How should I resolve java.lang.IllegalArgumentException: protocol = https host = null Exception?

URLs use forward slashes (/), not backward ones (as windows). Try:

serverURLS = "https://abc.my.domain.com:55555/update";

The reason why you get the error is that the URL class can't parse the host part of the string and therefore, host is null.

This code seems completely unnecessary:

String serverURLS = getRecipientURL(message);

serverURLS = "https:\\\\abc.my.domain.com:55555\\update";

if (serverURLS != null){
    serverURL = new URL(serverURLS);
}

1. serverURLS is assigned the result of getRecipientURL(message)
2. Then immediately you overwrite the value of serverURLS, making the previous statement a dead store
3. Then, because if (serverURLS != null) evaluates to true, since you just assigned the variable a value in the preceding statement, you assign a value to serverURL. It is impossible for if (serverURLS != null) to evaluate to false!
4. You never actually use the variable serverURLS beyond the previous line of code.

You could replace all of this with just:

serverURL = new URL("https:\\\\abc.my.domain.com:55555\\update");