#AfterReturning(value = "anyPublicMethod() && applyPrivacy()", returning = "result")
public Object afterReturning(JoinPoint joinPoint, Object result) {
return someService.createNewObjectWithHelpOfResult(result);
}
My intention was to fill some null values in result fields. So in method createNewObjectWithHelpOfResult I'm creating a new Object and setting only the required values. But return value is not reflecting after afterReturning method is finished. But if I do mutations on result. They're very well reflected after aspect #AfterReturning method ends, but I want the return value to be used? Is this not possible? I'll have to do mutation only?
What #M.Deinum explained, is documented in the Spring manual, section "After Returning Advice". The end of the section reads:
Please note that it is not possible to return a totally different reference when using after returning advice.
Therefore, you cannot just make your #AfterReturning advice have a return type other than void and hope it will magically return something. As the advice type name implies, all 3 types of #After* advices run after the method has returned already. There is nothing you can do to change the result (except for altering internal state of an object instance). You can merely read (and e.g. log) it.
The solution, like #M.Deinum said, is an #Around advice, see also again the Spring manual.
It is generally a good idea to at least study the manual and learn some basics or take a look at examples before asking questions in public. I am sure you did not find any valid example for an #After* advice with non-void return type.
I am using #AfterReturning on the methods whose return type is String but instead of String I am getting null as result
#AfterReturning(value = "execution(* com.example.demo.aop.business..(..))", returning = "result")
public void afterA(JoinPoint joinPoint, Object result) {
log.info("After method {} returned with value {}", joinPoint, result);
}
O/P - After method execution(void com.example.demo.aop.business.Business2.disp()) returned with value null
I got this piece of code, I am learning from tutorial. I want to return an element by url which looks like clients/1 instead of clients?id=1. How can I achieve this? Also, can the code below be made easier way?
#GetMapping
public Client getClient(#RequestParam int id) {
Optional<Client> first = clientList.stream().filter(element -> element.getId() == id).findFirst();
return first.get();
}
You may want to use #PathVariable as follows:
#Controller
#RequestMapping("/clients")
public class MyController {
#GetMapping("/{id}")
public Client getClient(#PathVariable int id) {
return clientList.stream().filter(element -> element.getId() == id).findFirst().orElseThrow();
}
Please note, the Optional can be unpacked with orElseThrow method. This will throw a NoSuchElementException in case there is no element found for the id.
Other solution would be to use orElse(new Client(...)) to return a default value if nothing is found.
get() is not really recommended to be used. From the JavaDoc of the get() method:
API Note:
The preferred alternative to this method is orElseThrow().
Even though get() may also throw a NoSuchElementException, similar to orElseThrow, usually the consensus is that get should not be used without isPresent, or should not be used at all. There several other methods to unpack the Optional without forcing you write an if.
The whole idea of the Optional is to overcome this by forcing you to think about the case when there is no value inside.
I have a small issue with doing a blocking operation in Spring Webflux. I retrieve a list of article documents and from the list of article documents, i would like to update another object.
When i execute the below, sometimes it works and sometimes it throws a "block()/blockFirst()/blockLast() are blocking, which is not supported in thread reactor-http-nio-2". Could you please suggest how to fix. I dont really want to make it blocking but not sure how to proceed. There are similar threads in stackoverflow but not with respective to my requirement.
It would be really nice if someone could suggest a way to work around ?
private OrderInfo setPrices(final OrderInfo orderInfo) {
final List<ArticleDocument> articleDocuments = getArticleDocuments(orderInfo).block(); // Problematic line
for (ArticleDocument article : articleDocuments) {
//Update orderInfo based on one of the article price and few more condition.
}
return orderInfo;
}
private Mono<List<ArticleDocument>> getArticleDocuments(final OrderInfo orderInfo) {
return this.articleRepository.findByArticleName(orderInfo.getArticleName()).collectList();
}
It has to be something like this. Please take note that I have not tested it on my IDE. To modify anything please comment and figure it out together.
private Mono<OrderInfo> setPrices(final OrderInfo orderInfo) {
getArticleDocuments(orderInfo)
.map(articleDocuments -> {
articleDocuments.forEach(article -> // UPDATE AS YOU NEED);
return orderInfo;
});
private Mono<List<ArticleDocument>> getArticleDocuments(final OrderInfo orderInfo) {
return this.articleRepository.findByArticleName(orderInfo.getArticleName()).collectList();
}
Remember, you have to put everything under chaining. that's why you have to return Mono<OrderInfo> instead of OrderInfo from setPrices method. If you find my suggested code is tough to adapt to your current coding structure, you can show me the full code. Let's find out we can build a good chain or not.
BTW, you were using getArticleDocuments(orderInfo).block();. See? you were using .block()? Don't do that in a chain. don't ever block anything in a request to the response chain process. you will return mono or flux from the controller and everything will be handled by webflux
I am writing some validation code and am not sure how to pass validation messages back to the calling code.
Exceptions come to mind, but I think that Exceptions should not be used in user input validation. As #Blowdart puts it:
Exceptions are not
control flow mechanisms. Users often get passwords wrong, it's not an
exceptional case. Exceptions should be a truly rare thing,
UserHasDiedAtKeyboard type situations.
From: https://stackoverflow.com/a/77175/125938. I'm extending that sentiment to all "incorrect" user input that a user might enter.
So the question is what to use instead of Exceptions. For certain situations, I could just use an IsValid… method that returns a bool for validity, but what if I want to pass an error message back with it? Should I create a custom "ValidationError" object, with a Message property? What makes sense and causes Least Astonishment (preferably a tried and tested pattern)?
If I were to do this in a truly object-oriented way, I'd adhere to the separation of concerns principle and compose a chain of classes that each deal with a separate step on the input - validation - output journey.
Let's say we are parsing a date from string as entered by the user.
My first class would encapsulate the raw value and attempt to parse the date (pseudo-code):
class TextualDate {
public TextualDate(string value) {
// just initialize with the provided value
}
public Option<Date> AsDate() {
// try parsing and either return the date or not
// the Option<Date> type is here to suggest that the conversion might not succeed
}
}
Next I'd have a validation class that instantiates the TextualDate class, invokes its AsDate() method and returns the validation result:
class ValidatedDate {
public ValidatedDate(TextualDate value) {
// initialize with the provided value
_textualDate = value;
}
private TextualDate _textualDate;
public ValidationResult Validated {
var maybeDate = _textualDate.AsDate();
// see whether we have a date or not
return new ValidationResult(...);
}
}
In our ValidationResult class, we might find some status property (OK, Failed), any error message either provided directly or as a key to then look-up in a message catalog etc.
This way, we can isolate concerns and only deal with the error messages on the UI layer while being able to use and reuse the validation logic independently.
I was faced with a similar dilemma in the past - I had to write a couple of services that takes data from a 3rd party, manipulating it in various ways, and send that data to other services for further processing.
All of these services might have failed because of wrong or incomplete data, but it was nor unexpected neither exceptional - and I refused to use exceptions for these cases.
I've done an extensive research, reading anything I could get my hands on in this subject in two days, and finally decided the following:
A method might need to return data and might not (sub in Visual Basic, void in Java/C#) - but in both cases, I wanted an indication for success/fail and a potential error message.
If your language of choice supports tuples, you could return a tuple from your methods:
public (bool Success, string ErrorMessage) DoSomething()
{
// implementation here
}
or
public (bool Success, someType Value, string ErrorMessage) DoSomething()
{
// implementation here
}
If not, you can do what I did (That was c#5 - so no value tuples) and create a result class:
public class Result
{
public static Result Success()
{
return new Result(true, null);
}
public static Result Fail(string errorMessage)
{
return new Result(false, errorMessage);
}
protected Result(bool success, string errorMessage)
{
Success = success;
ErrorMessage = errorMessage;
}
public bool Success {get; private set;}
public string ErrorMessage {get; private set;}
}
public class Result<T>
{
public static Result<T> Success(T value)
{
return new Result(true, null, value);
}
public new static Result<T> Fail(string errorMessage)
{
return new Result(false, errorMessage, default(T));
}
private Result<T>(bool success, string errorMessage, T value)
: base(success, errorMessage)
{
Value = value;
}
public T Value {get; private set;}
}
And use it like this:
public Result CouldBeVoid()
{
bool IsOk;
// implementation
return IsOk ?
Result.Success() :
Result.Fail("Something went wrong") ;
}
public Result<int> CouldBeInt()
{
bool IsOk;
// implementation
return IsOk ?
Result.Success(intValue) :
Result.Fail("Something went wrong") ;
}
var result = CouldBeVoid();
if(!result)
// do something with error message
var result = CouldBeInt()
if(result)
// do something with int value
else
// do something with error message
Users often get passwords wrong, it's not an exceptional case.
Yes and no. Whether to throw an exception or not depends on the question you're asking. And in the course of logging a user in, there are typically quite a number of questions being asked before you come to the conclusion whether the user can be logged in or not. The more you break down your code into specialised parts, the more it may make sense to raise exceptions in some of those parts.
Say you specify your login procedure the following way in an HTTP context:
Get the username* and password* from the request.
Fetch the user record* by its username from the database*.
Check whether the record's password* equals* the entered password.
If yes, start a session.
If any of the above steps do not successfully complete, output an appropriate error message.
Any of the items marked with an asterisk above may fail:
The request may not contain a username or password.
There may not be a user record for this username, or the database may be down.
For whatever reason, the record may not have a password and/or be corrupted. The stored password may, for whatever reason, use an unsupported hashing algorithm and hence can't be compared.
It should be rather obvious that in this process there are any number of cases that would be ideal to be implemented as an exception. The actual function which tests the password should probably not throw an exception in case the password is merely false; that should be a boolean return value. But it may still throw an exception for any other number of reasons. If you use exceptions properly, you'll end up with code that looks something like this (pseudo-pseudo code):
try {
username = request.get('username')
password = request.get('password')
user = db.get(username=username)
if (user.password.matches(password)) {
session.start()
} else {
print 'Nope, try again'
}
} catch (RequestDoesNotHaveThisDataException) {
logger.info('Invalid request')
response.status(400)
} catch (UserRecordNotFoundException) {
print 'Nope, try again'
} catch (UnsupportedHashingAlgorithmException, PasswordIsNullException) {
logger.error('Invalid password hash for user ' + user.id)
response.status(500)
print 'Sorry, please contact our support staff'
} catch (DatabaseDownException e) {
// mostly for illustration purposes,
// this exception should probably not even be caught here
logger.exception('SEND HALP!')
throw e
}
So, yes, this is a very simple process, but literally every step along the way has one or more exceptional cases. You ask the question "what is the username the user sent in the request?", and if there's no answer to this question because the user didn't sent any username, you have an exceptional case. Exceptions simplify control flow here a lot as opposed to trying to cover each of these cases with an if..else.
It is NOT an exception if the username is not valid or the password is not correct.
(From the answer you quote from.)
As you can see, we're testing whether the username is "valid" or not by trying to fetch its record from the database. If we have a function whose purpose is to fetch records of users from the database, and there is no such record, then an exception is an entirely valid response. If we defined that function to test whether such a record exists and null or false is a valid return value… fine. But in this case we didn't write it that way, and frankly, that results in simpler control flow I find.
Now, only the password validation itself does not use an exception, since the question asked there is "does this password match that password?", to which the answer can clearly be yes or no. Again, only if something exceptional like an unsupported hashing algorithm turns up can there be no answer to this question and an exception is entirely warranted.
Having said all this, you may notice that most of these cases, except the really fatal one with the database, does not outwardly result in an exception. The component here is expecting and handling certain cases that its sub-components regard as exceptional. This code here is asking the questions, and is prepared to handle Mu as an answer for some of them. Which is to say, a general rule that says "exceptions shouldn't be used in process X, Y or Z because it's not exceptional enough" is too dogmatic. It depends on the purpose of each individual piece of code whether an exception is warranted or not.
Having said all this, what you're asking about is some sort of form validation. The above code shows a case where two pieces of data may each be invalid, and it's using exceptions to in the end still result in a "yes" or "no" response. You can of course encapsulate that in an object like this:
val = new LoginFormValidator()
val.setDataFromRequest(request)
val.validate()
if (val.isValid) {
print 'Hurray'
} else {
print 'You have errors:'
for (error in val.errors) {
print error.fieldName + ': ' + error.reason
}
}
Whether this validator uses exceptions internally for any of this you do not need to care, but in the end it saves all of them as a "yes" or "no" result to its internal properties, from where you can take them either as an aggregate (val.isValid) or individually (for (error in val.errors)).
According to clean code laws, we want to have functions which do only one thing and are on the same "level of abstraction". But how to name function, whose work is just to check some condition and do the work if condition is true. For example, how could this function be named?
public void HowToNameThis(){
if(!ComponentIsInstalled()){
DisableCheckbox();
}
}
I thought about naming it like DisableCheckboxIfComponentIsNotInstalled, but then the name just repeats the code, which effectively means I have created a function but did not create any abstraction.
CleanCode also suggest that you stay as positive as you can in your code. If you reverse the logic within your method, then, naming becomes easier.
public void TryEnableComponent() {
if(ComponentIsInstalled()) {
EnableCheckbox();
}
}
I generally think really hard about if the IF is really deserving it's own function.
And then often end up inlining it:
Like this (pseudo):
void SetupInstallerWindow()
{
LoadLicenseAgreement();
if(!ComponentIsInstalled()){
DisableCheckbox();
}
BringWindowTop();
}
If that really gets to messy, here's an idea for a name might provide more context for the reader:
AllowReinstallationOfComponent()