Map<String, String> mapA = new HashMap<String, String>();
      Map<String, String> mapB = new HashMap<String, String>();
      Map<String, String> mapAdd = new HashMap<String, String>(mapB);
      Map<String, String> mapDel = new HashMap<String, String>();
      Map<String, String> mapChange = new HashMap<String, String>();
      Map<String, String> mapUnChange = new HashMap<String, String>();

      Iterator<String> it = mapA.keySet().iterator();

      while(it.hasNext()) {
         String key = it.next();
         String val = mapA.get(key);

         if(mapB.containsKey(key)) {
            String bVal = mapB.get(key);

            if(val != null && val.equals(bVal) || val == bVal) {
               mapUnChange.put(key, val);
            }
            else {
               mapChange.put(key, val);
            }

            mapAdd.remove(key);
         }
         else {
            mapDel.put(key, val);
         }
      }
   }

------解决方案--------------------
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