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Subject: Re: XML
Date: Sat, 13 Aug 2016 15:38:03 -0400
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On 8/10/2016 4:29 PM, Eric Douglas wrote:
> Now, I'm not sure the best API to manage records.  As the only method
> I found for storing multiple records with JAXB is a List of the
> DataRecord instances, how do I pass it a key value, get one or more
> of these record objects, update a field (or fields), and write it
> back out?  This RMFID.xsd maps to an RMFID Java class which gives me
> instances specific to this file name where I can call it's
> setFILENAME(), getFILENAME() methods, but I don't see an obvious way
> to get specific instances of the RMFID from the list aside from
> customizing these classes further to map out what keys I need and
> mapping them through the DataFile class. I'm wondering if it makes
> sense to keep going down this path or try something else, like JiBX
> which claims to do all this marshall/unmarshall stuff plus add code
> to the Java classes to make everything more efficient and support
> XPath queries to find records?

Here is a complete example showing some stuff.

First we have the data model:

package jaxbdemo;

public abstract class Data {
	private int iv;
	public Data() {
		this(0);
	}
	public Data(int iv) {
		super();
		this.iv = iv;
	}
	public int getIv() {
		return iv;
	}
	public void setIv(int iv) {
		this.iv = iv;
	}
}

package jaxbdemo;

public class DataA extends Data {
	private String sv;
	public DataA() {
		this(0, "");
	}
	public DataA(int iv, String sv) {
		super(iv);
		this.sv = sv;
	}
	public String getSv() {
		return sv;
	}
	public void setSv(String sv) {
		this.sv = sv;
	}
	@Override
	public String toString() {
		return String.format("{ %d, %s }", getIv(), getSv());
	}
}

package jaxbdemo;

public class DataB extends Data {
	private double xv;
	public DataB() {
		this(0, 0.0);
	}
	public DataB(int iv, double xv) {
		super(iv);
		this.xv = xv;
	}
	public double getXv() {
		return xv;
	}
	public void setXv(double xv) {
		this.xv = xv;
	}
	@Override
	public String toString() {
		return String.format("{ %d, %f }", getIv(), getXv());
	}
}

Completely standard.

Now we create a wrapper class handling all of the JAXB:

package jaxbdemo;

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

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlElements;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement(name="list")
public class DataContainer {
     private List<Data> list;
     public DataContainer() {
     	list = new ArrayList<>();
     }
     @XmlElements( { @XmlElement(name="a", type=DataA.class), 
@XmlElement(name="b", type=DataB.class) } )
     public List<Data> getList(){
     	return list;
     }
}

Now for usage.

First setup:

		// JAXB
		JAXBContext jxbctx = JAXBContext.newInstance(DataContainer.class);
		Marshaller m = jxbctx.createMarshaller();
		Unmarshaller um = jxbctx.createUnmarshaller();

Let us try write a file:

		DataContainer data = new DataContainer();
		data.getList().add(new DataA(123, "ABC"));
		data.getList().add(new DataB(456, 123.456));
		m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);
		try(OutputStream os = new FileOutputStream("/work/demo.xml")) {
			m.marshal(data, os);
		}

demo.xml looks like:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<list>
     <a>
         <iv>123</iv>
         <sv>ABC</sv>
     </a>
     <b>
         <iv>456</iv>
         <xv>123.456</xv>
     </b>
</list>

which I consider to be "nice" XML.

Reading the file again is simple:

		// load
		DataContainer data2 = null;
		try(InputStream is = new FileInputStream("/work/demo.xml")) {
			data2 = (DataContainer)um.unmarshal(is);
		}

Searching for various data is easy using the new Java 8 streams:

		// search
		Data o1 = data2.getList().stream().filter(item -> item.getIv() == 
456).findFirst().get();
		Data o2 = data2.getList().stream().filter(item -> item instanceof 
DataA && ((DataA)item).getSv().equals("ABC")).findFirst().get();

Objects can be update:

		// update
		o1.setIv(789);
		((DataA)o2).setSv("XXX");

And when written to another file:

		// save again
		try(OutputStream os = new FileOutputStream("/work/demo2.xml")) {
			m.marshal(data2, os);
		}

then demo2.xml has the expected content:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<list>
     <a>
         <iv>123</iv>
         <sv>XXX</sv>
     </a>
     <b>
         <iv>789</iv>
         <xv>123.456</xv>
     </b>
</list>

Arne