Java Reference
In-Depth Information
After you have identified the Schema Definition Language to be used, you can create a
Schema
object
from a schema definition. Here's an example of how you might do this:
File schemaFile = Paths.get(System.getProperty("user.home")).
resolve("Beginning Java Stuff").resolve("sketcher.xsd").toFile();
try {
Schema schema = sf.newSchema(schemaFile);
}catch(SAXException e) {
e.printStackTrace();
System.exit(1);
}
The
newSchema()
method for the
SchemaFactory
object creates and returns a
Schema
object from the
file specified by the
File
object you pass as the argument. There are versions of the
newSchema()
method
with parameters of type
java.net.URL
and
java.xml.transform.Source
. An object that implements the
Source
interface represents an XML source. There's also a version of
newSchema()
that accepts an argu-
ment that is an array of
Source
object references and generates a
Schema
object from the input from all of
the array elements.
Now that you have a
Schema
object, you can pass it to the
SAXParserFactory
object before you create
your
SAXParser
object to process XML documents:
SAXParserFactory spf = SAXParserFactory.newInstance();
spf.setSchema(schema);
The parser you create by calling the
newSAXParser()
method for this
SAXParserFactory
object valid-
ates documents using the schema you have specified. XML documents are validated in this instance, even
when the
isValidating()
method returns
false
, so it's not essential that you configure the parser to val-
idate documents.
In many situations the document itself identifies the schema to be used. In this case you call the
newS-
chema()
method for the
SchemaFactory
object with no argument specified:
try {
Schema schema = sf.newSchema();
}catch(SAXException e) {
e.printStackTrace();
System.exit(1);
}
A special
Schema
object is created by the
newSchema()
method that assumes the schema for the docu-
ment is identified by hints within the document. Note that you still need to call
newSchema()
within a
try
block here because the method throws an exception of type
SAXException
if the operation fails for some
reason. If the operation is not supported, an exception of type
UnsupportedOperationException
is thrown,
but because this is a subclass of
RuntimeException
, you are not obliged to catch it.
TRY IT OUT: Parsing a Schema Instance Document
Here's a variation on the
TrySAXHandler
class that parses a schema instance document:
