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Posted to dev@commons.apache.org by Simone Tripodi <si...@gmail.com> on 2010/01/06 13:38:50 UTC

New sandbox component: at-digester

Hi all guys
As a new ASF committer, I'm setting up a new Commons Sandbox, called "@Digester"

@Digester

The Apache commons-digester[1] is a great, light and fast XML parser;
it works with the SAX APIs and provides a serie of facilities to map
XML to POJOs.
It's configurable in the following ways:
* instancing and registering digester's rules into the digester;
* using the shorthand registration methods
* XML digester rules.

Even if these methods are excellent, they are limited - if Java
objects are due to be changed quickly, all previous methods need to be
extended/modified.

Inspired by the basic idea behind the JPA, JAXB's specifications, the
digester-annotations package would add some facilities to configure
the commons-digester using the Java5 language metadata annotations
support, it means creating the digester ruleset introspecting the
target POJOs, using a provided set of annotations. Using the annotated
Java object it's possible to create, in runtime the digester parser,
avoiding manual updates.

I mean, for example, given the following XML snippet

<web-app>
[...]
   <servlet>
       <servlet-name>action</servlet-name>
       <servlet-class>org.apache.struts.action.ActionServlet</servlet-class>
       <init-param>
           <param-name>application</param-name>
           <param-value>org.apache.struts.example.ApplicationResources</param-value>
       </init-param>
       <init-param>
           <param-name>config</param-name>
           <param-value>/WEB-INF/struts-config.xml</param-value>
       </init-param>
   </servlet>
[...]
</web-app>

It could be mapped as

@ObjectCreate("web-app/servlet")
public final class ServletBean {

   @BeanPropertySetter("web-app/servlet/servlet-name")
   private String servletName;

   @BeanPropertySetter("web-app/servlet/servlet-class")
   private String servletClass;

   private final Map<String, String> initParams = new HashMap<String,
String>();

   public String getServletName() {
       return this.servletName;
   }

   public void setServletName(String servletName) {
       this.servletName = servletName;
   }

   public String getServletClass() {
       return this.servletClass;
   }

   public void setServletClass(String servletClass) {
       this.servletClass = servletClass;
   }

   @CallMethod("web-app/servlet/init-param")
   public void
addInitParam(@CallParam("web-app/servlet/init-param/param-name")
String name,
           @CallParam("web-app/servlet/init-param/param-value") String value) {
       this.initParams.put(name, value);
   }

   [...]

}

and a special DigesterLoader is able to create Digester rules simply
by analizing the ServletBean class:

Digester digester = DigesterLoader.createDigester(ServletBean.class);

Of course, this approach has limitations too - i.e. it doesn't work
with 3rd part developed objects - but the combined use of the
different approaches should reduce the manually produced code.

Current status of code:
I've already done almoust the 80% of code on google-code[2] licensed
under ASF2 license and also submitted a deprecated patch[3] on
commons-digester Jira: I would like to remove the
project on google-code and complete the work in
the sandbox, then re-propose to commons-digester community the new
feature.

I really hope you'll find this new way of parsing XML interesting like I do :P
Thanks in advance, best regards!!!
Simone Tripodi

[1] http://commons.apache.org/digester/
[2] http://code.google.com/p/digester-annotations/source/browse/
[3] https://issues.apache.org/jira/browse/DIGESTER-135

-- 
http://www.google.com/profiles/simone.tripodi

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