question: @ Override public synchronized void addRequestProperty ( String key , String value ) { if ( connected || connecting ) throw new IllegalStateException ( "Already connected" ) ; if ( key == null ) throw new NullPointerException ( "key is null" ) ; if ( isExternalMessageHeaderAllowed ( key , value ) ) { requests . add ( key , value ) ; if ( ! key . equalsIgnoreCase ( "Content-Type" ) ) { userHeaders . add ( key , value ) ; } } }
target:  Adds a general request property specified by a key-value pair.  This method will not overwrite existing values associated with the same key.