oracle convenient way to connect

(1)Oracle JDBC Thin using a ServiceName:
jdbc:oracle:thin:@//<host>:<port>/<service_name>

    而PLSQL 同样,如果是双活库，TNS涉及两个scan域名，则选取主库scan域名，如：
      scan_primary:1521/pdbname_srv    ---12c，当然涉及双活切换，最好还是配置TNS才是最合理的@(3)

(2) Oracle JDBC Thin using an SID: br/>jdbc:oracle:thin:@<host>:<port>:<SID>
Usually the above situation is more common on a single instance

    (3) jdbc:oracle:thin:@<TNSName>