Schema Validation of XML/JAXB Annotated Object Containing MTOM Attachment [Code Snippet]

Issue: JIRA reference https://java.net/jira/browse/JAXB-588

Resolution: Won't Fix

Description: If an XML or its corresponding JAXB annotated object which contains an MTOM attachment is validated using javax.xml.validation.Validator against an XSD, the referenced MTOM attachment is lost.

Workaround: In this article, we will explain how can we validate an XML/JAXB annotated object containing an MTOM attachment against an XSD without losing the MTOM attachment. In case an XML is used, it is advised to convert the same into a JAXB annotated object as it makes it easier to manipulate with the element which contains the MTOM attachment. Below Code shows a sample XSD snippet and it's corresponding JAVA code for schema validation.

SampleSchema.xsd snippet :

<xs:element name="request">
    <xs:complexType>
        <xs:sequence>
            <xs:element name="requestDetails" type="ns:requestDetails" minOccurs="0" maxOccurs="1" nillable="true"/>
        </xs:sequence>
    </xs:complexType>
</xs:element>

<xs:complexType name="requestDetails">
    <xs:sequence>
        <xs:element name="fileName" type="xs:string" minOccurs="0"/>
        <xs:element xmlns:xmime="http://www.w3.org/2005/05/xmlmime" name="fileMtomAttachment" type="xs:base64Binary" xmime:expectedContentTypes="application/octet-stream"/>
    </xs:sequence>
</xs:complexType>

Code snippet :

import java.io.IOException;
import javax.xml.XMLConstants;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.util.JAXBSource;
import javax.xml.transform.Source;
import javax.xml.transform.stream.StreamSource;
import javax.xml.validation.Schema;
import javax.xml.validation.SchemaFactory;
import javax.xml.validation.Validator;

...

try {
    //creating Schema Source
    Source schemaFile = new StreamSource(new File("xsd/SampleSchema.xsd"));
    SchemaFactory schemaFactory = SchemaFactory .newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
    Schema schema = schemaFactory.newSchema(schemaFile);

    Validator validator = schema.newValidator();

    // refPayload is the reference to the JAXB annotated object representing the XML.
    Request request = (Request)refPayload; 

    //create a temporary handler to handle the original MTOM attachment
    javax.activation.DataHandler tempHandler = null;
    // check for availability of MTOM attachment
        if (null != request.requestDetails() && null != request.requestDetails().getValue().getFileMtomAttachment()) {
        // setting the original MTOM attachment in the temporary handler
        tempHandler = request.requestDetails().getValue().getFileMtomAttachment();

        // setting an empty object in the original JAXB annotated object which is to be validated
        request.requestDetails().getValue().setFileMtomAttachment(new javax.activation.DataHandler(new Object() , ""));

    } else {
        request.requestDetails().getValue().setFileMtomAttachment(null);
    }
    // Validate as JAXB source
    JAXBContext jaxbContext = JAXBContext.newInstance(Request.class);
    JAXBSource jaxbSource = new JAXBSource(jaxbContext, request);
    validator.validate(jaxbSource);

    System.out.println("Jaxb Object is valid");

    //Set original MTOM attachment in case Schema validation is successful
    request.requestDetails().getValue().setFileMtomAttachment(tempHandler);

} catch (SAXException se) {
    System.out.println("Jaxb Object is NOT valid");
    System.out.println("Reason: " + se.getLocalizedMessage());
} catch (IOException e) {
    e.printStackTrace();
}

This is a simple way to preserve the MTOM attachment while schema validating the rest of the elements and attributes inside an XML.