Objective

This example describes how you can allow arbitrary XML data to be added to a schema driven XML document using the XSD 'Any' Type, while at the same time validate such arbitrary data for wellformedness and correctness

Background

The XS Any element enables authors to extend the XML document with elements not specified by the schema. This allows placement of any arbitrary XML data type including simple and complex types. Suppose there is a schema named person.xsd.

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified"
           xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="person" type="personType"/>
    <xs:complexType name="personType">
        <xs:sequence>
            <xs:element name="firstname" type="xs:string"/>
            <xs:element name="lastname" type="xs:string"/>
            <xs:any namespace="##any" processContents="lax"/>
        </xs:sequence>
    </xs:complexType>
</xs:schema>

We can add any XML tag with any name after the lastname tag.

<firstname>Swapnonil Mukherjee</firstname>
<lastname>Mukherjee</lastname>
</otherInfo>Some other info</otherInfo>

And also nested tags as well.

<lastname>Mukherjee</lastname>
</otherInfo>
	<city></city>
</otherInfo>

Both are valid uses of the schema type xs:any. JAXB has specific ways to dealing with XS Any. There are 2 ways mainly.

1. Schema Driven: Create additional XSD for any additional schema and create a class that maps onto this additional schema. This document describes this approach.
2. DOM Driven: Create and Serialize org.w3.dom.Element inside JAXB classes and read the same as DOM element. This approach cannot be schema validated though and hence not described here.

We are going to explore the schema driven method here.

Schema Driven Method

Step1

Create an XSD Schema which has xs:any as part of its definition. Name it as person.xsd

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified"
           xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="person" type="personType"/>
    <xs:complexType name="personType">
        <xs:sequence>
            <xs:element name="firstname" type="xs:string"/>
            <xs:element name="lastname" type="xs:string"/>
            <xs:any namespace="##any" processContents="lax"/>
        </xs:sequence>
    </xs:complexType>
</xs:schema>

Step2

Create another XSD schema that describes the additional XML which will form a part of xs:any. Name it person-extra.xsd

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified"
           xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="address" type="addressType"/>
    <xs:complexType name="addressType">
        <xs:sequence>
            <xs:element name="street" type="xs:string"/>
            <xs:element name="city" type="xs:string"/>
        </xs:sequence>
    </xs:complexType>
</xs:schema>

Step 3

Generate Java Types for person.xsd

xjc –d [output directory] –p [packagename] person.xsd

This will generate two classes PersonType.java and ObjectFactory.java inside the named package. Also add the annotation XMLRootElement(name=”person”) to the PersonType.java file as JAXB does not add any root element annotation if the root element is an user defined type.

Step 4

Generate Java Types for person-extra.xsd

xjc –d [output directory] –p [packagename] person-extra.xsd

This will generate two classes PersonType.java and ObjectFactory.java inside the named package. Also add the annotation XMLRootElement(name=”address”) to the AddressType.java file.

Step5

Write the following code to try out this mechanism

package com.swapnonil;

import extra.AddressType;
import xsd.PersonType;

import javax.xml.bind.*;
import java.io.StringReader;
import java.io.StringWriter;

/**
 * Example of making xs:any work.
 */
public class App {
    private static String read;

    private static String xmlString;

    public static void main(String[] args) {
        writeDocument();
        readDocument();
    }

    private static void writeDocument() {
        try {
            JAXBContext context = JAXBContext.newInstance(PersonType.class, AddressType.class);
            Marshaller m = context.createMarshaller();
            m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.FALSE);
            StringWriter writer = new StringWriter();
            m.marshal(getPersonType(), writer);
            xmlString = writer.toString();
        } catch (JAXBException e) {
            e.printStackTrace();
        }
    }

    private static void readDocument() {

        try {
            JAXBContext context = JAXBContext.newInstance(PersonType.class, AddressType.class);
            Unmarshaller unmarshaller = context.createUnmarshaller();
            StringReader reader = new StringReader(xmlString);
            JAXBElement<PersonType> personType = (JAXBElement<PersonType>) unmarshaller.unmarshal(reader);
            PersonType value = personType.getValue();
            AddressType any = (AddressType) value.getAny();
            System.out.println(any.getStreet());
            System.out.println(any.getCity());
        } catch (JAXBException e) {
            e.printStackTrace();
        }
    }

    private static PersonType getPersonType() {
        PersonType root = new PersonType();
        root.setFirstname("Swapnonil");
        root.setLastname("Mukherjee");
        root.setAny(getAddressType());
        return root;
    }

    private static AddressType getAddressType() {
        AddressType addressType = new AddressType();
        addressType.setStreet("Shirley Road");
        addressType.setCity("London");
        return addressType;
    }
}

The example above creates a PersonType and also adds an AddressType. It serialises it to a StringWriter and then reads it off a StringReader again. To enable this ability to read and write both the Person and Address types it must be included in the JAXB Context

JAXBContext context = JAXBContext.newInstance(PersonType.class, AddressType.class);