// java.util.prefs.Preferences exportNode(java.io.OutputStream os)

//key and value pairs are not written in the output file user01.pfs file
//program and output are as shown below.


import java.util.prefs.*;
import java.util.*;
import java.io.*;

public class ExportNodeWrite {
  
    public static void main(String[] args) {
        try{
           Preferences userRoot = Preferences.userRoot();
           
           Preferences N1 = userRoot.node("N1");
           N1.removeNode();
           N1 = userRoot.node("N1");
           N1.put("k1","v1");
           Preferences N2 = N1.node("N2");
           N2.put("k2","v2");
           userRoot.flush();

           
           File systemFile = new File("user01.pfs");
           FileOutputStream fos = new FileOutputStream(systemFile);
           N2.exportNode(fos);
           fos.close();
           System.out.println("user01.pfs output");
           System.out.println();
           RandomAccessFile raf = new RandomAccessFile("user01.pfs","r");
           String line = null;
           while ( (line = raf.readLine()) !=null) {
              System.out.println(line);
           }
         } catch(Exception e) {
            System.out.println("exception thrown " + e);
         }
         
    
   }
 
}

//////////////output


I:\merlinTest\preferences\bug\exportNode>java ExportNodeWrite
user01.pfs output

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE preferences SYSTEM 'http://java.sun.com/dtd/preferences.dtd&#39;>

<preferences>
  <root type="user">
    <node name="N1">
      <node name="N2" />
    </node>
  </root>
</preferences>