Steve,
Thanks a lot for time to explain. This helps a lot !
Regards
Ajay
--- On Fri, 10/14/11, Steve Hathaway <shath...@e-z.net> wrote:
From: Steve Hathaway <shath...@e-z.net>
Subject: Re: How do implement EntityResolver for XSLT XML transformation
To: xalan-c-users@xml.apache.org
Date: Friday, October 14, 2011, 10:57 AM
Ajay,
If you are going to write and implement your own entity resolver, you need
to understand the API interface of the XercesC library. The Entity Resolver
(either class XMLEntityResolver or class EntityReslover) is instantiated
in by the current Xerces XMLReader to resolve external entities and make their
contents known by pushing a new XMLReader onto the stack, becoming the
new XMLReader. This interrupts the current bytestream of input with a
new bytestream of input. When the resolved entity bytestream has been
consumed, the reader is removed from the stack and the previous reader
resumes operation where interrupted. See also the Xerces ReaderMgr.
You should look at the various input sources in the xercesc/framework
directory.
Your entity resolver is actually an instance of a Xerces based class.
The knowledge of the resolver can be registered to the XalanTransformer
so it can be used in place of an insecure default entity resolver.
There are two classes for entity resolvers:
XMLEntityResolver and EntityResolver
The registration of one entity resolver class automatically removes the
registration of the other entity resolver class. You can check to see
if a custom entity resolver of either class has been registered.
Refer to:
class XalanTransformer
{
public:
void setEntityResolver(EntityResolver* theResolver)
{
m_entityResolver = theResolver;
if (theResolver != 0 && m_xmlEntityResolver != 0)
{
m_xmlEntityResolver = 0;
}
}
EntityResolver * getEntityResolver() const
{
return m_entityResolver;
}
void setXMLEntityResolver(XMLEntityResolver* theResolver)
{
m_xmlEentityResolver = theResolver;
if (theResolver != 0 && m_entityResolver != 0)
{
m_entityResolver = 0;
}
}
XMLEntityResolver * getXMLEntityResolver() const
{
return m_xmlEntityResolver;
}
private:
// data members
EntityResolver * m_entityResolver;
XMLEntityResolver * m_xmlEntityResolver;
}
------
The above active entity resolver get instantiated to the
Xerces::SAX2XMLReaderImpl
when when creating a XML reader and pushing it onto the active reader stack.
The actual EntityResolver or XMLEntityResolver is responsible for creating
the Xerces XML Reader to be pushed onto the stack as the active reader.
If no resource is resolved, then the current XML reader remains active.
-------
The application specific XML entity resolver should be registered with the
XalanTransformer if it is to be used to create Xerces XML readers.
If no application specific XML entity resolver is created, then a default
XML entity resolver is used. The insecurity of the default XML entity resolver
is that system data files are directly accessed, and a global DNS is used
to resolve network resources that are not local to the computer.
-------
Xalan has its own document handlers to use for Xerces reader callback
functions.
-------
The registered entity resolver in XalanTransformer becomes the
entityHandler() as known in the Xerces::SAX2XMLReaderImpl
fScanner->setEntityHandler(this);
The entity handler actually implements the class Xerces::XMLEntityHandler
as known by the ReaderMgr which controls the stack of active XML readers.
The entity handler is invoked by the current XML Scanner to place a new
reader on the stack as the active XML reader. This actually interrups
the XML scanning process to insert XML content from a resolved entity
resource.
--------
I hope this helps. Entity resolvers is a complex topic.
Trusted entity resolvers are required for trusted XML applications.
You might also wish to look at some of the specifications archived at:
http://www.oasis-open.org/standards#xmlcatalogsv1.1
Sincerely,
Steven J. Hathaway
On 10/12/2011 8:24 AM, ajay bhadauria wrote:
Hi,
I am using transform method to transform input xml source to output xml. In the
xslt, I have document () call to resolve external entities. The external enties
are available in memory instead of file-system files during transformation.
Please help me how do I write my own entity resolver to resolve external enties
during xml transformation . Any code example referenece will be great.
Thanks
Ajay
