David-
I think your idea is a great one. Ideally, you would configure the
BeanInfo for Map like classes with a readMethod that treats the names
of Map properties as keys. That way the evalulation expression
"foo.someMap.firstName" would result in 'firstName' being treated as a key
to be looked up in the Map and returned. This is the way the java
beans specification exposes hooks to "override" when the '.' operator
does.
Unfortunately, doing this in practice is quite difficult. Without going into
the details, if you investigate this method in the java beans API's you will
find it quite inflexible. However, the idea is right. We should be able to
explicitly define how properties of a given type are accessed and mutated.
I think the right way to implement this is to create an interface called
PropertyMapper and support a mechanism for linking property mappers
with java Classes via a PropertyMapperRegistry.
public interface PropertyMapper {
public Object getProperty(Object bean, String propName);
public Object setProperty(Object bean, String propName, Object propValue);
}
public class PropertyMapperRegistry {
public PropertyMapper getPropertyMapper(Class type);
public void registerPropertyMapper(Class type, PropertyMapper pm);
}
Then, the struts PropertyUtils.getPropertyValue and setPropertyValue methods
(I might have the names slightly wrong) would first look to see if a
PropertyMapper is registered for a given type, and use that PropertyMapper if
possible. If a PropertyMapper is not registered for a given type, then the
PropertyUtils falls back to the standard readMethod and writeMethod supplied
by the property's PropertyDescriptor.
Here is how you would implement a PropertyMapper for HashMaps
public class HashMapPropertyMapper implements PropertyMapper {
public Object getProperty(Object bean, String propName) {
return( ((HashMap)bean).get(propName) );
}
public Object setProperty(Object bean, String propName, Object propValue) {
return( ((HashMap)bean).put(propName, propValue) );
}
}
The reason I favor this approach is:
(1) This method is very close the initial spirit of the Java Beans spec
(2) No new syntax is introduced. We do not need { } and can utilize the
existing '.' (dot) operator.
(3) This solution is more general than a solution just for HashMaps.
Although this is applied really well to HashMaps, With this method,
we can implement PropertyMappers for any class. One example that comes to
mind is this (although slightly academic):
Imagine we have a FileManager class that we use to create java.io.File
objects (kind of a File Factory). We might want to abstractly define that
a properties of FileManagers are File objects obtained through the
FileManager, such that we can write expressions like this:
"someObject.myFileManager./usr/local/apache/logs/error"
To put it simply, we can make the '.' operator mean anything we want it to mean
for a given target class. Kind of cool. This kind of thing can also be seen
in the Python programming language where the developer can override the
imlementation of '.' and is also similar to 'tie' in Perl .
-will
David Winterfeldt writes:
> Here is the source. I've done some basic tests and I
> think everything is working.
>
> David
>
> --- David Winterfeldt <[EMAIL PROTECTED]> wrote:
> > For an array you can do this for a property
> > "type[index]". I don't know if this has been
> > suggested before, but what if you could also do this
> > for a Hashmap. I was thinking something like
> > form{name}. I'm sure there are lots of other uses,
> > but it could let you make a bean/form class that
> > just
> > used a Hashmap for rapid prototyping. This also
> > might
> > be a simple/temporary solution for the beans that
> > don't need setters and getters.
> >
> > public Hashmap getForm();
> >
> > <html:text property="form{firstName}" size="30"
> > maxlength="30"/>
> > <html:text property="form{lastName}" size="30"
> > maxlength="30"/>
> > <html:text property="form{address}" size="30"
> > maxlength="30"/>
> >
> >
> > David
> >
> > __________________________________________________
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>
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