[开发工具]MultiValueMap中put()与addAll()的区别

MultiValueMap的特点是一个key键可以对应多个键值，但有一点困扰了我，就是MultiValueMap同时提供了put(key,List<>)与addAll(key,List<>)方法，它们有什么区别呢？
首先来看下java文档
put()

    /**
     * Associates the specified value with the specified key in this map
     * (optional operation).  If the map previously contained a mapping for
     * the key, the old value is replaced by the specified value.  (A map
     * <tt>m</tt> is said to contain a mapping for a key <tt>k</tt> if and only
     * if {@link #containsKey(Object) m.containsKey(k)} would return
     * <tt>true</tt>.)
     *
     * @param key key with which the specified value is to be associated
     * @param value value to be associated with the specified key
     * @return the previous value associated with <tt>key</tt>, or
     *         <tt>null</tt> if there was no mapping for <tt>key</tt>.
     *         (A <tt>null</tt> return can also indicate that the map
     *         previously associated <tt>null</tt> with <tt>key</tt>,
     *         if the implementation supports <tt>null</tt> values.)
     * @throws UnsupportedOperationException if the <tt>put</tt> operation
     *         is not supported by this map
     * @throws ClassCastException if the class of the specified key or value
     *         prevents it from being stored in this map
     * @throws NullPointerException if the specified key or value is null
     *         and this map does not permit null keys or values
     * @throws IllegalArgumentException if some property of the specified key
     *         or value prevents it from being stored in this map
     */
    V put(K key, V value);

译文：
将指定的值与映射中的指定键关联(可选操作)。如果映射之前包含键的映射，则旧值将被指定的值替换。(当且仅当m. containskey (k)返回true时，表示映射m包含键k的映射。)

addAll()

	/**
	 * Add all the values of the given list to the current list of values for the given key.
	 * @param key they key
	 * @param values the values to be added
	 * @since 5.0
	 */
	void addAll(K key, List<? extends V> values);

译文：
将给定列表中的所有值添加到给定键的当前值列表中。

这里已经说明：put()方法是直接替换，addAll()方法是继续添加

测试案例：

@Test
    public void addMultiValueMap(){
        MultiValueMap<String, String> multiValueMap = new LinkedMultiValueMap<>();
        ArrayList<String> list1 = new ArrayList<>();
        list1.add("aa");
        list1.add("bb");
        ArrayList<String> list2 = new ArrayList<>();
        list2.add("cc");
        ArrayList<String> list3 = new ArrayList<>();
        list3.add("dd");
        multiValueMap.put("key1", list1);
        multiValueMap.put("key1", list2);
        multiValueMap.put("key1", list3);
        System.out.println(multiValueMap.get("key1"));

        multiValueMap.addAll("key2", list1);
        multiValueMap.addAll("key2", list2);
        multiValueMap.addAll("key2", list3);
        System.out.println(multiValueMap.get("key2"));
    }

输出结果