JAXB

Document Type Definitions (DTDs)

An XML document can be given a formal specification. There are several methods

• XML DTD
• XML Schema

A DTD for login-requests is

<!ELEMENT login-request (name, password)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT password (#PCDATA)>

A schema for login-requests is

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">

<xsd:element name="loginrequest" type="LoginRequest"/>

<xsd:complexType name="LoginRequest">
    <xsd:sequence>
        <xsd:element name="name" type="xsd:string"/>
        <xsd:element name="password" type="xsd:string"/>
    </xsd:sequence>
</xsd:complexType>

</xsd:schema>

XML Schema data types

JAXB

There are a number of ways of handling XML parsing in Java

• JAXP
• JAXB
• JDOM
• JAXM
• JAXR

We will use JAXB: a mechanism for

• writing out Java objects as XML (marshalling)
• creating Java objects from XML documents (unmarshalling)

The JAXB compiler is xjc and is found in the jaxb/bin directory of Sun's Web services pack. It can be used by

    xjc.sh -p package_dir login.xsd

public interface LoginRequest {

    java.lang.String getPassword();
    void setPassword(java.lang.String value);
    java.lang.String getName();
    void setName(java.lang.String value);

}

It also generates an ObjectFactory which includes methods

public class ObjectFactory
    extends impl.runtime.DefaultJAXBContextImpl
{

    public ObjectFactory() {
	// ...
    }

    public java.lang.Object newInstance(java.lang.Class javaContentInterface)
        throws javax.xml.bind.JAXBException
    {
	// ...
    }

    public LoginRequest createLoginRequest()
        throws javax.xml.bind.JAXBException
    {
	// ...
    }
}

A test program is

/**
 * TestLoginRequest.java
 */

import java.io.*;
import javax.xml.bind.*;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Unmarshaller;

import generated.LoginRequest;

public class TestLoginRequest{

    public static void main(String[] args){
	new TestLoginRequest();
    }

    public TestLoginRequest() {

	InputStream in = null;
	try {
	    in = new FileInputStream(new File("login.xml"));
	} catch(java.io.FileNotFoundException e) {
	    e.printStackTrace();
	    System.exit(1);
	}
	    
	LoginRequest request = null;
	try {
	// tmp is the package name used in the -p option to xjc
	JAXBContext jc = JAXBContext.newInstance("generated");

	Unmarshaller u = jc.createUnmarshaller();
	JAXBElement obj = (JAXBElement<LoginRequest>) u.unmarshal(in);
	System.out.println("Type: " +obj.getClass().toString());

        Object requestObj = obj.getValue();
	request = (LoginRequest) requestObj;
        System.out.println("TYpe: " + requestObj.getClass().toString());

	} catch(JAXBException e) {
	    e.printStackTrace();
	    System.exit(1);
	}

	System.out.println("Name is " + request.getName());
	System.out.println("Password is " + request.getPassword());

	System.exit(0);
    }
} // TestLoginRequest