Replace HashMap keys with values in Property file in Java

Question

I have to replace HashMap keys based on a property file mapping with old - new key mapping. Is the below approach best way of replacing keys?

KeyMapping.properties

newKey1 oldLKey1
newKey2 oldKey2


//Load property mapping file
ResourceBundle properties = ResourceBundle.getBundle("KeyMapping");

Enumeration<String> newKeys = properties.getKeys();
        Map<String, Object> result = new LinkedHashMap<>();

  while (newKeys.hasMoreElements()) {
    String newKey = (String) newKeys.nextElement();
    Iterator<Entry<String, Object>> iterator = mapToReplaceKeys.entrySet().iterator();

    while(iterator.hasNext()) {
       Entry<String, Object> entry = iterator.next();

      //If key matches the key in property file       
      if (entry.getKey().equals(newKey)) {

      //remove the entry from map mapToReplaceKeys
      iterator.remove();

      //add the key with the 'oldKey' and existing value
      result.put(properties.getString(newKey), entry.getValue());            
    }
  }
}

Ousmane D. · Answer 1 · 2018-11-22T00:47:08.260

What you're essentially doing is this:

Map<String, Object> result = Collections.list(properties.getKeys())
                .stream()
                .flatMap(element -> mapToReplaceKeys.entrySet()
                        .stream()
                        .filter(entry -> entry.getKey().equals(element)))
                .collect(toMap(e -> properties.getString(e.getKey()),
                        Map.Entry::getValue,
                        (l, r) -> r,
                        LinkedHashMap::new));

or you could also do:

Map<String, Object> result = new LinkedHashMap<>();
newKeys.asIterator()
       .forEachRemaining(e -> mapToReplaceKeys.forEach((k, v) -> {
             if(k.equals(e)) result.put(properties.getString(k), v);
       }));

Iterating over a `Map`, to find an equal key … that feels so … wrong… — Holger, Nov 22 '18 at 13:11

score 1 · Answer 2 · answered Nov 22 '18 at 13:10

Don’t iterate over a Map, just to check the keys for equality. That’s what the Map’s dedicated lookup methods are for:

ResourceBundle properties = ResourceBundle.getBundle("KeyMapping");
Map<String, Object> result = new LinkedHashMap<>();

for(String newKey: properties.keySet()) {
    Object value = mapToReplaceKeys.remove(newKey);
    if(value != null) result.put(properties.getString(newKey), value);
}

Since you want to remove the mappings, you can just use remove on the Map, which will do nothing and just return null when the key is not present.

Replace HashMap keys with values in Property file in Java

2 Answers2