Le 24/12/2015 01:41, Gilles a écrit :
> On Wed, 23 Dec 2015 20:18:10 +0100, Luc Maisonobe wrote:
>> Le 23/12/2015 14:32, Gilles a écrit :
>>> Hello.
>>>
>>> On Wed, 23 Dec 2015 10:38:03 +0100, luc wrote:
>>>> Le 2015-12-23 01:41, Gilles a écrit :
>>>>> On Tue, 22 Dec 2015 13:17:16 -0600, Ole Ersoy wrote:
>>>>>> On 12/22/2015 11:46 AM, Gilles wrote:
>>>>>>> Hi.
>>>>>>> On Mon, 21 Dec 2015 22:44:16 -0600, Ole Ersoy wrote:
>>>>>>>> On 12/21/2015 06:44 PM, Gilles wrote:
>>>>>>>>> On Mon, 21 Dec 2015 12:14:16 -0600, Ole Ersoy wrote:
>>>>>>>>>> Hi,
>>>>>>>>>> I was considering jumping into the JDKRandomGenerator exception
>>>>>>>>>> discussion, but I did not want to hijack it.
>>>>>>>>>> Not sure if any of you have had a chance to looks at this:
>>>>>>>>>> https://github.com/firefly-math/firefly-math-exceptions/
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> https://github.com/firefly-math/firefly-math-exceptions/blob/master/src/main/java/com/fireflysemantics/math/exception/MathException.java
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>> [...]
>>>>>>>>> But I did not see how localization is handled.
>>>>>>>> I did leave localization out. I think localization was a hard
>>>>>>>> requirement in earlier versions of CM, but I'm hoping that there is
>>>>>>>> some flexibility on this
>>>>>>> There was not, since I argued many times to leave it out.
>>>>>>> So unless you can show practically how it can work, I have my doubts
>>>>>>> that we'll be allowed to go forward with this approach.
>>>>>>>
>>>>>>>> and that future versions can defer to a
>>>>>>>> utility that uses the ExceptionTypes Enum instance as the key to
>>>>>>>> look
>>>>>>>> up the internationalized template string.
>>>>>>> Looks good. Where is the code? ;-)
>>>>>> So CM clients would:
>>>>>> catch(MathException e) {
>>>>>> String exceptionTemplate =
>>>>>> ResourceBundle.getBundle("cm.exception.templates", new Locale("en",
>>>>>> "US")).getString(e.getType());
>>>>>> String i18Nmessage = buildMessage(exceptionTemplate,
>>>>>> e.getContext());
>>>>>> ...
>>>>>> }
>>>>>> I can prototype that out more. Just trying to get a feel for how
>>>>>> viable the concept is first.
>>>>> I'm not sure I understand correctly.
>>>>> Does that mean that
>>>>> 1. Uncaught exceptions will lead to a message in English?
>>>>> 2. Every "catch" must repeat the same calls (although the arguments
>>>>> are likely
>>>>> to be the same for all clauses (and for all applications)?
>>>>> Comparing this with the current behaviour (where the translated
>>>>> message String
>>>>> is created when "e.getLocalizedMessage()" is called) is likely to
>>>>> make people
>>>>> unhappy.
>>>>
>>>> This could be made simpler with some task delegating between user
>>>> code and CM code.
>>>> What about :
>>>>
>>>> interface ExceptionLocalizer {
>>>> /** Localize an exception message.
>>>> * @param locale locale to use
>>>> * @param me exception to localize
>>>> * @return localized message for the exception
>>>> */
>>>> String localize(Locale locale, MathException me);
>>>> }
>>>>
>>>> and having ExceptionFactory hold a user-provided implementation of
>>>> this interface?
>>>>
>>>> public class ExceptionFactory {
>>>>
>>>> private static ExceptionLocalizer localizer = new NoOpLocalizer();
>>>>
>>>> public static setLocalizer(ExceptionLocalizer l) {
>>>> localizer = l;
>>>> }
>>>
>>> I think that this is potentially dangerous for two reasons (if I'm
>>> not mistaken): it's not thread-safe and it can be called by any
>>> library used by the main application.
>>
>> Intermedaite libraries could also call it, and I hope they would be
>> designed to use a consistent way for their own exception (they should
>> let the user specify the localization mechanism, use it for themselves
>> and pass the configuration to CM).
>
> I'm not sure I follow.
>
> IIUC the implications, libraries should be forbidden to call a method
> such as "setLocalizer".
It's a design choice for the upper libraries, not for CM.
>
> In fact "localizer" should be final. [It could be initialized in a way
> similar to what is done by "slf4j". But this is a lot of work not worth
> it if we can drop direct support for localiszation in CM.]
This would be over-engineering IMHO. From a theoretical point of view,
yes it would be cleaner, but this is really nitpicking. Documenting
proper use case seems sufficient.
>
>>
>> Thread safety here is really not a concern (but we could protect it
>> if desired). This setting is a configuration level setting, it is
>> usually done once near the beginning of the main program. You don't
>> change the mechanism every millisecond.
>>
>>>
>>> I think that the "localizer" instance must be obtained in a way which
>>> the end-user controls.
>>
>> The user controls it. The setLocalizer method can be called directly by
>> user, and in fact I expect the user to do it.
>
> The user is not in control because any code he calls can override the
> setting.
>
>>>>
>>>> public static String localize(Locale locale, MathException me) {
>>>> return localizer.localize(locale, me);
>>>> }
>>>>
>>>> /** Default implementation of the localizer that does nothing. */
>>>> private static class NoOpLocalizer implements ExceptionLocalizer {
>>>> /** {@inheritDoc} */
>>>> @Override
>>>> public String localize(MathException me) {
>>>> return me.getMessage();
>>>> }
>>>> }
>>>>
>>>> }
>>>>
>>>> and MathException could implement both getLocalizedMessage() and
>>>> even getMessage(Locale) by delegating to the user code:
>>>>
>>>> public class MathException {
>>>>
>>>> public String getLocalizedMessage() {
>>>> return ExceptionFactory.localize(Locale.getDefault(), this);
>>>> }
>>>>
>>>> public String getMessage(Locale locale) {
>>>> return ExceptionFactory.localize(locale, this);
>>>> }
>>>>
>>>> ...
>>>>
>>>> }
>>>>
>>>> One thing that would be nice would be that in addition to the get
>>>> method,
>>>> MathException also provides a getKeys to retrieve all keys and a
>>>> getType
>>>> to retrieve the type. The later correspond to the getPatern (or
>>>> getLocalizable)
>>>> I asked for a few years ago in ExceptionContext. The point for these
>>>> methods
>>>> is that if we provide users a way to retrieve the parameters that were
>>>> used
>>>> in the exception construction, then we can delegate localization to
>>>> users
>>>> as they can do their own code that will rebuild a complete meaasage as
>>>> they
>>>> want. When you have only the keys and they have reused names like
>>>> OPERATOR
>>>> or VECTOR, it can't be delegated.
>>>
>>> If those are available (as suggested in Ole's example above), would you
>>> indeed
>>> be OK that localization is not a CM concern anymore?
>>
>> Yes at the condition that user can use it to implement something like
>> the ExceptionLocalizer interface and this interface is already supported
>> by CM exceptions to implement getLocalizedMessage (at least). The
>> getLocalizedMessage is a standard method inherited directly from
>> Throwable, it is not an addition from us (on the other hand
>> getMessage(Locale) *is* an extension I promoted).
>
> I don't follow: I thought that if Ole's "MathException" provides "getType",
> "getKeys" and ("getValues" ?), then you have the same building blocks
> to define a custom formatting (and localization).
Yes, and this is what is used at user level to implement ExceptionLocalizer.
>
> By "dropping support", I mean dropping support. ;-)
> I.e. no more "Localize..." classes under "org.apache.commons.math4"
Then -1.
When our users build a large application, they rely on numerous
different libraries and tools, both open-source and proprietary.
These libraries do have standard interfaces so they can be used
together. The Java standard library is one of them. the
getLocalizedMessage method is specified there. Many of the libraries
and tolls user will assemble rely on it. Deciding that for the sake
of Apache Commons Math we do not abide to this and decide that all
other existing code should adapt to a different design is a clear
no go for me.
Look at it, it is *only* one field with its setter and two one line
methods defined in the top level MathException class in order to
abide to a standardized interface widely used.
>
> The list of translated type could still be maintained here, in the same
> way the unit tests and user guide are.
I'm not sure. If we decide to delegate the localization to the user
and simply provide the two one-liners hook to call it, then we can
remove the list of translated types and let the user handle it. It
would also allow them to support additional languages. For now,
we support only one, we could drop it using this delegation mechanism.
>
>> This getLocalizedMessage is the standard way many existing frameworks
>> use to display the message to end users, and we can't change this
>> behaviour to have them call the user localization code. So this user
>> localization code must lie somewhere beneath the standard
>> getLocalizedMessage call. The proposal above allow to divert it to
>> user code with CM providing only the required plumbing (but it must
>> still provide the plumbing).
>>
>>>
>>> We could provide code of how to perform the translation in the
>>> userguide.
>>
>> Yes.
>>
>>>
>>>> Note that this is independent of the fact there is one or several
>>>> hierarchies.
>>>> If there are several ones, the two one-liners above must simply be
>>>> copied
>>>> (yeah, code duplication, I know).
>>>>
>>>>>
>>>>>>>>>
>>>>>>>>>> I think it satisfies everyone's requirements with:
>>>>>>>>>> - A single MathException (No hierarchy)
>>>>>>>>> That would not satisfy everyone. :-!
>>>>>>>>>
>>>>>>>>>> - The ExceptionTypes Enum contains all the exception types
>>>>>>>>>> - The ExceptionTypes Enum 'key' maps to the corresponding
>>>>>>>>>> message 1 to 1
>>>>>>>>>> - The ExceptionFactory (Utility) throws exceptions, if necessary,
>>>>>>>>>> that have always have a single unique root cause, such as NPEs
>>>>>>>>> I was wondering whether the "factory" idea could indeed satisfy
>>>>>>>>> everyone.
>>>>>>>>> Rather than throwing the non-standard "MathException", the
>>>>>>>>> factory would
>>>>>>>>> generate one of the standard exceptions, constructed with the
>>>>>>>>> internal
>>>>>>>>> "MathException" as its cause:
>>>>>>>> I think it's good that CM throws CM specific exceptions. This way
>>>>>>>> when I write the handler I can know that the exception is CM
>>>>>>>> specific
>>>>>>>> without having to unwrap it.
>>>>>>> But if there are several CM exceptions hierarchies, the handler
>>>>>>> will have
>>>>>>> to check for every base type, leading to more code.
>>>>>> True dat - but if there are no CM exception hierarchies then they
>>>>>> don't :).
>>>>> I'd be interested in settling the matter of whether we must use a
>>>>> single
>>>>> hierarchy because of technical limitations, or if it is a good
>>>>> solution
>>>>> on its own, i.e. extending standard exceptions is not a better
>>>>> practice
>>>>> after all.
>>>>>
>>>>>>> We could provide a utility:
>>>>>>> public boolean isMathException(RuntimeException e) {
>>>>>>> if (e instanceof MathException) {
>>>>>>> return true;
>>>>>>> }
>>>>>>> final Throwable t = e.getCause();
>>>>>>> if (t != null) {
>>>>>>> if (e instanceof MathException) {
>>>>>>> return true;
>>>>>>> }
>>>>>>> }
>>>>>>> return false;
>>>>>>> }
>>>>>> Or just not wrap.
>>>>> Of course, but choosing one or the other is not a technical problem;
>>>>> it's design decision. Do we have arguments (or reference to them)?
>>>>>
>>>>>>>>> public class ExceptionFactory {
>>>>>>>>> public static void throwIllegalArgumentException(MathException
>>>>>>>>> e) {
>>>>>>>>> throw new IllegalArgumentException(e);
>>>>>>>>> }
>>>>>>>>> public static void throwNullPointerException(MathException e) {
>>>>>>>>> throw new NullPointerException(e);
>>>>>>>>> }
>>>>>>>>> // And so on...
>>>>>>>>> }
>>>>>>>>> So, CM code would be
>>>>>>>>> public class Algo {
>>>>>>>>> public void evaluate(double value) {
>>>>>>>>> // Check precondition.
>>>>>>>>> final double min = computeMin();
>>>>>>>>> if (value < min) {
>>>>>>>>> final MathException e = new
>>>>>>>>> MathException(NUMBER_TOO_SMALL).put(CONSTRAINT, min).put(VALUE,
>>>>>>>>> value);
>>>>>>>>> ExceptionFactory.throwIllegalArgumentException(e);
>>>>>>>>> }
>>>>>>>>> // Precondition OK.
>>>>>>>>> }
>>>>>>>>> }
>>>>>>>> Another thing that I hinted to is that the the factory builds in
>>>>>>>> the
>>>>>>>> precondition check in the throw method. So that the line:
>>>>>>>> if (value < min) {
>>>>>>>> can be nixed.
>>>>>>> It seems nice to ensure that the exception raised is consistent
>>>>>>> with the
>>>>>>> checked condition.
>>>>>> That's the idea.
>>>>> OK, but do you foresee that all precondition checks will be handle by
>>>>> factory methods.
>>>>> It would not be so nice to have explicit checks sprinkled here and
>>>>> there.
>>>>>
>>>>>>> Then, a factory method like
>>>>>>> throwNotStrictlyPositiveException(Number value, String key)
>>>>>>> should probably be renamed to
>>>>>>> checkNotStrictlyPositiveException(Number value, String key)
>>>>>> 'check' is good. I'm going to change it to check.
>>>>
>>>> as the name was changed to checkSomething, the last part Exception in
>>>> the name could be dropped.
>>>>
>>>>>>> Also, shouldn't the "key" argument should be optional?
>>>>>> The key is used to initialize the exception context with the Number
>>>>>> instance. Different modules could have different keys. For example
>>>>>> the Arithmetic module has keys X and Y. So if Y caused the exception
>>>>>> then Y would be passed as the key. So if we are checking both we
>>>>>> would do this:
>>>>>> checkNotStrictlyPositiveException(x, X);
>>>>>> checkNotStrictlyPositiveException(y, Y);
>>>>>>>
>>>>>>>>> Then, in an application's code:
>>>>>>>>> public void appMethod() {
>>>>>>>>> // ...
>>>>>>>>> // Use CM.
>>>>>>>>> try {
>>>>>>>>> Algo a = new Algo();
>>>>>>>>> a.evaluate(2);
>>>>>>>>> } catch (IllegalArgumentException iae) {
>>>>>>>>> final Throwable cause = iae.getCause();
>>>>>>>>> if (cause instanceof MathException) {
>>>>>>>>> final MathException e = (MathException) cause;
>>>>>>>>> // Rethrow an application-specific exception that will make more
>>>>>>>>> sense
>>>>>>>>> // to my customers.
>>>>>>>>> throw new InvalidDataInputException(e.get(CONSTRAINT),
>>>>>>>>> e.get(VALUE));
>>>>>>>>> }
>>>>>>>>> }
>>>>>>>>> }
>>>>>>>>> This is all untested.
>>>>>>>>> Did I miss something?
>>>>
>>>> In the code above, if the iae does not have a cause, or if it is not
>>>> a MathException,
>>>> the iae should be rethrown.
>>>
>>> Indeed!
>>> The updated code (also unstested):
>>>
>>> try {
>>> Algo a = new Algo();
>>> a.evaluate(2);
>>> } catch (IllegalArgumentException iae) {
>>> final MathException e = ExceptionFactory.getMathException(iae);
>>>
>>> if (e != null) {
>>> // Rethrow an application-specific exception that will make more
>>> sense
>>> // to my customers.
>>> throw new InvalidDataInputException(e.get(CONSTRAINT),
>>> e.get(VALUE));
>>> } else {
>>> throw iae;
>>> }
>>> }
>>>
>>>>>>>> I think you got it all...But the handler will be shorter if the
>>>>>>>> exception is not wrapped.
>>>>>>> But not significantly, I guess.
>>>>>>> We could also provide
>>>>>>> public MathException getMathException(RuntimeException e) {
>>>>>>> if (e instanceof MathException) {
>>>>>>> return (MathException) e;
>>>>>>> }
>>>>>>> final Throwable t = e.getCause();
>>>>>>> if (t != null) {
>>>>>>> if (e instanceof MathException) {
>>>>>>> return (MathException) e;
>>>>>>> }
>>>>>>> }
>>>>>>> return null;
>>>>>>> }
>>>>>>> And then define the other utility as:
>>>>>>> public boolean isMathException(RuntimeException e) {
>>>>>>> return getMathException(e) != null;
>>>>>>> }
>>>>>>>
>>>>>>>> The pattern I'm used to is that libraries
>>>>>>>> wrap the exceptions of other libraries in order to offer a
>>>>>>>> standardized facade to the user. For example Spring wraps
>>>>>>>> Hibernate
>>>>>>>> exceptions, since Spring is a layer on top of Hibernate and other
>>>>>>>> data
>>>>>>>> access providers.
>>>>>>> What do they advertize? Standard exception, possibly extended, or
>>>>>>> specific ones, possibly belonging to single hierarchy?
>>>>>> Spring namespaced - single hierarchy:
>>>>>>
>>>>>>
>>>>>> http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/dao/DataAccessException.html
>>>>>>
>>>>>>
>>>>>> BTW - this is blue sky thinking - but Spring Boot has an
>>>>>> @ExceptionHandler annotation that allows the developer to wire up an
>>>>>> exception handler. It might be worth exploring something similar for
>>>>>> the purpose of automating I18N requirements.
>>>>>> @ExceptionHandler(MathException.class)
>>>>>> someClientCodeThatUsesCM();
>>>>>
>>>>> That would be quite necessary I'm afraid. ;-)
>>>>
>>>> Not necessarily. The above support for I18N is quite simple.
>>>
>>> Maybe too simple... ;-)
>>> [What did they say about global variables?]
>>
>> If the static fields hurts your feelings,
>
> It's not just that.
>
>> we can always hide
>> it using an official design pattern like the singleton for
>> ExceptionFactory, and even use the Initialization-on-demand
>> holder idiom to store the singleton. Then the localizer would
>> be an instance field and there would be a static getInstance()
>> method in the factory. Well, a singleton design pattern plus
>> a IODH idiom design pattern are really only a global variable
>> in a pretty dress, so it is only hiding the fact.
>
> Unless I'm mistaken, other singletons in CM are initialized by CM,
> and cannot be changed afterwards.
>
>> At the root, yes global variables are frowned upon, but they
>> do have some use for configuration and making sure some
>> configuration data can be retrieved from everywhere reliably.
>> There are many other places were global variables are used in
>> Java. Just to mention one example that is deirectly related
>> to our topic, Locale.getDefault() and Locale.setDefault() are
>> semantically really accesses to a global variable too.
>
> I think that this is not something to introduce lightly.
> When/if we'll want to explore multi-threading, it will add to
> the problems.
I don't agree at all with this statement.
This is a configuration setting, expected to be called once
at start time! I cannot see any case with users attempting
to do it hundreds of time per seconds with different localizers
to handle localization. This can be documented and users can be
warned against.
What I do expect is, in cases of server applications, having
a server answering to remote requests using different languages.
This is what the new getMessage(Locale) is designed for. Here,
the locale changes, not the mechanism to support it, and it
is not a global variable, just a method argument. It is already
safe in multi-threaded environments.
The setLocalizer method is not a computation algorithm expected
to be called millions of times and that therefore could experience
clashes in case of concurrency.
best regards,
Luc
> If the localization feature can be achieved without resorting
> to a global setting, we should favour it.
>
> Best,
> Gilles
>
>>
>> best regards,
>> Luc
>>
>>>
>>> Best regards,
>>> Gilles
>>>
>>>>
>>>> best regards,
>>>> Luc
>>>>
>>>>> Best regards,
>>>>> Gilles
>>>>>
>>>>>> Cheers,
>>>>>> Ole
>
>
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