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  • Should client-server code be written in one "project" or two?

    - by Ricket
    I've been beginning a client-server application. At first I naturally created two projects in Eclipse, two source control repositories, etc. But I'm quickly seeing that there is a bit of shared code between the two that would probably benefit to sharing instead of copying. In addition, I've been learning and trying test-driven development, and it seems to me that it would be easier to test based on real client components rather than having to set up a huge amount of code just to mock something, when the code is probably mostly in the client. My biggest concern in merging the client and server is of security; how do I ensure that the server pieces of the code do not reach an user's computer? So especially if you are writing client-server applications yourself (and especially in Java, though this can turn into a language-agnostic question if you'd like to share your experience with this in other languages), what sort of separation do you keep between your client and server code? Are they just in different packages/namespaces or completely different binaries using shared libraries, or something else entirely? How do you test the code together and yet ship separately?

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  • what makes a Tomcat5.5 cannot be "aware" of new Java Web Applications?

    - by Michael Mao
    This is for uni homework, but I reckon it is more a generic problem to the Tomcat Server(version 5.5.27) on my uni. The problem is, I first did a skeleton Java Web Application (Just a simple Servlet and a welcome-file, nothing complicated, no lib included) using NetBeans 6.8 with the bundled Tomcat 6.0.20 (localhost:8084/WSD) Then, to test and prove it is "portable" and "auto-deploy-able", I cleaned and built a WSD.war file and dropped it onto my Xampp Tomcat (localhost:8080/WSD). The war extracted everything accordingly and I can see identical output from this Tomcat. So far, so good. However, after I tried to drop to war onto uni server, funny thing happens: uni server Even though I've changed the war permission to 755, it is simply not "responding". I then copied the extracted files to uni server, the MainServlet cannot be recognized from within its Context Path "/WSD", basically nothing works, expect the static index.jsp. I tried several times to stop and restart uni Tomcat, it doesn't help? I wonder what makes this happen? Is there anything I did wrong with my approach? To be frank I paid no attention to a server not under my control, and I am unfortunately not a real active day-to-day Java Programmer now. I understand the fundamentals of MVC, Servelets, JSPs, JavaBeans, but I really feel frustrated by this, as I cannot see why... Or, should I ask, a Java Web Application, after cleaned and built by NetBeans6.8, is self-contained and self-configured so ready to be deployed to any Java Web Container? I know, I can certainly program everything in plain old JSP, but this is soooo... unacceptable to myself... Update : I am now wondering if there is any free Tomcat Hosting so that I would like to see if my war file and/or my web app can go with them without any configuration at all?

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  • managing html rich text selections

    - by swami
    Hi, I am writing a component for a web app which will display some html, and let me capture and manipulate the selection boundaries (of the text selected by the user). I have done this successfully (for Mozilla) with a simple div element using window.getSelection(). However, the browser selection API is different for IE. If I were to use a textarea instead (for interacting with the selection api), is there a uniform API across the browsers? Then I would need to overlay a DIV on top of this to display the styled text, and presumably I'd need to manage the cursor etc... Basically I want a rich text editor - but without editing. Does anyone have any advice on the best way to go about this, which is quick, simple and cross browser compatible. I don't want to spend ages reinventing the wheel... (If anyone's interested - this is for an online xml editor. I capture the users selection on a html version of the xml doc and then send the selection offsets info to the server, where the real xml doc gets marked up). Kind Regards Swami

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  • Scala and Java BigDecimal

    - by geejay
    I want to switch from Java to a scripting language for the Math based modules in my app. This is due to the readability, and functional limitations of mathy Java. For e.g, in Java I have this: BigDecimal x = new BigDecimal("1.1"); BigDecimal y = new BigDecimal("1.1"); BigDecimal z = x.multiply(y.exp(new BigDecimal("2")); As you can see, without BigDecimal operator overloading, simple formulas get complicated real quick. With doubles, this looks fine, but I need the precision. I was hoping in Scala I could do this: var x = 1.1; var y = 0.1; print(x + y); And by default I would get decimal-like behaviour, alas Scala doesn't use decimal calculation by default. Then I do this in Scala: var x = BigDecimal(1.1); var y = BigDecimal(0.1); println(x + y); And I still get an imprecise result. Is there something I am not doing right in Scala? Maybe I should use Groovy to maximise readability (it uses decimals by default)?

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  • How can I sign a Windows Mobile application for internal use?

    - by AR
    I'm developing a Windows Mobile application for internal company use, using the Windows Mobile 6 Professional SDK. Same old story: I've developed and tested on the emulator and all is well, but as soon as I deploy to advice I get an UnauthorizedAccessException when writing files or creating directories. I'm aware that an application installed to a device needs to be signed but I'm running into roadblocks at every turn: Using the project properties 'Devices' window I select 'Sign the project output with this certificate, and choose one of the sample certificates from the SDK. This results in a build error: "The signer's certificate is not valid for signing" when running SignTool. If I try to run SignTool.exe from the commandline, I get an error telling me to run SignTool.exe from a location in the system's PATH. I can't use the 'Signing' tab in the Project Properties to create a test certificate - this is greyed out (presumably for WinMobile projects?). If at all possible, I would like to avoid having to go through Versign or the like to get a Mobile2Market certificate. If I have to go this route for a final version that's fine, but I need to at least be able to test the app on real devices. Any advice would be most welcome!

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  • Nmock2 and Event Expectations

    - by Kildareflare
    Im in the process of writing a test for a small application that follows the MVP pattern. Technically, I know I should have written the test before the code, but I needed to knock up a demo app quick smart and so im now going back to the test before moving on to the real development. In short I am attempting to test the presenter, however I cannot even get an empty test to run due to an Internal.ExpectationException. The exception is raised on a unexpected invocation of an event assignation. Here is the presenter class, public LBCPresenter(IView view, IModel model) { m_model = model; m_model.BatteryModifiedEvent += new EventHandler(m_model_BatteryModifiedEvent); } Model Interface public interface IModel { event EventHandler BatteryModifiedEvent; } And here is the test class, I can't see what im missing, ive told NMock to expect the event... [TestFixture] public class MVP_PresenterTester { private Mockery mocks; private IView _mockView; private IViewObserver _Presenter; private IModel _mockModel; [SetUp] public void SetUp() { mocks = new Mockery(); _mockView = mocks.NewMock<IView>(); _mockModel = mocks.NewMock<IModel>(); _Presenter = new LBCPresenter(_mockView, _mockModel); } [Test] public void TestClosingFormWhenNotDirty() { Expect.Once.On(_mockModel).EventAdd("BatteryModifiedEvent", NMock2.Is.Anything); //makes no difference if following line is commented out or not //mocks.VerifyAllExpectationsHaveBeenMet(); } } Every time I run the test I get the same expectation Exception. Any ideas?

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  • How to Open Multiple PopUp windows with JQuery on form submission (popUps should be relative to form

    - by Ole Jak
    I have A HTML form like this: <form> <fieldset class="ui-widget-content ui-corner-all"> <select id="Streams" class="multiselect ui-widget-content ui-corner-all" multiple="multiple" name="Streams[]"> <option value="35"> Example Name (35)</option> <option value="44"> Example Name (44)</option> <option value="5698"> Example Name (5698)</option> <option value="777"> Example Name (777)</option> <option value="12"> Example Name (12)</option> </select> <input type="submit" class="ui-state-default ui-corner-all" name="submitForm" id="submitForm" value="Play Stream from selected URL's!"/> </fieldset> </form> in my JS + HTML page I use JQuery. As you can see I allow user to select multiple Items. I want to open on Submit button click as many popup windows as many Items he selected in a list. Each popUp window should open some url like www.example.com/test.php?id=OPTION_SELECTED . And here I mean by PopUp Window a real browser window. So for each of the selected options I ll get a pop up window whith diferent url. Please Help.

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  • What if you used the wrong language?

    - by HS
    A reply to another question made me remember a project from some years ago when it turned out that Java was not the right tool to use. I typically only learn a new language when I have a problem that it solves better than the ones I already know. [...] Then I write whatever program I wanted to learn that language for in the first place. [...] By the time I've gotten my target program written, I've usually got a decent handle on the language, not to mention any other features it has, and I've got other ideas to use it for. I did just that back then with Java, because the client thought it to be the right language to use (platform independent) and initial evaluation confirmed that. However, much later in the project there were some issue (can't really remember all the details by now). So, the project that started as a nice learning experience turned into a nightmare toward the end. I was at the brink of switching over to my trusted C++ and doing a complete rewrite. The client was not so much of a problem to convince back then, but my supervisor was strongly opposed because of all the work that already went into the Java version. In hindsight, he was right and the project was complete more or less with the intended features kind of working, but it was the project that I am least proud of by now. Long story short: what do you think, when is it too much and the switch to another technology is worthwhile? I personally would estimate the point of no return to be around 50% of the planned effort, but really want to know, if anyone has real experience with such a switch. And to answer the inevitable question: I do not really care, if the technology switched to is proven or another new thing. The latter would basically need more initial scrutiny based on the past experiences in the problematic project.

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  • Getting table schema from a query

    - by Appu
    As per MSDN, SqlDataReader.GetSchemaTable returns column metadata for the query executed. I am wondering is there a similar method that will give table metadata for the given query? I mean what tables are involved and what aliases it has got. In my application, I get the query and I need to append the where clause programically. Using GetSchemaTable(), I can get the column metadata and the table it belongs to. But even though table has aliases, it still return the real table name. Is there a way to get the aliase name for that table? Following code shows getting the column metadata. const string connectionString = "your_connection_string"; string sql = "select c.id as s,c.firstname from contact as c"; using(SqlConnection connection = new SqlConnection(connectionString)) using(SqlCommand command = new SqlCommand(sql, connection)) { connection.Open(); SqlDataReader reader = command.ExecuteReader(CommandBehavior.KeyInfo); DataTable schema = reader.GetSchemaTable(); foreach (DataRow row in schema.Rows) { foreach (DataColumn column in schema.Columns) { Console.WriteLine(column.ColumnName + " = " + row[column]); } Console.WriteLine("----------------------------------------"); } Console.Read(); } This will give me details of columns correctly. But when I see BaseTableName for column Id, it is giving contact rather than the alias name c. Is there any way to get the table schema and aliases from a query like the above? Any help would be great!

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  • What would be different in Java if Enum declaration didn't have the recursive part

    - by atamur
    Please see http://stackoverflow.com/questions/211143/java-enum-definition and http://stackoverflow.com/questions/3061759/why-in-java-enum-is-declared-as-enume-extends-enume for general discussion. Here I would like to learn what exactly would be broken (not typesafe anymore, or requiring additional casts etc) if Enum class was defined as public class Enum<E extends Enum> I'm using this code for testing my ideas: interface MyComparable<T> { int myCompare(T o); } class MyEnum<E extends MyEnum> implements MyComparable<E> { public int myCompare(E o) { return -1; } } class FirstEnum extends MyEnum<FirstEnum> {} class SecondEnum extends MyEnum<SecondEnum> {} With it I wasn't able to find any benefits in this exact case. PS. the fact that I'm not allowed to do class ThirdEnum extends MyEnum<SecondEnum> {} when MyEnum is defined with recursion is a) not relevant, because with real enums you are not allowed to do that just because you can't extend enum yourself b) not true - pls try it in a compiler and see that it in fact is able to compile w/o any errors PPS. I'm more and more inclined to believe that the correct answer here would be "nothing would change if you remove the recursive part" - but I just can't believe that.

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  • SQLite Databases and Grid Hosting

    - by jocull
    I'm considering moving my site from a GoDaddy shared hosting account to a Media Temple grid hosting account in anticipation of traffic. However, I first have some concerns with the grid hosting setup. My site stores a large personal set of data on a per-user basis (possibly 3-4MB per user). At this rate I was worried about blowing over a 1GB MySQL limit in no time. To deal with this I created distributed SQLite databases per user to store large data objects. It's worked wonderfully so far. SQLite is super fast and simple. I know that reading from and writing to files is different in a Grid Hosting environment. I need to know if this setup is going to cause serious problems. These databases are not (and will not be) highly trafficked. They are personal to the user and will only be touched maybe two locations at the same time (one updating the data hourly at the most, and one or more reading on demand). I'd like to keep this setup as getting additional space (beyond 4GB) on a MySQL database seems to be a real trouble point. Will Grid Hosting cause me serious problems? Thanks.

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  • Telerik RadGrid: grid clientside pagination

    - by ram
    I have a web service which returns me some data,I am massaging this data and using this as datasource for my radgrid (telerik). The datasource is quite large, and would like to paginate it. I found couple of problems when I paginate it in the server side I have to bind the grid again for pagination, which essentially means I have to make a call to WS again to get the data. This is an expensive call for me. I would rather forgo the benefits of pagination and would display all the results in the same page, except for it would be a bit clumsy During the postback RadGrid1.Items.Count happens to be the number of items getting paginated (25- in my case) which is expected as all the items in the datasource are not getting bound. This of course is not an issue. The real issue is that we have some checkboxes which get checked based on some business condition. We add this to our business object/DB later. So if the user has not navigated all the pages, these "checked" items do not get added as pagination limits the "Items" in the grid to those which get bound for that particular page index. My Thoughts: I would rather have some sort of client side pagination, where we can hide/show contents than going to the server and doing a databind every time. Though it will return all the results, the UI will not be clumsy and the grid would have "all the items" during postback Is there a way to do it ? If it were a regular asp.net gridView, can someone point me to a good article which would serve my purpose Ram PS: who else think radgrid is crazy ? (unfortunately I did not make this choice)

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  • Architecture for database analytics

    - by David Cournapeau
    Hi, We have an architecture where we provide each customer Business Intelligence-like services for their website (internet merchant). Now, I need to analyze those data internally (for algorithmic improvement, performance tracking, etc...) and those are potentially quite heavy: we have up to millions of rows / customer / day, and I may want to know how many queries we had in the last month, weekly compared, etc... that is the order of billions entries if not more. The way it is currently done is quite standard: daily scripts which scan the databases, and generate big CSV files. I don't like this solutions for several reasons: as typical with those kinds of scripts, they fall into the write-once and never-touched-again category tracking things in "real-time" is necessary (we have separate toolset to query the last few hours ATM). this is slow and non-"agile" Although I have some experience in dealing with huge datasets for scientific usage, I am a complete beginner as far as traditional RDBM go. It seems that using column-oriented database for analytics could be a solution (the analytics don't need most of the data we have in the app database), but I would like to know what other options are available for this kind of issues.

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  • Big trouble after app update. CoreData migration error

    - by MrBr
    this morning we had a big trouble with our iphone app. We had to even take it off the store. The thing is that we made real small changes to our xcdatamodel. We thought that the update process is automatically taking care about exchanging it the right way until we found out something like CoreData migration exists. We are using the UIManagedDocument to connect to the persistent store. How is it possible to exchange this file with the new one? While we were developing we just uninstalled the whole app from the device and then installed it again and everything worked. How can we simulate this process in the app store with updates? UPDATE I try to set the migration option like this _database = [[UIIManagedDocument alloc] init]; NSMutableDictionary *options = [[NSMutableDictionary alloc] init]; [options setObject:[NSNumber numberWithBool:YES] forKey:NSMigratePersistentStoresAutomaticallyOption], _database.persistentStoreOptions = options; but the app is still crashing with ** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'This NSPersistentStoreCoordinator has no persistent stores. It cannot perform a save operation.'

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  • Multi threading in WCF RIA Services

    - by synergetic
    I use WCF RIA Services to update customer database. In domain service: public void UpdateCustomer(Customer customer) { this.ObjectContext.Customers.AttachAsModified(customer); syncCustomer(customer); } After update, a database trigger launches and depending on the columns updated it may insert a new record in CustomerChange table. syncCustomer(customer) method is executed to check for a new record in the CustomerChange table and if found it will create a text file which contains customer information and forwards that file to external system for import. Now this synchronization may take a time so I wanted to execute it in different thread. So: private void syncCustomer(Customer customer) { this.ObjectContext.SaveChanges(); new Thread(() => syncCustomerInfo(customer.CustomerID)) { IsBackground = true }.Start(); } private void syncCustomerInfo(int customerID) { //Thread.Sleep(2000); //does real job here ... ... } The problem is in most cases syncCustomerInfo method cannot find any new CustomerChange record even if it was definitely there. If I force thread sleep then it finds a new record. I also looked Entity Framework events but the only event provided by object context is SavingChanges which occur before changes are saved. Please suggest me what else to try.

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  • How to get to the key name of a referenced entity property from an entity instance without a datastore read in google app engine?

    - by Sumeet Pareek
    Consider I have the following models - class Team(db.Model): # say I have just 5 teams name = db.StringProperty() class Player(db.Model): # say I have thousands of players name = db.StringProperty() team = db.ReferenceProperty(Team, collection_name="player_set") Key name for each Team entity = 'team_' , and for each Player entity = 'player_' By some prior arrangement I have a Team entity's (key_name, name) mapping available to me. For example (team_01, United States Of America), (team_02, Russia) etc I have to show all the players and their teams on a page. One way of doing this would be - players = Player.all().fetch(1000) # This is 1 DB read for player in players: # This will iterate 1000 times self.response.out.write(player.name) # This is obviously not a DB read self.response.out.write(player.team.name) #This is a total of 1x1000 = 1000 DB reads That is a 1001 DB reads for a silly thing. The interesting part is that when I do a db.to_dict() on players, it shows that for every player in that list there is 'name' of the player and there is the 'key_name' of the team available too. So how can I do the below ?? players = Player.all().fetch(1000) # This is 1 DB read for player in players: # This will iterate 1000 times self.response.out.write(player.name) # This is obviously not a DB read self.response.out.write(team_list[player.<SOME WAY OF GETTING TEAM KEY NAME>]) # Here 'team_list' already has (key_name, name) for all 5 teams I have been struggling with this for a long time. Have read every available documentation. I could just hug the person that can help me here :-) Disclaimer: The above problem description is not a real scenario. It is a simplified arrangement that represents my problem exactly. I have run into it in a rater complex and big GAE appication.

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  • Is Stream.Write thread-safe?

    - by Mike Spross
    I'm working on a client/server library for a legacy RPC implementation and was running into issues where the client would sometimes hang when waiting to a receive a response message to an RPC request message. It turns out the real problem was in my message framing code (I wasn't handling message boundaries correctly when reading data off the underlying NetworkStream), but it also made me suspicious of the code I was using to send data across the network, specifically in the case where the RPC server sends a large amount of data to a client as the result of a client RPC request. My send code uses a BinaryWriter to write a complete "message" to the underlying NetworkStream. The RPC protocol also implements a heartbeat algorithm, where the RPC server sends out PING messages every 15 seconds. The pings are sent out by a separate thread, so, at least in theory, a ping can be sent while the server is in the middle of streaming a large response back to a client. Suppose I have a Send method as follows, where stream is a NetworkStream: public void Send(Message message) { //Write the message to a temporary stream so we can send it all-at-once MemoryStream tempStream = new MemoryStream(); message.WriteToStream(tempStream); //Write the serialized message to the stream. //The BinaryWriter is a little redundant in this //simplified example, but here because //the production code uses it. byte[] data = tempStream.ToArray(); BinaryWriter bw = new BinaryWriter(stream); bw.Write(data, 0, data.Length); bw.Flush(); } So the question I have is, is the call to bw.Write (and by implication the call to the underlying Stream's Write method) atomic? That is, if a lengthy Write is still in progress on the sending thread, and the heartbeat thread kicks in and sends a PING message, will that thread block until the original Write call finishes, or do I have to add explicit synchronization to the Send method to prevent the two Send calls from clobbering the stream?

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  • How to get the most out of a 3 month intern?

    - by firoso
    We've got a software engineering intern coming in who's fairly competent and shows promise. There's one catch: we have him for 3 months full time and can't count on anything past that. He still has a year of school left, which is why we can't say for sure that we have him past 3 months. We have a specific project we're putting him on. How can we maximize his productivity while still giving him a positive learning experience? He wants to learn about development cycles and real-world software engineering. Anything that you think would be critical that you wish you had learned earlier? Nearly six months later: He's preformed admirably and even I have learned a lot from him. Thank you all for the input. Now I want to provide feedback to YOU! He has benefited most from sitting down and writing code. However, he has had a nasty history of bad software engineering practices which I'm trying to replace with good habits (properly finishing a method before moving on, not hacking code together, proper error channeling, etc). He has also really gained a lot by feeling involved in design decisions, even if most of the time they're related to my own design plans.

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  • Java object graph -> xml when direction of object association needs to be reversed.

    - by Sigmoidal
    An application I have been working on has objects with a relationship similar to below. In the real application both objects are JPA entities. class Underlying{} class Thing { private Underlying underlying; public Underlying getUnderlying() { return underlying; } public void setUnderlying(final Underlying underlying) { this.underlying = underlying; } } There is a requirement in the application to create xml of the form: <template> <underlying> <thing/> <thing/> <thing/> </underlying> </template> So we have a situation where the object graph expresses the relationship between Thing and Underlying in the opposite direction to how it's expressed in the xml. I expect to use JAXB to create the xml but ideally I don't want to have to create a new object hierarchy to reflect the associations in the xml. Is there any way to create xml of the form required from the entities in their current form (through the use of xml annotations or something)? I don't have any experience using JAXB but from the limited research I've done it doesn't seem like it's possible to reverse the direction of association in any straightforward way. Any help/advice would be greatly appreciated. One other option that has been suggested is to use XLST to transform the xml into the correct format. I have done no research on this topic as yet but I'll add to the question when I have some more info. Thanks, Matt.

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  • JAX-RS --- How to return JSON and HTTP Status code together?

    - by masato-san
    I'm writing REST web app (Netbean6.9, JAX-RS, Toplink-essential) and trying to return JSON and Http status code. I have code ready and working just to return JSON when HTTP GET Method is called from client. Code snippet @Path("get/id") @GET @Produces("application/json") public M_?? getMachineToUpdate(@PathParam("id") String id) { //some code to return JSON . . return myJson But I also want to return HTTP status code (500, 200, 204 etc) along with returning JSON. I tried using HttpServletResponse object, response.sendError("error message", 500); But this made browser to think it's real 500 so output web page was regular Http 500 error page. What I want to is just to return status code so that my Javascript on client side can handle some logic depending on what HTTP status code is returned. (maybe just to display the error code and message on html page.) Is it possible to do so? or should HTTP status code not be used for such thing?

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  • Screen information while Windows system is locked (.NET)

    - by Matt
    We have a nightly process that updates applications on a user's pc, and that requires bringing the application down and back up again (not looking to get into changing that process). The problem is that we are building a Windows AppBar on launch which requires a valid screen, and when the system is locked there isn't one in the Screen class. So none of the visual effects are enabled and it shows up real ugly. The only way we currently have around this is to detect a locked screen and just spin and wait until the user unlocks the desktop, then continue launching. Leaving it down isn't an option, as this is a key part of our user's workflow, and they expect it to be up and running if they left it that way the night before. Any ideas?? I can't seem to find the display information anywhere, but it has to be stored off someplace, since the user is still logged in. The contents of the Screen.AllScreens array: ** When Locked: Device Name : DISPLAY Primary : True Bits Per Pixel : 0 Bounds : {X=-1280,Y=0,Width=2560,Height=1024} Working Area : {X=0,Y=0,Width=1280,Height=1024} ** When Unlocked: Device Name : \\.\DISPLAY1 Primary : True Bits Per Pixel : 32 Bounds : {X=0,Y=0,Width=1280,Height=1024} Working Area : {X=0,Y=0,Width=1280,Height=994} Device Name : \\.\DISPLAY2 Primary : False Bits Per Pixel : 32 Bounds : {X=-1280,Y=0,Width=1280,Height=1024} Working Area : {X=-1280,Y=0,Width=1280,Height=964}

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  • How to solve generic algebra using solver/library programmatically? Matlab, Mathematica, Wolfram etc?

    - by DevDevDev
    I'm trying to build an algebra trainer for students. I want to construct a representative problem, define constraints and relationships on the parameters, and then generate a bunch of Latex formatted problems from the representation. As an example: A specific question might be: If y < 0 and (x+3)(y-5) = 0, what is x? Answer (x = -3) I would like to encode this as a Latex formatted problem like. If $y<0$ and $(x+constant_1)(y+constant_2)=0$ what is the value of x? Answer = -constant_1 And plug into my problem solver constant_1 > 0, constant_1 < 60, constant_1 = INTEGER constant_2 < 0, constant_2 > -60, constant_2 = INTEGER Then it will randomly construct me pairs of (constant_1, constant_2) that I can feed into my Latex generator. Obviously this is an extremely simple example with no real "solving" but hopefully it gets the point across. Things I'm looking for ideally in priority order * Solve algebra problems * Definition of relationships relatively straight forward * Rich support for latex formatting (not just writing encoded strings) Thanks!

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  • How to encrypt/decrypt a file in Java?

    - by Petike
    Hello, I am writing a Java application which can "encrypt" and consequently "decrypt" whatever binary file. I am just a beginner in the "cryptography" area so I would like to write a very simple application for the beginning. For reading the original file, I would probably use the java.io.FileInputStream class to get the "array of bytes" byte originalBytes[] of the file. Then I would probably use some very simple cipher, for example "shift up every byte by 1" and then I would get the "encrypted" bytes byte encryptedBytes[] and let's say that I would also set a "password" for it, for example "123456789". Next, when somebody wants to "decrypt" that file, he has to enter the password ("123456789") first and after that the file could be decrypted (thus "shift down every byte by 1") and consequently saved to the output file via java.io.FileOutputStream I am just wondering how to "store" the password information to the encrypted file so that the decrypting application knows if the entered password and the "real" password equals? Probably it would be silly to add the password (for example the ASCII ordinal numbers of the password letters) to the beginning of the file (before the encrypted data). So my main question is how to store the password information to the encrypted file?

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  • Event feed implementation - will it scale?

    - by SlappyTheFish
    Situation: I am currently designing a feed system for a social website whereby each user has a feed of their friends' activities. I have two possible methods how to generate the feeds and I would like to ask which is best in terms of ability to scale. Events from all users are collected in one central database table, event_log. Users are paired as friends in the table friends. The RDBMS we are using is MySQL. Standard method: When a user requests their feed page, the system generates the feed by inner joining event_log with friends. The result is then cached and set to timeout after 5 minutes. Scaling is achieved by varying this timeout. Hypothesised method: A task runs in the background and for each new, unprocessed item in event_log, it creates entries in the database table user_feed pairing that event with all of the users who are friends with the user who initiated the event. One table row pairs one event with one user. The problems with the standard method are well known – what if a lot of people's caches expire at the same time? The solution also does not scale well – the brief is for feeds to update as close to real-time as possible The hypothesised solution in my eyes seems much better; all processing is done offline so no user waits for a page to generate and there are no joins so database tables can be sharded across physical machines. However, if a user has 100,000 friends and creates 20 events in one session, then that results in inserting 2,000,000 rows into the database. Question: The question boils down to two points: Is this worst-case scenario mentioned above problematic, i.e. does table size have an impact on MySQL performance and are there any issues with this mass inserting of data for each event? Is there anything else I have missed?

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  • SQL Server Long Query

    - by thormj
    Ok... I don't understand why this query is taking so long (MSSQL Server 2005): [Typical output 3K rows, 5.5 minute execution time] SELECT dbo.Point.PointDriverID, dbo.Point.AssetID, dbo.Point.PointID, dbo.Point.PointTypeID, dbo.Point.PointName, dbo.Point.ForeignID, dbo.Pointtype.TrendInterval, coalesce(dbo.Point.trendpts,5) AS TrendPts, LastTimeStamp = PointDTTM, LastValue=PointValue, Timezone FROM dbo.Point LEFT JOIN dbo.PointType ON dbo.PointType.PointTypeID = dbo.Point.PointTypeID LEFT JOIN dbo.PointData ON dbo.Point.PointID = dbo.PointData.PointID AND PointDTTM = (SELECT Max(PointDTTM) FROM dbo.PointData WHERE PointData.PointID = Point.PointID) LEFT JOIN dbo.SiteAsset ON dbo.SiteAsset.AssetID = dbo.Point.AssetID LEFT JOIN dbo.Site ON dbo.Site.SiteID = dbo.SiteAsset.SiteID WHERE onlinetrended =1 and WantTrend=1 PointData is the biggun, but I thought its definition should allow me to pick up what I want easily enough: CREATE TABLE [dbo].[PointData]( [PointID] [int] NOT NULL, [PointDTTM] [datetime] NOT NULL, [PointValue] [real] NULL, [DataQuality] [tinyint] NULL, CONSTRAINT [PK_PointData_1] PRIMARY KEY CLUSTERED ( [PointID] ASC, [PointDTTM] ASC ) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY] GO CREATE NONCLUSTERED INDEX [IX_PointDataDesc] ON [dbo].[PointData] ( [PointID] ASC, [PointDTTM] DESC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] GO PointData is 550M rows, and Point (source of PointID) is only 28K rows. I tried making an Indexed View, but I can't figure out how to get the Last Timestamp/Value out of it in a compatible way (no Max, no subquery, no CTE). This runs twice an hour, and after it runs I put more data into those 3K PointID's that I selected. I thought about creating LastTime/LastValue tables directly into Point, but that seems like the wrong approach. Am I missing something, or should I rebuild something? (I'm also the DBA, but I know very little about A'ing a DB!)

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