Ultrashort JAXB tutorial

By Confusion on Tuesday 3 February 2009 20:49 - Comments (3)
Categories: Java, Software engineering, XML, Views: 7.104

Today I had to use JAXB for XML-object binding. While searching for an introduction, I noted that most articles handling JAXB seemed to be overly long and concerned with all kinds of asides that detracted from the basics, which were all I needed. Therefore I now present: an ultrashort JAXB tutorial.

I will expect you know:

What XML-object binding is and why you would want to use it.
How to use Java and solve classpath issues and such
How to use Linux (or translate the instructions to Windows).
How to determine intermediate steps I left out (like 'extract the zip')

Requirements:

An XML file that you wish to 'unmarshal' into an object tree. Example:
XML:

<?xml version="1.0" encoding="UTF-8"?>
<rootElement xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://some.sensible.url/foo"
    xsi:schemaLocation="http://some.sensible.url/foo foo.xsd">

    <subElement>
        <foo>1</foo>
        <baz>2</baz>
    </subElement>
    <subElement>
        <foo>2</foo>
        <baz>4</baz>
    </subElement>
    
</rootElement>

An XML Schema description of the structure of the XML. Example:

XML:

<?xml version="1.0" encoding="UTF-8"?>
<schema xmlns="http://www.w3.org/2001/XMLSchema" 
    targetNamespace="http://some.sensible.url/foo" 
    xmlns:f="http://some.sensible.url/foo" 
    elementFormDefault="qualified">

    <element name="rootElement">
        <complexType>
            <sequence>
                <element name="subElement" type="f:subElement"
 maxOccurs="unbounded" />
            </sequence>
        </complexType>
    </element>
    
    <complexType name="subElement">
        <sequence>
            <element name="foo" type="int" />
            <element name="baz" type="int" />
        </sequence>
    </complexType>
</schema>

Tutorial

Use a Java 6 SDK (which has JAXB) or download JAXB (and use a Java 5+ JDK)

Generate the objects from the xml schema by issuing

jaxb-ri/bin/xjc.sh -p com.company.app.pakkage.of.objects \
-d /path/to/com/company/app/pakkage/of/objects \
/path/to/xml-structure.xsd

Assuming the root element of your xml is named 'rootElement' (and available as com.company.app.pakkage.of.objects.RootElement):

Java:

package com.company.app;

import java.io.File;
import javax.xml.bind.*;
import com.company.app.pakkage.of.objects.*;

public class Example {

    public static void main(String[] args) throws JAXBException {
        
        final JAXBContext jaxbContext =
            JAXBContext.newInstance("com.company.app.pakkage.of.objects");
        final Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
        final RootElement rootElement =
            (RootElement) unmarshaller.unmarshal(new File("/path/to/xml.xml"));
    }
}

Profit.

02-'09 Is there more bad PHP than bad Java?
02-'09 More dangerous than a decline in prosperity.

Comments

By ViperNL, Tuesday 3 February 2009 23:07

4. ???
5. Profit!!!

By Confusion, Wednesday 4 February 2009 21:55

The
n. ???
n+1. Profit!!!
meme only lends itself when it is unclear how one may obtain profit using the process described by steps 1 .. n - 1. In this case, the ??? is obvious

By Kettrick, Thursday 5 February 2009 21:38

Useful link for those who want to play around with jaxb and wonder why boolean's are ******

http://www.mojavelinux.co...e_great_jaxb_api_blunder/

Comments are closed

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Ultrashort JAXB tutorial

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