Presents your 
JAVA E-NEWSLETTER for November 25, 2002

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NOTICE TO SUBSCRIBERS: Due to the Thanksgiving holiday, the Java
newsletter will not be delivered on Thursday, Nov. 28, 2002. Look for 
your next edition of the Java TechMail on Monday, Dec. 2, 2002.

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APPLY THE POWER OF XPATH TO JAVABEANS

Asking a JavaBean for 'addressbook[1].state.code' is a common way of
interacting with JavaBeans nowadays, but you can go a step further and 
use the more powerful XPath specification.

XPath was created to access and modify data in XML, but a new project
from the Apache Jakarta group allows you to apply the powerful XPath
specification to ordinary JavaBeans.

To provide an example, we'll use a JavaBean with the following
structure:

Person.name      is a String
Person.age       is an int
Person.birthtown is a Town
Person.address   is an array of Address

Town.name        is a String

Address.number   is a String
Address.street   is a String
Address.town     is a Town

(The code isn't shown to maintain brevity.)

Given a person object, you can get the object's name with "name"; you
can get the name of birthtown with "birthtown/name"; and you can get 
the name of the town associated with an address (e.g., 21) with
"address[number='21']/town/name".

The main difference between XPath and typical bean notation, apart from
being more powerful, is the use of '/' rather than '.' to separate
elements. Once you get used to that aspect, it all becomes quite easy.

The following code shows how simple it is to use JXPath to apply XPath
notation to our JavaBean structure:

import org.apache.commons.jxpath.JXPathContext;

    ....
        Person person = ....;
        JXPathContext context = JXPathContext.newContext(person);
        System.out.println(context.getValue("name"));
        System.out.println(context.getValue("age"));
        System.out.println(context.getValue("birthtown/name"));
       
System.out.println(context.getValue("address[number='21']/street"));
       
System.out.println(context.getValue("address[number='21']/town/name"));
   ....

XPath can be used to set values and to create beans, as well as to get
values. For more information on XPath and its JXPath implementation, 
see the JXPath Web site.
http://jakarta.apache.org/commons/jxpath/

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