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• Exception while running an EJB program [closed]

  - by rajesh

  I'm a newbie to JEE. I'm trying a sample EJB3 program given in this website. while trying to run the client program, I get an exception like this [JBossManagedConnectionPool] Throwable while attempting to get a new connection: null org.jboss.resource.JBossResourceException: Could not create connection; - nested throwable: (org.jboss.resource.JBossResourceException: Failed to register driver for: com.mysql.jdbc.Driver; - nested throwable: (java.lang.ClassNotFoundException: com.mysql.jdbc.Driver from BaseClassLoader@4c19dd{VFSClassLoaderPolicy@35fd58{name=vfszip:/home/rajesh/workspace/jboss-5.1.0.GA/server/default/deploy/FirstJPAproject.jar/ domain=ClassLoaderDomain@17380fc{name=DefaultDomain parentPolicy=BEFORE parent=org.jboss.bootstrap.NoAnnotationURLClassLoader@76cbf7} roots=[MemoryContextHandler@9160338[path= context=vfsmemory://3j001-rho3wm-h8v3wfs4-1-h8v5pkwn-9u real=vfsmemory://3j001-rho3wm-h8v3wfs4-1-h8v5pkwn-9u], DelegatingHandler@25335794[path=FirstJPAproject.jar context=file:/home/rajesh/workspace/jboss-5.1.0.GA/server/default/deploy/ real=file:/home/rajesh/workspace/jboss-5.1.0.GA/server/default/deploy/FirstJPAproject.jar] I'm using Jboss5.1.0 and ejb 3.0 Please help me to get rid of this.

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• JSP Include: one large bean or bean for each include

  - by shylynx

  I want to refactor a webapp that consists of very distorted JSPs and servlets. Because we can't switch to a web framework easily we have to keep JSPs and Servlets, and now we are in doubt how to include pages into another and how to setup the use:bean-directives effectively. At the first step we want to decouple the code for the core-actions and the bean-creation into servlets. The servlets should forward to their corresponding pages, which should use the bean. The problem here is, that each jsp consists of different sub- and sub-sub-jsp that are included into another. Here is a shortend extract (because reality is more complex): head header top navigation actionspanel main header actionspanel foot footer Moreover each jsp (also the header and footer) use dynamic data. For example title and actionspanel can change on each page-reload or do have links and labels that depend on the processing by the preceding servlet. I know that jsp-include-directives should only be used for static content und should be avoided for dynamic content. But here we have very large pages, that consist of many parts. Now the core questions: Should I use one big bean for each page, so that each bean holds also data for header and footer beside its core data, so that each subsequent included jsp uses the same bean-directive? For example: DirectoryJSP <- DirectoryBean CompareJSP <- CompareBean Or should I use one bean for each jsp, so that each bean only holds the data for one jsp and its own purpose. For example: DirectoryJSP <- DirectoryBean HeaderJSP <- HeaderBean FooterJSP <- FooterBean CompareJSP <- CompareBean HeaderJSP <- HeaderBean FooterJSP <- FooterBean In the second case: should the subsequent beans be a member of the corresponding parent bean, so that only the parent bean is attached as attribute to the request? Or should each bean attached to the request?

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• IL and case-sensitivity

  - by Ali .NET

  Quoted from A Brief Introduction To IL code, CLR, CTS, CLS and JIT In .NET CLS stands for Common Language Specifications. It is a subset of CTS. CLS is a set of rules or guidelines which if followed ensures that code written in one .NET language can be used by another .NET language. For example one rule is that we cannot have member functions with same name with case difference only i.e we should not have add() and Add(). This may work in C# because it is case-sensitive but if try to use that C# code in VB.NET, it is not possible because VB.NET is not case-sensitive. Based on above text I want to confirm two points here: Does the case-sensitivity of IL is a condition for member functions only, and not for member properties? Is it true that C# wouldn't be inter-operable with VB.NET if it didn't take care of the case sensitivity?

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• Why don't we use dynamic (server-side generated) CSS?

  - by ern0

  As server-side generated HTML is trivial (and it was the only way to make dynamic webpages before AJAX), server-side generated CSS is not. Actually, I've never seen it. There are CSS compilers, but they generate CSS files which can be used as static. Technically, it requires no special libraries, the HTML style tag should reference to the PHP(/ASP/whatever) templater script instead of the static CSS file, and the script should send out CSS content-type header - that's all. Does it have cache problems? I don't think so. The script should send out no-cache etc. headers. Is it problem for designers? No, they should edit the CSS template (as they edit the HTML template). Why we don't use dynamic CSS generators? Or if there's any, please let me know.

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• What should be the minimal design/scope documentation before development begins?

  - by Oliver Hyde

  I am a junior developer working on my own in the programming aspect of projects. I am given a png file with 5-6 of the pages designed, most times in specific detail. From this I'm asked to develop the back end system needed to maintain the website, usually a cataloging system with products, tags and categories and match the front end to the design. I find myself in a pickle because when I make decisions based on assumptions about the flow of the website, due to a lack of outlining details, I get corrected and am required to rewrite the code to suit what was actually desired. This process happens multiple times throughout a project, often times on the same detail, until it's finally finished, with broken windows all through it. I understand that projects have scope creep, and can appreciate that I need to plan for this, but I feel that in this situation, I'm not receiving enough outlining details to effectively plan for the project, resulting in broken code and a stressed mind. What should be the minimal design/scope documentation I receive before I begin development?

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• *Code owner* system: is it an efficient way?

  - by sergzach

  There is a new developer in our team. An agile methodology is in use at our company. But the developer has another experience: he considers that particular parts of the code must be assigned to particular developers. So if one developer had created a program procedure or module it would be considered normal that all changes of the procedure/module would be made by him only. On the plus side, supposedly with the proposed approach we save common development time, because each developer knows his part of the code well and makes fixes fast. The downside is that developers don't know the system entirely. Do you think the approach will work well for a medium size system (development of a social network site)?

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• Returning null vs Throwing exceptions

  - by Svish

  Is in a bit of disagreement with a more experienced developer on this issue, and was wondering what you guys here think about this. Environment is Java, EJB 3, services, etc. The code I wrote calls a service to get things and to create things. Problem was that I got null pointer exceptions in places that didn't make sense. For example when I asked the service to create an object, I got null back. And when I tried to look up an object with an id I knew existed, I still got null back. Was like it was ignoring me. Spent some time trying to figure out what was wrong in my code (since I'm less experienced I usually assume I have messed up). Turns out the reason was security. If the user principal using my service didn't have the right permissions to use the service I called from my service, then that service simply returned null. The services that are here already are usually not documented either, so this is just something you have to know... somehow... So here is the thing: I mean that this is rather confusing as a developer interacting with this service. To me it would make much more sense if that service thew an exception which would tell me that hey, you don't have the proper permissions to get info about this thing or to create this new thing. I would then immediately know why my service wasn't working as expected. However, he argued that asking is not wrong. Exceptions should only be thrown when there is an error and asking for a thing is not an error. Even if you don't have permission to "see" that the thing you asked for. The things are often looked up in a GUI by users and for those users not having the right permissions, these things simply "do not exist". So, in short: Asking is not wrong, hence no exception. Get methods return null because to those users those things "doesn't exist". Create methods return null because nothing was created, since the user wasn't allowed to create anything. So, what do you guys think? Is this normal and/or good practice? I prefer exceptions as I prefer throwing and catching exceptions because I find it much easier to know what's going on. So I would for example also prefer to throw a NotFoundException if you asked for an id which didn't exist, rather than returning null. Anyways, just curious to what others think about this as I'm not the most experienced developer yet.

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• Interviewing a DBA

  - by kev

  Our Company is in the Process of recuiting a DBA. I have built a group test of questions from basic questions such as Pk and Fk constraints, simple querries(fizzbuzz style) to more advanced things such as indexes, Collation, isolation levels and how to trace deadlocks. However, that is the limit of my knowledge. So my question to all the DBA's is what is the base level knowledge that all DBA's should have? We are really looking for someone that will be able to manage our replication, analyzing some of our slower running queries(that the devs can go to for help) and someone that can trace some of the deadlock issues that we are having. Any help would be most appreciated!

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• Is there a LOGO interpreter that actually has a turtle?

  - by Tim Post

  This is not a repeat of the now infamous "How do I move the turtle in LOGO?" Recently, I had the following conversation with my five year old daughter: Daughter: Daddy, do you write programs? Me: Yes! Daughter: Daddy, what's a program? Me: A program is a set of instructions that a computer follows. Daughter: Daddy, can I write a program too? Me: Sure! This got me scrambling to think of a very basic language that a five year old could get some satisfaction from mastering rather quickly. I'm ashamed to admit that the first thing that came to mind was this: 10 INPUT "Tell me a secret" A$ 20 PRINT "Wow really? :" A$ 30 GOTO 10 That isn't going to hold a five year old's attention for very long and it requires too much of a lecture. However, moving a turtle around and drawing neat pictures might just work. Sadly, my search for a LOGO interpreter yielded noting but ad ridden sites, flight simulators and a whole bunch of other stuff that I really don't want. I'm hoping to find a cross platform (Java / Python) LOGO interpreter (dare I call it simulator?) with the following features: Can save / replay commands (stored programs) Has an actual turtle Sound effects are a plus Have you stumbled across something like this, if so, can you provide a link? I hate to ask a 'shopping' sort of question, but it seemed much better than "Is LOGO appropriate for a five year old?"

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• Dictionary as DataMember in WCF after installing .NET 4.5 [migrated]

  - by Mauricio Ulate

  After installing .NET Framework 4.5 with Visual Studio 2012, whenever I want to obtain the reference from a WCF service, my dictionaries are changed into arrays. For example, Dictionary<int, double> is changed into ArrayOfKeyValueOfintdoubleKeyValueOfintdouble. This happens in both Visual Studio 2012 and 2010 (both Express). I've reviewed my configuration and the dictionary data type in the service reference configuration is System.Collection.Generic.Dictionary. Changing this doesn't make a difference. Reverting to just using Visual Studio 2010 and .NET 4.0 is not an option.

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• Security of logging people in automatically from another app?

  - by Simon

  I have 2 apps. They both have accounts, and each account has users. These apps are going to share the same users and accounts and they will always be in sync. I want to be able to login automatically from one app to the other. So my solution is to generate a login_key, for example: 2sa7439e-a570-ac21-a2ao-z1qia9ca6g25 once a day. And provide a automated login link to the other app... for example if the user clicks on: https://account_name.securityhole.io/login/2sa7439e-a570-ac21-a2ao-z1qia9ca6g25/user/123 They are logged in automatically, session created. So here we have 3 things that a intruder has to get right in order to gain access; account name, login key, and the user id. Bad idea? Or should I can down the path of making one app an oauth provider? Or is there a better way?

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• Linux Learning curve for a 'Lifetime' windows user [closed]

  - by gary

  I am using windows for almost 8-10 years and have never worked on linux. Mostly i used to work in VB, VC++ MFC and little bit of .NET(C# and VB) so i didn't bother about Linux. But now when i got an opportunity to work with linux i dont want to miss it, here are my questions : Where can i find useful resources for Linux newbies? Which books/Tutorials will you suggest to start? Which distro shall i use? What was your experience while moving from Windows to Linux?

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• How does the GPL work in regards to languages like Dart which compile to other languages?

  - by Peter-W

  Google's Dart language is not supported by any Web Browsers other than a special build of Chromium known as Dartium. To use Dart for production code you need to run it through a Dart-JavaScript compiler/translator and then use the outputted JavaScript in your web application. Because JavaScript is an interpreted language everyone who receives the "binary"(Aka, the .js file) has also received the source code. Now, the GNU General Public License v3.0 states that: "The “source code” for a work means the preferred form of the work for making modifications to it." Which would imply that the original Dart code in addition to the JavaScript code must also be provided to the end user. Does this mean that any web applications written in Dart must also provide the original Dart code to all visitors of their website even though a copy of the source code has already been provided in a human readable/writable/modifiable form?

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• How to publish paid Android apps if you're not from US/UK

  - by Sheikh Aman

  I was pretty excited while creating one of my apps but as it turns out you can't actually sign up for Google Checkout if you don't live either in the USA or in the UK. And since Google Checkout is the only way Android Market will pay you, all my efforts seem to be going in vain. So because I live in India, I can't sell my apps. I tried contacting Google by various means on this, but haven't got any response so far. I tried searching the web as well just to find out that one can't be paid via any other way. I am pretty sure that many people here might have gone through the same problem. How did you solve it? I have a PayPal account and an AdSense account as well. Can they help in any way? And if nothing works out, how am I supposed to be selling my app?

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• Data Aggregation of CSV files java

  - by royB

  I have k csv files (5 csv files for example), each file has m fields which produce a key and n values. I need to produce a single csv file with aggregated data. I'm looking for the most efficient solution for this problem, speed mainly. I don't think by the way that we will have memory issues. Also I would like to know if hashing is really a good solution because we will have to use 64 bit hashing solution to reduce the chance for a collision to less than 1% (we are having around 30000000 rows per aggregation). For example file 1: f1,f2,f3,v1,v2,v3,v4 a1,b1,c1,50,60,70,80 a3,b2,c4,60,60,80,90 file 2: f1,f2,f3,v1,v2,v3,v4 a1,b1,c1,30,50,90,40 a3,b2,c4,30,70,50,90 result: f1,f2,f3,v1,v2,v3,v4 a1,b1,c1,80,110,160,120 a3,b2,c4,90,130,130,180 algorithm that we thought until now: hashing (using concurentHashTable) merge sorting the files DB: using mysql or hadoop or redis. The solution needs to be able to handle Huge amount of data (each file more than two million rows) a better example: file 1 country,city,peopleNum england,london,1000000 england,coventry,500000 file 2: country,city,peopleNum england,london,500000 england,coventry,500000 england,manchester,500000 merged file: country,city,peopleNum england,london,1500000 england,coventry,1000000 england,manchester,500000 The key is: country,city. This is just an example, my real key is of size 6 and the data columns are of size 8 - total of 14 columns. We would like that the solution will be the fastest in regard of data processing.

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• How can I become a better Javascript programmer?

  - by Elliot Bonneville

  I've been programming with Javascript for a few years now, and I guess I'm okay at it. I can solve pretty much any problem I come across, and while my solutions may not be that great, they work. However, I want to become a better Javascript programmer. I'd like to learn all the best-practices, tricks of the trade, things to avoid, and anything else I should know so that my code will be 100% optimized and as readable as possible. How do I do that? I realize this question has been loosely asked before here, but the OP was something of beginner. I want to get into the more advanced side of Javascript programming with this question. Is this possible or am I just being way too impatient? Do I just need to spend loads of time programming?

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• Building a database class in PHP

  - by Sprottenwels

  I wonder if I should write a database class for my application, and if so, how to accomplish it? Over there on SO, a guy mentioned it should be written as an abstract class. However, I can't understand why this would be a benefit. Do I understand correctly, that if I would write an abstract class, every other class that methods will need a database connection, could simply extend this abstract class and have it's own database object? If so, how is this different from a "normal" class where I could instantiate an database object? Another method would be to completely forget about my own class and to instantiate a mysqli object on demand. What do you recommend?

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• Releasing an open source project without getting embarrassed

  - by Hopeful

  I've been working by myself on a fairly large open source project for quite a while and it's nearing the point where I'd like to release it. However, I'm self-taught and I don't really know anyone who could adequately review my project. A few years ago, I had released a small bit of code which pretty much got ripped apart (in a critical sense) on the forum where I released it. Even though the code worked, the criticism was accurate but brutal. It prompted me to begin searching for best practices for everything and in the end I feel that it made me a much better developer. I've gone over everything in my project so many times trying to make it perfect that I've lost count. I believe in my project and think it has the potential to help a lot of people and I feel like I've done some cool things in interesting ways with it. Still, because I'm self-taught, I can't help but wonder what gaps exist in my self-education. The way my code was ripped apart last time isn't something I'd like to repeat. I think my two biggest fears with releasing my project that I've poured countless hours into are being absolutely embarrassed because I missed some patently obvious things because of my self-education or, worse, releasing it to the sound of crickets. Is there anyone who has been in a similar situation? I'm not afraid of constructive criticism, so long as it is constructive and not just a rant on how I screwed up. I know there is a code review site on StackExchange, but it's not really set up for large projects and I didn't feel like the community there is large enough yet to get good feedback if I were to post parts of my project piecemeal (I tried with one file). What can I do to give my project at least some measure of success without getting embarrassed or devestated in the process?

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• Concerns on first ASP.NET cloud application

  - by RPK

  I am writing a small ASP.NET Web Application. My worries are that I want to keep the architecture same giving me the option to install it on an Intranet or on a Cloud Platform. I am not using MVC but lately learned that Azure only supports ASP.NET MVC applications. I want to know whether ASP.NET Web Forms application work on Azure/AppHarbor or not. Do I need to convert this application to MVC if Web Forms is not supported? Will the same application run on Intranet as well?

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• How to protect a peer-to-peer network from inappropriate content?

  - by Mike

  I’m developing a simple peer-to-peer app in .Net which should enable users to share specific content (text and picture files). As I've learned with my last question, inappropriate content can “relatively” easily be identified / controlled in a centralized environment. But what about a peer-to-peer network, what are the best methods to protect a decentralized system from unwanted (illegal) content? At the moment I only see the following two methods: A protocol (a set of rules) defines what kind of data (e.g. only .txt and jpg-files, not bigger than 20KB etc.) can be shared over the p2p-network and all clients (peers) must implement this protocol. If a peer doesn’t, it gets blocked by other peers. Pro: easy to implement. Con: It’s not possible to define the perfect protocol (I think eMail-Spam filters have the same problem) Some kind of rating/reputation system must be implemented (similar to stackoverflow), so “bad guys” and inappropriate content can be identified / blocked by other users. Pro: Would be very accurate. Con: Would be slow and in my view technically very hard to implement. Are there other/better solutions? Any answer or comment is highly appreciated.

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• Is it wise to ask about design decisions made on a product during an interview?

  - by Desolate Planet

  I've been thinking about interview questions lately and I've been reflecting on bad interview experiences I've had in the past. One of particular note is where I had asked the interviewer why the team chose to use Spring over EJB3 in their product. The interviewer pretty much tore my face off, yelling "Because Spring is not the be all and end all of Java software development, do you want this job or not?". In response to this, I told him that this probably wasn't the job for me and I walked out the interview. He told me at the start of the interview that they had high stuff turnover, the product had gone from Modula 3 to Perl to Java then after asking him a technical question, he went in flames. It seemed obvious to me that he was toxic to the company with that kind of attitude. Question: Is it a good idea to probe on architectural choices taken in an interview? If not, why? From my own point of view, an interview is a two-way process. If the interviewers are testing me on my technical skills, I've got every right to ask them the same questions to 1) Figure out what their mindset and attitudes towards developing software solutions are and 2) To figure out if there are in line with how I would approach problems of that kind. It's very possible that the interviewer who got angry was a bad interviewer and forgot that an interview is a two-way process. If I was asked this, I would have simply said something along the lines of wanting to leverage the container more, but I certainly wouldn't have tried to put him in a state of meek capitulation. The interviewer in question was the lead developer in the team.

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• Why prefer a wildcard to a type discriminator in a Java API (Re: Effective Java)

  - by Michael Campbell

  In the generics section of Bloch's Effective Java (which handily is the "free" chapter available to all: http://java.sun.com/docs/books/effective/generics.pdf), he says: If a type parameter appears only once in a method declaration, replace it with a wildcard. (See page 31-33 of that pdf) The signature in question is: public static void swap(List<?> list, int i, int j) vs public static void swap(List<E> list, int i, int j) And then proceeds to use a static private "helper" function with an actual type parameter to perform the work. The helper function signature is EXACTLY that of the second option. Why is the wildcard preferable, since you need to NOT use a wildcard to get the work done anyway? I understand that in this case since he's modifying the List and you can't add to a collection with an unbounded wildcard, so why use it at all?

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• Logic to create common Serverlet3 Login

  - by user3696143

  I am using Servlet3 Login to Authenticate User in website I have these Login Website Normal Login(Fill the Sigup form) Facebook Login (From Facebook Id) Twitter Login (From Twitter) And I am already authenticate user by below code HttpServletRequest request = (HttpServletRequest) FacesContext.getCurrentInstance().getExternalContext().getRequest(); request.login(username, password); And it is working fine for Website Login as user gave his/her EMailId and password and it store in DB. Now I modified table and added more columns to save Facebookid in same user table and also password for Facebook login FacebookId work as a Password as well. Same I will do for Twitter But I want the same Servlet3 to authenticate user. How can I achieve it? And also added context.xml file inside META-INF folder <Realm localDataSource="true" debug="99" className="org.apache.catalina.realm.JDBCRealm" connectionName="user" connectionPassword="password" connectionURL="jdbc:mysql://localhost:3306/ ccc" digest="md5" driverName="com.mysql.jdbc.Driver" roleNameCol="role_name" userCredCol="password" userNameCol="email_id" userRoleTable="users_list" userTable="user_list_view" /> Also it is possible to check which query fired by realm entry?

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• What is the right way to process inconsistent data files?

  - by Tahabi

  I'm working at a company that uses Excel files to store product data, specifically, test results from products before they are shipped out. There are a few thousand spreadsheets with anywhere from 50-100 relevant data points per file. Over the years, the schema for the spreadsheets has changed significantly, but not unidirectionally - in the sense that, changes often get reverted and then re-added in the space of a few dozen to few hundred files. My project is to convert about 8000 of these spreadsheets into a database that can be queried. I'm using MongoDB to deal with the inconsistency in the data, and Python. My question is, what is the "right" or canonical way to deal with the huge variance in my source files? I've written a data structure which stores the data I want for the latest template, which will be the final template used going forward, but that only helps for a few hundred files historically. Brute-forcing a solution would mean writing similar data structures for each version/template - which means potentially writing hundreds of schemas with dozens of fields each. This seems very inefficient, especially when sometimes a change in the template is as little as moving a single line of data one row down or splitting what used to be one data field into two data fields. A slightly more elegant solution I have in mind would be writing schemas for all the variants I can find for pre-defined groups in the source files, and then writing a function to match a particular series of files with a series of variants that matches that set of files. This is because, more often that not, most of the file will remain consistent over a long period, only marred by one or two errant sections, but inside the period, which section is inconsistent, is inconsistent. For example, say a file has four sections with three data fields, which is represented by four Python dictionaries with three keys each. For files 7000-7250, sections 1-3 will be consistent, but section 4 will be shifted one row down. For files 7251-7500, 1-3 are consistent, section 4 is one row down, but a section five appears. For files 7501-7635, sections 1 and 3 will be consistent, but section 2 will have five data fields instead of three, section five disappears, and section 4 is still shifted down one row. For files 7636-7800, section 1 is consistent, section 4 gets shifted back up, section 2 returns to three cells, but section 3 is removed entirely. Files 7800-8000 have everything in order. The proposed function would take the file number and match it to a dictionary representing the data mappings for different variants of each section. For example, a section_four_variants dictionary might have two members, one for the shifted-down version, and one for the normal version, a section_two_variants might have three and five field members, etc. The script would then read the matchings, load the correct mapping, extract the data, and insert it into the database. Is this an accepted/right way to go about solving this problem? Should I structure things differently? I don't know what to search Google for either to see what other solutions might be, though I believe the problem lies in the domain of ETL processing. I also have no formal CS training aside from what I've taught myself over the years. If this is not the right forum for this question, please tell me where to move it, if at all. Any help is most appreciated. Thank you.

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• What is the point of the prototype method?

  - by Mild Fuzz

  I am reading through Javascript: The Good Parts, and struggled to get my head around the section on prototypes. After a little google, I came to the conclusion that it is to add properties to objects after the objects declaration. Using this script gleamed from w3schools, I noticed that removing the line adding the prototype property had no effect. So what is the point? //Prototyping function employee(name,jobtitle,born) { this.name=name; this.jobtitle=jobtitle; this.born=born; } var fred=new employee("Fred Flintstone","Caveman",1970); employee.prototype.salary=null; // <--- try removing this line fred.salary=20000; document.write(fred.salary);

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