import java.io.FileInputStream;

/**
 * 
 * @author jkerr88
 *
 * You need the code from here:
 *
 *  http://www.minecraftwiki.net/wiki/NBT_class
 *  
 * saved as Tag.java in the same folder as this one.  This file should be saved as ReportPlayerLocation.java
 * 
 */
public class ReportPlayerLocation implements Runnable{
   
   static ReportPlayerLocation iThis;
   static String isCurrentFile;
   
   public static void main(String argv[]){
      
      iThis = new ReportPlayerLocation();
      Thread t = new Thread(iThis);    
      t.start();
   
   } // main
   
   public void run() {     
      
      String sWorldFolder = "C:\\Documents and Settings\\Jeff\\Application Data\\.minecraft\\saves\\World1";
            
      try{
            
         Tag datFileTag = Tag.readFrom(new FileInputStream(sWorldFolder + "\\level.dat"));
         reportPlayerPositionFromTag(datFileTag);
         
      }catch(Exception e){
         System.out.println(e);
         return;   
      }
      
      System.out.println("\nDone!");
   
   } 
 

   private void reportPlayerPositionFromTag(Tag p_tag){
      
      Tag.Type type = p_tag.getType();
      if (type == Tag.Type.TAG_End)
         return;
      
      String sName = p_tag.getName();
      
      if (type == Tag.Type.TAG_Byte_Array) {
         
      } else if (type == Tag.Type.TAG_List) {
         Tag[] subtags = (Tag[]) p_tag.getValue();
         for (Tag st : subtags) {
            reportPlayerPositionFromTag(st);
         }
         
         if(sName.equals("Pos")){
            System.out.println("Found Player Pos: (X is NS, Y is Altitude, Z is EW");
            
            Double nX = (Double) subtags[0].getValue();
            Double nY = (Double) subtags[1].getValue();
            Double nZ = (Double) subtags[2].getValue();
            
            System.out.println("X: " + Math.round(nX.doubleValue()));
            System.out.println("Y: " + Math.round(nY.doubleValue()));
            System.out.println("Z: " + Math.round(nZ.doubleValue()));

            System.out.println("\nChunk: (x/16, z/16)");
            
            System.out.println("xPos: " + Math.floor(nX.doubleValue()/16));
            System.out.println("zPos: " + Math.floor(nZ.doubleValue()/16));
            
         }
         
      } else if (type == Tag.Type.TAG_Compound) {
         Tag[] subtags = (Tag[]) p_tag.getValue();
         for (Tag st : subtags) {
            reportPlayerPositionFromTag(st);
         }
      } else {
         
      }
      
   }
   
}

Find and report player position in Minecraft save file

Java