Cocoon: A Framework for Web Services

Wednesday, April 19, 2023

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Cocoon: A Framework for Web ServicesUsing Cocoon to consume and produce Web Services

Pankaj [email protected] Services Architect,HP Middleware



Presentation Goals

Understand Apache Cocoon, Web Services and how Cocoon can be used to build –Web Applications that consume Web

Services; and–Web Services that process huge XML

documents



Speakers’ Qualifications

• More than 12 years of System Programming experience

• Development manager in HP E-speak development• Development manager of HP XML Application

Frameworks ( Cocoon connection … )• Currently Web Services Architect at HP

Middleware ( Web Services connection … )• Contributor to Cocoon project• JAX-RPC and JSR109 Expert Group Member• Personal web-site: http://www.pankaj-k.net



Presentation Topics

• What is Cocoon?• Exploring Cocoon• What are Web Services?• Cocoon and Web Services• A Simple Cocoon Web Application



What is Cocoon?



Apache Cocoon

• XML based publishing Framework• An Apache Software Foundation opensource project• Written in Java, runs as a servlet ( not strictly true ! )• Project Home Page: http://xml.apache.org/cocoon• Started as a simple servlet based XSL styling engine for

http://java.apache.org site• Current version is in the second generation of evolution• Designed for scalability ( uses SAX processing ) -- can

process huge documents using small amount of memory



Apache Cocoon ( Contd. )

• Promotes separation of Content, Logic, Presentation and Management in web-site design.



Exploring Cocoon



Getting Started

• Download Cocoon Distribution from http://xml.apache.org/cocoon– I used Cocoon 2.0.1 for this presentation

• Unzip the distribution file cocoon-2.0.1-bin.zip.

• Drop cocoon.war to webapps directory of your Servlet Container– I used Tomcat 4.0.1 as the Servlet Container

• Start the Servlet Container• Point your browser to http://localhost:8080/cocoon



Cocoon Welcome Page



Cocoon ServletDirs. & FilesDirectory for auto mounting

sub-sitemaps

Cocoon Configuration file

A sub-sitemap directory

Main sitemap file

Directory for log files



Cocoon Sitemap

• Why Sitemap ?– need to de-couple exposed URI space from actual

location of resources– need easily changeable specification of processing steps

• What does it contain?– Component declarations

– generators, transformers, serializers, ...

– Resource declarations– named collection of pipeline components

– Pipeline declarations– sequential arrangement of components for processing



Cocoon Sitemap ( Contd. )

• A sitemap is an XML file• Sitemaps are hierarchical -- A sitemap can point,

explicitly or implicitly, to sub-sitemaps• A sitemap is translated into a java program and is

compiled to bytecode• Changes to sitemaps can be loaded dynamically

and asynchronously.• Cocoon community has debated extensively on

philosophical aspects of Sitemap but nothing better has come out ( yet ! ).



A sample pipeline<map:pipeline> <map:match pattern="hello.html"> <map:generate src="docs/samples/hello-page.xml"/> <map:transform src="stylesheets/page/simple-page2html.xsl"/> <map:serialize type="html"/> </map:match>

<map:match pattern="images/**.png"> <map:read src="resources/images/{1}.png" mime-type="image/png"/> </map:match>

<map:handle-errors> <map:transform src="context://stylesheets/system/error2html.xsl"/> <map:serialize status-code="500"/> </map:handle-errors></map:pipeline>



Request Processing By Cocoon• Request is dispatched to matching pipeline

• Basic pipeline operation– The generator generates XML content– Zero or more transformers transform the content– The serializer writes it to the output stream

• Different Kinds of generators– File, Directory, XSP, JSP, Stream, …

• Different Kinds of transformers– XSLT, I18N, Log, …

• Different Kind of Serializers– HTML, XML, Text, PDF, SVG, ...



Dynamic Content from XSP

<xsp:page language="java” xmlns:xsp=“http://apache.org/xsp” > <page> <title>A Simple XSP Page</title> <content> <para>dynamically generated list:</para> <ul> <xsp:logic> for (int i=0; i < 3; i++) { <li> Item <xsp:expr>i</xsp:expr> </li> } </xsp:logic> </ul> </content> </page>

</xsp:page>



What Are Web Services?



Defining Web ServicesMost commonly used definition:

• Web Services are– described in WSDL– exchange SOAP messages– use HTTP as transport– optionally, registered in UDDI registry

• Interaction can happen using RPC style or Document Exchange style, synchronously or asynchronously

• Knowledge of Implementation language or deployment platform is not required for interaction.

• Web Services promise Interoperability.



SOAP 1.1

• XML based protocol for exchange of information– Encoding rules for datatype

instances

– Convention for representing RPC invocations

• Designed for loosely-coupled distributed computing

• Used with XML Schema• Transport independent• SOAP with Attachments allow

arbitrary data to be packaged.

SOAP 1.1 Message StructureSOAP Envelope

[HeaderElement]

HeaderEntries

Body Element

[FaultElement]



WSDL 1.1

• A WSDL document describes– What the service can do

– Where it resides

– How to invoke it

• WSDL are like IDL but lot more flexible and extensible

• Defines binding for SOAP1.1, HTTP GET/POST and MIME

• WSDL descriptions can be made available from an UDDI registry

WSDL 1.1 Document StructureWSDLDocument

{Messages}

[Types]

{Services}

{PortTypes}

{Bindings}



What is a Web Services Platform ?

Environment, tools, libraries and other resources for:– Development of web services

– top down -- start with user code and generate WSDL

– bottom up -- start with WSDL and generate interfaces

– middle out -- a combination

– discovery of service interfaces

– Deployment of web services– publishing of services

– pre and post processing of SOAP requests, responses

– processing requests for WSDL descriptions

– Consumption of Web Services– discovery of Web Service

– invocation of/interaction with Web Services



Java Platforms and Standards• Java Platforms for Web Services

– HP WSP, HP WSR, HP WST– Apache SOAP 2.2, Apache Axis, UDDI4J, Cocoon– JWSDK ( Reference Implementation from Sun )– …

• Emerging Java Standards for Web Services– JAXM ( Java XML Messaging )– JAX-RPC ( Java Web Service Client Prog. model)– JSR 109 ( Java Web Service Prog. Model, deployment, ...)– JAXR ( Java API to access Web Service Registries )– J2EE 1.4 ( J2EE platform for Web Services )

• Java standards promise portability



Observations on Java Platforms and Standards

• Handle synchronous RPC style Web Services quite well• Not so good at supporting Web Services with document

exchange style, especially with asynchronous interface• Have difficulty dealing with large data• Many approaches to build and consume Web Services ( but

must adhere to wire protocols )• Standards in many areas are still emerging

– routing, reliable messaging

– security

– transactioning

– ...



Cocoon and Web Services



Cocoon as a Presentation Framework for Web-Services

Client Tier Web Tier

Web Services

WS Registry

Enterprise Apps

Servlet Container

Cocoon



Cocoon as a Processing Framework for Web Services

Client Tier Web Tier

Web Services

WS Registry

Enterprise Apps

Servlet ContainerCocoon

P1

P2



A Simple Cocoon Web Application



Problem Statement

Use Google Web Services API from http://www.google.com/apis

to create a simple web application that accepts a search string from user and displays the list of result entries.

Acknowledgement: This example is based on the XSP contributed by Ugo Cei in Cocoon-dev mailing list.



Application Components

sitemap.xmap -- Sitemap for this application

index.html -- HTML file to accept search string

google.xsp -- XSP file that makes the SOAP call to Google Web Service using SOAP logicsheet.

search-results.xsl -- XSL stylesheet to transform SOAP response from Google Web Service to HTML page

Downloadable from

http://www.pankaj-k.net/sdwest2002/google.zip



Application Architecture

Browser Google WSCocoon Servlet

http://<host>/cocoon/mount/google/

index.html

…/search?q=...

executes google.xsp

SOAP request

SOAP response

Search results in HTML

Maps request to index.html

Applies search-results.xsl



Demo Architecture

Browser Cocoon Servlet

http://<host>/cocoon/mount/google/welcome-local

index.html

…/search-local?q=...

Search results in HTML

Maps request to index-local.html

Applies search-results.xsl

Reads google.results



Web Application Demo

[Walk through the

Design, Sources

and the Demo]

Documents

Cocoon: A Framework for Web Services