineering a lot of these problems the same way and ultimately using similar technique to program them that I'm really comfortable with. To give you brief insight, I like to create graphs where nodes are represented with objects. These object hold data such as coordinates, positions and of course references to other neighboring objects. I'll place them all in a data structure and make decisions on this information in a "game loop". While this is a brief example, its not exact in all situations. It's just one way I feel really comfortable with. Is this bad?

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• Basics of ERP for dummies

  - by DarenW

  A situation has arisen where (if I don't scream and run away) I will be involved in an ERP system. This project will be using OpenERP specifically. My background is entirely science/engineering/music/games/art/whatever. I've never set foot in the realm of business systems or anything describable with the word "enterprise". What is a good introduction to the whole ERP concept, OpenERP and business systems in general suitable for those with flat zero experience in that world? The ideal intro would explain, from no assumptions, what the main ideas are, terminology, they style of work and thinking of people in that world, and maybe some concrete suggestions how one can tinker around with a copy of OpenERP to gain basic familiarity.

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• What does the English word "for" exactly mean in "for" loops?

  - by kol

  English is not my first language, but since the keywords in programming languages are English words, I usually find it easy to read source code as English sentences: if (x > 10) f(); = "If variable x is greater than 10, then call function f." while (i < 10) ++i; = "While variable i is less than 10, increase i by 1." But how a for loop is supposed to be read? for (i = 0; i < 10; ++i) f(i); = ??? I mean, I know what a for loop is and how it works. My problem is only that I don't know what the English word "for" exactly means in for loops.

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• Software, script or a tool to automate managing which tests to run

  - by laggingreflex

  I have a batch file that lists all the test files I have and asks me which test I want to perform, like Test. [U]nit, [I]ntegration : i (user input) Integration. [A]ll, [2][U]serInteraction, [3][R]esultGeneration : u 2 User Interaction. Running "mocha integration\2userint.js" ... So essentially I have configured a batch "option" for each test file I have, which I can choose to run individually or all together. But adding and removing tests is a pain. I have to update the batch file everytime a new file is added or changed. Is there a software, script or a tool, that does this automatically, or makes it easier for me to do so? I basically need it to be aware of and ask me which file(s) I want to test. A GUI with checkboxes would be ultimate! but I'll take anything. I'm working in node.js

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• How to set-up a simple subversion workflow

  - by Milen Bilyanov

  I am trying to set-up a simple SVN workflow at home. I am new to subversion (and programming) so I have been reading the official PDF documentations but still not sure about how to set-up my repository. I am working mainly with python, bash and rsl (Renderman Shading Language) So I already have a /dev structure on my disk as this: http://imageshack.us/f/708/devstructure.png/ And I have a /site structure that links to my /dev folder: http://imageshack.us/f/651/sitestructure.png/ So obviously starting to use SVN will change this approach that I already have in place. The question is when I am setting-up my SVN repository for the work I do in my /dev folder: Will I set-up a separate repository for each different programming platform? and Where exactly I should be placing my repository? Thanks.

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• Where can I find a good Hibernate Criteria tutorial that doesn't use cats and kittens? [closed]

  - by cbmeeks

  I've been using Hibernate a little while (HQL) and want to try Criteria's for a few scenarios we have here. I'm trying to get a few inner joins (2 layers deep) and am struggling a little. I go to the official site and they teach by cats and kittens. I don't care about cats and kittens and find the analogy hard to follow. Orders, details, shipments, etc. Nice, boring business references is what I enjoy. I tried to Google it but all I get are early 2000's websites with so many flashing GIF's, cluttered displays, flash overs and "tummy tuck" ads I want to puke. Why can't the java world have sites like http://guides.rubyonrails.org/? And no, I'm not advocating I volunteer to create a similar site. :-) Anyway, any good site that can give a nice tutorial on Criteria based searches would be appreciated.

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• UPOS RFIDScanner data format

  - by Robert Snyder

  A lot of work that I do currently is based in the OPOS/UPOS world. My company has a device that can read 13.56Mhz tags (RFID), Smart Cards, and Mag Stripe cards. Up until somewhat recently I have only been working with RFID for a very specific scenario. That was to read UltraLight C and Desfire cards. These cards were all setup very specifically so that I could take the data read from those cards and force it into a MSR track2 format. The past couple of weeks, however, I have been working on reading RFID credit cards (since I have a Visa card I've been using mine), and Smart Card credit cards. (The visa card I have has both) In learning how to communicate with SmartCard and reading ISO7816 and EMVCO documents I became a little more familiar with how info is stored. But now I have a question regarding UPOS. The RFID data on my Visa is stored (and read) very similar to how the data is stored and read from the Smart Card on my Visa. Cool. Well in the UPOS spec for SmartCardRW the ReadData method returns a byte array. That's cool, I can just return all that data and then parse it as my heart desires. The RFID though has a LinkedList of Tags. Well this makes sense in terms of my Visa card (reminds me of a question I have in regards to SmartCard, but that is for another question) but what about ULC and Desfire, or for that matter any Mifare card. Pages, Files, Purses don't exactly fit the Tag profile. For instance lets just say I read pages 4-12 on my ULC card. Each page I read is 4 bytes long. Does this mean I have 9 tags in my LinkedList? Is my Tag id the page number? Or then how does that translate to Desfire? I open application 123456 and read file 1 and file 2, Do I have 2 tags? and if so what is my tag id? At least with my Visa I think that I have to use the Tag id (ex 5F24 for my expiration date) and value of {0x15, 0x10, 0x31} Part of me says yes..that makes sense. Another part of me says, "well if that is the case then why doesn't SmartCardRW have Tags?" So that is my question. How do I format my data from those different types of media? or is that the job of my Control Object (the application)? Is so how does it know? The only protocols I have are: // Summary: // Enumerates the available predefined RFID tag protocols the device supports. [Flags] public enum RFIDProtocols { EpcClass0 = 1, RFIDSdt0Plus = 2, EpcClass1 = 4, EpcClass1Gen2 = 8, EpcClass2 = 16, Iso14443A = 4096, Iso14443B = 8192, Iso15693 = 12288, Iso180006B = 16384, Other = 16777216, All = 1073741824, } If I use that well all of my cards that I have are all Iso14443A. I use the ATQA and the SAK to know what type of card I really have. There is no RFID property that lets me specify that. So I'm lost.

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