Generally, the SQL SERVER JDBC URL will be in this format.
the default port is 1433
Get your Servername properly
jdbc:sqlserver://[serverName[\instanceName][:portNumber]][;property=value[;property=value]]
Reference: https://learn.microsoft.com/en-us/sql/connect/jdbc/building-the-connection-url?view=sql-server-ver16
You can try this way
jdbc:mysql://localhost/ExternalDB