I created a Remote Procedure Call. The Server-Side connects to Webservices, to get Information, which it hands over to the Client-Side. This is the Client-Side Code.
public void statusFor(GwtLaneServiceAsync laneProxy){
AsyncCallback<LaneInformation> callback = new AsyncCallback<LaneInformation>()
{
#Override
public void onFailure(Throwable caught)
{
}
#Override
public void onSuccess(LaneInformation information)
{
doStatusForSuccess(information);
}
};
for (Lane lane : this.mainmenu.getSlidePanel().getLaneMenu().getProperLanes().values())
{
if (lane.isChecked().booleanValue())
laneProxy.statusFor("admin", "password", true, lane.getId(), callback);
else
laneProxy.statusFor("admin", "password", false, lane.getId(), callback);
this.laneIndex++;
}
}
Now i wanna do the following...
When the Server can't reach the Webservice, a WebServiceException is thrown. If that happens, I wanna type "Offline" on one of my Buttons of the GUI. BUT I need to tell on which button. It can't be hard coded, cause it depends on which "lane" the Webservice failed.
I need to catch the Exceptions
I need to tell the "onFailure"-Part, on which lane, the Service failed.
Can I somehow deliver the statusFor()-Parameters to that part?
There is no of ways to handle such case. you can throw any custom exception from server side while server can't reach the webservice. then it will come onFailure block. or you can return any message string in response variable. Here response variable you are using LaneInformation bean. so take new variable there like result, and set message as per your requirement.
OnFailure it comes only when any exception occurred or any wrong thing happens in RPC call.
Why not wrap your LaneInformation in a generic response object and add the exception/an error code to that response, to signal that something went wrong on the server side, eg.:
public class RemoteResult<T>
{
T payload;
String errorCode;
}
and
public abstract class AbstractAsyncCallBack<T> implements AsyncCallback<RemoteResult<T>>
{
public void onSuccess( RemoteResult<T> rr )
{
if ( rr.getErrrorCode() != null ) { failure( rr.getErrorCode() ); }
else { success( rr.getPayload() ); }
}
public abstract void success( T payload );
public void failure( String errorCode ) { /* Ignore by default */ }
}
To conclude, you shouldn't throw an exception on the server side when the server can't connect to some other service, you should communicate that nicely to the client, and that's not by (re)throwing the exception :-)
The onFailure() method is mostly for when things go wrong in the RPC communication proper.
Cheers,
Related
I have a consumer (RabbitListner) in RPC mode and I would like to know if it is possible to throw exception that can be treated by the publisher.
To make more clear my explication the case is as follow :
The publisher send a message in RPC mode
The consumer receive the message, check the validity of the message and if the message can not be take in count, because of missing parameters, then I would like to throw Exception. The exception can be a specific business exception or a particular AmqpException but I want that the publisher can handle this exception if it is not go in timeout.
I try with the AmqpRejectAndDontRequeueException, but my publisher do not receive the exception, but just a response which is empty.
Is it possible to be done or may be it is not a good practice to implement like that ?
EDIT 1 :
After the #GaryRussel response here is the resolution of my question:
For the RabbitListner I create an error handler :
#Configuration
public class RabbitErrorHandler implements RabbitListenerErrorHandler {
#Override public Object handleError(Message message, org.springframework.messaging.Message<?> message1, ListenerExecutionFailedException e) {
throw e;
}
}
Define the bean into a configuration file :
#Configuration
public class RabbitConfig extends RabbitConfiguration {
#Bean
public RabbitTemplate getRabbitTemplate() {
Message.addWhiteListPatterns(RabbitConstants.CLASSES_TO_SEND_OVER_RABBITMQ);
return new RabbitTemplate(this.connectionFactory());
}
/**
* Define the RabbitErrorHandle
* #return Initialize RabbitErrorHandle bean
*/
#Bean
public RabbitErrorHandler rabbitErrorHandler() {
return new RabbitErrorHandler();
}
}
Create the #RabbitListner with parameters where rabbitErrorHandler is the bean that I defined previously :
#Override
#RabbitListener(queues = "${rabbit.queue}"
, errorHandler = "rabbitErrorHandler"
, returnExceptions = "true")
public ReturnObject receiveMessage(Message message) {
For the RabbitTemplate I set this attribute :
rabbitTemplate.setMessageConverter(new RemoteInvocationAwareMessageConverterAdapter());
When the messsage threated by the consumer, but it sent an error, I obtain a RemoteInvocationResult which contains the original exception into e.getCause().getCause().
See the returnExceptions property on #RabbitListener (since 2.0). Docs here.
The returnExceptions attribute, when true will cause exceptions to be returned to the sender. The exception is wrapped in a RemoteInvocationResult object.
On the sender side, there is an available RemoteInvocationAwareMessageConverterAdapter which, if configured into the RabbitTemplate, will re-throw the server-side exception, wrapped in an AmqpRemoteException. The stack trace of the server exception will be synthesized by merging the server and client stack traces.
Important
This mechanism will generally only work with the default SimpleMessageConverter, which uses Java serialization; exceptions are generally not "Jackson-friendly" so can’t be serialized to JSON. If you are using JSON, consider using an errorHandler to return some other Jackson-friendly Error object when an exception is thrown.
What worked for me was :
On "serving" side :
Service
#RabbitListener(id = "test1", containerFactory ="BEAN CONTAINER FACTORY",
queues = "TEST QUEUE", returnExceptions = "true")
DataList getData() {
// this exception will be transformed by rabbit error handler to a RemoteInvocationResult
throw new IllegalStateException("mon expecion");
//return dataHelper.loadAllData();
}
On "requesting" side :
Service
public void fetchData() throws AmqpRemoteException {
var response = (DataList) amqpTemplate.convertSendAndReceive("TEST EXCHANGE", "ROUTING NAME", new Object());
Optional.ofNullable(response)
.ifPresentOrElse(this::setDataContent, this::handleNoData);
}
Config
#Bean
AmqpTemplate amqpTemplate(ConnectionFactory connectionFactory, MessageConverter messageConverter) {
var rabbitTemplate = new RabbitTemplate(connectionFactory);
rabbitTemplate.setMessageConverter(messageConverter);
return rabbitTemplate;
}
#Bean
MessageConverter jsonMessageConverter() {
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
objectMapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
objectMapper.registerModule(new JavaTimeModule());
var jsonConverter = new Jackson2JsonMessageConverter(objectMapper);
DefaultClassMapper classMapper = new DefaultClassMapper();
Map<String, Class<?>> idClassMapping = Map.of(
DataList.class.getName(), DataList.class,
RemoteInvocationResult.class.getName(), RemoteInvocationResult.class
);
classMapper.setIdClassMapping(idClassMapping);
jsonConverter.setClassMapper(classMapper);
// json converter with returned exception awareness
// this will transform RemoteInvocationResult into a AmqpRemoteException
return new RemoteInvocationAwareMessageConverterAdapter(jsonConverter);
}
You have to return a message as an error, which the consuming application can choose to treat as an exception. However, I don't think normal exception handling flows apply with messaging. Your publishing application (the consumer of the RPC service) needs to know what can go wrong and be programmed to deal with those possibilities.
Using Play Framework 2.1 with OpenID, if I cancel my authentication from the OpenID Provider, I get this exception :
[RuntimeException: play.api.libs.openid.Errors$AUTH_CANCEL$]
Here's my code :
Promise<UserInfo> userInfoPromise = OpenID.verifiedId();
UserInfo userInfo = userInfoPromise.get(); // Exception thrown here
But since it's a Runtime exception, I can't catch it with a try/catch so I'm stuck on how to avoid exception and returns something nicer than a server error to the client.
How can I do that?
A Promise is success biased, for all its operations, it assumes it actually contains a value and not an error.
You get the exception because you try to call get on a promise which contains an untransformed error.
What you want is to determine if the Promise is a success or an error, you can do that with pattern matching for instance.
try this code:
AsyncResult(
OpenID.verifiedId.extend1( _ match {
case Redeemed(info) => Ok(info.attributes.get("email").getOrElse("no email in valid response"))
case Thrown(throwable) => {
Logger.error("openid callback error",throwable)
Unauthorized
}
}
)
)
You may want to read more on future and promises, I recommend this excellent article :
http://danielwestheide.com/blog/2013/01/09/the-neophytes-guide-to-scala-part-8-welcome-to-the-future.html
edit :
checking the documentation (http://www.playframework.com/documentation/2.1.0/JavaOpenID) in java it seems you are supposed to catch and handle exceptions yourself.
In any case, you should catch exceptions and if one is thrown redirect
back the user to the login page with relevant information.
something like this should work :
public class Application extends Controller {
public static Result index() {
return ok("welcome");
}
public static Result auth() {
Map<String, String> attributes = new HashMap<String, String>();
attributes.put("email", "http://schema.openid.net/contact/email");
final Promise<String> stringPromise = OpenID.redirectURL("https://www.google.com/accounts/o8/id", "http://localhost:9000/auth/callback",attributes);
return redirect(stringPromise.get());
}
public static Result callback() {
try{
Promise<UserInfo> userInfoPromise = OpenID.verifiedId();
final UserInfo userInfo = userInfoPromise.get();
System.out.println("id:"+userInfo.id);
System.out.println("email:"+userInfo.attributes.get("email"));
return ok(userInfo.attributes.toString());
} catch (Throwable e) {
System.out.println(e.getMessage());
e.printStackTrace();
return unauthorized();
}
}
}
i use RequestFactory for communicating with server and RequestFactoryEditorDriver on the client side. So editing workflow looks like such way. Create new proxy for editing:
RequestContext reqCtx = clientFactory.getRequestFactory().Request();
UserAndAccountProxy userAndAccountProxy = reqCtx.create(UserAndAccountProxy.class);
reqCtx.saveAndReturnProfileAndAccount(userAndAccountProxy).to(
new Receiver<UserAndAccountProxy>() {
#Override
public void onSuccess(UserAndAccountProxy response) {
...
}
#Override
public void onFailure(ServerFailure error) {
...
}}
And Save button click handling:
RequestContext reqCtx = view.getEditorDriver().flush();
reqCtx.fire();
On server side saveAndReturnProfileAndAccount method can throw exceptions on persisting, which i can handle in onFailure method. After that if I create new proxy with new request context and pass it to my editor all fields will be blanked.
So what is proper way to execute request and if something goes wrong use data that user allready fill or maybe I made mistake in my editing worklow?
So, I think, I found solution. I made changes to function, which create RequestContext:
private void edit(MyProxy proxy) {
RequestContext reqCtx = clientFactory.getRequestFactory().Request();
if (proxy == null) {
// create proxy first time
proxy = reqCtx.create(UserAndAccountProxy.class);
} else {
// create immutable copy
proxy = reqCtx.edit(proxy);
}
final UserAndAccountProxy tmp = proxy;
reqCtx.saveAndReturnMyProxy(proxy).to(new Receiver<MyProxy>() {
#Override
public void onFailure(ServerFailure error) {
eventBus.showErrorInformation(error.getMessage());
//recursive call with already filled proxy
edit(tmp);
}
#Override
public void onSuccess(UserAndAccountProxy response) {
eventBus.showInformation("It`s ok!");
eventBus.goToMainPage(null);
}
});
// start editing with editor
getView().onEdit(tmp, reqCtx);
}
When we start editing proxy function edit need to bee called with null argument and new clean proxy will be created. After that we start edit it with Editor. On Save button click we execute request to server. If it ends with success - we open another page. If request ends with error, we create new immutable copy ant push it to editor.
Say I have a constructor where it's initialization can potentially throw an exception due to reasons beyond my control.
FantasticApiController(IAwesomeGenerator awesome,
IBusinessRepository repository, IIceCreamFactory factory)
{
Awesome = awesome;
Repository = repository;
IceCream = factory.MakeIceCream();
DoSomeInitialization(); // this can throw an exception
}
Ordinarily, when a Controller action in WebAPI throws an exception I can handle it via a csutom ExceptionFilterAttribute:
public class CustomErrorHandler
{
public override void OnException(HttpActionExecutedContext context)
{
// Critical error, this is real bad.
if (context.Exception is BubonicPlagueException)
{
Log.Error(context.Exception, "CLOSE EVERYTHING!");
Madagascar.ShutdownAllPorts();
}
// No big deal, just show something user friendly
throw new HttpResponseException(new HttpResponseMessage
{
Content = new StringContent("Hey something bad happened. " +
"Not closing the ports though"),
StatusCode = HttpStatusCode.InternalServerError;
});
}
So if I have a have a BoardPlane API method which throws a BubonicPlagueException, then my CustomerErrorHandler will shut down the ports to Madagascar and log it as an error as expected. In other instances when it's not really serious, I just display some user friendly message and return a 500 InternalServerError.
But in those cases where DoSomeInitialization throws an exception, this does absolutely nothing. How can I handle exceptions in WebAPI controller constructors?
The WebApi Controllers are created, and thus constructors called via HttpControllerActivators. The default activator is System.Web.Http.Dispatcher.DefaultHttpControllerActivator.
Very rough examples for options 1 & 2 on github here https://github.com/markyjones/StackOverflow/tree/master/ControllerExceptionHandling/src
Option 1 which works quite nicely involves the use of a DI container (you may well be using one already). I have used Ninject for my example and have used "Interceptors" Read More to intercept and try/catch calls to the Create method on the DefaultHttpControllerActivator. I know of at least AutoFac and Ninject that can do something simlar to to the following:
Create the interceptor
I don't know what the lifetime scope of your Madagascar and Log items are but they could well be injected into your Interceptor
public class ControllerCreationInterceptor : Ninject.Extensions.Interception.IInterceptor
{
private ILog _log;
private IMadagascar _madagascar;
public ControllerCreationInterceptor(ILog log, IMadagascar madagascar)
{
_log = log;
_madagascar = madagascar;
}
But keeping to the example in your question where Log and Madagascar are some kind of Static global
public class ControllerCreationInterceptor : Ninject.Extensions.Interception.IInterceptor
{
public void Intercept(Ninject.Extensions.Interception.IInvocation invocation)
{
try
{
invocation.Proceed();
}
catch(InvalidOperationException e)
{
if (e.InnerException is BubonicPlagueException)
{
Log.Error(e.InnerException, "CLOSE EVERYTHING!");
Madagascar.ShutdownAllPorts();
//DO SOMETHING WITH THE ORIGIONAL ERROR!
}
//DO SOMETHING WITH THE ORIGIONAL ERROR!
}
}
}
FINALLY Register the interceptor In global asax or App_Start (NinjectWebCommon)
kernel.Bind<System.Web.Http.Dispatcher.IHttpControllerActivator>()
.To<System.Web.Http.Dispatcher.DefaultHttpControllerActivator>().Intercept().With<ControllerCreationInterceptor>();
Option 2 is to implement your own Controller Activator implementing the IHttpControllerActivator interface and handle the error in creation of the Controller in the Create method. You could use the decorator pattern to wrap the DefaultHttpControllerActivator:
public class YourCustomControllerActivator : IHttpControllerActivator
{
private readonly IHttpControllerActivator _default = new DefaultHttpControllerActivator();
public YourCustomControllerActivator()
{
}
public System.Web.Http.Controllers.IHttpController Create(System.Net.Http.HttpRequestMessage request, System.Web.Http.Controllers.HttpControllerDescriptor controllerDescriptor, Type controllerType)
{
try
{
return _default.Create(request, controllerDescriptor, controllerType);
}
catch (InvalidOperationException e)
{
if (e.InnerException is BubonicPlagueException)
{
Log.Error(e.InnerException, "CLOSE EVERYTHING!");
Madagascar.ShutdownAllPorts();
//DO SOMETHING WITH THE ORIGIONAL ERROR!
}
//DO SOMETHING WITH THE ORIGIONAL ERROR!
return null;
}
}
}
Once you have your own custom activator the default activator can be switched out in the global asax :
GlobalConfiguration.Configuration.Services.Replace(typeof(IHttpControllerActivator), new YourCustomControllerActivator());
Option 3 Of course if your initialisation in the constructor doesn't need access to the actual Controllers methods, properties etc... i.e. assuming it could be removed from the constructor... then it would be far easier to just move the initialisation to a filter e.g.
public class MadagascarFilter : AbstractActionFilter
{
public override void OnActionExecuting(System.Web.Http.Controllers.HttpActionContext actionContext)
{
try{
DoSomeInitialization(); // this can throw an exception
}
catch(BubonicPlagueException e){
Log.Error(e, "CLOSE EVERYTHING!");
Madagascar.ShutdownAllPorts();
//DO SOMETHING WITH THE ERROR
}
base.OnActionExecuting(actionContext);
}
public override void OnActionExecuted(System.Web.Http.Filters.HttpActionExecutedContext actionExecutedContext)
{
base.OnActionExecuted(actionExecutedContext);
}
public override bool AllowMultiple
{
get { return false; }
}
}
I just started using LINQ to SQL classes, and really like how this helps me write readable code.
In the documentation, typical examples state that to do custom validation, you create a partial class as so::
partial class Customer
{
partial void OnCustomerIDChanging(string value)
{
if (value=="BADVALUE") throw new NotImplementedException("CustomerID Invalid");
}
}
And similarly for other fields...
And then in the codebehind, i put something like this to display the error message and keep the user on same page so to correct the mistake.
public void CustomerListView_OnItemInserted(object sender, ListViewInsertedEventArgs e)
{
string errorString = "";
if (e.Exception != null)
{
e.KeepInInsertMode = true;
errorString += e.Exception.Message;
e.ExceptionHandled = true;
}
else errorString += "Successfully inserted Customer Data" + "\n";
errorMessage.Text = errorString;
}
Okay, that's easy, but then it stops validating the rest of the fields as soon as the first Exception is thrown!! Mean if the user made mode than one mistake, she/he/it will only be notified of the first error.
Is there another way to check all the input and show the errors in each ?
Any suggestions appreciated, thanks.
This looks like a job for the Enterprise Library Validation Application Block (VAB). VAB has been designed to return all errors. Besides this, it doesn't thrown an exception, so you can simply ask it to validate the type for you.
When you decide to use the VAB, I advise you to -not- use the OnXXXChanging and OnValidate methods of LINQ to SQL. It's best to override the SubmitChange(ConflictMode) method on the DataContext class to call into VAB's validation API. This keeps your validation logic out of your business entities, which keeps your entities clean.
Look at the following example:
public partial class NorthwindDataContext
{
public ValidationResult[] Validate()
{
return invalidResults = (
from entity in this.GetChangedEntities()
let type = entity.GetType()
let validator = ValidationFactory.CreateValidator(type)
let results = validator.Validate(entity)
where !results.IsValid
from result in results
select result).ToArray();
}
public override void SubmitChanges(ConflictMode failureMode)
{
ValidationResult[] this.Validate();
if (invalidResults.Length > 0)
{
// You should define this exception type
throw new ValidationException(invalidResults);
}
base.SubmitChanges(failureMode);
}
private IEnumerable<object> GetChangedEntities()
{
ChangeSet changes = this.GetChangeSet();
return changes.Inserts.Concat(changes.Updates);
}
}
[Serializable]
public class ValidationException : Exception
{
public ValidationException(IEnumerable<ValidationResult> results)
: base("There are validation errors.")
{
this.Results = new ReadOnlyCollection<ValidationResult>(
results.ToArray());
}
public ReadOnlyCollection<ValidationResult> Results
{
get; private set;
}
}
Calling the Validate() method will return a collection of all errors, but rather than calling Validate(), I'd simply call SubmitChanges() when you're ready to persist. SubmitChanges() will now check for errors and throw an exception when one of the entities is invalid. Because the list of errors is sent to the ValidationException, you can iterate over the errors higher up the call stack, and present them to the user, as follows:
try
{
db.SubmitChanges();
}
catch (ValidationException vex)
{
ShowErrors(vex.ValidationErrors);
}
private static void ShowErrors(IEnumerable<ValidationResult> errors)
{
foreach(var error in errors)
{
Console.WriteLine("{0}: {1}", error.Key, error.message);
}
}
When you use this approach you make sure that your entities are always validated before saving them to the database
Here is a good article that explains how to integrate VAB with LINQ to SQL. You should definitely read it if you want to use VAB with LINQ to SQL.
Not with LINQ. Presumably you would validate the input before giving it to LINQ.
What you're seeing is natural behaviour with exceptions.
I figured it out. Instead of throwing an exception at first failed validation, i store an error message in a class with static variable. to do this, i extend the DataContext class like this::
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
/// <summary>
/// Summary description for SalesClassesDataContext
/// </summary>
public partial class SalesClassesDataContext
{
public class ErrorBox
{
private static List<string> Messages = new List<string>();
public void addMessage(string message)
{
Messages.Add(message);
}
public List<string> getMessages()
{
return Messages;
}
}
}
in the classes corresponding to each table, i would inherit the newly defined class like this::
public partial class Customer : SalesClassesDataContext.ErrorBox
only in the function OnValidate i would throw an exception in case the number of errors is not 0. Hence not attempting to insert, and keeping the user on same input page, without loosing the data they entered.