Creating a Validation Context

<< Validating an XML Signature | XML Signature Fails to Validate >>

VALIDATE

XAMPLE

223

ment.getElementsByTagNameNS

, passing it the XML Signature namespace URI

and the tag name of the

Signature

element, as shown:

NodeList nl = doc.getElementsByTagNameNS

(XMLSignature.XMLNS, "Signature");

if (nl.getLength() == 0) {

throw new Exception("Cannot find Signature element");

}

This returns a list of all

Signature

elements in the document. In this example,

there is only one

Signature

element.

Creating a Validation Context

We create an

XMLValidateContext

instance containing input parameters for val-

idating the signature. Since we are using DOM, we instantiate a

DOMValidate-

Context

instance (a subclass of

XMLValidateContext

), and pass it two

parameters, a

KeyValueKeySelector

object and a reference to the

Signature

element to be validated (which is the first entry of the

NodeList

we generated

earlier):

DOMValidateContext valContext = new DOMValidateContext

(new KeyValueKeySelector(), nl.item(0));

The

KeyValueKeySelector

explained

greater

detail

Using

KeySelectors (page 225).

Unmarshaling the XML Signature

We extract the contents of the

Signature

element into an

XMLSignature

object.

This process is called unmarshalling. The

Signature

element is unmarshalled

using an

XMLSignatureFactory

object. An application can obtain a DOM

implementation of

XMLSignatureFactory

by calling the following line of code:

XMLSignatureFactory factory =

XMLSignatureFactory.getInstance("DOM");