Visitor-pattern to work with throws -declaration
------------------------------------------------
Key: QI-249
URL: http://issues.ops4j.org/browse/QI-249
Project: Qi4j
Issue Type: Improvement
Components: API, Core Runtime
Affects Versions: 1.1
Environment: Any environment capable of running Qi4j-application.
Reporter: Stanislav Muhametsin
Assignee: Rickard Öberg
Currently, for example the org.qi4j.api.property.StateHolder has method "public
void visitProperties( StateVisitor visitor);" where StateVisitor has one method
"public void visitProperty(...);". It is supposed to be used something like
"holder.visitProperties(new StateVisitor() { [implementation of visitProperty]
});". This works great as long as code implementing visitProperty doesn't
invoke anything that has "throws XXXException" in its method declaration. If
this happens, things start to get really awkward - one must catch exception,
wrap it into something that extends RuntimeException (preferably class unique
to this usecase), then catch it outside invokation of visitProperties(...), and
possibly unwrap exception and throw it again.
To easen up implementing this scenario, each interface which has visitXXX
method working as visitor-pattern, could have additional method, like this:
public <T> void visitXXXWithThrowable(XXXVisitorWithThrowable<T> visitor)
throws T;
where XXXVisitorWithThrowable could be something like this:
public interface XXXVisitorWithThrowable<T>
{
public void visitXXX(...) throws T;
}
Client code may then invoke, for example,
holder.visitPropertiesWithThrowable(new StateVisitorWithThrowable<SQLException>
{ [implementation of visitProperty(...) throw SQLException] } );
Because the method has different name, and there are no changes (only
additions) to any working interfaces and APIs, this improvement would be
backwards-compatible too.
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