License     Codehaus     OpenEJB     OpenJMS     OpenORB     Tyrex     
 

Main
  Home
  About
  Features
  Download
  Maven 2 support
  API
  DTD & Schemas
  Recent changes
  RSS news feed

Development/Support
  Mailing Lists
  SVN/JIRA
  Contributing
  Support
  Prof. services

Related projects
  Spring ORM support
  Spring XML factories

XML
  Using XML
  XML Mapping
  XML FAQ
  XML HOW-TOs
  Custom Handlers
  Best practice

XML Code Generator
  Code Generator
  Properties
  Custom bindings
  Ant task
  Schema Support
  Example

JDO
  Introduction
  Using JDO
  JDO Config
  Types
  JDO Mapping
  JDO FAQ
  JDO Examples
  JDO HOW-TOs
  Other Features
  JDO sample JAR

Advanced JDO
  Caching
  OQL
  Trans. & Locks
  Design
  KeyGen
  Long Trans.
  Nested Attrs.
  Pooling Examples
  LOBs
  Best practice

More
  Presentations
  The Examples
  3rd Party Tools
  JDO Tests
  XML Tests
  Configuration
  Tips & Tricks
  Full JavaDoc
  CastorWiki
 
 

About
  License
  Contributors
  Marketplace
  Status, Todo
  Changelog
  Library
  Contact
  Project Name

  



How to fetch DTDs and XML Schemas from JAR files using Castor


Intended Audience
Prerequisites
What Dependencies?
An Introduction to the EntityResolver
The Castor DTDResolver
The Hitch: Defining the Correct IDs
References


Intended Audience

Anyone who wants to retrieve DTDs and/or schemas from a local JAR file rather than the network.

This document helps people to get familiar with the basic concepts and discusses some implementation details.

Prerequisites

None. All the required files reside in the Castor JAR, but what version of Castor you have will determine the public/system IDs are recognized by the DTDResolver.

What Dependencies?

XML files often reference other files. The most common dependencies are either document type definitions (DTDs) from the DOCTYPE declaration or XML Schemas from the schemaLocation attribute.

Parsers usually only request schemas for validation, but more parsers are now requesting the DTDs whether validation is on or off. This allows the parser to resolve any entity references (i.e. & or <) that might be used in the document and defined in the DTD. This behavior can cause problems for machines with limited network connectivity, and in certain situations it is simply undesirable to have the parser going to the internet for each dependency.

An Introduction to the EntityResolver

The org.xml.sax.EntityResolver interface is the key to retrieving XML dependencies from locations other than the defined system location. The interface has one method:

public InputSource resolveEntity( String publicId, String systemId )
    throws SAXException, IOException

During parsing, before it attempts to retrieve any external files, the parser will call the above method, giving the public and/or system ID for the file. The implementing object can then either return an InputSource through which the parser can access the file, or null if the parser should fetch the file via normal channels.

The Castor DTDResolver

In Castor, the org.exolab.castor.util.DTDResolver class provides an implementation of EntityResolver that is designed to fetch all the Castor dependencies from the Castor JAR file. This includes:

-Mapping file DTD
-Mapping file schema
-JDOConf DTD
-JDOConf schema
-XML Schema Part 1: Structures DTD
-XML Schema Part 1: Structures schema
-XML Schema Part 2: Datatypes DTD

Castor automatically uses a DTDResolver when loading a mapping file, but must be told to use one during unmarshalling:

   public static void main( String[] args ) {
      String filename = args[0];

      try {
         Mapping mapping = new Mapping();
            
         // Castor will internally create and use a DTDResolver here
         mapping.loadMapping( "fooMap.xml" );

         Unmarshaller um1 = new Unmarshaller( mapping );
            
         // Castor needs to be told to use a DTDResolver here
         um1.setEntityResolver( new DTDResolver() );
         
         Foo foo = (foo)um1.unmarshal(new FileReader(filename));
      }
      catch( IOException e ) {
         e.printStackTrace();
      }
      catch( MappingException e ) {
         e.printStackTrace();
      }    
   }
        

The DTDResolver can also wrap another EntityResolver to allow resolver chaining. DTDResolver calls the nested EntityResolver before attempting to resolve the ID(s) itself.

The Hitch: Defining the Correct IDs

For the DTDResolver to retrieve the desired file from the Castor JAR, either the public ID or the system ID must match exactly. Below are lists of public and system IDs for the versions of Castor, but when in doubt, check the code of DTDResolver.

Since Castor v0.9.9.1 the following IDs are preferred:

Mapping DTD
Public: -//EXOLAB/Castor Mapping DTD Version 1.0//EN
System: http://castor.org/mapping.dtd
Mapping Schema
Public: -//EXOLAB/Castor Mapping Schema Version 1.0//EN
System: http://castor.org/mapping.xsd
JDO Configuration DTD
Public: -//EXOLAB/Castor JDO Configuration DTD Version 1.0//EN
System: http://castor.org/jdo-conf.dtd
JDO Configuration Schema
Public: -//EXOLAB/Castor JDO Configuration Schema Version 1.0//EN
System: http://castor.org/jdo-conf.xsd
XML Schema Part 1: Structures DTD
Public: -//W3C//DTD XMLSCHEMA 19991216//EN
System: http://www.w3.org/TR/2000/WD-xmlschema-1-20000225/structures.dtd
XML Schema Part 1: Structures Schema
System: http://www.w3.org/TR/2000/WD-xmlschema-1-20000225/structures.xsd
XML Schema Part 2: Datatypes DTD
System: http://www.w3.org/TR/2000/WD-xmlschema-2-20000225/datatypes.dtd

For older distributions, the following IDs have been accepted since Castor v0.9.5:

Mapping DTD
Public: -//EXOLAB/Castor Mapping DTD Version 1.0//EN
System: http://castor.exolab.org/mapping.dtd
Mapping Schema
Public: -//EXOLAB/Castor Mapping Schema Version 1.0//EN
System: http://castor.exolab.org/mapping.xsd
JDO Configuration DTD
Public: -//EXOLAB/Castor JDO Configuration DTD Version 1.0//EN
System: http://castor.exolab.org/jdo-conf.dtd
JDO Configuration Schema
Public: -//EXOLAB/Castor JDO Configuration Schema Version 1.0//EN
System: http://castor.exolab.org/jdo-conf.xsd
XML Schema Part 1: Structures DTD
Public: -//W3C//DTD XMLSCHEMA 19991216//EN
System: http://www.w3.org/TR/2000/WD-xmlschema-1-20000225/structures.dtd
XML Schema Part 1: Structures Schema
System: http://www.w3.org/TR/2000/WD-xmlschema-1-20000225/structures.xsd
XML Schema Part 2: Datatypes DTD
System: http://www.w3.org/TR/2000/WD-xmlschema-2-20000225/datatypes.dtd

References

- EntityResolver JavaDoc
 
   
  
   
 


Copyright © 1999-2005 ExoLab Group, Intalio Inc., and Contributors. All rights reserved.
 
Java, EJB, JDBC, JNDI, JTA, Sun, Sun Microsystems are trademarks or registered trademarks of Sun Microsystems, Inc. in the United States and in other countries. XML, XML Schema, XSLT and related standards are trademarks or registered trademarks of MIT, INRIA, Keio or others, and a product of the World Wide Web Consortium. All other product names mentioned herein are trademarks of their respective owners.