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From Andrew Hughes <ahhug...@gmail.com>
Subject Re: JXPath over Generic Collection<?>, How?
Date Wed, 11 Feb 2009 01:06:20 GMT
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
> > >>>>
> > >>>>
> > >>>
> > >>
> > >
>
>
>
>
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