src/sax/EntityResolver.hpp

/*
 * The Apache Software License, Version 1.1
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 * Copyright (c) 1999 The Apache Software Foundation.  All rights 
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 * This software consists of voluntary contributions made by many
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/**
 * $Log$
 * Revision 1.1  1999/11/09 01:07:44  twl
 * Initial revision
 *
 * Revision 1.3  1999/11/08 20:44:56  rahul
 * Swat for adding in Product name and CVS comment log variable.
 *
 */


#ifndef ENTITYRESOLVER_HPP
#define ENTITYRESOLVER_HPP

#include <util/XML4CDefs.hpp>

class InputSource;

/**
  * Basic interface for resolving entities.
  *
  * <p>If a SAX application needs to implement customized handling
  * for external entities, it must implement this interface and
  * register an instance with the SAX parser using the parser's
  * setEntityResolver method.</p>
  *
  * <p>The parser will then allow the application to intercept any
  * external entities (including the external DTD subset and external
  * parameter entities, if any) before including them.</p>
  *
  * <p>Many SAX applications will not need to implement this interface,
  * but it will be especially useful for applications that build
  * XML documents from databases or other specialised input sources,
  * or for applications that use URI types other than URLs.</p>
  *
  * <p>The following resolver would provide the application
  * with a special character stream for the entity with the system
  * identifier "http://www.myhost.com/today":</p>
  *
  *<pre>
  *#include <sax/EntityResolver.hpp>
  *#include <sax/InputSource.hpp>
  *
  *class MyResolver : public EntityResolver {
  *  public:
  *    InputSource resolveEntity (const XMLCh* const publicId, 
  *                               const XMLCh* const systemId);
  *   ...
  *   };
  *
  *  MyResolver::resolveEntity {
  *    if (XMLString::compareString(systemId, "http://www.myhost.com/today")) {
  *      MyReader* reader = new MyReader();
  *      return new InputSource(reader);
  *    } else {
  *      return null;
  *    }
  *  }
  *
  *</pre>
  *
  * <p>The application can also use this interface to redirect system
  * identifiers to local URIs or to look up replacements in a catalog
  * (possibly by using the public identifier).</p>
  *
  * <p>The HandlerBase class implements the default behaviour for
  * this interface, which is simply always to return null (to request
  * that the parser use the default system identifier).</p>
  *
  * $Log$
  * Revision 1.1  1999/11/09 01:07:44  twl
  * Initial revision
  *
  * Revision 1.3  1999/11/08 20:44:56  rahul
  * Swat for adding in Product name and CVS comment log variable.
  *
  * @see Parser#setEntityResolver
  * @see InputSource#InputSource
  * @see HandlerBase#HandlerBase 
  */
class SAX_EXPORT EntityResolver
{
public:
    /** @name Constructors and Destructor */
    //@{

    /** Default Constructor */
    EntityResolver()
    {
    }

    /** Destructor */
    virtual ~EntityResolver()
    {
    }

    //@}

    /** @name The EntityResolver interface */
    //@{

  /**
    * Allow the application to resolve external entities.
    *
    * <p>The Parser will call this method before opening any external
    * entity except the top-level document entity (including the
    * external DTD subset, external entities referenced within the
    * DTD, and external entities referenced within the document
    * element): the application may request that the parser resolve
    * the entity itself, that it use an alternative URI, or that it
    * use an entirely different input source.</p>
    *
    * <p>Application writers can use this method to redirect external
    * system identifiers to secure and/or local URIs, to look up
    * public identifiers in a catalogue, or to read an entity from a
    * database or other input source (including, for example, a dialog
    * box).</p>
    *
    * <p>If the system identifier is a URL, the SAX parser must
    * resolve it fully before reporting it to the application.</p>
    *
    * @param publicId The public identifier of the external entity
    *        being referenced, or null if none was supplied.
    * @param systemId The system identifier of the external entity
    *        being referenced.
    * @return An InputSource object describing the new input source,
    *         or null to request that the parser open a regular
    *         URI connection to the system identifier.
    * @exception SAXException Any SAX exception, possibly
    *            wrapping another exception.
    * @exception IOException An IO exception,
    *            possibly the result of creating a new InputStream
    *            or Reader for the InputSource.
    * @see InputSource#InputSource
    */
    virtual InputSource* resolveEntity
    (
        const   XMLCh* const    publicId
        , const XMLCh* const    systemId
    ) = 0;

    //@}

private :
    /** Unimplemented constructors and operators */

    //@{

    /** Copy constructor */
    EntityResolver(const EntityResolver&);

    /** Assignment operator */
    void operator=(const EntityResolver&);

    //@}
};

#endif