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• handling pointer to member functions within hierachy in C++

  - by anatoli

  Hi, I'm trying to code the following situation: I have a base class providing a framework for handling events. I'm trying to use an array of pointer-to-member-functions for that. It goes as following: class EH { // EventHandler virtual void something(); // just to make sure we get RTTI public: typedef void (EH::*func_t)(); protected: func_t funcs_d[10]; protected: void register_handler(int event_num, func_t f) { funcs_d[event_num] = f; } public: void handle_event(int event_num) { (this->*(funcs_d[event_num]))(); } }; Then the users are supposed to derive other classes from this one and provide handlers: class DEH : public EH { public: typedef void (DEH::*func_t)(); void handle_event_5(); DEH() { func_t f5 = &DEH::handle_event_5; register_handler(5, f5); // doesn't compile ........ } }; This code wouldn't compile, since DEH::func_t cannot be converted to EH::func_t. It makes perfect sense to me. In my case the conversion is safe since the object under this is really DEH. So I'd like to have something like that: void EH::DEH_handle_event_5_wrapper() { DEH *p = dynamic_cast<DEH *>(this); assert(p != NULL); p->handle_event_5(); } and then instead of func_t f5 = &DEH::handle_event_5; register_handler(5, f5); // doesn't compile in DEH::DEH() put register_handler(5, &EH::DEH_handle_event_5_wrapper); So, finally the question (took me long enough...): Is there a way to create those wrappers (like EH::DEH_handle_event_5_wrapper) automatically? Or to do something similar? What other solutions to this situation are out there? Thanks.

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• Exception handling in Spring MVC with 3 layer architecture

  - by Chorochrondochor

  I am building a simple web applications with 3 layers - DAO, Service, MVC. When in my Controller I want to delete menu group and it contains menus I am getting ConstraintViolationException. Where should I handle this exception? In DAO, Service, or in Controller? Currently I am handling the exception in Controller. My code below. DAO method for deleting menu groups: @Override public void delete(E e){ if (e == null){ throw new DaoException("Entity can't be null."); } getCurrentSession().delete(e); } Service method for deleting menu groups: @Override @Transactional(readOnly = false) public void delete(MenuGroupEntity menuGroupEntity) { menuGroupDao.delete(menuGroupEntity); } Controller method for deleting menu groups in Controller: @RequestMapping(value = "/{menuGroupId}/delete", method = RequestMethod.GET) public ModelAndView delete(@PathVariable Long menuGroupId, RedirectAttributes redirectAttributes){ MenuGroupEntity menuGroupEntity = menuGroupService.find(menuGroupId); if (menuGroupEntity != null){ try { menuGroupService.delete(menuGroupEntity); redirectAttributes.addFlashAttribute("flashMessage", "admin.menu-group-deleted"); redirectAttributes.addFlashAttribute("flashMessageType", "success"); } catch (Exception e){ redirectAttributes.addFlashAttribute("flashMessage", "admin.menu-group-could-not-be-deleted"); redirectAttributes.addFlashAttribute("flashMessageType", "danger"); } } return new ModelAndView("redirect:/admin/menu-group"); }

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• Any guidelines for handling the Headset and Bluetooth AVRC transport controls in Android 2.2

  - by StefanK

  I am trying to figure out what is the correct (new) approach for handling the Intent.ACTION_MEDIA_BUTTON in Froyo. In pre 2.2 days we had to register a BroadcastReceiver (either permanently or at run-time) and the Media Button events would arrive, as long as no other application intercepts them and aborts the broadcast. Froyo seems to still somewhat support that model (at least for the wired headset), but it also introduces the registerMediaButtonEventReceiver, and unregisterMediaButtonEventReceiver methods that seem to control the "transport focus" between applications. During my experiments, using registerMediaButtonEventReceiver does cause both the bluetooth and the wired headset button presses to be routed to the application's broadcast receiver (the app gets the "transport focus"), but it looks like any change in the audio routing (for example unplugging the headset) shits the focus back to the default media player. What is the logic behind the implementation in Android 2.2? What is correct way to handle transport controls? Do we have to detect the change in the audio routing and try to re-gain the focus? This is an issue that any 3rd party media player on the Android platform has to deal with, so I hope that somebody (probably a Google Engineer) can provide some guidelines that we can all follow. Having a standard approach may make headset button controls a bit more predictable for the end users. Stefan

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• How to use interfaces in exception handling

  - by vikp

  Hi, I'm working on the exception handling layer for my application. I have read few articles on interfaces and generics. I have used inheritance before quite a lot and I'm comfortable with in that area. I have a very brief design that I'm going to implement: public interface IMyExceptionLogger { public void LogException(); // Helper methods for writing into files,db, xml } I'm slightly confused what I should be doing next. public class FooClass: IMyExceptionLogger { // Fields // Constructors } Should I implement LogException() method within FooClass? If yes, than I'm struggling to see how I'm better of using an interface instead of the concrete class... I have a variety of classes that will make a use of that interface, but I don't want to write an implementation of that interface within each class. In the same time If I implement an interface in one class, and then use that class in different layers of the application I will be still using concrete classes instead of interfaces, which is a bad OO design... I hope this makes sense. Any feedback and suggestions are welcome. Please notice that I'm not interested in using net4log or its competitors because I'm doing this to learn. Thank you Edit: Wrote some more code. So I will implement variety of loggers with this interface, i.e. DBExceptionLogger, CSVExceptionLogger, XMLExceptionLogger etc. Than I will still end up with concrete classes that I will have to use in different layers of my application.

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• Event Dispatching, void pointer and alternatives

  - by PeeS

  i have my event dispatching / handling functionality working fine, but there is one issue that i need to resolve. Long story short, here are the details. // The event structure struct tEventMessage { // Type of the event int Type; // (void*) Allows those to be casted into per-Type objects void *pArgument1; void *pArgument2; }; I am sending events from different modules in my engine by using the above structure, which requires a pointer to an argument. All messages are queued, and then dispatched on the next ::Tick(). It works fine, untill i try to send something that doesn't exist in next ::Tick, for example: When a mouse click is being handled, it calculates the click coordinates in world space. This is being sent with a pointer to a vector representing that position, but after my program quits that method, this pointer gets invalid obviously, cause local CVector3 is destructed: CVector2 vScreenSpacePosition = vAt; CVector3 v3DPositionA = CVector3(0,0,0); CVector3 v3DPositionB = CVector3(0,0,0); // Screen space to World space calculation for depth zNear v3DPositionA = CMath::UnProject(vScreenSpacePosition, m_vScreenSize, m_Level.GetCurrentCamera()->getViewMatrix(), m_Level.GetCurrentCamera()->getProjectionMatrix(), -1.0 ); // Screen space to World space calculation for depth zFar v3DPositionB = CMath::UnProject(vScreenSpacePosition, m_vScreenSize, m_Level.GetCurrentCamera()->getViewMatrix(), m_Level.GetCurrentCamera()->getProjectionMatrix(), 1.0); // Send zFar position and ScreenSpace position to the handlers // Obviously both vectors won't be valid after this method quits.. CEventDispatcher::Get()->SendEvent(CIEventHandler::EVENT_SYSTEM_FINGER_DOWN, static_cast<void*>(&v3DPositionB), static_cast<void*>(&vScreenSpacePosition)); What i want to ask is, if there is any chance i could make my tEventMessage more 'template', so i can handle sending objects like in the above situation + use what is already implemented? Can't figure it out at the moment.. What else can be done here to allow me to pass some locally available data ? Please can somebody shed a bit of light on this please?

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• Is it OK to set state within Event Raising methods?

  - by Greg

  I ran across this pattern in the code of a library I'm using. It sets state within the event raising method, but only if the event is not null. protected virtual void OnMyEvent(EventArgs e) { if(MyEvent != null) { State = "Executing"; // Only sets state if MyEvent != null. MyEvent(this,e); } } Which means that the state is not set when overriding the method: protected override void OnMyEvent(EventArgs e) { base.OnMyEvent(e); Debug.Assert( State == "Executing" ); // This fails } but is only set when handling the event: foo.MyEvent += (o, args) => Debug.Assert(State == "Executing"); // This passes Setting state within the if(MyEvent != null) seems like bad form, but I've checked the Event Design Guidelines and it doesn't mention this. Do you think this code is incorrect? If so, why? (Reference to design guidelines would be helpful). Edit for Context: It's a Control, I'm trying to create subclass of it, and the state that it's setting is calling EnsureChildControls() conditionally based upon there being an event handler. I can call EnsureChildControls() myself, but I consider that something of a hack.

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• How to show useful error messages from a database error callback in Phonegap?

  - by Magnus Smith

  Using Phonegap you can set a function to be called back if the whole database transaction or the individual SQL statement errors. I'd like to know how to get more information about the error. I have one generic error-handling function, and lots of different SELECTs or INSERTs that may trigger it. How can I tell which one was at fault? It is not always obvious from the error message. My code so far is... function get_rows(tx) { tx.executeSql("SELECT * FROM Blah", [], lovely_success, statement_error); } function add_row(tx) { tx.executeSql("INSERT INTO Blah (1, 2, 3)", [], carry_on, statement_error); } function statement_error(tx, error) { alert(error.code + ' / ' + error.message); } From various examples I see the error callback will be passed a transaction object and an error object. I read that .code can have the following values: UNKNOWN_ERR = 0 DATABASE_ERR = 1 VERSION_ERR = 2 TOO_LARGE_ERR = 3 QUOTA_ERR = 4 SYNTAX_ERR = 5 CONSTRAINT_ERR = 6 TIMEOUT_ERR = 7 Are there any other properties/methods of the error object? What are the properties/methods of the transaction object at this point? I can't seem to find a good online reference for this. Certainly not on the Phonegap website!

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• Task Parallel Library exception handling

  - by user1680766

  When handling exceptions in TPL tasks I have come across two ways to handle exceptions. The first catches the exception within the task and returns it within the result like so: var task = Task<Exception>.Factory.StartNew( () => { try { // Do Something return null; } catch (System.Exception e) { return e; } }); task.ContinueWith( r => { if (r.Result != null) { // Handle Exception } }); The second is the one shown within the documentation and I guess the proper way to do things: var task = Task.Factory.StartNew( () => { // Do Something }); task.ContinueWith( r => { if (r.Exception != null) { // Handle Aggregate Exception r.Exception.Handle(y => true); } }); I am wondering if there is anything wrong with the first approach? I have received 'unhandled aggregate exception' exceptions every now and again using this technique and was wondering how this can happen?

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• Handling nulls in Datawarehouse

  - by rrydman

  I'd like to ask your input on what the best practice is for handling null or empty data values when it pertains to data warehousing and SSIS/SSAS. I have several fact and dimension tables that contain null values in different rows. Specifics: 1) What is the best way to handle null date/times values? Should I make a 'default' row in my time or date dimensions and point SSIS to the default row when there is a null found? 2) What is the best way to handle nulls/empty values inside of dimension data. Ex: I have some rows in an 'Accounts' dimensions that have empty (not NULL) values in the Account Name column. Should I convert these empty or null values inside the column to a specific default value? 3) Similar to point 1 above - What should I do if I end up with a Facttable row that has no record in one of the dimension columns? Do I need default dimension records for each dimension in case this happens? 4) Any suggestion or tips in regards to how to handle these operation in Sql server integration services (SSIS)? Best data flow configurations or best transformation objects to use would be helpful. Thanks :-)

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• INotifyPropertyChanged event listener within respective class not firing on client side (silverlight)

  - by Rob

  I'm trying to work out if there's a simple way to internalize the handling of a property change event on a Custom Entity as I need to perform some bubbling of the changes to a child collection within the class when the Background Property is changed via a XAML binding: public class MyClass : INotifyPropertyChanged { [Key] public int MyClassId { get; set; } [DataMember] public ObservableCollection<ChildMyClass> MyChildren { get; set; } public string _backgroundColor; [DataMember] public string BackgroundColor { get { return this._backgroundColor; } set { this._backgroundColor = value; if (this.PropertyChanged != null) { this.PropertyChanged(this, new PropertyChangedEventArgs("BackgroundColor")); } } } public MyClass() { this.BackgroundColor = "#FFFFFFFF"; this.PropertyChanged += MyClass_PropertyChanged; } public event PropertyChangedEventHandler PropertyChanged; void MyClass_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e) { //Do something here - fires client side but not server side } } I can listen to the event by externalizing it without any problems but it's an ugly way to handle something that want to set and forget inside my class e.g.: public class SomeOtherClass { public SomeOtherClass() { MyClass mc = new MyClass(); mc.PropertyChanged += MyClass_PropertyChanged; } void MyClass_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e) { MyClass mc = (MyClass)sender; mc.UpdateChildren(); } }

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• How to catch this low level MySQL (?) error in PHP/Magento

  - by andnil

  When I'm executing the following statement in Magento with a really large $sku, the execution terminates without any errors thrown what so ever. There are no errors in either Magento's, Apache's or PHP's error logs. Mage::getModel('catalog/product')-loadByAttribute('sku', $sku); Question: How do I catch the error? I've tried to set custom error handlers, and for testing purposes I've also managed to trigger error situations where each of the error handler functions are invoked. But when running the previously mentioned Magento code with a large $sku, none of the error handling functions are executed. error_reporting( -1 ); set_error_handler( array( 'Error', 'captureNormal' ) ); set_exception_handler( array( 'Error', 'captureException' ) ); register_shutdown_function( array( 'Error', 'captureShutdown' ) ); For completeness, this is the $sku I'm passing to loadByAttribute(). (The sku is invalid, but that is not the issue) 1- 9685 0102046|1- 9685 1212100|1- 9685 1212092|1- 9685 1212096|1- 9685 1102100|1- 9685 1102108|1- 9685 1102112|1- 9685 1102092|1- 9685 0102048|1- 9685 0102054|1- 9685 0102056|1- 9685 0102058|1- 9685 1212104|1- 9685 1212108|1- 9685 0212058|1- 9685 0104050|1- 9685 0212050|1- 9685 0212056|1- 9685 0212044|1- 9685 0212048|1- 9685 0212052|1- 9685 0212054|1- 9685 1102104|1- 9685 1102124 Any insight into this matter is much appreciated! Update: Upon further investigation, this is the exact point in the code where execution terminates. when the foreach is executed I guess Magento goes into MySQL world and starts loading up data from the database. \Mage\Catalog\Model\Abstract.php public function loadByAttribute($attribute, $value, $additionalAttributes = '*') { $collection = $this->getResourceCollection() ->addAttributeToSelect($additionalAttributes) ->addAttributeToFilter($attribute, $value) ->setPage(1,1); foreach ($collection as $object) { // <--------------- HERE return $object; } return false; } Note, I'm ONLY interested in finding out how to properly CATCH these kinds of errors, not "fix" the logic. This is so that I can present a proper error message to the user. The example above with the malformed sku is contrived and I have no desire to make my Magento app work with those erroneous skus.

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• Handling return value from Web Service Call Wrapper

  - by coffeeaddict

  I created this method below which makes an HTTP call to a 3rd party API. I just want opinions on if I'm handling this the best way. If the call fails, I need to return the ExistsInList bool value only if the response is not null. But in the last return statement, wouldn't I have to essentially do another return selectResponse == null ? false : selectResponse.ExistsInList; to check for null first just like the previous return in the catch? Just seems redundant the way I'm approaching this and I don't know if I really need to check for null again in the final return but I figure yes, because you can't always rely on the response to give you a valid response even if there were no errors picked up. public static bool UserExistsInList(string email, string listID) { SelectRecipientRequest selectRequest = new SelectRecipientRequest(email, listID); SelectRecipientResponse selectResponse = null; try { selectResponse = (SelectRecipientResponse)selectRequest.SendRequest(); } catch (Exception) { return selectResponse == null ? false : selectResponse.ExistsInList; } return selectResponse.ExistsInList; }

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• Is re-throwing an exception legal in a nested 'try'?

  - by Alexander Gessler

  Is the following well-defined in C++, or not? I am forced to 'convert' exceptions to return codes (the API in question is used by many C users, so I need to make sure all C++ exceptions are caught & handled before control is returned to the caller). enum ErrorCode {…}; ErrorCode dispatcher() { try { throw; } catch (std::bad_alloc&) { return ErrorCode_OutOfMemory; } catch (std::logic_error&) { return ErrorCode_LogicError; } catch (myownstdexcderivedclass&) { return ErrorCode_42; } catch(...) { return ErrorCode_UnknownWeWillAllDie; } } ErrorCode apifunc() { try { // foo() might throw anything foo(); } catch(...) { // dispatcher rethrows the exception and does fine-grained handling return dispatcher(); } return ErrorCode_Fine; } ErrorCode apifunc2() { try { // bar() might throw anything bar(); } catch(...) { return dispatcher(); } return ErrorCode_Fine; } I hope the sample shows my intention. My guess is that this is undefined behaviour, but I'm not sure. Please provide quotes from the standard, if applicable. Alternative approaches are appreciated as well. Thanks!

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• Another way to handle a common JQuery event handling pattern

  - by bradgonesurfing

  I have the following code for example $("a.foo").bind(function (e){ var t; if ( $(e.target).is("a") ){ t = $(e.target); }else{ t = $(e.target).parent("a"); } var data = t.attr("data-info"); }); In english. I might have a list of anchors within which there may be a number of spans. Each anchor is declared as <a class="foo" href="#" data-info="1"> <span> ... </span> <span> ... </span> </a> <a class="foo" href="#" data-info="2"> <span> ... </span> <span> ... </span> </a> ... ... I bind a handler to the click event of the anchor but the event object comes back with the anchor OR one of the spans depending on where I click. So to get my html5 "data-info" value into the callback I have to insert a bit of messy code. This is now appearing throughout my code to the point where I am guessing there might be an idiomatic JQuery way of handling this.

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• OpenGL multiple threads, variable handling [closed]

  - by toeplitz

  I have written an OpenGL program which runs in the following way: Main: - Initialize SDL - Create thread which has the OpenGL context: - Renderloop - Set camera (view) matrix with glUniform. - glDrawElements() .... etc. - Swapbuffers(); - Main SDL loop handling input events and such. - Update camera matrix of type glm::mat4. This is how I pass my camera object to the class that handles opengl. Camera *cam = new Camera(); gl.setCam(cam); where void setCam(Camera *camera) { this->camera = camera; } For rendering in the opengl context thread, this happens: glm::mat4 modelView = camera->view * model; glUniformMatrix4fv(shader->bindUniform("modelView"), 1, GL_FALSE, glm::value_ptr(modelView)); In the main program where my SDL and other things are handles I then recompute the view matrix. This his working fine without me using any mutex locks. Is this correct? On the other hand, I add objects to my scene by an "upload queue" and in this case I have to mutex lock my upload queue vector (vector class type) when adding items to it or else the program crashes. In summary: I recompute my matrix in a different thread and then use it in the opengl thread without any mutex lock. Why is this working? Edit: I think my question is similar to what was asked here: Should I lock a variable in one thread if I only need it's value in other threads, and why does it work if I don't?, only in my case it is even more simple with only one matrix being changed.

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• How to make custom WCF error handler return JSON response with non-OK http code?

  - by John

  I'm implementing a RESTful web service using WCF and the WebHttpBinding. Currently I'm working on the error handling logic, implementing a custom error handler (IErrorHandler); the aim is to have it catch any uncaught exceptions thrown by operations and then return a JSON error object (including say an error code and error message - e.g. { "errorCode": 123, "errorMessage": "bla" }) back to the browser user along with an an HTTP code such as BadRequest, InteralServerError or whatever (anything other than 'OK' really). Here is the code I am using inside the ProvideFault method of my error handler: fault = Message.CreateMessage(version, "", errorObject, new DataContractJsonSerializer(typeof(ErrorMessage))); var wbf = new WebBodyFormatMessageProperty(WebContentFormat.Json); fault.Properties.Add(WebBodyFormatMessageProperty.Name, wbf); var rmp = new HttpResponseMessageProperty(); rmp.StatusCode = System.Net.HttpStatusCode.InternalServerError; rmp.Headers.Add(HttpRequestHeader.ContentType, "application/json"); fault.Properties.Add(HttpResponseMessageProperty.Name, rmp); -- This returns with Content-Type: application/json, however the status code is 'OK' instead of 'InternalServerError'. fault = Message.CreateMessage(version, "", errorObject, new DataContractJsonSerializer(typeof(ErrorMessage))); var wbf = new WebBodyFormatMessageProperty(WebContentFormat.Json); fault.Properties.Add(WebBodyFormatMessageProperty.Name, wbf); var rmp = new HttpResponseMessageProperty(); rmp.StatusCode = System.Net.HttpStatusCode.InternalServerError; //rmp.Headers.Add(HttpRequestHeader.ContentType, "application/json"); fault.Properties.Add(HttpResponseMessageProperty.Name, rmp); -- This returns with the correct status code, however the content-type is now XML. fault = Message.CreateMessage(version, "", errorObject, new DataContractJsonSerializer(typeof(ErrorMessage))); var wbf = new WebBodyFormatMessageProperty(WebContentFormat.Json); fault.Properties.Add(WebBodyFormatMessageProperty.Name, wbf); var response = WebOperationContext.Current.OutgoingResponse; response.ContentType = "application/json"; response.StatusCode = HttpStatusCode.InternalServerError; -- This returns with the correct status code and the correct content-type! The problem is that the http body now has the text 'Failed to load source for: http://localhost:7000/bla..' instead of the actual JSON data.. Any ideas? I'm considering using the last approach and just sticking the JSON in the HTTP StatusMessage header field instead of in the body, but this doesn't seem quite as nice?

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• What to Return? Error String, Bool with Error String Out, or Void with Exception

  - by Ranger Pretzel

  I spend most of my time in C# and am trying to figure out which is the best practice for handling an exception and cleanly return an error message from a called method back to the calling method. For example, here is some ActiveDirectory authentication code. Please imagine this Method as part of a Class (and not just a standalone function.) bool IsUserAuthenticated(string domain, string user, string pass, out errStr) { bool authentic = false; try { // Instantiate Directory Entry object DirectoryEntry entry = new DirectoryEntry("LDAP://" + domain, user, pass); // Force connection over network to authenticate object nativeObject = entry.NativeObject; // No exception thrown? We must be good, then. authentic = true; } catch (Exception e) { errStr = e.Message().ToString(); } return authentic; } The advantages of doing it this way are a clear YES or NO that you can embed right in your If-Then-Else statement. The downside is that it also requires the person using the method to supply a string to get the Error back (if any.) I guess I could overload this method with the same parameters minus the "out errStr", but ignoring the error seems like a bad idea since there can be many reasons for such a failure... Alternatively, I could write a method that returns an Error String (instead of using "out errStr") in which a returned empty string means that the user authenticated fine. string AuthenticateUser(string domain, string user, string pass) { string errStr = ""; try { // Instantiate Directory Entry object DirectoryEntry entry = new DirectoryEntry("LDAP://" + domain, user, pass); // Force connection over network to authenticate object nativeObject = entry.NativeObject; } catch (Exception e) { errStr = e.Message().ToString(); } return errStr; } But this seems like a "weak" way of doing things. Or should I just make my method "void" and just not handle the exception so that it gets passed back to the calling function? void AuthenticateUser(string domain, string user, string pass) { // Instantiate Directory Entry object DirectoryEntry entry = new DirectoryEntry("LDAP://" + domain, user, pass); // Force connection over network to authenticate object nativeObject = entry.NativeObject; } This seems the most sane to me (for some reason). Yet at the same time, the only real advantage of wrapping those 2 lines over just typing those 2 lines everywhere I need to authenticate is that I don't need to include the "LDAP://" string. The downside with this way of doing it is that the user has to put this method in a try-catch block. Thoughts? Is there another way of doing this that I'm not thinking of?

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• c++ exceptions and program execution logic

  - by Andrew

  Hello everyone, I have been thru a few questions but did not find an answer. I wonder how should the exception handling be implemented in a C++ software so it is centralized and it is tracking the software progress? For example, I want to process exceptions at four stages of the program and know that exception happened at that specific stage: 1. Initialization 2. Script processing 3. Computation 4. Wrap-up. At this point, I tried this: int main (...) { ... // start logging system try { ... } catch (exception &e) { cerr << "Error: " << e.what() << endl; cerr << "Could not start the logging system. Application terminated!\n"; return -1; } catch(...) { cerr << "Unknown error occured.\n"; cerr << "Could not start the logging system. Application terminated!\n"; return -2; } // open script file and acquire data try { ... } catch (exception &e) { cerr << "Error: " << e.what() << endl; cerr << "Could not acquire input parameters. Application terminated!\n"; return -1; } catch(...) { cerr << "Unknown error occured.\n"; cerr << "Could not acquire input parameters. Application terminated!\n"; return -2; } // computation try { ... } ... This is definitely not centralized and seems stupid. Or maybe it is not a good concept at all?

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• Good style for handling constructor failure of critical object

  - by mtlphil

  I'm trying to decide between two ways of instantiating an object & handling any constructor exceptions for an object that is critical to my program, i.e. if construction fails the program can't continue. I have a class SimpleMIDIOut that wraps basic Win32 MIDI functions. It will open a MIDI device in the constructor and close it in the destructor. It will throw an exception inherited from std::exception in the constructor if the MIDI device cannot be opened. Which of the following ways of catching constructor exceptions for this object would be more in line with C++ best practices Method 1 - Stack allocated object, only in scope inside try block #include <iostream> #include "simplemidiout.h" int main() { try { SimpleMIDIOut myOut; //constructor will throw if MIDI device cannot be opened myOut.PlayNote(60,100); //..... //myOut goes out of scope outside this block //so basically the whole program has to be inside //this block. //On the plus side, it's on the stack so //destructor that handles object cleanup //is called automatically, more inline with RAII idiom? } catch(const std::exception& e) { std::cout << e.what() << std::endl; std::cin.ignore(); return 1; } std::cin.ignore(); return 0; } Method 2 - Pointer to object, heap allocated, nicer structured code? #include <iostream> #include "simplemidiout.h" int main() { SimpleMIDIOut *myOut; try { myOut = new SimpleMIDIOut(); } catch(const std::exception& e) { std::cout << e.what() << std::endl; delete myOut; return 1; } myOut->PlayNote(60,100); std::cin.ignore(); delete myOut; return 0; } I like the look of the code in Method 2 better, don't have to jam my whole program into a try block, but Method 1 creates the object on the stack so C++ manages the object's life time, which is more in tune with RAII philosophy isn't it? I'm still a novice at this so any feedback on the above is much appreciated. If there's an even better way to check for/handle constructor failure in a siatuation like this please let me know.

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• .NET and C# Exceptions. What is it reasonable to catch.

  - by djna

  Disclaimer, I'm from a Java background. I don't do much C#. There's a great deal of transfer between the two worlds, but of course there are differences and one is in the way Exceptions tend to be thought about. I recently answered a C# question suggesting that under some circstances it's reasonable to do this: try { some work } catch (Exeption e) { commonExceptionHandler(); } (The reasons why are immaterial). I got a response that I don't quite understand: until .NET 4.0, it's very bad to catch Exception. It means you catch various low-level fatal errors and so disguise bugs. It also means that in the event of some kind of corruption that triggers such an exception, any open finally blocks on the stack will be executed, so even if the callExceptionReporter fuunction tries to log and quit, it may not even get to that point (the finally blocks may throw again, or cause more corruption, or delete something important from the disk or database). May I'm more confused than I realise, but I don't agree with some of that. Please would other folks comment. I understand that there are many low level Exceptions we don't want to swallow. My commonExceptionHandler() function could reasonably rethrow those. This seems consistent with this answer to a related question. Which does say "Depending on your context it can be acceptable to use catch(...), providing the exception is re-thrown." So I conclude using catch (Exception ) is not always evil, silently swallowing certain exceptions is. The phrase "Until .NET 4 it is very bad to Catch Exception" What changes in .NET 4? IS this a reference to AggregateException, which may give us some new things to do with exceptions we catch, but I don't think changes the fundamental "don't swallow" rule. The next phrase really bothers be. Can this be right? It also means that in the event of some kind of corruption that triggers such an exception, any open finally blocks on the stack will be executed (the finally blocks may throw again, or cause more corruption, or delete something important from the disk or database) My understanding is that if some low level code had lowLevelMethod() { try { lowestLevelMethod(); } finally { some really important stuff } } and in my code I call lowLevel(); try { lowLevel() } catch (Exception e) { exception handling and maybe rethrowing } Whether or not I catch Exception this has no effect whatever on the excution of the finally block. By the time we leave lowLevelMethod() the finally has already run. If the finally is going to do any of the bad things, such as corrupt my disk, then it will do so. My catching the Exception made no difference. If It reaches my Exception block I need to do the right thing, but I can't be the cause of dmis-executing finallys

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• User Defined Exceptions with JMX

  - by Daniel

  I have exposed methods for remote management in my application server using JMX by creating an MXBean interface, and a class to implement it. Included in this interface are operations for setting attributes on my server, and for getting the current value of attributes. For example, take the following methods: public interface WordManagerMXBean { public void addWord(String word); public WordsObject getWords(); public void removeWord(String word); } The WordsObject is a custom, serializable class used to retrieve data about the state of the server. Then I also have a WordManager class that implements the above interface. I then create a JMX agent to manage my resource: MBeanServer mbs = ManagementFactory.getPlatformMBeanServer(); ObjectName wordManagerName = new ObjectName("com.example:type=WordManager"); mbs.registerMBean(wordManager, wordManagerName); I have created a client that invokes these methods, and this works as expected. However, I would like to extend this current configuration by adding user defined exceptions that can be sent back to my client. So I would like to change my interface to something like this: public interface WordManagerMXBean { public void addWord(String word) throws WordAlreadyExistsException; public WordsObject getWords(); public void removeWord(String word); } My WordAlreadyExistsException looks like this: public class WordAlreadyExistsException extends Exception implements Serializable { private static final long serialVersionUID = -9095552123119275304L; public WordAlreadyExistsException() { super(); } } When I call the addWord() method in my client, I would like to get back a WordAlreadyExistsException if the word already exists. However, when I do this, I get an error like this: java.rmi.UnmarshalException: Error unmarshaling return; nested exception is: java.lang.ClassNotFoundException: com.example.WordAlreadyExistsException The WordAlreadyExistsException, the WordsObject and the WordManagerMXBean interface are all in a single jar file that is available to both the client and the server. If I call the getWords() method, the client has no difficulty handling the WordsObject. However, if a user defined exception, like the one above, is thrown, then the client gives the error shown above. Is it possible to configure JMX to handle this exception correctly in the client? Following some searching, I noticed that there is an MBeanException class that is used to wrap exceptions. I'm not sure if this wrapping is performed by the agent automatically, or if I'm supposed to do the wrapping myself. I tried both, but in either case I get the same error on the client. I have also tried this with both checked and unchecked exceptions, again the same error occurs. One solution to this is to simply pass back the error string inside a generic error, as all of the standard java exceptions work. But I'd prefer to get back the actual exception for processing by the client. Is it possible to handle user defined exceptions in JMX? If so, any ideas how?

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• How do I 'globally' catch exceptions thrown in object instances.

  - by SleepyBobos

  I am currently writing a winforms application (C#). I am making use of the Enterprise Library Exception Handling Block, following a fairly standard approach from what I can see. IE : In the Main method of Program.cs I have wired up event handler to Application.ThreadException event etc. This approach works well and handles the applications exceptional circumstances. In one of my business objects I throw various exceptions in the Set accessor of one of the objects properties set { if (value > MaximumTrim) throw new CustomExceptions.InvalidTrimValue("The value of the minimum trim..."); if (!availableSubMasterWidthSatisfiesAllPatterns(value)) throw new CustomExceptions.InvalidTrimValue("Another message..."); _minimumTrim = value; } My logic for this approach (without turning this into a 'when to throw exceptions' discussion) is simply that the business objects are responsible for checking business rule constraints and throwing an exception that can bubble up and be caught as required. It should be noted that in the UI of my application I do explictly check the values that the public property is being set to (and take action there displaying friendly dialog etc) but with throwing the exception I am also covering the situation where my business object may not be used by a UI eg : the Property is being set by another business object for example. Anyway I think you all get the idea. My issue is that these exceptions are not being caught by the handler wired up to Application.ThreadException and I don't understand why. From other reading I have done the Application.ThreadException event and it handler "... catches any exception that occurs on the main GUI thread". Are the exceptions being raised in my business object not in this thread? I have not created any new threads. I can get the approach to work if I update the code as follows, explicity calling the event handler that is wired to Application.ThreadException. This is the approach outlined in Enterprise Library samples. However this approach requires me to wrap any exceptions thrown in a try catch, something I was trying to avoid by using a 'global' handler to start with. try { if (value > MaximumTrim) throw new CustomExceptions.InvalidTrimValue("The value of the minimum..."); if (!availableSubMasterWidthSatisfiesAllPatterns(value)) throw new CustomExceptions.InvalidTrimValue("Another message"); _minimumTrim = value; } catch (Exception ex) { Program.ThreadExceptionHandler.ProcessUnhandledException(ex); } I have also investigated using wiring a handler up to AppDomain.UnhandledException event but this does not catch the exceptions either. I would be good if someone could explain to me why my exceptions are not being caught by my global exception handler in the first code sample. Is there another approach I am missing or am I stuck with wrapping code in try catch, shown above, as required?

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• Enteprise Library Exception Handling for WCF Fault Contracts - CLIENT SIDE

  - by Huw

  I have a Windows Service which communicates with WCF services. The WCF services are all fault shielded and generate custom UserFaultContracts and ServiceFaultContracts. No problems there. In the Windows Service I am using EntLib for exception handling and logging. I do not want to try catch for faults try { } catch (FaultException<UserFaultContract>) { } I want to use EntLib try { } catch (Exception ex) { var rethrow = ExceptionPolicy.HandleException(ex, "Transaction Policy"); if (rethrow) throw; } This also works, however, in my Tranasaction Policy I want to Log the details of the UserFaultContract. This is where I am unglued. And I hate becoming unglued. The fault is captured and logged...but I can't get the details of the fault. My exception policy is <add name="Transaction Policy"> <exceptionTypes> <add type="System.Exception, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" postHandlingAction="None" name="Exception"> <exceptionHandlers> <add logCategory="General" eventId="200" severity="Error" title="Transaction Error" formatterType="Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.TextExceptionFormatter, Microsoft.Practices.EnterpriseLibrary.ExceptionHandling, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" priority="2" useDefaultLogger="true" type="Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.Logging.LoggingExceptionHandler, Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.Logging, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" name="Logging Handler" /> </exceptionHandlers> </add> <add type="System.ServiceModel.FaultException, System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" postHandlingAction="None" name="FaultException"> <exceptionHandlers> <add logCategory="General" eventId="200" severity="Error" title="Service Fault" formatterType="Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.TextExceptionFormatter, Microsoft.Practices.EnterpriseLibrary.ExceptionHandling, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" priority="2" useDefaultLogger="true" type="Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.Logging.LoggingExceptionHandler, Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.Logging, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" name="Logging Handler" /> </exceptionHandlers> </add> </exceptionTypes> </add> The exception logged is: Timestamp: 5/13/2010 14:53:40 Message: HandlingInstanceID: e9038634-e16e-4d87-ab1e-92379431838b An exception of type 'System.ServiceModel.FaultException`1[[LCI.DispatchMaster.FaultContracts.ServiceFaultContract, LCI.DispatchMaster.FaultContracts, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]' occurred and was caught. 05/13/2010 10:53:40 Type : System.ServiceModel.FaultException`1[[LCI.DispatchMaster.FaultContracts.ServiceFaultContract, LCI.DispatchMaster.FaultContracts, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]], System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 Message : There was an internal fault at the DispatchMaster service. Source : mscorlib Help link : Detail : LCI.DispatchMaster.FaultContracts.ServiceFaultContract Action : http://LCI.DispatchMaster.LogicalChoices.com/ITruckMasterService/MergeScenarioServiceFaultContractFault Code : System.ServiceModel.FaultCode Reason : There was an internal fault at the DispatchMaster service. Data : System.Collections.ListDictionaryInternal TargetSite : Void HandleReturnMessage(System.Runtime.Remoting.Messaging.IMessage, System.Runtime.Remoting.Messaging.IMessage) Stack Trace : In the fault contact there is an ID and a Message. I would, as you can see, like the ID and Message to be logged by EntLib. I am assuming that I'm going to have to write a custom handler to exctract the fault details - but thought I'd ask if I'm missing something in EntLib which might help me avoid that task. Thanks to anyone who is willing to help.

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• No EJB receiver available for handling [appName:,modulename:HelloWorldSessionBean,distinctname:]

  - by zoit

  I'm trying to develop my first EJB with an Example I found, I have the next mistake: Exception in thread "main" java.lang.IllegalStateException: No EJB receiver available for handling [appName:,modulename:HelloWorldSessionBean,distinctname:] combination for invocation context org.jboss.ejb.client.EJBClientInvocationContext@41408b80 at org.jboss.ejb.client.EJBClientContext.requireEJBReceiver(EJBClientContext.java:584) at org.jboss.ejb.client.ReceiverInterceptor.handleInvocation(ReceiverInterceptor.java:119) at org.jboss.ejb.client.EJBClientInvocationContext.sendRequest(EJBClientInvocationContext.java:181) at org.jboss.ejb.client.EJBInvocationHandler.doInvoke(EJBInvocationHandler.java:136) at org.jboss.ejb.client.EJBInvocationHandler.doInvoke(EJBInvocationHandler.java:121) at org.jboss.ejb.client.EJBInvocationHandler.invoke(EJBInvocationHandler.java:104) at $Proxy0.sayHello(Unknown Source) at com.ibytecode.client.EJBApplicationClient.main(EJBApplicationClient.java:16) I use JBOSS 7.1, and the code is this: HelloWorld.java package com.ibytecode.business; import javax.ejb.Remote; @Remote public interface HelloWorld { public String sayHello(); } HelloWorldBean.java package com.ibytecode.businesslogic; import com.ibytecode.business.HelloWorld; import javax.ejb.Stateless; /** * Session Bean implementation class HelloWorldBean */ @Stateless public class HelloWorldBean implements HelloWorld { /** * Default constructor. */ public HelloWorldBean() { } public String sayHello() { return "Hello World !!!"; } } EJBApplicationClient.java: package com.ibytecode.client; import javax.naming.Context; import javax.naming.NamingException; import com.ibytecode.business.HelloWorld; import com.ibytecode.businesslogic.HelloWorldBean; import com.ibytecode.clientutility.ClientUtility; public class EJBApplicationClient { public static void main(String[] args) { // TODO Auto-generated method stub HelloWorld bean = doLookup(); System.out.println(bean.sayHello()); // 4. Call business logic } private static HelloWorld doLookup() { Context context = null; HelloWorld bean = null; try { // 1. Obtaining Context context = ClientUtility.getInitialContext(); // 2. Generate JNDI Lookup name String lookupName = getLookupName(); // 3. Lookup and cast bean = (HelloWorld) context.lookup(lookupName); } catch (NamingException e) { e.printStackTrace(); } return bean; } private static String getLookupName() { /* The app name is the EAR name of the deployed EJB without .ear suffix. Since we haven't deployed the application as a .ear, the app name for us will be an empty string */ String appName = ""; /* The module name is the JAR name of the deployed EJB without the .jar suffix. */ String moduleName = "HelloWorldSessionBean"; /*AS7 allows each deployment to have an (optional) distinct name. This can be an empty string if distinct name is not specified. */ String distinctName = ""; // The EJB bean implementation class name String beanName = HelloWorldBean.class.getSimpleName(); // Fully qualified remote interface name final String interfaceName = HelloWorld.class.getName(); // Create a look up string name String name = "ejb:" + appName + "/" + moduleName + "/" + distinctName + "/" + beanName + "!" + interfaceName; return name; } } ClientUtility.java package com.ibytecode.clientutility; import java.util.Properties; import javax.naming.Context; import javax.naming.InitialContext; import javax.naming.NamingException; public class ClientUtility { private static Context initialContext; private static final String PKG_INTERFACES = "org.jboss.ejb.client.naming"; public static Context getInitialContext() throws NamingException { if (initialContext == null) { Properties properties = new Properties(); properties.put("jboss.naming.client.ejb.context", true); properties.put(Context.URL_PKG_PREFIXES, PKG_INTERFACES); initialContext = new InitialContext(properties); } return initialContext; } } properties.file: remote.connectionprovider.create.options.org.xnio.Options.SSL_ENABLED=false remote.connections=default remote.connection.default.host=localhost remote.connection.default.port = 4447 remote.connection.default.connect.options.org.xnio.Options.SASL_POLICY_NOANONYMOUS=false This is what I have. Why I have this?. Thanks so much. Regards

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• handling long running large transactions with perl dbi

  - by 1stdayonthejob

  I've got a large transaction comprising of getting lots of data from database A, do some manipulations with this data, then inserting the manipulated data into database B. I've only got permissions to select in database A but I can create tables and insert/update etc in database B. The manipulation and insertion part is written in perl and already in use for loading data into database B from other data sources, so all that's required is to get the necessary data from database A and using it to initialize the perl classes. How can I go about doing this so I can easily track back and pick up from where the error happened if any error occurs during the manipulation or insertion procedures (database disconnection, problems with class initialization because of invalid values, hard disk failure etc...)? Doing the transaction in one go doesn't seem like a good option because the amount data from database A means it would take at least a day or 2 for data manipulation and insertion into database B. The data from database A can be grouped into around 1000 groups using unique keys, with each key containing 1000s of rows each. One way I thought I could do is to write a script that does commits per group, meaning I've got to track which group has already been inserted into database B. The only way I can think of to track the progress of which groups have been processed or not is either in a log file or in a table in database B. A second way I thought could work is to dump all the necessary fields needed for loading the classes for manipulation and insertion into a flatfile, read the file to initialize the classes and insert into database B. This also means that I got to do some logging, but should narrow it down to the exact row in the flatfile if any error occurs. The script will look something like this: use strict; use warnings; use DBI; #connect to database A my $dbh = DBI->connect('dbi:oracle:my_db', $user, $password, { RaiseError => 1, AutoCommit => 0 }); #statement to get data based on group unique key my $sth = $dbh->prepare($my_sql); my @groups; #I have a list of this already open my $fh, '>>', 'my_logfile' or die "can't open logfile $!"; eval { foreach my $g (@groups){ #subroutine to check if group has already been processed, either from log file or from database table next if is_processed($g); $sth->execute($g); my $data = $sth->fetchall_arrayref; #manipulate $data, then use it to load perl classes for insertion into database B #. #. #. } print $fh "$g\n"; }; if ($@){ $dbh->rollback; die "something wrong...rollback"; } So if any errors do occur, I can just run this script again and it should skip the groups or rows that have been processed and continue. Both these methods is just variations on the same theme, and both require going back to where I've been tracking my progress (in table or file), skip the ones that've been commited to database B and process the remaining data. I'm sure there's a better way of doing this but am struggling to think of other solutions. Is there another way of handling large transactions between databases that require data manipulation between getting data out from one and inserting into another? The process doesn't need to be all in Perl, as long as I can reuse the perl classes for manipulating and inserting the data into the database.

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