The MultivaluedMapImpl class is an implementation class of the javax.ws.rs.core.MultivaluedMap interface. For details on the specifications for the methods of the MultivaluedMapImpl class, see the JAX-RS API documentation.

This section describes the notes on using the constructors and methods of the MultivaluedMapImpl class.

• The MultivaluedMapImpl class is not thread safe.
• The MultivaluedMapImpl class is a simple implementation class and only provides minimum functions. You can only use the add method, getFirst method, and putSingle method of the javax.ws.rs.core.MultivaluedMap interface.
  You cannot invoke the other methods of the java.util.Map interface (such as the put method and remove method). If the methods other than the add method, getFirst method, and putSingle method are used, the operations of the JAX-RS engine are not guaranteed.
  
• If the functionality of the MultivaluedMapImpl class is not available, separately create a class where the javax.ws.rs.core.MultivaluedMap interface is implemented.
• If null is specified in the value parameter for the add(String key, String value) method and putSingle(String key, String value) method, an empty string ("") is added as a value instead of null.