Hi Adam,
The fix I've just checked in SVN should solve your issue. You now can check
whether your request generated an error by solely looking at the response's
status code. In your case, it would return a CONNECTOR_ERROR_INTERNAL
because we don't fully deal with invalid URIs. In the future, we might
improve the precision of the status. In your case you could also expect a
CLIENT_ERROR_BAD_REQUEST because:
- you provided a non HTTP URI ("aaaaaaaaaaaaaaaaa")
- you didn't provide a Request's hostRef property to indicate the host to
connect to
I understand your preference for checked exceptions. For a Java-centric API
I would design like you propose, but for a REST/HTTP API, I think it's
better and more consistent to reuse and extend the HTTP status mechanism.
Best regards,
Jerome
> -----Message d'origine-----
> De : Adam Taft [mailto:[EMAIL PROTECTED]
> Envoyé : vendredi 1 juin 2007 06:05
> À : discuss@restlet.tigris.org
> Objet : Re: Please Don't Eat Exceptions
>
>
> I don't necessarily understand where the "first stage" and
> the "second
> stage" are in the code you're referring to. So, I can't guess as to
> whether it's a good solution.
>
> Maybe think about a lower level functional class (ie.
> basically what is
> Client right now) throwing checked exceptions out of the
> handle method.
> And then, having a "convenience" class that extends Client
> and wraps
> the exceptions to produce an appropriate error Status code.
> This would
> allow the best of both worlds, by allowing the checked
> exceptions to be
> dealt with programatically by the end user/developer, while also
> allowing a non-checked configuration for those who want it.
>
> A developer who wants the checked exceptions would do:
>
> Client client = new Client();
>
> A developer who wants to do if-then-else testing on the status code
> would do:
>
> UncheckedClient client = new UncheckedClient();
>
> Where UncheckedClient extends Client.
>
> Regardless, down in the depths of the specification, it's in my mind
> that the handle method should throw exceptions.
>
> Just some additional thoughts, I guess.
>
> Adam
>
>
> Thierry Boileau wrote:
> > Hello,
> >
> > we had a discussion with Jerome, and we plainly agree with the fact
> > there is a problem in HttpClientHelper#handle [1] method as
> pointed out
> > thanksfully by Adam and Jim.
> > This method first builds a call object then sends this call
> and gets the
> > server's response.
> > The try/catch block is very problematic in the case the
> build step of
> > the call fails. We've decided to remove it.
> > That is to say that all errors detected in this first step
> will be in
> > charge of the caller code which is "responsible to give
> correct data".
> >
> > A contrario, the errors detected in the second phase should
> generate a
> > status code:
> > - Status.CONNECTOR_ERROR_XXX (where XXX stands for CONNECTION,
> > COMMUNICATION and INTERNAL) for all errors detected before
> the request
> > is sent. This is the current behaviour.
> > - HTTP status received from the server.
> >
> >
> > What do you think about?
> >
> > best regards,
> > Thierry Boileau
> > [1]
> > public void handle(Request request, Response response) {
> > try {
> > HttpClientCall httpCall =
> getConverter().toSpecific(this,
> > request);
> > getConverter().commit(httpCall, request, response);
> > } catch (Exception e) {
> > getLogger().log(Level.WARNING,
> > "Error while handling an HTTP client call: ",
> > e.getMessage());
> > getLogger().log(Level.INFO,
> > "Error while handling an HTTP client call", e);
> > }
> > }
> >
> >
> >>
> >> I made some comments to the bug, by the way.
> >>
> >> One thing that came to mind, about handling different 3rd
> party client
> >> apis, is to deal with it like Spring deals with JDBC
> exceptions. In
> >> essence, they wrap and catch the various jdbc/driver
> exceptions and
> >> then map it to a set of common spring defined exceptions.
> >>
> >> In my mind, the Status code in the Response object should
> be a direct
> >> mapping to the HTTP status codes. This is really the
> intent you guys
> >> had. Of course, the status code is undefined for a request that
> >> cannot establish a connection with the host, due to
> various problems
> >> (physical connection, dns, proxy related issues, no route
> to host, etc.)
> >>
> >> Without the ability to "detect" these kind of connectivity
> issues in
> >> developer code, the Client class is pretty worthless. Having a
> >> generic isError() method or a bogus status code in the response
> >> doesn't give the level of detail needed.
> >>
> >> You're also forcing developers to use the nasty pattern of
> switch or
> >> if/else statements to check for the appropriate conditions in the
> >> Response object. If I'm making multiple requests to the
> server (which
> >> is common in a RESTful design), and the first call results
> in a 404
> >> Not Found, I don't want to have to keep checking under
> each statement
> >> for the various status codes. I just want to have the
> requests one
> >> per line and get an exception thrown for problems.
> >>
> >> This is why I mentioned, in the bug, about the wrapper I use that
> >> throws a UnexpectedStatusException (a custom exception
> class). The
> >> use of the code looks like this:
> >>
> >> try {
> >> Client client = new Client(...);
> >> client.handle(request1, response1, Status.SUCCESS_OK);
> >> client.handle(request2, response2, Status.SUCCESS_OK);
> >>
> >> } catch (IOException e) {
> >> // something bad has happened
> >> // like no connection, host name dns failure, etc.
> >>
> >> } catch (UnexpectedStatusException e) {
> >> // this is where you can put your if/then checking
> >> if (e.getStatus().equals(Status.CLIENT_ERROR_NOT_FOUND)) {
> >> // 404 Not Found message to user
> >> return;
> >> }
> >>
> >> // other handling here, or just some generic handling code
> >>
> >> }
> >>
> >> Note the additional parameter for the "expected" status in the
> >> handle() method.
> >>
> >> Anyway, the point is, you could in theory force all the
> client related
> >> exceptions into either IOException or UnexpectedStatusException.
> >> Then, you'd have a consistent API for dealing with both
> HTTP status
> >> code related issues as well as the other connectivity
> problems related
> >> to the physical connection. Defining handle() to throw
> both of these
> >> is, in my mind, the right direction.
> >>
> >> Adam
> >>
> >>
> >> Thierry Boileau wrote:
> >>> Adam,
> >>>
> >>> I just want to explain why this behaviour happens, not to plainly
> >>> justify it.
> >>> As you point, it has been decided to show the failures by
> the way of
> >>> the status code and not by the way of the exceptions.
> >>> One reason is that for example, the connectors are based on other
> >>> externals projects that may throw exceptions of different
> nature even
> >>> for equivalent issues, and the connectors may throw themselves
> >>> distinct exceptions for equivalent issues (equivalent
> from the API's
> >>> point of view).
> >>> Then, it has seemed difficult to potentially have to
> catch a growing
> >>> list of distinct exceptions in some part of the code (not
> the whole
> >>> code, of course). Thus, it has been decided, and it's a design
> >>> choice, to use the status codes instead of the exceptions.
> >>> However, this behaviour may be updated, the discussion is open.
> >>>
> >>> best regards,
> >>> Thierry Boileau
> >>>
> >>>> Oops, didn't see your reply here. I just replied to
> your other thread.
> >>>>
> >>>> Actually, I disagree. I think the problem is that the
> method should
> >>>> have originally been defined to through checked exceptions.
> >>>>
> >>>> I want to be to notify the user of the exceptions inside
> of the client
> >>>> itself. If my end user has entered a bad url, then I want to be
> >>>> able to
> >>>> notify them about that, for example.
> >>>>
> >>>> Setting a status code is not the way to handle this.
> You propose
> >>>> status
> >>>> code 404, but that's not an appropriate response for a
> "host not found"
> >>>> type of problem. Likewise, it's also not an appropriate
> status code if
> >>>> the url itself was poorly formed (like, without a
> leading protocol
> >>>> scheme).
> >>>>
> >>>> Anyway, my point is, there are many reason which a
> request could fail.
> >>>> I want to see these in my own code so that I can do
> what's appropriate
> >>>> with the exception.
> >>>>
> >>>> Adam
> >>>>
> >>>>
> >>>> Jim Alateras wrote:
> >>>>> Adam,
> >>>>>
> >>>>> I came across the same problem and I believe the
> problem is more
> >>>>> around not setting the response status code on failure.
> >>>>>
> >>>>> cheers
> >>>>> </jima>
> >>>>>
> >>>>> Adam Taft wrote:
> >>>>>>
> >>>>>> Here's a test case to look at...
> >>>>>>
> >>>>>> public class TestClass {
> >>>>>> public static void main(String[] args) {
> >>>>>> try {
> >>>>>> Request request = new Request(Method.GET,
> >>>>>> "aaaaaaaaaaaaaaaaa");
> >>>>>> Client client = new Client(Protocol.HTTP);
> >>>>>> client.handle(request);
> >>>>>> System.out.println("This code shouldn't
> >>>>>> run!");
> >>>>>> } catch (Throwable t) {
> >>>>>> // eat everything
> >>>>>> }
> >>>>>> }
> >>>>>> }
> >>>>>>
> >>>>>> The offending code is in HttpClientHelper#handle ...
> >>>>>>
> >>>>>> public void handle(Request request, Response response) {
> >>>>>> try {
> >>>>>> HttpClientCall httpCall =
> >>>>>> getConverter().toSpecific(this, request);
> >>>>>> getConverter().commit(httpCall, request, response);
> >>>>>> } catch (Exception e) {
> >>>>>> getLogger().log(Level.WARNING,
> >>>>>> "Error while handling an HTTP
> client call: ",
> >>>>>> e.getMessage());
> >>>>>> getLogger().log(Level.INFO,
> >>>>>> "Error while handling an HTTP
> client call", e);
> >>>>>> }
> >>>>>> }
> >>>>>>
> >>>>>>
> >>>>>> As soon as I get my email confirmation from tigris,
> I'll file a
> >>>>>> bug report. I just wanted to mention this in case
> there are other
> >>>>>> areas you know about with similar code. If the goal
> is to log the
> >>>>>> exception, that's ok, but it needs to be re-thrown.
> >>>>>>
> >>>>>> Thanks!
> >>>>>>
> >>>>>> Adam
> >>>>>>
> >>>>
> >>
