How to implement and serialize nested Maps?

[Siegfried Heintze]

The code below serializes a hashmap in class Bean. There is a second map in there just to demonstrate sun's bug where maps by default won't serialize.

Let's say I want hash map that looks like this:

Map<String,Map><String,Map><String,String>>> map;

How would I modify my class bean to contain such a map of maps of maps?

I would want to use templates so I'm not contrained to using strings for keys or values. How would this work?

Thanks,
Siegfried

/*
 * Begin commands to execute this file using Java with bash
 * if [ `uname` == 'Linux' ]
 * then
 * export CLASSPATH=bin:.
 * else
 * export CLASSPATH=bin\;.
 * fi
 * pushd ../../
 * if [ -e "bin" ]
 * then
 * echo "already have build (bin) directory"
 * else
 * echo "mkdir bin"
 * mkdir bin
 * fi
 * javac -g com/heintze/DemoMaps.java -d bin
 * java  com.heintze.DemoMaps "/demoMaps/datum[1]/value/text()" '/demoMaps/datum[@name="abc"]' <<EOF 
 * ><?xml version="1.0" encoding="UTF-8" standalone="yes"?>
 *   <demoMaps><map/>
 *     <map2>
 *       <map>
 *         <item value="mumble" key="fratz"/>
 *       </map>
 *     </map2>
 *   <datum name="xyz"><value>Insert your sample data here</value></datum>
 *   <datum name="abc"><value>def</value></datum>
 * </demoMaps>
 * EOF
 * rm bin/com/heintze/DemoMaps.class
 * popd
 * End commands to execute this file using Java with bash
 *
 */

package com.heintze;
import java.io.FileReader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;
import javax.xml.bind.annotation.adapters.XmlAdapter;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;

@XmlType
class Pair{
  Pair(){}
  Pair(String name, String value){ this.name = name; this.value = value; }
  @XmlAttribute
  String name;
  @XmlElement
  String value;
}

// http://www.caucho.com/resin/doc/jaxb-annotations.xtp#@XmlJavaTypeAdapter
@XmlRootElement
class Bean {
  @XmlJavaTypeAdapter(MyMapAdapter.class)
	  public HashMap<String,String> map = new HashMap<String,String>();
}

class MyMapAdapter
  extends XmlAdapter<Item[],java.util.Map><String,String>> {
// http://weblogs.java.net/blog/kohsuke/archive/2005/04/xmladapter_in_j.html 
	@Override
	public Item[] marshal(Map<String, String> map) throws Exception {
		Item[] result=new Item[map.size()];
		int ii=0;
		for(String key:map.keySet()){
			result[ii]=new Item();
			result[ii].key=key;
			result[ii].value=map.get(key);
			ii = ii + 1;
		}
		return result;
	}

	@Override
	public Map<String, String> unmarshal(Item[] value) throws Exception {
	    Map<String,String> r = new HashMap<String,String>();
	    for( Item c : value )
	      r.put(c.key, c.value);
	    return r;
	}
}

class Item {
  @XmlAttribute
	  public String key;

  @XmlAttribute
	  public String value;
}

class Temp {
  @XmlElement
	  private List<Item> entry = new java.util.ArrayList<Item>();
}

@XmlRootElement
public class DemoMaps {
  static java.io.PrintStream out = System.out;
  public static void main(String[] args) {
    DemoMaps data = new DemoMaps();
    try {
      JAXBContext context = JAXBContext.newInstance(DemoMaps.class);
      Marshaller m = context.createMarshaller();
      
      Unmarshaller um = context.createUnmarshaller();
      data = (DemoMaps)um.unmarshal(new FileReader(java.io.FileDescriptor.in) );
      data.datum[0].name+="_modified";
      data.datum[0].value+="_modified";
      
      data.map.put("hello", "world");
      data.map2.map.put("hello", "world");
      m.marshal(data, System.out);
    } catch (JAXBException e) {
      e.printStackTrace();
    }
  }
  @XmlElement
  Pair[] datum =new Pair[0];
  @XmlElement(nillable=true, required=false)
  TreeMap<String,String> map=new TreeMap<String,String>();
  @XmlElement()
  Bean map2 = new Bean();
 }

[Siegfried Heintze]

I figured it out. Now please see my new post on converting it to generics.