Validation with the JDOM API
To validate using the JDOM API, download the JDOM 1.0 parser binaries. Add <JDOM>/jdom-1.0/build/jdom.jar file to classpath, where <JDOM> is the directory in which JDOM is installed. The JAXP 1.3 validation API is available in JWSDP 2.0 and in JDK 5.0. In this example, I used JDK 5.0.
The JDOM API uses the SAXBuilder class to parse an XML document. This class is integrated with a SAXParser class. To get started, you need to import the SAXBuilder class:
import org.jdom.input.SAXBuilder;
The SAXBuilder(java.lang.String saxDriverClass, boolean validate) constructor creates a new SAXBuilder with the specified SAX parser. In the example JDOM application, the org.apache.xerces.parsers.SAXParser driver class is used for parsing:
SAXBuilder saxBuilder = new SAXBuilder ("org.apache.xerces.parsers.SAXParser", true);
In the SAXBuilder constructor used, the second argument is a flag for validation. true indicates that you are ready to validate your XML document. To report validation errors, set the validation feature to true. To report validation errors against a schema, set the validation/schema feature to true. To enable full schema grammar constraint checking, set the validation/schema-full-checking feature:
saxBuilder.setFeature ("http://xml.org/sax/features/validation", true);
saxBuilder.setFeature ("http://apache.org/xml/features/validation/schema", true);
saxBuilder.setFeature ("http://apache.org/xml/features/validation/schema-full-checking", true);
The particular XML schema with which you validate an XML document may be specified with either the schema/external-noNamespaceSchemaLocation or the schema/external-schemaLocation property. The schema/external-noNamespaceSchemaLocation parser property is used for an XML document without namespaces, and the schema/external-schemaLocation parser property is used for an XML document with namespaces. This example uses an XML document without namespaces:
saxBuilder.setProperty ("http://apache.org/xml/properties/schema/external-
noNamespaceSchemaLocation",SchemaUrl);
To specify an ErrorHandler for the SAXBuilder parser, create an instance of the Validator class, which extends the DefaultHandler class. The DefaultHandler class implements the ErrorHandler interface. The Validator class is used as an ErrorHandler. To validate an XML document with the SAXBuilder, set an ErrorHandler on the SAXBuilder object and parse the example XML document with SAXBuilder:
Validator handler=new Validator ();
saxBuilder.setErrorHandler (handler);
saxBuilder.parse (XmlDocumentUrl);
The validation errors you generate get registered with the ErrorHandler. In the example program that you'll use to validate catalog.xml (with respect to the example XML Schema, catalog.xsd, using the JDOM API), is shown in Listing 3.
Run the JDOMValidator application in your command line or in a Java IDE, like Eclipse. The output from the application should say:
XML Document is Valid
To demonstrate error handling, add an error in catalog.xml. For example, add the following element under the catalog element:
<title>Schema Validation</title>
Now, run the JDOMValidator with the modified catalog.xml. The schema validation should generate the error below:
XML Document has Error:true cvc-complex-type.2.4.a:
Invalid content was found starting with element 'title'.
One of '{journal}' is expected.
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