Hello,
My application throws unchecked exceptions; I derived StatusService so that
I can decide what status code and representation to send to the client.
It works as expected except when the exception is thrown from a resource
constructor.
Because Finder.createResource uses reflection to call my resource constructor,
the unchecked exception gets wrapped into an InvocationTargerException;
this (checked) exception is caught by the method's 'catch (Exception e)'
block, which logs a message and returns null:
public Resource createResource(Request request, Response response) {
Resource result = null;
if (getTargetClass() != null) {
try {
[...]
result = constructor.newInstance(getContext(), request,response);
[...]
} catch (Exception e) {
getLogger().log(...);
}
}
return result;
}
My unchecked exception has been swallowed- and now, Finder.handle assumes it's
a 404:
public void handle(Request request, Response response) {
[...]
Resource target = findTarget(request, response);
if (!response.getStatus().equals(Status.SUCCESS_OK)) {
// Probably during the instantiation of the target resource, or
// earlier the status was changed from the default one. Don't go
// further.
} else if (target == null) {
// If the currrent status is a success but we couldn't find the
// target resource for the request's resource URI, then we set
// the response status to 404 (Not Found).
response.setStatus(Status.CLIENT_ERROR_NOT_FOUND);
}
[...]
}
My solution is to provide my own Finder, catch InvocationTargetException,
and rethrow the cause (it it's an error):
class MyFinder extends Finder {
public Resource createResource(Request request, Response response) {
Resource result = null;
Error error = null;
try {
[...]
try {
[...]
} catch (NoSuchMethodException nsme) {
[...]
} }
catch(InvocationTargetException e){
if (e.getCause() instanceof Error){
error =(Error) e.getCause();
}
}
} catch (Exception e) {
getLogger().log([...]);
}
}
// rethrow the Error that was wrapped in InvocationTargetException
if (error != null){
throw error;
}
return result;
}
The alternative would by to catch Error in all my resource constructors,
set the response status to SERVER_ERROR, and rethrow the error. Not
very compelling.
Do you see the current behavior as a design flaw? I agree that resource
constructor should not throw check exceptions because we know they're
created by reflection, but we should let unchecked exceptions bubble up.
-Vincent.
