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  • What the best way to wire up Entity Framework database context (model) to ViewModel in MVVM WPF?

    - by hal9k2
    As in the question above: What the best way to wire up Entity Framework database model (context) to viewModel in MVVM (WPF)? I am learning MVVM pattern in WPF, alot of examples shows how to implement model to viewModel, but models in that examples are just simple classes, I want to use MVVM together with entity framework model (base first approach). Whats the best way to wire model to viewModel. Thanks for answers. //ctor of ViewModel public ViewModel() { db = new PackageShipmentDBEntities(); // Entity Framework generated class ListaZBazy = new ObservableCollection<Pack>(db.Packs.Where(w => w.IsSent == false)); } This is my usual ctor of ViewModel, think there is a better way, I was reading about repository pattern, not sure if I can adapt this to WPF MVVM

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  • Selecting Items in a GeoToolkit Driven Map

    - by Geertjan
    When you take a look at all the tools provided by GeoToolkit, you'll be quite impressed. For example, within the US map shown in yesterday's blog entry, you can drill down into individual states by selecting them via the mouse, as shown below: With that, the basis of a more complex application is laid, since all the map-related functionality is handed to you out of the box. The sample referred to yesterday has been updated, if you check it out and run it (assuming you've taken the additional steps mentioned yesterday), you'll see the above. http://java.net/projects/nb-api-samples/sources/api-samples/show/versions/7.3/tutorials/geospatial/geotoolkit/MyGeospatialSystem

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  • Comprehensive system for documentation and handoff of developer project

    - by Uzumaki Naruto
    I work on a technology team that typically develops projects for a period of time, and then hands off to other groups for long-term maintenance and improvements. My team currently uses ad hoc methods of handing off documentations, such as diagrams, API references, etc. Is there a open source solution (or even proprietary one) that enables us to manage: Infrastructure/architecture/software diagrams API documentation Directory structures/file structures Overall documentation summaries in one place? E.g., instead of using multiple systems like Swagger, Wikis, etc. - is there a solution that can seamlessly combine all of these? And enable us to generate a package including all 4 key items with one click to hand off to other teams.

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  • Getting Started Plugging into the "Find in Projects" Dialog

    - by Geertjan
    In case you missed it amidst all the code in yesterday's blog entry, the "Find in Projects" dialog is now pluggable. I think that's really cool. The code yesterday gives you a complete example, but let's break it down a bit and deconstruct down to a very simple hello world scenario. We'll end up with as many extra tabs in the "Find in Projects" dialog as we need, for example, three in this case:  And clicking on any of those extra tabs will, in this simple example, simply show us this: Once we have that, we'll be able to continue adding small bits of code over the next few blog entries until we have something more useful. So, in this blog entry, you'll literally be able to display "Hello World" within a new tab in the "Find in Projects" dialog: import javax.swing.JComponent; import javax.swing.JLabel; import org.netbeans.spi.search.provider.SearchComposition; import org.netbeans.spi.search.provider.SearchProvider; import org.netbeans.spi.search.provider.SearchProvider.Presenter; import org.openide.NotificationLineSupport; import org.openide.util.lookup.ServiceProvider; @ServiceProvider(service = SearchProvider.class) public class ExampleSearchProvider1 extends SearchProvider { @Override public Presenter createPresenter(boolean replaceMode) { return new ExampleSearchPresenter(this); } @Override public boolean isReplaceSupported() { return false; } @Override public boolean isEnabled() { return true; } @Override public String getTitle() { return "Demo Extension 1"; } public class ExampleSearchPresenter extends SearchProvider.Presenter { private ExampleSearchPresenter(ExampleSearchProvider1 sp) { super(sp, true); } @Override public JComponent getForm() { return new JLabel("Hello World"); } @Override public SearchComposition composeSearch() { return null; } @Override public boolean isUsable(NotificationLineSupport nls) { return true; } } } That's it, not much code, works fine in NetBeans IDE 7.2 Beta, and is easier to digest than the big chunk from yesterday. If you make three classes like the above in a NetBeans module, and you install it, you'll have three new tabs in the "Find in Projects" dialog. The only required dependencies are Dialogs API, Lookup API, and Search in Projects API. Read the javadoc linked above and then in next blog entries we'll continue to build out something like the sample you saw in yesterday's blog entry.

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  • Cleaning a dataset of song data - what sort of problem is this?

    - by Rob Lourens
    I have a set of data about songs. Each entry is a line of text which includes the artist name, song title, and some extra text. Some entries are only "extra text". My goal is to resolve as many of these as possible to songs on Spotify using their web API. My strategy so far has been to search for the entry via the API - if there are no results, apply a transformation such as "remove all text between ( )" and search again. I have a list of heuristics and I've had reasonable success with this but as the code gets more and more convoluted I keep thinking there must be a more generic and consistent way. I don't know where to look - any suggestions for what to try, topics to study, buzzwords to google?

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  • Code to simulate a users actions, such as logging in

    - by Gortron
    I've recently begun working on a PHP application, replacing another developer. I believed the application was using an API to communicate with a remote service but when I looked through the code I found that it was using a set of functions to actually log in, fill out forms and submit them as a user might do in a browser. My intention is to replace this code, to use the services API instead. I've considered leaving the code as is and not replace it. It makes me wonder though is this a common practice in the software industry? To have a programme simulate a users actions in a browser to perform a set of actions? It feels to me that this is clever but poor programming, Have any other developers seen this?

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  • LuaJit FFI and hiding C implementation details

    - by wirrbel
    I would like to extend an application using LuaJit FFI. Having seen http://luajit.org/ext_ffi_tutorial.html this is surprisingly easy when comparing this to the Lua C API. So far so good. However I do not plainly want to wrap C functions but provide a higher level API to users writing scripts for the application. Especially I do not want users to be able to access "primitives", i.e. the ffi.* namespace. Is this possible or will that ffi namespace be available to user's Lua scripts? On the issue of Sandboxing Lua I found http://lua-users.org/wiki/SandBoxes which is not talking about FFI though. Furthermore, the plan I have described above is assuming that the introduction of abstraction layers happens on the lua side of code. Is this an advisable approach or would you rather abstract functionality on the statically compiled code (on the C-side)?

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  • Dynamic Bind9 + DHCP

    - by AcidRod75
    i have been working on setup a server for my internal network, so far i have a working isc-dhcp-server that can upgrade a chrooted BIND9 (on the same machine), i need to add some static entries on the DNS, so users can resolve the websites that resides in our DMZ. What i had tryed all ready was to modify the /etc/bind/named.conf.local with this info: // // Do any local configuration here // // Consider adding the 1918 zones here, if they are not used in your // organization //include "/etc/bind/zones.rfc1918"; key DHCP_UPDATER { algorithm HMAC-MD5.SIG-ALG.REG.INT; secret "MySuperSecretHash"; (this is not the real value BTW) }; zone "quality.internal" IN { type master; file "/var/lib/bind/quality.internal.db"; allow-update { key DHCP_UPDATER; }; }; zone "0.10.10.in-addr.arpa" { type master; file "/var/lib/bind/rev.10.10.0.in-addr.arpa"; allow-update { key DHCP_UPDATER; }; }; logging { channel query.log { file "/var/log/named/query.log"; severity debug 3; }; category queries { query.log; }; }; --- EOF ---- then i added this 2 entries: zone "ourserver.internal" IN { type master; file "/var/lib/bind/ourserver.internal.db"; }; zone "0.16.172.in-addr.arpa" { type master; file "/var/lib/bind/rev.172.16.0.in-addr.arpa"; }; ---- EOF ---- So.. i created the files ourserver.internal.db and rev.172.16.0.in-addr.arpa placed them BOTH in /var/lib/bind/ and changed the permisions so the bind user can access them, restated the service... when i do a NSLOOKUP www.ourserver.internal i get: Server: 127.0.0.1 Address: 127.0.0.1#53 ** server can't find www.ourserver.internal: NXDOMAIN BUT when i do a reverse lookup.... Server: 127.0.0.1 Address: 127.0.0.1#53 5.0.16.172.in-addr.arpa name = www.ourserver.internal I do not understand what's wrong. Some help with this will save me from installing a new DNS server at the DMZ JUST to host internal site names- TY in advance BTW: the server i'm using has Ubuntu Server 11.10 fully patched.

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  • The performance implications of IEnumerable vs. IQueryable

    It all started innocently enough. I was implementing a "Older Posts/Newer Posts" feature for my new web site and was writing code like this:IEnumerable<Post> FilterByCategory(IEnumerable<Post> posts, string category) {  if( !string.IsNullOrEmpty(category) ) { return posts.Where(p => p.Category.Contains(category)); }}...  var posts = FilterByCategory(db.Posts, category);  int count = posts.Count();... The "db" was an EF object context object, but it could just as...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • The performance implications of IEnumerable vs. IQueryable

    It all started innocently enough. I was implementing a "Older Posts/Newer Posts" feature for my new web site and was writing code like this:IEnumerable<Post> FilterByCategory(IEnumerable<Post> posts, string category) {  if( !string.IsNullOrEmpty(category) ) { return posts.Where(p => p.Category.Contains(category)); }}...  var posts = FilterByCategory(db.Posts, category);  int count = posts.Count();... The "db" was an EF object context object, but it could just as...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Servlet : Usage of Constants.java class vs context param

    - by Pongsakorn Semsuwan
    I'm just wondering whether to keep some of my variables in Constants class or keep it in web.xml Say, I want to keep a variable of Facebook graph API prefix or api_key, client_id From my understand, the difference between Constants.java and web.xml is web.xml is easier to rewrite on compile using ant. So, you can replace your variables in web.xml according to what environment you are building you app for. (client_id varies by development environment/production environment, for example) If I understand it right, then Facebook graph API prefix should be kept in Constants.java (because it always is "https://graph.facebook.com/") and api_key, client_id should be kept in web.xml? What's the proper way to use them?

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  • Is hierarchical product backlog a good idea in TFS 2012-2013?

    - by Matías Fidemraizer
    I'd like to validate I'm not in the wrong way. My team project is using Visual Studio Scrum 2.x. Since each area/product has a lot of kind of requirements (security, user interface, HTTP/REST services...), I tried to manage this creating "parent backlogs" which are "open forever" and they contain generic requirements. Those parent backlogs have other "open forever" backlogs, and/or sprint backlogs. For example: HTTP/REST Services (forever) ___ Profiles API (forever) ________ POST profile (forever) _______________ We need a basic HTTP/REST profiles' API to register new user profiles (sprint backlog) Is it the right way of organizing the product backlog? Note: I know there're different points of view and that would be right for some and wrong for others. I'm looking for validation about if this is a possible good practice on TFS with Visual Studio Scrum.

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  • How to Implement Project Type "Copy", "Move", "Rename", and "Delete"

    - by Geertjan
    You've followed the NetBeans Project Type Tutorial and now you'd like to let the user copy, move, rename, and delete the projects conforming to your project type. When they right-click a project, they should see the relevant menu items and those menu items should provide dialogs for user interaction, followed by event handling code to deal with the current operation. Right now, at the end of the tutorial, the "Copy" and "Delete" menu items are present but disabled, while the "Move" and "Rename" menu items are absent: The NetBeans Project API provides a built-in mechanism out of the box that you can leverage for project-level "Copy", "Move", "Rename", and "Delete" actions. All the functionality is there for you to use, while all that you need to do is a bit of enablement and configuration, which is described below. To get started, read the following from the NetBeans Project API: http://bits.netbeans.org/dev/javadoc/org-netbeans-modules-projectapi/org/netbeans/spi/project/ActionProvider.html http://bits.netbeans.org/dev/javadoc/org-netbeans-modules-projectapi/org/netbeans/spi/project/CopyOperationImplementation.html http://bits.netbeans.org/dev/javadoc/org-netbeans-modules-projectapi/org/netbeans/spi/project/MoveOrRenameOperationImplementation.html http://bits.netbeans.org/dev/javadoc/org-netbeans-modules-projectapi/org/netbeans/spi/project/DeleteOperationImplementation.html Now, let's do some work. For each of the menu items we're interested in, we need to do the following: Provide enablement and invocation handling in an ActionProvider implementation. Provide appropriate OperationImplementation classes. Add the new classes to the Project Lookup. Make the Actions visible on the Project Node. Run the application and verify the Actions work as you'd like. Here we go: Create an ActionProvider. Here you specify the Actions that should be supported, the conditions under which they should be enabled, and what should happen when they're invoked, using lots of default code that lets you reuse the functionality provided by the NetBeans Project API: class CustomerActionProvider implements ActionProvider { @Override public String[] getSupportedActions() { return new String[]{ ActionProvider.COMMAND_RENAME, ActionProvider.COMMAND_MOVE, ActionProvider.COMMAND_COPY, ActionProvider.COMMAND_DELETE }; } @Override public void invokeAction(String string, Lookup lkp) throws IllegalArgumentException { if (string.equalsIgnoreCase(ActionProvider.COMMAND_RENAME)) { DefaultProjectOperations.performDefaultRenameOperation( CustomerProject.this, ""); } if (string.equalsIgnoreCase(ActionProvider.COMMAND_MOVE)) { DefaultProjectOperations.performDefaultMoveOperation( CustomerProject.this); } if (string.equalsIgnoreCase(ActionProvider.COMMAND_COPY)) { DefaultProjectOperations.performDefaultCopyOperation( CustomerProject.this); } if (string.equalsIgnoreCase(ActionProvider.COMMAND_DELETE)) { DefaultProjectOperations.performDefaultDeleteOperation( CustomerProject.this); } } @Override public boolean isActionEnabled(String command, Lookup lookup) throws IllegalArgumentException { if ((command.equals(ActionProvider.COMMAND_RENAME))) { return true; } else if ((command.equals(ActionProvider.COMMAND_MOVE))) { return true; } else if ((command.equals(ActionProvider.COMMAND_COPY))) { return true; } else if ((command.equals(ActionProvider.COMMAND_DELETE))) { return true; } return false; } } Importantly, to round off this step, add "new CustomerActionProvider()" to the "getLookup" method of the project. If you were to run the application right now, all the Actions we're interested in would be enabled (if they are visible, as described in step 4 below) but when you invoke any of them you'd get an error message because each of the DefaultProjectOperations above looks in the Lookup of the Project for the presence of an implementation of a class for handling the operation. That's what we're going to do in the next step. Provide Implementations of Project Operations. For each of our operations, the NetBeans Project API lets you implement classes to handle the operation. The dialogs for interacting with the project are provided by the NetBeans project system, but what happens with the folders and files during the operation can be influenced via the operations. Below are the simplest possible implementations, i.e., here we assume we want nothing special to happen. Each of the below needs to be in the Lookup of the Project in order for the operation invocation to succeed. private final class CustomerProjectMoveOrRenameOperation implements MoveOrRenameOperationImplementation { @Override public List<FileObject> getMetadataFiles() { return new ArrayList<FileObject>(); } @Override public List<FileObject> getDataFiles() { return new ArrayList<FileObject>(); } @Override public void notifyRenaming() throws IOException { } @Override public void notifyRenamed(String nueName) throws IOException { } @Override public void notifyMoving() throws IOException { } @Override public void notifyMoved(Project original, File originalPath, String nueName) throws IOException { } } private final class CustomerProjectCopyOperation implements CopyOperationImplementation { @Override public List<FileObject> getMetadataFiles() { return new ArrayList<FileObject>(); } @Override public List<FileObject> getDataFiles() { return new ArrayList<FileObject>(); } @Override public void notifyCopying() throws IOException { } @Override public void notifyCopied(Project prjct, File file, String string) throws IOException { } } private final class CustomerProjectDeleteOperation implements DeleteOperationImplementation { @Override public List<FileObject> getMetadataFiles() { return new ArrayList<FileObject>(); } @Override public List<FileObject> getDataFiles() { return new ArrayList<FileObject>(); } @Override public void notifyDeleting() throws IOException { } @Override public void notifyDeleted() throws IOException { } } Also make sure to put the above methods into the Project Lookup. Check the Lookup of the Project. The "getLookup()" method of the project should now include the classes you created above, as shown in bold below: @Override public Lookup getLookup() { if (lkp == null) { lkp = Lookups.fixed(new Object[]{ this, new Info(), new CustomerProjectLogicalView(this), new CustomerCustomizerProvider(this), new CustomerActionProvider(), new CustomerProjectMoveOrRenameOperation(), new CustomerProjectCopyOperation(), new CustomerProjectDeleteOperation(), new ReportsSubprojectProvider(this), }); } return lkp; } Make Actions Visible on the Project Node. The NetBeans Project API gives you a number of CommonProjectActions, including for the actions we're dealing with. Make sure the items in bold below are in the "getActions" method of the project node: @Override public Action[] getActions(boolean arg0) { return new Action[]{ CommonProjectActions.newFileAction(), CommonProjectActions.copyProjectAction(), CommonProjectActions.moveProjectAction(), CommonProjectActions.renameProjectAction(), CommonProjectActions.deleteProjectAction(), CommonProjectActions.customizeProjectAction(), CommonProjectActions.closeProjectAction() }; } Run the Application. When you run the application, you should see this: Let's now try out the various actions: Copy. When you invoke the Copy action, you'll see the dialog below. Provide a new project name and location and then the copy action is performed when the Copy button is clicked below: The message you see above, in red, might not be relevant to your project type. When you right-click the application and choose Branding, you can find the string in the Resource Bundles tab, as shown below: However, note that the message will be shown in red, no matter what the text is, hence you can really only put something like a warning message there. If you have no text at all, it will also look odd.If the project has subprojects, the copy operation will not automatically copy the subprojects. Take a look here and here for similar more complex scenarios. Move. When you invoke the Move action, the dialog below is shown: Rename. The Rename Project dialog below is shown when you invoke the Rename action: I tried it and both the display name and the folder on disk are changed. Delete. When you invoke the Delete action, you'll see this dialog: The checkbox is not checkable, in the default scenario, and when the dialog above is confirmed, the project is simply closed, i.e., the node hierarchy is removed from the application. However, if you truly want to let the user delete the project on disk, pass the Project to the DeleteOperationImplementation and then add the children of the Project you want to delete to the getDataFiles method: private final class CustomerProjectDeleteOperation implements DeleteOperationImplementation { private final CustomerProject project; private CustomerProjectDeleteOperation(CustomerProject project) { this.project = project; } @Override public List<FileObject> getDataFiles() { List<FileObject> files = new ArrayList<FileObject>(); FileObject[] projectChildren = project.getProjectDirectory().getChildren(); for (FileObject fileObject : projectChildren) { addFile(project.getProjectDirectory(), fileObject.getNameExt(), files); } return files; } private void addFile(FileObject projectDirectory, String fileName, List<FileObject> result) { FileObject file = projectDirectory.getFileObject(fileName); if (file != null) { result.add(file); } } @Override public List<FileObject> getMetadataFiles() { return new ArrayList<FileObject>(); } @Override public void notifyDeleting() throws IOException { } @Override public void notifyDeleted() throws IOException { } } Now the user will be able to check the checkbox, causing the method above to be called in the DeleteOperationImplementation: Hope this answers some questions or at least gets the discussion started. Before asking questions about this topic, please take the steps above and only then attempt to apply them to your own scenario. Useful implementations to look at: http://kickjava.com/src/org/netbeans/modules/j2ee/clientproject/AppClientProjectOperations.java.htm https://kenai.com/projects/nbandroid/sources/mercurial/content/project/src/org/netbeans/modules/android/project/AndroidProjectOperations.java

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  • exact point oh a rotating sphere

    - by nkint
    I have a sphere that represents the heart textured with real pictures. It's rotating about the x axis, and when user click down it has to show me the exact place he clicked on. For example if he clicked on Singapore and the system should be able to: understand that user clicked on the sphere (OK, I'll do it with unProject) understand where user clicked on the sphere (ray-sphere collision?) and take into account the rotation transform sphere-coordinate to some coordinate system good for some web-api service ask to api (OK, this is the simpler thing for me ;-) some advice?

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  • GeoToolkit Demo Embedded in an Application Framework via Maven

    - by Geertjan
    As a follow on to yesterday's blog entry, here's the equivalent starter application for GeoToolkit (also known as Geotk) on the NetBeans Platform, which ends up looking like this: The above is a border.shp file I found on-line, while here's a USA states shape file rendered in the application: Note that the navigation bar is also included, though that could later be migrated into the menu bar of the NetBeans Platform.  Download the Maven based NetBeans Platform application with GeoToolkit integration here: http://java.net/projects/nb-api-samples/sources/api-samples/show/versions/7.3/tutorials/geospatial/geotoolkit/MyGeospatialSystem It was quite tricky getting this sample together, parts of it, especially the installer, which creates the database, comes from the Puzzle GIS project, while the files come from on-line locations, with the JAI-related dependencies providing problems of their own. But it's definitely a starting point and you now have the basic Maven structure needed for getting started with GeoToolkit in the context of all the services and components provided by the NetBeans Platform.  Many thanks to Johann Sorel for his patience and help. 

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  • Even More Steroids for JEditorPane

    - by Geertjan
    Got some help from Ralph today and now the JEditorPane is as I want it, e.g., code folds are now supported once you click in the JEditorPane, though there are still some side effects, since this is not how anyone anticipated NetBeans editor APIs being used. But, so far, the side effects (e.g., now the hyperlinks work, but they open a new JavaScript file when you click on one of them, instead of jumping within the JEditorPane itself) are not so terrible. Error checking is also done now, which wasn't there before, i.e., red underlines and error annotations in the right margin. And maybe it's my imagination, but the editor feels a lot snappier, e.g., in code completion, than before. I've checked in the changes, they're all in this file: http://java.net/projects/nb-api-samples/sources/api-samples/content/versions/7.3/misc/CMSBackOffice2/CMSBackOffice2-editor/src/main/java/com/mycompany/cmsbackoffice2editor/GeneralTab.java

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  • Map, Set use cases in a general web app

    - by user2541902
    I am currently working on my own Java web app (to be shown in interview to get a Java job). So I've not worked on Java in professional environment, so no guidance. I have database, entity classes, JPA relationships. Use cases are like, user has albums, album has pics, user has locations, location has co-ordinates etc. I used List (ArrayList) everywhere. I can do anything with List and DB, get some entry, find etc. For example, I will keep the list of users in List, then use queries to get some entry (why would I keep them in Map with id/email as key?). I know very well the working and features, implementing classes of Map, Set. I can use them for solving some algorithm, processing some data etc. In interviews, I get asked have you worked with these, where have you used them etc. So, Please tell me cases where they should be used (DB or any popular real use case).

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  • SS7(M3UA, SCCP, TCAP, MAP) Stack

    - by Ammar Hameed
    I'm building an open source SMSC from scratch; it's almost finished, The SRI and the forwardSM operations are working, but I still have few things to do for the receiving part. I've built the SS7 stack already, but I'm using DB for saving the TCAP transactions IDs to be updated later to get/generate responses. My approach is this: I created memory table (heap table), saved the TCAP TID in the database, then compared the received TCAP TID with the TIDs saved in the database and then decide whether to end the TCAP session or continue. What is the best way to implement it? I'm thinking of doubly linked list that holds the TCAP TID. Am I going towards the right direction, or should I use another technique other than database or D-linked list? Should I leave it as it is, and let the database do the job for saving the TIDs? Please note that I'm using SCTP implementation available on Linux (lsctp) as a transport protocol, the language I'm using is C and the DB is MYSQL.

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  • Is there other ways to do insert/update/delete on a remote oracle database?

    - by gunbuster363
    I asked a question recently concerning the speed of execution of insert/update/delete using JDBC driver in a remote machine, but the problem cannot be solved easily. I would like to ask, is there any other way to execute the insert/update/delete to the oracle? The current situation is this: the DB is on a seperate machine than the java program used to update the DB. I looked up the internet and found people suggesting using pure sql or pl/sql to do the update, is that possible? And do we need to operate the sql or pl/sql in a local machine? Because I have no knowledge about pl/sql, so I am not sure if we can create some kind of script and call it on a remote machine. Let say the situation is like this: the input data is on machine A, and the original java program are also on machine A, but the oracle is on machine B. is there any other approach other than JDBC?

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  • Does my approach for building a real time monitoring system make sense? [closed]

    - by sameer
    I am developing an application that will display a dashboard that will display data from different SQL databases. This needs to happen in almost real time, our refresh time is about 5 minutes. My approach so far is: Develop a Windows service to accumulate the data from various SQL Server instances. Persist those details into a SQL DB, from which the dashboard will display them on the web page. Trigger fetching of data from the Windows service will every x minutes. The details of the SQL Server instances will be stored in the SQL DB which the Windows service will be referring. Does my approach make sense?

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  • Collaborative Whiteboard using WebSocket in GlassFish 4 - Text/JSON and Binary/ArrayBuffer Data Transfer (TOTD #189)

    - by arungupta
    This blog has published a few blogs on using JSR 356 Reference Implementation (Tyrus) as its integrated in GlassFish 4 promoted builds. TOTD #183: Getting Started with WebSocket in GlassFish TOTD #184: Logging WebSocket Frames using Chrome Developer Tools, Net-internals and Wireshark TOTD #185: Processing Text and Binary (Blob, ArrayBuffer, ArrayBufferView) Payload in WebSocket TOTD #186: Custom Text and Binary Payloads using WebSocket One of the typical usecase for WebSocket is online collaborative games. This Tip Of The Day (TOTD) explains a sample that can be used to build such games easily. The application is a collaborative whiteboard where different shapes can be drawn in multiple colors. The shapes drawn on one browser are automatically drawn on all other peer browsers that are connected to the same endpoint. The shape, color, and coordinates of the image are transfered using a JSON structure. A browser may opt-out of sharing the figures. Alternatively any browser can send a snapshot of their existing whiteboard to all other browsers. Take a look at this video to understand how the application work and the underlying code. The complete sample code can be downloaded here. The code behind the application is also explained below. The web page (index.jsp) has a HTML5 Canvas as shown: <canvas id="myCanvas" width="150" height="150" style="border:1px solid #000000;"></canvas> And some radio buttons to choose the color and shape. By default, the shape, color, and coordinates of any figure drawn on the canvas are put in a JSON structure and sent as a message to the WebSocket endpoint. The JSON structure looks like: { "shape": "square", "color": "#FF0000", "coords": { "x": 31.59999942779541, "y": 49.91999053955078 }} The endpoint definition looks like: @WebSocketEndpoint(value = "websocket",encoders = {FigureDecoderEncoder.class},decoders = {FigureDecoderEncoder.class})public class Whiteboard { As you can see, the endpoint has decoder and encoder registered that decodes JSON to a Figure (a POJO class) and vice versa respectively. The decode method looks like: public Figure decode(String string) throws DecodeException { try { JSONObject jsonObject = new JSONObject(string); return new Figure(jsonObject); } catch (JSONException ex) { throw new DecodeException("Error parsing JSON", ex.getMessage(), ex.fillInStackTrace()); }} And the encode method looks like: public String encode(Figure figure) throws EncodeException { return figure.getJson().toString();} FigureDecoderEncoder implements both decoder and encoder functionality but thats purely for convenience. But the recommended design pattern is to keep them in separate classes. In certain cases, you may even need only one of them. On the client-side, the Canvas is initialized as: var canvas = document.getElementById("myCanvas");var context = canvas.getContext("2d");canvas.addEventListener("click", defineImage, false); The defineImage method constructs the JSON structure as shown above and sends it to the endpoint using websocket.send(). An instant snapshot of the canvas is sent using binary transfer with WebSocket. The WebSocket is initialized as: var wsUri = "ws://localhost:8080/whiteboard/websocket";var websocket = new WebSocket(wsUri);websocket.binaryType = "arraybuffer"; The important part is to set the binaryType property of WebSocket to arraybuffer. This ensures that any binary transfers using WebSocket are done using ArrayBuffer as the default type seem to be blob. The actual binary data transfer is done using the following: var image = context.getImageData(0, 0, canvas.width, canvas.height);var buffer = new ArrayBuffer(image.data.length);var bytes = new Uint8Array(buffer);for (var i=0; i<bytes.length; i++) { bytes[i] = image.data[i];}websocket.send(bytes); This comprehensive sample shows the following features of JSR 356 API: Annotation-driven endpoints Send/receive text and binary payload in WebSocket Encoders/decoders for custom text payload In addition, it also shows how images can be captured and drawn using HTML5 Canvas in a JSP. How could this be turned in to an online game ? Imagine drawing a Tic-tac-toe board on the canvas with two players playing and others watching. Then you can build access rights and controls within the application itself. Instead of sending a snapshot of the canvas on demand, a new peer joining the game could be automatically transferred the current state as well. Do you want to build this game ? I built a similar game a few years ago. Do somebody want to rewrite the game using WebSocket APIs ? :-) Many thanks to Jitu and Akshay for helping through the WebSocket internals! Here are some references for you: JSR 356: Java API for WebSocket - Specification (Early Draft) and Implementation (already integrated in GlassFish 4 promoted builds) Subsequent blogs will discuss the following topics (not necessary in that order) ... Error handling Interface-driven WebSocket endpoint Java client API Client and Server configuration Security Subprotocols Extensions Other topics from the API

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  • What HTML and CSS markup is best for SEO for a list of questions (like on Stack Exchange sites)

    - by Oleg9
    On the StackOverflow a question block (in the q-list on the index page and so on) represented by the following html code: <div class="question-summary narrow tagged-interesting" id="question-summary-19832613"> <div onclick="window.location.href='/questions/19832613/how-to-display-only-transit-routesfor-trains-in-google-maps-api'" class="cp"> <div class="votes"> <div class="mini-counts">0</div> <div>votes</div> </div> <div class="status unanswered"> <div class="mini-counts">0</div> <div>answers</div> </div> <div class="views"> <div class="mini-counts">3</div> <div>views</div> </div> </div> <div class="summary"> <h3>...</h3> <div class="tags t-javascript t-google-maps t-google t-google-maps-api-3"> </div> <div class="started"> <a href="/questions/19832613/how-to-display-only-transit-routesfor-trains-in-google-maps-api" class="started-link"><span title="2013-11-07 09:52:29Z" class="relativetime">1 min ago</span></a> <a href="/users/1309392/shirish">Shirish</a> <span class="reputation-score" title="reputation score " dir="ltr">189</span> </div> </div> </div> It uses float positioning. My questions is: Would use of css styled tables be a better choice? (It's a table, isn't it?) Or it just depends on what are you prefer to use and doesn't affect the technical side (search engines or something)? The background information (such as number of views, votes etc.) comes first in the code. And I know that search engines have a limit at viewing each page. So would it better to place div's depending on their importance and then markup them on the page using css methods (like negative margins and absolute positioning)? Or it isn't so important in this instance?

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