LinkedCaseInsensitiveMap
LinkedCaseInsensitiveMap<V> implements Map<String, V>, Serializable, Cloneable
key忽略大小写的LinkedMap，不支持null作为key
private final LinkedHashMap<String, V> targetMap; 真实的容器，key=真实key，value=存放的value
private final HashMap<String, String> caseInsensitiveKeys; key=真实key小写后的值，value=真实key
private final Locale locale; key转换为小写时使用的Locale -> key.toLowerCase(getLocale());
#public boolean containsKey(Object key) key是String类型 且 caseInsensitiveKeys的keys中包含参数key的小写
@Nullable
#public V get(Object key) 从caseInsensitiveKey获取真实key再从targetMap获取value
@Nullable
#public V getOrDefault(Object key, V defaultValue) 获取不到则返回默认值
@Nullable
#public V put(String key, @Nullable V value) value可以为null，返回之前的value(可能为null)
#public void putAll(Map<? extends String, ? extends V> map) forEach使用put
@Nullable
#public V putIfAbsent(String key, @Nullable V value) value可以为null，返回之前的value(可能为null)
@Nullable
#public V computeIfAbsent(String key, Function<? super String, ? extends V> mappingFunction) 若旧的key已存在 且 value不是null，则返回value；否则使用function创建value，put value，并return value
@Nullable
#public V remove(Object key)
