B.2. Authoring the schema

Creating an XML configuration extension for use with Spring's IoC container starts with authoring an XML Schema to describe the extension. What follows is the schema we'll use to configure SimpleDateFormat objects. The emphasized line contains an extension base for all tags that will be identifiable (meaning they have an id attribute that will be used as the bean identifier in the container).

#### myns.xsd (inside package org/springframework/samples/xml)

<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns="http://www.springframework.org/schema/myns"

   <xsd:import namespace="http://www.springframework.org/schema/beans"/>
   <xsd:element name="dateformat">
            <xsd:extension base="beans:identifiedType">
               <xsd:attribute name="lenient" type="xsd:boolean"/>
               <xsd:attribute name="pattern" type="xsd:string" use="required"/>

The above schema will be used to configure SimpleDateFormat objects, directly in an XML application context file using the myns:dateformat configuration directive. As noted above, the id attribute will (in this case) be used as the bean identifier for the SimpleDateFormat bean.

<myns:dateformat id="dateFormat" 
    pattern="yyyy-MM-dd HH:mm"

Note that after we've created the infrastructure classes, the above snippet of XML will essentially be exactly the same as the following XML snippet. In other words, we're just creating a bean in the container, identified by dateFormat of type SimpleDateFormat, with a couple of properties set.

<bean id="dateFormat" class="java.text.SimpleDateFormat">
    <constructor-arg value="yyyy-HH-dd HH:mm"/>
    <property name="lenient" value="true"/>


The schema-based approach to creating configuration format, allows for tight integration with an IDE that has a schema-aware XML editor. Using a properly authored schema, you can for example use autocompletion to have a user choose between several configuration options defined in the enumeration.