在Java中用属性文件中的值替换HashMap键

Question

我必须将基于属性文件映射的HashMap键替换为新旧键映射。下面的方法是替换密钥的最佳方式吗？

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());            
    }
  }
}

Answer 1

你实际上是这样做的：

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));

或者你也可以这样做：

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

Answer 2

不要在Map上迭代，只是为了检查键是否相等。这就是Map的专用查找方法的用途：

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);
}

因为您希望删除映射，所以可以只在Map上使用remove，它不会做任何事情，只会在键不存在时返回null。