Javaのマップをキーでソートできますか?

package test;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;
import java.util.Map.Entry;

public class MapSortDemo {

    /**
     * @param args
     */
    public static void main(String[] args) {
        Map hMap = new HashMap();
        hMap.put("a", "3");
        hMap.put("z", "2");
        hMap.put("b", "6");
        hMap.put("o", "9");

        System.out.println("根据key升序排序"); 
        Map sortByKeyResultMap = sortMapByKey(hMap);    //按Key进行排序
        Iterator> sortByKeyEntries = sortByKeyResultMap.entrySet().iterator(); 
        while (sortByKeyEntries.hasNext()) { 
          Map.Entry entry = sortByKeyEntries.next(); 
          System.out.println("Key = " + entry.getKey() + "------->Value = " + entry.getValue()); 
        }
        
        System.out.println("------------------------------"); 
        
        System.out.println("根据value降序排序"); 
        Map sortByValueResultMap = sortMapByValue(hMap); //按Value进行排序
        Iterator> sortByValueEntries = sortByValueResultMap.entrySet().iterator(); 
        while (sortByValueEntries.hasNext()) { 
          Map.Entry entry = sortByValueEntries.next(); 
          System.out.println("Key = " + entry.getKey() + "------->Value = " + entry.getValue()); 
        }
    }
    /**
     * 使用 Map按key进行排序
     * @param map
     * @return
     */
    public static Map sortMapByKey(Map map) {
        if (map == null || map.isEmpty()) {
            return null;
        }
//        Map sortMap = new TreeMap(new MapKeyComparator());
        Map sortMap = new TreeMap(new Comparator() {
            public int compare(String obj1, String obj2) {
                return obj1.compareTo(obj2);//升序排序
            }
        });
        sortMap.putAll(map);
        return sortMap;
    }
    
    /**
     * 使用 Map按value进行排序
     * @param map
     * @return
     */
    public static Map sortMapByValue(Map map) {
        if (map == null || map.isEmpty()) {
            return null;
        }
        Map sortedMap = new LinkedHashMap();
        List> entryList = new ArrayList>(map.entrySet());
//        Collections.sort(entryList, new MapValueComparator());
        Collections.sort(
            entryList, 
            new Comparator>(){
                   public int compare(Entry o1, Entry o2) {
                       return o2.getValue().compareTo(o1.getValue());// 降序排序
                   }
            }
        );

        Iterator> iter = entryList.iterator();
        Map.Entry tmpEntry = null;
        while (iter.hasNext()) {
            tmpEntry = iter.next();
            sortedMap.put(tmpEntry.getKey(), tmpEntry.getValue());
        }
        return sortedMap;
    }
}