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From Matt Benson <gudnabr...@yahoo.com>
Subject Re: JXPath over Generic Collection<?>, How?
Date Wed, 11 Feb 2009 04:27:57 GMT

It should be as simple as Thing _containing_ a List<Thing> rather than _being_ a List<Thing>.
 Composition over inheritance, do you see?

HTH,
Matt


--- On Tue, 2/10/09, Andrew Hughes <ahhughes@gmail.com> wrote:

> From: Andrew Hughes <ahhughes@gmail.com>
> Subject: Re: JXPath over Generic Collection<?>, How?
> To: "Commons Users List" <user@commons.apache.org>, gudnabrsam@yahoo.com
> Date: Tuesday, February 10, 2009, 7:06 PM
> Matt, Thank You.
> 
> Is there any other data structure I can use that would work
> with JXPath? My
> requirement is that... a "Thing" can have contain
> multiple child "Thing(s)"
> (and the children are allowed to be non-unique).
> This is equivalent to an XML element as it can contain
> multiple child
> elements, how do these guy's handle it I wonder?
> 
> --Andrew
> 
> 
> On Wed, Feb 11, 2009 at 9:09 AM, Matt Benson
> <gudnabrsam@yahoo.com> wrote:
> 
> >
> > I admit I hadn't looked at this with a highly
> critical eye, but this
> > business of Thing extending ArrayList<Thing>
> seems quite strange to me.
> >  JXPath basically functions by "opening up"
> collections automatically, so
> > the very fact that Thing is itself a Collection
> implies that a Thing will be
> > opened up, and its children will be searched... but in
> this example, either
> > there are no children, at the leaves, or the children
> themselves are
> > (possibly empty) collections.  It looks as though
> you're trying to represent
> > a tree structure.  This may be a good example of a
> reason for the idea of
> > composition over inheritance.  I don't think
> you're going to get any
> > traction using JXPath with this object model.
> >
> > Sorry for the bad news,
> > Matt
> >
> >
> > --- On Tue, 2/10/09, Andrew Hughes
> <ahhughes@gmail.com> wrote:
> >
> > > From: Andrew Hughes <ahhughes@gmail.com>
> > > Subject: Re: JXPath over Generic
> Collection<?>, How?
> > > To: "Commons Users List"
> <user@commons.apache.org>
> > > Date: Tuesday, February 10, 2009, 7:16 AM
> > > Still busted. Example is now simplified. As soon
> as a
> > > generic Collection
> > > becomes involved BOOM!
> > >
> > > The Main Method to exec:
> > > public class App {
> > >     public static void main( String[] args ){
> > >         JXPathContext context =
> > > JXPathContext.newContext(new ThingRoot());
> > >
> > >
> System.out.println(((Thing)context.getValue("/root")).getName());
> > >     }
> > > }
> > >
> > > The (populated) context root I am using, where
> root is a
> > > single object
> > > holding a List of Thing's.
> > > package jxpathresearch;
> > >
> > > import java.util.ArrayList;
> > > import java.util.List;
> > >
> > > public class ThingRoot {
> > >     private List<Thing> root new
> ArrayList(); //this
> > > will serve as the root.
> > >     public ThingRoot() {
> > >         Thing animal = new
> Thing("Animal");
> > >         root.add(animal);//Animal
> > >         Thing dog = new Thing("Dog");
> > >         animal.add(dog);//Animal.Dog
> > >         dog.add(new
> > >
> Thing("Labrador"));//Animal.Dog.Labrador
> > >         dog.add(new
> > > Thing("Boxer"));//Animal.Dog.Boxer
> > >     }
> > >     public List<Thing> getRoot() { return
> root; }
> > > }
> > >
> > > Finally here's a very simple 'Thing'
> that
> > > contains a List of Thing(s):
> > > public class Thing extends ArrayList<Thing>
> {
> > >     public Thing(String name){this.name = name;}
> > >     private String name = "";
> > >     public String getName() {return name;}
> > > }
> > >
> > > I can't query anything beyond /root, it
> doesn't
> > > seem to ever get traversed.
> > > I would expect results for //Thing and
> > > //Thing[@name='Labrador'] etc but I
> > > get no results only exceptions.
> > >
> > >
> > > My brain is hurting.
> > >
> > >
> > >
> > > On Tue, Feb 10, 2009 at 12:22 AM, Andrew Hughes
> > > <ahhughes@gmail.com> wrote:
> > >
> > > > I've noew tested a whole heap of
> expressions even
> > > //name='Tiger' nothing
> > > > works.
> > > >
> > > > On Tue, Feb 10, 2009 at 12:01 AM, Andrew
> Hughes
> > > <ahhughes@gmail.com>wrote:
> > > >
> > > >> I got cracking on testing this out... no
> luck
> > > (yet). Here's my testing
> > > >> code if some kind person could please
> take a
> > > look....
> > > >> First my generic collection hierarchy
> (which only
> > > contains a name and
> > > >> children)...
> > > >>
> > > >> package jxpathresearch;
> > > >>
> > > >> import java.util.ArrayList;
> > > >>
> > > >> public class HierarchyPojo extends
> > > ArrayList<HierarchyPojo> {
> > > >>
> > > >>     public HierarchyPojo(String name){
> > > >>         this.setName(name);
> > > >>     }
> > > >>     private String name = "";
> > > >>
> > > >>     public String getName() {
> > > >>         return name;
> > > >>     }
> > > >>     public void setName(String name) {
> > > >>         this.name = name;
> > > >>     }
> > > >>
> > > >> }
> > > >>
> > > >>
> > > >> Next, the wrapper for the root context
> (as Matt
> > > suggested) and populated
> > > >> with animals...
> > > >>
> > > >> package jxpathresearch;
> > > >>
> > > >>
> > > >> public class CollectionRoot {
> > > >>
> > > >>
> > > >>     private HierarchyPojo hierarchyPojo;
> > > >>
> > > >>
> > > >>     public CollectionRoot(){
> > > >>
> > > >>         //Animal
> > > >>
> > > >>         hierarchyPojo = new
> > > HierarchyPojo("Animal");
> > > >>
> > > >>         //Animal.Dog
> > > >>
> > > >>         HierarchyPojo dog = new
> > > HierarchyPojo("Dog");
> > > >>
> > > >>         //Animal.Dog.Labrador
> > > >>
> > > >>         dog.add(new
> > > HierarchyPojo("Labrador"));
> > > >>
> > > >>         //Animal.Dog.Boxer
> > > >>
> > > >>         dog.add(new
> > > HierarchyPojo("Boxer"));
> > > >>
> > > >>         //Animal.Dog.Mastiff
> > > >>
> > > >>         dog.add(new
> > > HierarchyPojo("Mastiff"));
> > > >>
> > > >>         //Animal.Cat
> > > >>
> > > >>         HierarchyPojo cat = new
> > > HierarchyPojo("Cat");
> > > >>
> > > >>         //Animal.Cat.Tiger
> > > >>
> > > >>         cat.add(new
> > > HierarchyPojo("Tiger"));
> > > >>
> > > >>         //Animal.Cat.Cougar
> > > >>
> > > >>         cat.add(new
> > > HierarchyPojo("Cougar"));
> > > >>
> > > >>         //Animal.Cat.Leopard
> > > >>
> > > >>         cat.add(new
> > > HierarchyPojo("Leopard"));
> > > >>
> > > >>         //Add Animal.Dog &
> Animal.Cat
> > > >>
> > > >>         hierarchyPojo.add(dog);
> > > >>
> > > >>         hierarchyPojo.add(cat);
> > > >>
> > > >>     }
> > > >>
> > > >>
> > > >>     public HierarchyPojo
> getHierarchyPojo()
> > > {return hierarchyPojo;}
> > > >>
> > > >>
> > > >>     public void
> setHierarchyPojo(HierarchyPojo
> > > hierarchyPojo)
> > > >> {this.hierarchyPojo = hierarchyPojo;}
> > > >>
> > > >>
> > > >> }
> > > >>
> > > >>
> > > >> Finally invoke and test...
> > > >>
> > > >> public class App
> > > >>
> > > >> {
> > > >>
> > > >>     public static void main( String[]
> args )
> > > >>
> > > >>     {
> > > >>
> > > >>         JXPathContext context =
> > > JXPathContext.newContext(new
> > > >> CollectionRoot());
> > > >>
> > > >>         String query =
> > >
> "//hierarchyPojo[@name='Tiger']";
> > > >>
> > > >>         String fName =
> > > context.getValue(query).toString();
> > > >>
> > > >>         System.out.println("Ran
> > > '"+query+"' and got
> > > '"+fName+"'");
> > > >>
> > > >>     }
> > > >>
> > > >> }
> > > >>
> > > >>
> > > >>
> > > >> Above, should find one entry for
> > > 'name=Tiger' but it does not, I get an
> > > >> exception. This still doesn't seem
> to traverse
> > > the Collection correctly. Any
> > > >> help would be most welcome.
> > > >> Exception in thread "main"
> > > >>
> org.apache.commons.jxpath.JXPathNotFoundException:
> > > No value for xpath:
> > > >> //hierarchyPojo[@name='Tiger']
> > > >>
> > > >> Thanks for reading,
> > > >> Andrew
> > > >>
> > > >>
> > > >>
> > > >> On Mon, Feb 9, 2009 at 10:24 PM, Andrew
> Hughes
> > > <ahhughes@gmail.com>wrote:
> > > >>
> > > >>> Thanks Matt - I will test this out
> tomorrow
> > > when I am back in the
> > > >>> office...
> > > >>>
> > > >>> Being constructive...
> > > >>> Surely this should at least be a
> precondition
> > > check and throw a specific
> > > >>> exception if it's not supported?
> > > >>> Thank You
> > > >>> --Andrew
> > > >>>
> > > >>>
> > > >>> On Mon, Feb 9, 2009 at 2:27 PM, Matt
> Benson
> > > <gudnabrsam@yahoo.com>wrote:
> > > >>>
> > > >>>>
> > > >>>> Most likely your problem is not
> with
> > > generics, but simply with the fact
> > > >>>> that JXPath has a hard time
> using a
> > > collection as its root.  The easiest
> > > >>>> workaround is to use some parent
> object to
> > > hold a reference to your
> > > >>>> container.
> > > >>>>
> > > >>>> HTH,
> > > >>>> Matt
> > > >>>>
> > > >>>>
> > > >>>> --- On Sun, 2/8/09, Andrew
> Hughes
> > > <ahhughes@gmail.com> wrote:
> > > >>>>
> > > >>>> > From: Andrew Hughes
> > > <ahhughes@gmail.com>
> > > >>>> > Subject: JXPath over
> Generic
> > > Collection<?>, How?
> > > >>>> > To: "Commons Users
> List"
> > > <user@commons.apache.org>
> > > >>>> > Date: Sunday, February 8,
> 2009, 5:09
> > > PM
> > > >>>> > Hi All,
> > > >>>> > Hopefully the solution is
> as easy as
> > > the question. I would
> > > >>>> > like to perform
> > > >>>> > evaluation on a (very
> simple) generic
> > > collection... as you
> > > >>>> > can see below
> > > >>>> > (HeirarchyPojo). I should
> be able to
> > > ask for a
> > > >>>> > HeirarchyPojo's with
> > > >>>> > name='Bill' or the
> 3rd
> > > Child... The problem is that
> > > >>>> > nothing ever evaluate on
> > > >>>> > this data structure.
> What's the
> > > deal with Generic
> > > >>>> > Collections and JXPath?
> > > >>>> >
> > > >>>> > p.s this is not in the
> userguide and
> > > would be a most
> > > >>>> > welcomed addition (if
> > > >>>> > we can nut this out with
> your help).
> > > >>>> >
> > > >>>> > Cheers.
> > > >>>> >
> > > >>>> >
> > > >>>> > package xpath.and.generics;
> > > >>>> >
> > > >>>> > import java.util.ArrayList;
> > > >>>> >
> > > >>>> > public class HeirarchyPojo
> extends
> > > >>>> >
> ArrayList<HeirarchyPojo>{
> > > >>>> >
> > > >>>> >     public
> HeirarchyPojo(){}
> > > >>>> >
> > > >>>> >     private String id;
> > > >>>> >     private String name;
> > > >>>> >
> > > >>>> >     public String getId() {
> > > >>>> >         return id;
> > > >>>> >     }
> > > >>>> >
> > > >>>> >     public void
> setId(String id) {
> > > >>>> >         this.id = id;
> > > >>>> >     }
> > > >>>> >
> > > >>>> >     public String getName()
> {
> > > >>>> >         return name;
> > > >>>> >     }
> > > >>>> >
> > > >>>> >     public void
> setName(String name)
> > > {
> > > >>>> >         this.name = name;
> > > >>>> >     }
> > > >>>> >
> > > >>>> > }
> > > >>>>
> > > >>>>
> > > >>>>
> > > >>>>
> > > >>>>
> > >
> ---------------------------------------------------------------------
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> > > user-unsubscribe@commons.apache.org
> > > >>>> For additional commands, e-mail:
> > > user-help@commons.apache.org
> > > >>>>
> > > >>>>
> > > >>>
> > > >>
> > > >
> >
> >
> >
> >
> >
> ---------------------------------------------------------------------
> > To unsubscribe, e-mail:
> user-unsubscribe@commons.apache.org
> > For additional commands, e-mail:
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> >
> >


      

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