Intercepting All Accesses to External Entities During XML SAX Parsing
This capability is useful in situations where the public or system id
in an XML file do not refer to actual resources and must be
redirected. An EntityResolver object must be installed on the parser
in order to intercept the accesses. If a mapping is made, the entity
resolver must return an InputSource object to the resource.
This is the sample input for the example:
The resulting system ids passed into MyResolve.resolveEntity() are:
try {
// Create an XML parser
DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
// Install the entity resolver
builder.setEntityResolver(new MyResolver());
// Parse the XML file
Document doc = builder.parse(new File("infilename.xml"));
} catch (SAXException e) {
// A parsing error occurred; the xml input is not valid
} catch (ParserConfigurationException e) {
} catch (IOException e) {
}
public class MyResolver implements EntityResolver {
// This method is called whenever an external entity is accessed
// for the first time.
public InputSource resolveEntity (String publicId, String systemId) {
try {
// Wrap the systemId in a URI object to make it convenient
// to extract the components of the systemId
URI uri = new URI(systemId);
// Check if external source is a file
if ("file".equals(uri.getScheme())) {
String filename = uri.getSchemeSpecificPart();
return new InputSource(new FileReader(filename));
}
} catch (URISyntaxException e) {
} catch (IOException e) {
}
// Returning null causes the caller to try accessing the systemid
return null;
}
}
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE root SYSTEM "System.dtd" [
<!ENTITY entity1 SYSTEM "External.xml">
<!ENTITY entity2 SYSTEM "http://hostname.com/my.dtd">
<!ENTITY % entity3 SYSTEM "More.dtd">
%entity3;
]>
<root>
&entity1;
&entity2;
</root>
file:d:/almanac/1.4/egs/org.xml.sax/More.dtd
file:d:/almanac/1.4/egs/org.xml.sax/Systemid.dtd
file:d:/almanac/1.4/egs/org.xml.sax/External.dtd
http://hostname.com/my.dtd
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