Serialize a Java Collection with the streaming API

Details: Published: 08 November 2009

Writing a Collection to xml is more efficiently done using xml streaming techniques rather than creating a DOM and then serializing it; unless, of course, you want to make use of the DOM other than purely as an object to serialize.

Collections other than Map are even easier to handle, so that code for that is not given here as it should be possible to derive it easily from the code HERE

import javax.xml.stream.*;
import java.io.*;
import java.util.*;

public class Map2Xml {
    public static void main(String[] args) {
        Map<String, Integer> m = Map2Xml.createRandomMap();
        System.out.println("Starting map:");
        System.out.println(m);
        // Now write it as xml
        try {
            Map2Xml.toXml(m, new FileWriter(args[0]));
        }
        catch(IOException e) {
            e.printStackTrace();
        }
        catch(XMLStreamException e) {
            e.printStackTrace();
        }
    }

    public static Map<String, Integer> createRandomMap() {
        Map<String, Integer> m = new HashMap<String, Integer>(5);
        for(char i = 'a';i < 'f';i++) {
            m.put(String.valueOf(i), (int)(Math.random() * 99));
        }
        return m;
    }

    public static <K,V> void toXml(Map<K, V> map, Writer out) throws IOException, XMLStreamException {
        XMLStreamWriter xsw = null;
        try {
            try {
                XMLOutputFactory xof = XMLOutputFactory.newInstance();
                // If you want pretty-printing, you can use:
                //xsw = new javanet.staxutils.IndentingXMLStreamWriter(xof.createXMLStreamWriter(out));
                xsw = xof.createXMLStreamWriter(out);
                xsw.writeStartDocument("utf-8", "1.0");
                xsw.writeStartElement("entries");

                // Do the Collection
                for(Map.Entry<K, V> e : map.entrySet()) {
                    xsw.writeStartElement("entry");
                    xsw.writeAttribute("key", e.getKey().toString());
                    xsw.writeAttribute("value", e.getValue().toString());
                    xsw.writeEndElement();
                }
                xsw.writeEndElement();
                xsw.writeEndDocument();
            }
            finally {
                if (out != null) {
                    try { out.close() ; } catch(IOException e) { /* ignore */ }
                }
            }// end inner finally
        }
        finally {
            if (xsw != null) {
                try { xsw.close() ; } catch(XMLStreamException e) { /* ignore */ }
            }
        }
    }

}