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# Understanding Apache Cocoon

## Overview

This document is intended for both Users and Developers and presents an overall picture of Apache Cocoon.

- Prerequisites
- A Little History
- What problem does Cocoon solve?
- Basic Mechanisms.
- Architecture.
- Abstraction.
- Apache Cocoon Configuration.
- Apache Cocoon Work Area.
- Use with Tomcat

## Prerequisites

What You Should know:

- XML, XML Namespaces
- Basics of XPath, XSLT
- Java language
- Servlets, HTTP

What You need not know:

- Cocoon 1

## A Little History

### Cocoon 1

- Cocoon project was founded in Jan. 1999 by Stefano Mazzocchi as an open source project under Apache Software Foundation.
- Started as a simple servlet for XSL styling of XML content.
- Was based on DOM level 1 API. This choice turned out to be quite limiting for speed/memory efficiency.
- Used reactor pattern to connect components. This allowed the reaction instructions to be placed inside the documents. Though appealing, it caused difficulties in managing highly dynamic web-sites.
- Allowed context overlap to happen by having processing instructions in documents/stylesheets.

### Apache Cocoon

- A separate codebase to incorporate Cocoon 1 learnings.
- Designed for execution speed/memory efficiency and scalability to process very large documents by switching processing model from DOM to SAX.
- Centralizes the management functions by allowing processing pipeline specification in a sitemap (an XML file), replacing the embedded processing instruction model.
- Better support for pre-compilation, pre-generation and caching for better performance.

## What problem does Cocoon solve?

Basic problem to be solved:

### Separation of content, style, logic and management functions in an XML content based web site (and web services).

### Data Mapping

## Basic Mechanisms.

Basic mechanisms for processing XML documents:

- Dispatching based on Matchers.
- Generation of XML documents (from content, logic, Relation DB, objects or any combination) through Generators
- Transformation (to another XML, objects or any combination) of XML documents through Transformers
- Aggregation of XML documents through Aggregators
- Rendering XML through Serializers

### Pipeline Processing

Sequence of Interactions

Pipeline

## Architecture.

### Core Cocoon

- Avalon framework for logging, configuration, threading, context etc.
- Caching mechanism
- Pipeline handling
- Program generation, compilation, loading and execution.
- Base classes for generation, transformation, serialization, components.
- ...

### Cocoon Components

- Specific generators
- Specific transformers
- Specific matchers
- Specific serializers
- ...

### Built-in Logicsheets

- sitemap.xsl
- xsp.xsl
- esql.xsl
- request.xsl
- response.xsl
- ...

### Site specific configuration, components, logicsheets and content

- ...

## Abstraction.

### eXtensible Server Pages (XSPs)

An XSP page is an XML page with following requirements:

- The document root must be `<xsp:page>`
- It must have language declaration as an attribute in the `<xsp:page>` element.
- It must have namespace declaration for xsp as an attribute in the `<xsp:page>` element.
- For an XSP to be useful, it must also require at least an `<xsp:logic>` and an `<xsp:expr>` element.

    <?xml version="1.0" encoding="ISO-8859-1"?>

    <xsp:page language="java" xmlns:xsp="http://apache.org/xsp">

      <xsp:logic>
      static private int counter = 0;
      private synchronized int count()
      {
        return counter++;
      }
      </xsp:logic>

      <page>
      <p>I have been requested <xsp:expr>count()</xsp:expr> times.</p>
      </page>

    </xsp:page>

An XSP page is used by a generator to generate XML document.

### XSP Processing (Code Generation)

    package org.apache.cocoon.www.docs.samples.xsp;

    import java.io.File;
    // A bunch of other imports

    public class counter_xsp extends XSPGenerator {
       // .. Bookkeeping stuff commented out.
      /* User Class Declarations */
      static private int counter = 0;
      private synchronized int count() {
        return counter++;
      }
      /* Generate XML data. */
      public void generate() throws SAXException {
        this.contentHandler.startDocument();
        AttributesImpl xspAttr = new AttributesImpl();
        this.contentHandler.startPrefixMapping("xsp", "http://apache.org/xsp");
        this.contentHandler.startElement("", "page", "page", xspAttr);
        // Statements to build the XML document (Omitted)
        this.contentHandler.endElement("", "page", "page");
        this.contentHandler.endPrefixMapping("xsp");
        this.contentHandler.endDocument();
      }

### Ways of Creating XSPs

#### Embedded Logic

- Code is embedded in the XML page
- No separation of content and logic
- Okay for small examples but terrible for large systems.

#### Included Logicsheet

- Code is in a separate logicsheet (an XSL file)
- Effective separation of content and logic
- Preferred way to create XSPs

#### Logicsheet as tag library

- The logicsheet is packaged as a reusable tag library and registered with Cocoon in cocoon.xconf file.
- Tag library has a namespace declaration, declared in the original logicsheet and matched in `<xsp:page>` xmlns:... attribute.
- Effective separation of content, logic and management

### Sitemap

    <?xml version="1.0"?>
    <map:sitemap xmlns:map="http://apache.org/cocoon/sitemap/1.0">

    <map:components>
    ...
    </map:components>

    <map:views>
    ...
    </map:views>
    <map:pipelines>
    <map:pipeline>
    <map:match>
    ...
    </map:match>
    ...
    </map:pipeline>
    ...
    </map:pipelines>
    ...
    </map:sitemap>

Sitemap contains configuration information for a Cocoon engine:

- list of matchers
- list of generators
- list of transformers
- list of readers
- list of serializers
- list of selectors
- list of processing pipelines with match patterns
- ...

Sitemap is an XML file corresponding to a sitemap DTD.

Sitemap can be edited to add new elements.

Sitemap is generated into a program and is compiled into an executable unit.

### Matchers

A Matcher attempts to match an URI with a specified pattern for dispatching the request to a specific processing pipeline.

Different types of matchers:

- wildcard matcher
- regexp matcher

More matchers can be added without modifying Cocoon.

Matchers help in specifying a specific pipeline processing for a group of URIs.

Sitemap entries for different types of matchers

    <map:matchers default="wildcard">
     <map:matcher name="wildcard" factory="org.apache.cocoon.matching.WildcardURIMatcher"/>
     <map:matcher name="regexp" factory="org.apache.cocoon.matching.RegexpURIMatcher"/>
    </map:matchers>

Pipeline entries in sitemap file

    <map:match pattern="jsp/*">
      <map:generate type="jsp" src="/docs/samples/jsp/{1}.jsp"/>
      ...
      </map:match>
    <map:match pattern="hello.pdf">
    </map:match

### Generators

A Generator is used to create an XML structure from an input source (file, directory, stream ...)

Different types of generators:

- file generator
- directory generator
- XSP generator
- JSP generator
- Request generator
- ...

More generators can be added without modifying Cocoon.

Sitemap entries for different types of generators

    <map:generators default="file">
     <map:generator name="file"
                    src="org.apache.cocoon.generation.FileGenerator"
                    label="content"/>
     <map:generator name="directory"
                    src="org.apache.cocoon.generation.DirectoryGenerator"
                    label="content"/>
     <map:generator name="serverpages"
                    src="org.apache.cocoon.generation.ServerPagesGenerator"
                    label="content"/>
     <map:generator name="request"
                    src="org.apache.cocoon.generation.RequestGenerator"/>
     ...
    </map:generators>

A sample generator entries in a 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>

A Generator turns an XML document, after applying appropriate transformations, into a compiled program whose output is an XML document.

An XSP generator applies all the logicsheets specified in the source XML file before generating the program.

Generators cache the compiled programs for better runtime efficiency.

### Transformers

A Transformer is used to map an input XML structure into another XML structure.

Different types of transformers:

- XSLT Transformer
- Log Transformer
- SQL Transformer
- I18N Transformer
- ...

Log Transformer is a good debugging tool.

More transformers can be added without modifying Cocoon.

Sitemap entries for different types of transformers

    <map:transformers default="xslt">
       <map:transformer name="xslt" src="org.apache.cocoon.transformation.TraxTransformer">
        <use-request-parameters>false</use-request-parameters>
        <use-browser-capabilities-db>false</use-browser-capabilities-db>
       </map:transformer>
       <map:transformer name="log" src="org.apache.cocoon.transformation.LogTransformer"/>
    ...

    </map:transformers>

A sample transformer entry in a 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>

### Serializers

A Serializer is used to render an input XML structure into some other format (not necessarily XML)

Different types of serializers:

- HTML Serializer
- FOP Serializer
- Text Serializer
- XML Serializer
- ...

More serializers can be added without modifying Cocoon.

Sitemap entries for different types of serializers

    <map:serializers default="html">
     <map:serializer name="xml"
                     mime-type="text/xml"
                     src="org.apache.cocoon.serialization.XMLSerializer"/>
     <map:serializer name="html"
                     mime-type="text/html"
                     src="org.apache.cocoon.serialization.HTMLSerializer"/>
     <map:serializer name="fo2pdf"
                     mime-type="application/pdf"
                     src="org.apache.cocoon.serialization.FOPSerializer"/>
     <map:serializer name="vrml"
                     mime-type="model/vrml"
                     src="org.apache.cocoon.serialization.TextSerializer"/>
     ...
    </map:serializers>

A sample serializer entry in a 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>

### Pipeline Processing

The sitemap configuration allows dynamic setup of processing pipelines consisting of a generator, multiple transformers and a serializer.

Requests are dispatched to a pipeline based on request URI and the pipeline matching pattern (either with wildcards or as a regexp)

The pipeline is setup in the generated file `sitemap_xmap.java` (This file gets generated [possibly asynchronously] everytime the `sitemap.xmap` is modified.

### Logicsheets

Logicsheets are XSL files with an associated namespace.

Primary mechanism to add program logic (code) to XSPs.

These need to be registered in configuration file cocoon.xconf.

Logicsheets are used by the generator to transform XML structure before generating program.

Cocoon comes with a no. of built-in logic sheets:

- request.xsl
- response.xsl
- session.xsl
- cookie.xsl
- esql.xsl
- log.xsl
- ...

Log.xsl structure

    <xsl:stylesheet  version="1.0"
                     xmlns:xsp="http://apache.org/xsp"
                     xmlns:log="http://apache.org/xsp/log"
                     xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

    <xsl:template match="log:logger">
    ... variable and xsp:logic statements ...
    </xsl:template>

    <xsl:template match="log:debug">
      <xsp:logic>
       if(getLogger() != null)
         getLogger().debug("<xsl:value-of select="."/>");
      </xsp:logic>
    </xsl:template>
    <xsl:template match="log:error">
    ...
    </xsl:template>
    </xsl:stylesheet>

A sample use

    <xsp:page language="java"
              xmlns:xsp="http://apache.org/xsp"
              xmlns:log="http://apache.org/xsp/log">

      <page>
      <log:logger name="test" filename="test.log"/>
      <log:debug>Test Message</log:debug>
      </page>
    </xsp:page>

## Apache Cocoon Configuration.

Cocoon is highly configurable. Main configuration files, assuming Cocoon deployment as a servlet in a servlet container, are (directory locations assume Tomcat servlet container):

- `sitemap.xmap`: the sitemap file. By default, located in `$TOMCAT_HOME/webapps/cocoon` directory.
- `cocoon.xconf`: configuration file having logicsheet registrations. Specifies, sitemap.xmap location and other such parameters. By default, located in `$TOMCAT_HOME/webapps/cocoon` directory.
- `web.xml`: servlet deployment descriptor. Specifies location of cocoon.xconf, log file location and other such parameters. Located in `$TOMCAT_HOME/webapps/cocoon/WEB-INF` directory.
- `cocoon.roles`: mapping file for Core Cocoon components name and implementation classes. For example, if you want to use a parser other than the default one, you need to modify this file.

## Apache Cocoon Work Area

Cocoon produces execution log entries for debugging/auditing.

- The amount of data to be logged can be controlled by log-level parameter in web.xml file. The default is DEBUG (maximum data).
- By default, the log file is: `$TOMCAT_HOME/webapps/cocoon/WEB-INF/logs/cocoon.log`.

Cocoon keeps the generated .java files in a directory tree starting at (by default):
`$TOMCAT_HOME/webapps/work/localhost_8080%2Fcocoon/org/apache/cocoon/www`.

You can find sitemap_xmap.java here.

Files created by LogTransformer are kept (by default) in `$TOMCAT_HOME` directory.

## Use with Tomcat

Download Tomcat from Apache site.

Download Cocoon sources from Apache CVS. [Command assume UNIX Bourne shell]

    export CVSROOT=:pserver:anoncvs@cvs.apache.org:/home/cvspublic
    cvs login
    Password: anoncvs
    cvs checkout cocoon-2.1

Build sources as per instruction in Install file.

Move the `cocoon.war` file to `$TOMCAT_HOME/webapps` directory.

Start the servlet engine. Type-in the URL `http://localhost:8080/cocoon` in your browser. You should see the Cocoon welcome message.

Consult Install file if you face problems.

Errors and Improvements? If you see any errors or potential improvements in this document please help us: View, Edit or comment on the latest development version (registration required).