JAXB unmarshalling multiple XML elements into single class

Question

I have the following XML structure, which is modelling a single concept across multiple XML elements. This format is not in my control.

  <         


        

Answer 1

@XmlElementWrapper will do the job:

@XmlElementWrapper(name="Wrapper")
@XmlElement(name="Channel")
private List<Channel> channels;

For more advanced cases you can use the @XmlPath extension in EclipseLink JAXB (MOXy):

• http://bdoughan.blogspot.com/2010/09/xpath-based-mapping-geocode-example.html

---

Here is what I have so far. I'm still trying to eliminate the need for the helper objects. This example requires EclipseLink JAXB (MOXy).

Model Objects

Your model objects are:

package example;

import java.util.ArrayList;
import java.util.List;

public class Wrapper {

    private List<Channel> channels = new ArrayList<Channel>();

    public List<Channel> getChannels() {
        return channels;
    }

    public void setChannels(List<Channel> channels) {
        this.channels = channels;
    }

}

and:

package example;

import javax.xml.bind.annotation.XmlID;

public class Channel {

    private String id;
    private String type;
    private String name;

    @XmlID
    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

Helper Objects

My current solution involves some helper objects:

package example.adapted;

import java.util.List;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlElementWrapper;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlTransient;
import javax.xml.bind.annotation.XmlType;

import example.Channel;
import example.Wrapper;

@XmlRootElement(name="Output")
@XmlType(propOrder={"channels", "channelNames"})
public class AdaptedWrapper {

    private Wrapper wrapper = new Wrapper();
    private List<ChannelName> channelNames;

    @XmlTransient
    public Wrapper getWrapper() {
        for(ChannelName channelName : channelNames) {
            channelName.getChannel().setName(channelName.getName());
        }
        return wrapper;
    }

    @XmlElementWrapper(name="Wrapper")
    @XmlElement(name="Channel")
    public List<Channel> getChannels() {
        return wrapper.getChannels();
    }

    public void setChannels(List<Channel> channels) {
        wrapper.setChannels(channels);
    }

    @XmlElementWrapper(name="Wrapper")
    @XmlElement(name="ChannelName")
    public List<ChannelName> getChannelNames() {
        return channelNames;
    }

    public void setChannelNames(List<ChannelName> channelNames) {
        this.channelNames = channelNames;
    }

}

and:

package example.adapted;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlIDREF;

import example.Channel;

public class ChannelName {

    private String name;
    private Channel channel;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @XmlIDREF
    @XmlElement(name="id")
    public Channel getChannel() {
        return channel;
    }

    public void setChannel(Channel channel) {
        this.channel = channel;
    }

}

Demo Code

package example;

import java.io.File;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.Unmarshaller;

import example.adapted.AdaptedWrapper;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(AdaptedWrapper.class);

        File xml = new File("input.xml");
        Unmarshaller unmarshaller = jc.createUnmarshaller();
        AdaptedWrapper adaptedWrapper = (AdaptedWrapper) unmarshaller.unmarshal(xml);
        Wrapper wrapper = adaptedWrapper.getWrapper();

        for(Channel channel : wrapper.getChannels()) {
            System.out.println(channel.getName());
        }
    }

}

Answer 2

You can save your coding time by automating this process in JAXB:

Create a XML schema for your XML using the link below as save it as output.xsd file: http://www.xmlforasp.net/CodeBank/System_Xml_Schema/BuildSchema/BuildXMLSchema.aspx

Run the batch script file (name it as output.bat) below from the project root folder (.) using JDK as only JDK has xjc.exe tool (fill in the necessary details):

"C:\Program Files\Java\jdk1.6.0_24\bin\xjc.exe" -p %1 %2 -d %3

where...

syntax: output.bat %1 %2 %3
%1 = target package name
%2 = full file path name of the generated XML schema .xsd 
%3 = root source folder to store generated JAXB java files

Example:

let say project folder is organized as follows:

.
\_src

Run following at command prompt from (.):

output.bat com.project.xml .\output.xsd .\src

It will create a few files:

.
\_src
  \_com
    \_project
      \_xml
        |_ObjectFactory.java
        |_Output.java

Then, you can create a few useful methods below to manipulate Output objects:

private JAXBContext jaxbContext = null;
private Unmarshaller unmarshaller = null;
private Marshaller marshaller = null;

public OutputManager(String packageName) {
    try {
        jaxbContext = JAXBContext.newInstance(packageName);
        unmarshaller = jaxbContext.createUnmarshaller();
        marshaller = jaxbContext.createMarshaller();
    } catch (JAXBException e) {
    }
}

public Output loadXML(InputStream istrm) {

    Output load = null;

    try {
        Object o = unmarshaller.unmarshal(istrm); 

        if (o != null) {

            load = (Output) o;

        }

    } catch (JAXBException e) {

        JOptionPane.showMessageDialog(null, e.getLocalizedMessage(), e.getClass().getSimpleName(), JOptionPane.ERROR_MESSAGE);

    }
    return load;
}

public void saveXML(Object o, java.io.File file) {

    Output save = null;

    try {
        save = (Output) o;

        if (save != null) {
            marshaller.marshal(save, file);
        }

    } catch (JAXBException e) {

        JOptionPane.showMessageDialog(null, e.getLocalizedMessage(), e.getClass().getSimpleName(), JOptionPane.ERROR_MESSAGE);

    }
}

public void saveXML(Object o, FileOutputStream ostrm) {

    Output save = null;

    try {

        save = (Output) o;

        if (save != null) {
            marshaller.marshal(save, ostrm);
        }

    } catch (JAXBException e) {

        JOptionPane.showMessageDialog(null, e.getLocalizedMessage(), e.getClass().getSimpleName(), JOptionPane.ERROR_MESSAGE);

    }
}