Validating Against an XML Schema

If you would like to validate your objects against an XML Schema during marshalling and unmarshalling, you can make use of JAXB's ValidationEventHandler.

Example 2-25 Sample XML Schema

In this example we would like to validate our objects against the following XML schema:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
 
    <xs:element name="customer">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="name" type="stringMaxSize5"/>
                <xs:element ref="phone-number" maxOccurs="2"/>
             </xs:sequence>
        </xs:complexType>
    </xs:element>
 
    <xs:element name="phone-number">
        <xs:complexType>
            <xs:sequence/>
        </xs:complexType>
    </xs:element>
 
    <xs:simpleType name="stringMaxSize5">
        <xs:restriction base="xs:string">
            <xs:maxLength value="5"/>
        </xs:restriction>
    </xs:simpleType>
 
</xs:schema>

Notice the following constraints:

The customer's name cannot be longer than five (5) characters.
The customer cannot have more than two (2) phone numbers.

The Customer class is shown below. Notice that the class does not contain any validation code.

Example 2-26 Sample Customer Class

package example;
 
import java.util.ArrayList;
import java.util.List;
 
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
 
@XmlRootElement
public class Customer {
   private String name;
 
   private List<PhoneNumber> phoneNumbers = new ArrayList<PhoneNumber>();
 
   public String getName() {
      return name;
   }
 
   public void setName(String name) {
      this.name = name;
   }
 
   @XmlElement(name="phone-number")
   public List<PhoneNumber> getPhoneNumbers() {
      return phoneNumbers;
   }
 
   public void setPhoneNumbers(List<PhoneNumber> phoneNumbers) {
      this.phoneNumbers = phoneNumbers;
   }
}

Using a ValidationEventHandler

You can receive JAXB validation events by providing your own subclass of ValidationEventHandler. The event is represented as an instance of ValidationEvent, and provides many details about the issue. The data is similar to what is available from a SAXParseException.

Returning false from the handleEvent method will cause the JAXB operation to stop.
Returning true will allow the method to continue, if possible.

In Example 2-27, we will simply print out an event's data when one is received:

Example 2-27 Sample ValidationEventHandler

package example;
 
import javax.xml.bind.ValidationEvent;
import javax.xml.bind.ValidationEventHandler;
 
public class MyValidationEventHandler implements ValidationEventHandler {
 
    public boolean handleEvent(ValidationEvent event) {
        System.out.println("\nEVENT");
        System.out.println("SEVERITY:  " + event.getSeverity());
        System.out.println("MESSAGE:  " + event.getMessage());
        System.out.println("LINKED EXCEPTION:  " + event.getLinkedException());
        System.out.println("LOCATOR");
        System.out.println("    LINE NUMBER:  " + event.getLocator().getLineNumber());
        System.out.println("    COLUMN NUMBER:  " + event.getLocator().getColumnNumber());
        System.out.println("    OFFSET:  " + event.getLocator().getOffset());
        System.out.println("    OBJECT:  " + event.getLocator().getObject());
        System.out.println("    NODE:  " + event.getLocator().getNode());
        System.out.println("    URL:  " + event.getLocator().getURL());
        return true;
    }
 
}

Enabling Validation

In addition to providing an implementation of ValidationEventHandler, an instance of Schema must be set on the Marshaller or Unmarshaller.

Example 2-28 Sample Java Code

package example;
 
import java.io.File;
import javax.xml.XMLConstants;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.Unmarshaller;
import javax.xml.validation.Schema;
import javax.xml.validation.SchemaFactory;
 
public class UnmarshalDemo {
 
    public static void main(String[] args) throws Exception {
        SchemaFactory sf = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
        Schema schema = sf.newSchema(new File("customer.xsd"));
 
        JAXBContext jc = JAXBContext.newInstance(Customer.class);
 
        Unmarshaller unmarshaller = jc.createUnmarshaller();
        unmarshaller.setSchema(schema);
        unmarshaller.setEventHandler(new MyValidationEventHandler());
        Customer customer = (Customer) unmarshaller.unmarshal(new File("input.xml"));
    }
 
}

Input (input.xml File)

<customer>
   <name>Jane Doe</name>
   <phone-number/>
   <phone-number/>
   <phone-number/>
</customer>

Output

The validation performed during the unmarshal raised three events. The first two events are related to the text value of the name element being too long. The third event is related to the extra phone-number element.

EVENT
SEVERITY:  1
MESSAGE:  cvc-maxLength-valid: Value 'Jane Doe' with length = '8' is not facet-valid with respect
          to maxLength '5' for type 'stringWithMaxSize5'.
LINKED EXCEPTION:  org.xml.sax.SAXParseException: cvc-maxLength-valid: Value 'Jane Doe' with length = '8'
                   is not facet-valid with respect to maxLength '5' for type 'stringWithMaxSize5'.
LOCATOR
    LINE NUMBER:  3
    COLUMN NUMBER:  25
    OFFSET:  -1
    OBJECT:  null
    NODE:  null
    URL:  null
 
EVENT
SEVERITY:  1
MESSAGE:  cvc-type.3.1.3: The value 'Jane Doe' of element 'name' is not valid.
LINKED EXCEPTION:  org.xml.sax.SAXParseException: cvc-type.3.1.3: The value 'Jane Doe' of element
                   'name' is not valid.
LOCATOR
    LINE NUMBER:  3
    COLUMN NUMBER:  25
    OFFSET:  -1
    OBJECT:  null
    NODE:  null
    URL:  null
 
EVENT
SEVERITY:  1
MESSAGE:  cvc-complex-type.2.4.d: Invalid content was found starting with element 'customer'. No child
          element '{phone-number}' is expected at this point.
LINKED EXCEPTION:  org.xml.sax.SAXParseException: cvc-complex-type.2.4.d: Invalid content was found starting
                   with element 'customer'. No child element '{phone-number}' is expected at this point.
LOCATOR
    LINE NUMBER:  7
    COLUMN NUMBER:  12
    OFFSET:  -1
    OBJECT:  null
    NODE:  null
    URL:  null