Generating XML

You should generate XML programmatically whenever possible to help ensure well-formedness. In Java, the XMLWriter class lets us do this. You can get XMLWriter from David Megginson, the author. Unfortunately, XMLWriter performs only minimal well-formedness checks - in particular it doesn't ensure that open and close tags are balanced. It wouldn't be hard to write a subclass of XMLWriter that did that checking, though.

XMLWriter is very easy to use. An example: 

import java.io.FileWriter;
import com.megginson.sax.XMLWriter;
import org.xml.sax.helpers.AttributesImpl;

public class GenerateXML
{

    public static void main (String args[])
	throws Exception
    {
	XMLWriter writer = new XMLWriter(new FileWriter("output.xml"));

	writer.startDocument();

        AttributesImpl attribs = new AttributesImpl();
        attribs.addAttribute("","class","","","simple");
	writer.startElement("","greeting","",attribs);
        writer.characters("Hello, world!");
        writer.endElement("greeting");
        writer.endDocument();

    }

}

Let's go through the example line by line: 

import java.io.FileWriter;
import com.megginson.sax.XMLWriter;
import org.xml.sax.helpers.AttributesImpl;
This just lets Java know what classes we want to use. package. 
XMLWriter writer = new XMLWriter(new FileWriter("output.xml"));
This creates a new XMLWriter object with output directed to output.xml. To write to standard output, omit the output argument. To write to a string, we could use a StringWriter. Going back to our example, we next insert an an XML declaration: 
writer.startDocument()
The declaration that writer.startDocument() emits lets us know that the output is XML. 
<?xml version="1.0" standalone="yes"?>
Then we create a new attribute set and add the attribute class = "simple", open a <greeting> element with those attributes and write the characters Hello, world! and finally close the <greeting> tag. All the empty strings are various arguments to support namespaces; normally they should be blank. There are convenience methods that allow you to omit these arguments if neither namespaces nor attributes are being used; see the XMLWriter javadoc for more info. 
AttributesImpl attribs = new AttributesImpl();
attribs.addAttribute("","class","","","simple");
writer.startElement("","greeting","",attribs);
writer.characters("Hello, world!");
writer.endElement("greeting");
This produces 
<greeting class="simple">Hello, world!</greeting>

Then we clean up by telling writer we're done writing.

writer.endDocument();