Jakarta Commons Cookbook

12.3. Search a Collection of Simple Objects

Problem

You need to select objects from a Collection using XPath predicates.

Solution

Use Jakarta Commons JXPath to select objects from a Collection using predicates in XPath expressions. The iterate( ) method on JXPathContext takes an XPath expression and returns an Iterator that contains each node satisfying that expression. The following example uses simple XPath predicates to select Person objects from a List by age, first name, and position:

import org.apache.commons.jxpath.JXPathContext; // Create a List of Person objects List people = new ArrayList( ); people.add(new Person("Ahmad", "Russell", 28 ); people.add(new Person("Tom", "Russell", 35 ); people.add(new Person("Ahmad", "Abuzayedeh", 33 ); // Select all people older than 30 System.out.println( "** People older than 30"); JXPathContext context = JXPathContext.newContext( people ); Iterator iterator = context.iterate(".[@age > 30]"); printPeople(iterator); // Select all people with a first name of 'Ahmad' context = JXPathContext.newContext( people ); System.out.println( "** People with first name 'Ahmad'" ); iterator = context.iterate(".[@firstName = 'Ahmad']"); printPeople(iterator); // Select the second person from the List context = JXPathContext.newContext( people ); System.out.println( "** Third Person in List" ); Person p = (Person) context.getValue(".[2]"); System.out.println( "Person: " + p.getFirstName( ) + " " + p.getLastName( ) + ", age: " + p.getAge( ) ); // A method ...