Connection to DB from client server through jdbc:Oracle:Oci8 fail

We tried to use to connect to DB using jdbc:Oracle:Oci8:@<SERVICE-A> . Connection fail / refuse with one DB .But its working with other databases.
But through toad , jdbc thin client were able to connect. But this has happen suddenly and were able to connect previously. How to navigate this issue to resolve.

alternative arrangement :
we currently connecting to DB Through JDBC Thin Client(

ODI_MASTER_URL=jdbc:oracle:thin:@oda-nc-tst-scan:1521/<SERVICE-A>

Issue found: connection through jdbc:Oracle:Oci8:@<SERVICE-A>

error:
-----

Caused by: java.sql.SQLException: Exception occurred while getting connection: oracle.ucp.UniversalConnectionPoolException: Cannot get Connection from Datasource: java.sql.SQLRecoverableException: IO Error: Connection reset
        at oracle.ucp.util.UCPErrorHandler.newSQLException(UCPErrorHandler.java:488)
        at oracle.ucp.util.UCPErrorHandler.throwSQLException(UCPErrorHandler.java:163)
        at oracle.ucp.jdbc.PoolDataSourceImpl.getConnection(PoolDataSourceImpl.java:943)
        at oracle.ucp.jdbc.PoolDataSourceImpl.getConnection(PoolDataSourceImpl.java:873)
        at oracle.ucp.jdbc.PoolDataSourceImpl.getConnection(PoolDataSourceImpl.java:863)
        at oracle.odi.jdbc.datasource.LoginTimeoutDatasourceAdapter.doGetConnection(LoginTimeoutDatasourceAdapter.java:99)
       at oracle.odi.jdbc.datasource.LoginTimeoutDatasourceAdapter.getConnection(LoginTimeoutDatasourceAdapter.java:62)
        at org.springframework.jdbc.datasource.DataSourceUtils.doGetConnection(DataSourceUtils.java:113)
    at org.springframework.jdbc.datasource.DataSourceUtils.getConnection\(DataSourceUtils.java:79\)

---------- Post updated at 05:50 AM ---------- Previous update was at 05:43 AM ----------

How to trace specific connection come to DB using port, service name, username, oci8.

Please note now same user already connected through ( jdbc:oracle:thin:@oda-nc-tst-scan:1521/<SERVICE-A> )