...

        } else if(messageType.equals("SENDMESSAGE") || messageType.equals("SENDMSG")) {
            String[] bodyParts = messageBody.split(" ");
            if(bodyParts.length > 1) {
                String recipient = bodyParts[0];
                String message = messageBody.substring(recipient.length()+1, messageBody.length());
                //find recipient
                Optional<ConnectedClient> recipientClient = connectedClients.stream().filter(c -> c.getUsername().equals(recipient)).findAny();
                if(recipientClient.isPresent()) {
                    recipientClient.get().send(client.getUsername() + " -> " + recipientClient.get().getUsername() + ": " + message);
                    client.send("Message sent");
                } else {
                    client.send("Message could not be sent: no recipient by that name");
                }
            }

    ...