I would like to access all the Synchronization's that were added to an exchange during a camel route.
The reason for this is that when a particular type of exception happens, I want to route the message to an error handling component and let that error handling component execute the "onCompletion" of those synchronizations even though there was an exception.
the synchronizations are added by using
exchange.getUnitofWork().addSynchronization(new MySyncAdapter());
and I was trying to access them with
exchange.handoverCompletions();
However, I think I must be doing something wrong because no matter which component I try to get the completions from (my real component, or the error component), the list is null.
Edit:
According tot he answer below, this should work:
exchange.addOnCompletion(new MySyncAdapter());
List<Synchronization> syncs = exchange.handoverCompletions();
however, syncs is still null. Any suggestions?
The Exchange in this case does not have the Completions/Synchronizations, the UnitOfWork instance does so when you call exchange.handoverCompletions() you will get a null. You also do not have access to the synchronizations in the UnitOfWork because it is being handled in a different thread. Any attempt to modify them, which is what handoverCompletion does, causes a concurrency exception.
In reality you are trying to use something in a way it wasn't intended. Exchange errors should be handled by invoking the Exception Clause DSL outlined here. It is designed to capture exchange errors in a fine grained manner by allowing a developer to define the Exception type and forward the Exchange to a route for further processing by your error handling component.
Best Regards,
Scott ES
Related
Normally I try to use exceptions only for "exceptional" conditions ("Effective Java ", Issue 69). My personal interpretation is:
if I hit a condition in a specific part in code (normally a method or constructor) where I can't give a meaningful answer or outcome anymore I throw an exception and whoever called the piece of code has to handle it.
In the special case of HTTP endpoints I can always give a meaningful answer - a response with a status code.
Handling bad requests thus belongs to normal program flow of endpoint methods and should not raise new exception.
E.g. an endpoint that returns a resource should just return 404 in case the resource is not found. In my opinion it would be bad practice to raise a "SomethingNotFoundExcetion" (that could be handled by an error handler and create 404 response)
My question is: It is bad practice to use Spring Boot's error handling mechanism for bad requests (4xy) that relies on exceptions to create specific HTTP responses. (It is really fine for all uncovered errors yielding 500)
(I am just writing a review of code and I am not sure if I should suggest to not use error handler for "normal" API interaction)
Answer/Comment to current answers
It seems that the most of you missed the important part of my reasoning:
(citing Effective Java, Item 69):
Use exceptions only for exceptional
conditions ...
this reasoning:
• Because exceptions are designed for exceptional circumstances, there is little
incentive for JVM implementors to make them as fast as explicit tests.
• Placing code inside a try-catch block inhibits certain optimizations that
JVM implementations might otherwise perform.
The main point for me is:
A well-designed API
must not force its clients to use exceptions for ordinary control flow.
Especially in case of rest API. It should be easy to use any API in a way to avoid exceptions at all. This means for me. No correct (defined e.g. in Open API) usage of a Rest API should raise an exception.
To put another point: The standard for SOAP (another http based API stuff) forbids to use "SOAP fault" for correct (defined by WSDL) requests.
For me raising exception in remote APIs on not exceptional cases are even worse then in classic API (via dependency).
It depends on your project, it's really a matter of opinion/architectural decision. I'd say either-or.
The advantage of using specific Exceptions and then using a Spring handler to map them is that it removes the tedious construction of responses with the correct code from the actual application logic code (it's not dissimilar from aspects in that respect): just throw the correct exception and be done with it.
OTOH, the distance to the error handling code means that 1. if something doesn't work, it may be difficult to track down the issue 2. you need to know what exceptions to throw, and that is not immediately obvious and needs to be documented well.
It is not a bad practice, but a matter of architectural decision. It could be good to have an error handler that will produce a 4xx response and will do some additional error handling work, such as logging, and/or sending a notification by mail or queue or (like in my project) write errors in the table so they could be reviewed by user using GUI component of an application and may be even edited and re-submitted if it makes sense. It also unifies the error handling to a single code (code re-use). But if you really just need to send a 4xx response and nothing else, then its OK not raise exception and just do it in your code. Raising exception is expensive performance-wise and shouldn't be done just for the sake of raising exception alone. But in this particular case my opinion is to use Exception/Spring boot Error handling mechanism
I am developing a J2EE website for a mini project, and I’m puzzled about exception handling. I have defined several custom exception classes, and they’re thrown from several parts of the website, and they are captured in a custom exception handler. But, i am yet to find a good way to map the occurred Exception to an error message.
To put it simply, if an exception occurs somewhere, I have a global exception handler which captures the thrown exception ( i won't swallow it within a local catch block ), but i need an efficient mechanism by which i should be able to convert it into a suitable error message to be displayed to the end users.
Also, the custom exceptions have a tree hierarchy , which means the top of the tree will have general exceptions and the leaves of the tree would have exceptions defined for a very specific purpose.
The tree would be like
CustomException
Type1Exception
Type11Exception
Type12Exception
Type121Exception
Type122Exception
Type13Exception
Type2Exception
Type21Exception
Type211Exception
Type22Exception
Type3Exception
Type31Exception
Type32Exception
Type33Exception
Type4Exception
Type41Exception
Type411Exception
Type4111Exception
Type4112Exception
Type421Exception
Type4211Exception
Type42Exception
Each exception branch would represent exceptions occurring in specific part of the website. The tree will grow more in future, if more features are added to the website What is the best practice to map the bunch of exceptions to error messages ?
And, is using instanceOf operator and isInstance() method , to check the type of exception, a good practice (in aspects of performance ,scalability and code standards) ?
Each exception branch would represent exceptions occurring in specific
part of the website.
But what if the exception happens in a common component shared by different parts of the website?
Exceptions already tell you where they happened (that's what the stacktrace is for), you don't need to put it in the name. The name is for the reason of the exception (such as IllegalArgumentException or EOFException.
Your design is poor in many ways. You should handle exceptions where you can, either locally with a specific error message (if let's say a user wants to pick a username that's already taken) or globally with a general error message.
Edit:
There are thousands of potential error situations in an application. You can divide them into categories based on what you can do to them. Let's say you try to insert a duplicate username into the database, and an exception is thrown. You catch this and tell the user to choose a different username.
That's the least exceptional case, you might even bypass this by checking if the username exists, instead of relying on an exception.
Then you have a bit more exceptional, let's say you can't connect to the database at all. You don't know why, but you're still prepared, you tell the user that something is wrong with the database, and please try again.
Then you have the most exceptional. You're not prepared for it, you don't have a catch clause for it, it flies up to the global exception handler. All you can do is show the user a generic error message that "Something went wrong", log the error, and notify the maintenance team.
Now the way to design exceptions is based on how much information you know about what happened. You might have a DatabaseException class for all DB related errors, and a DuplicateUserException that extends it to provide more detail. Also note that a DuplicateUserException would never propagate up to a global exception handler. You'd handle it right there, showing the user the screen with the error message. The error message which you'd get from a resource bundle not with the name of the exception, but a general key, such as "exception.user.duplicate".
I think your basic mistake is thinking that you can create a single place responsible for exception handling, just based on the exception type. I suggest that you let that idea go. The global handler should only handle (mainly log) the exception when nobody else will.
I am confused with the following question:
You are implementing a model component. You realize that an IOException might arise if you lose connection to the database. Following are the option:
Implement multipathing to provide redundant connectivity to the database, thereby avoiding that risk of connection failure.
Provide an error handler page, and use the page directive in the invoking ISP to redirect to that page if the error arises.
Use the JSTL tag to take control if the exception arises.
Surround the problem area with a try/catch block and implement appropriate recovery or fallback behavior.
I think answer is option no 4 but it's written answer is 3 i don't know how?
IMO, the assumption is once an IOException is thrown, there is no way to reconnect to the database, hence you are left with JSTL, the view component, to display the appropriate error message.
I understand throwing exceptions specific to the application layer you're in, but what is the purpose of all of this exception handling overhead if you're:
Just going to let the exceptions bubble up to the top.
Never going to do anything "unique" with the wrapped exception.
For example, I have a DAO that throws a SQLException, and the next layer up is a manager that calls the DAO. The commonly accepted paradigm is that I create a manager exception, wrap my SQLException, and then throw the manager exception. Why? If another class up the chain is going to deal with it anyhow, then why wrap it?
In your example, it might not be useful. But suppose you're writing an interface with many possible implementations. Suppose for example that two years from now, you switch from a SQL database to a NoSQL one. Your DAO will then be forced to declare NoSQLException, and all the calling code will have to be rewritten. Whereas if the SQLException or NoSQLException is wrapped inside your custom exception, the calling code can stay as it is.
In your specific example, if you have a service layer that calls the DAO, you don't want clients to see SQL Exceptions such as "ORA-00118: unique constraint (BLABLA) violated".
Making such exception messages meaningful to upper level layers is one reason why you might consider wrapping them into more meaningful exceptions.
Catching and re-throwing is not handling anything. Better to let it bubble up in that case.
Catching a checked exception and re-throwing as unchecked can be a useful thing to do, but it's better to add more specific information.
You should only wrap and throw an exception if you're going to add some useful info to it, or to make it specific to your domain. Otherwise you should just be letting an exception bubble up to where it can be handled. I'm guessing that you're looking at some suspect code for your examples.
One example for wrapping exceptions, that might actually be useful, is to "convert" implementation-specific exceptions to something more specific to a framework in an IoC/DI scenario. For example, if you have a framework that does some work, you want to shield the client code from having to "know" a bunch of specific exceptions. So you create a set of common exceptions that your plug-ins throw and that your client code knows and can handle. Like data access exceptions for a bunch of different back ends.
java enforces you to explicitly declare which exceptions can be thrown. wrapping exceptions prevent:
1. expose what is your specific implementation (the higher level might not know that you are using sql as your data base, so you can just throw MyAppException).
2. otherwise, the list of declared exceptions would increase overtime, which will enforce the higher level to take care of all of them, which might be not very neat.
I think it all depends on how specific you want to be and if you want to include more information in your custom exception. Otherwise, you can just allow exceptions thrown by other methods to bubble up and handle them however you see fit.
In your case, SQLException might be too generic, so wrapping it in your own custom exception can help more easily determine where it was thrown in your application and to include more specific information.
So different implementations of the DAO using different datastores can transform the different storage-specific exceptions to the same abstracted storage exception. Then they just include the original for debugging purposes.
I would suggest that in many cases, exceptions could be most usefully handled by reducing them to three types:
OperationFailedStateOkException
The operation could not be completed, but the local and global system state is okay except to the extent implied by that failure (e.g. trying to reference a non-existent item in a Dictionary).
OperationFailedLocalStateCorruptException
The operation could not be completed, and the local system state is corrupt (e.g. trying to reference an item from a corrupted Dictionary).
OperationFailedGlobalStateCorruptException
The operation could not be completed, and the global system state is corrupt (e.g. a shared cache got corrupted).
Note that in many cases the caller of a routine won't be nearly as interested in why it failed as in what the failure implies about the state of the system. Exceptions of the first type may generally be safely caught, and execution resumed, if the programmer knows why they might occur and what to do about them. In some cases, they may need to be rethrown as exceptions of the second type (e.g. if the system was unable to perform some operation which would be necessary to maintain consistency in a data structure). Those of the second type should only be caught and rethrown as the first type at a level where the corrupt state is going to be abandoned (e.g. a "Load document" routine might catch such exceptions and rethrow as a "state ok" exception if any corrupt data structures used in the failed attempt to load a document are going to be jettisoned). Those of the third type should generally trigger a program shut down.
To be sure, it may be useful to have some gradations between the different types (e.g. indicating a global problem sufficient that the program should be shut down gently, saving user data, versus indicating that things are so bad that attempting to save user data would corrupt things worse). Nonetheless, catching exceptions and rethrowing one that indicates something about the system state may be nicer than simply leaving higher levels of the code to wonder what to do with an InvalidArgumentException.
I am currently adding functionality to a JSF/Richfaces application and we are now integrating with external web services.
Actions done with the services include: get user, get account, update user, update account, create user, create account.
These services, along with the unexpected soapfaultexceptions, can return error codes in their response types. Mainly for failures along the lines of: login already exists, password doesn't meet criteria, account number already exists, and no user found.
The calls are like so: BackingBean > Manager Level Class (mainly a pass through) > Web Service Client (makes the actual WS call). For the GET actions, the ID (username or account number) is passed down and the Account or User object is passed back up. The Updates pass around User/Account objects, same with the Creates.
What would be the best way to get these errors back up to the backingbean so I can handle them via the UI?
Of course I could check for error codes in the response, throw an exception and keep throwing it to the backing bean where I would handle it there.
I could implement a Result type that would hold an Error Type and POJO/DTO that I was populating from the service.
One of my colleagues recommended I use the decorator to decorate my USER or ACCOUNT objects with validators that I would also need to create. Basically I suppose my decorator would just hold custom Error types and the Validate() would just check to see if (List!= null && !(Size>0)). Correct?
What are your thoughts on the proposed methods? #1 is the easiest, #2 seems to be more elegant and still simple, #3 is the "toughest" to me since I've never used the decorator pattern. However, #3 seems to be the most elegant while also being the most time consuming to implement.
Let me know if you need any more clarification.
Thanks, SO!
It's always best to limit programatically using exceptions(When to throw an exception).
First ask yourself is this an exceptional situation? In your case it isn't its just a validation error. Exceptions come with a cost, and there is no guarantee that you will be able to catch the exception further down the chain.
Both 2/3 are similar solutions in the fact you are just trying to return additional information back to the controller.
Option 3, could be considered cleaner, but if you have access to the user/account classes, you could always add an additional property to the class that could contain validation errors.
A good example of this pattern is ActiveRecord within ruby, same type of model. You call save on a model object, if an error occurs it populates an error property.
Throw a custom exception or one of a set of custom exceptions and handle it at the higher level. This is my preferred way of handling it versus status codes in Java where everything is pass by value, and frees up a return variable for other purposes.
In regards to "keep throwing it," don't catch and re-throw at each level, but only catch at the level where you can do something about it, ie. the backing bean / UI in this case.