An exception to a database connection was reported by someone today:

Could not get JDBC Connection; nested exception is org.apache.commons.dbcp.SQLNestedException: Cannot create PoolableConnectionFactory (Io Exceptions: NL Exception was generated)
org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is org.apache.commons.dbcp.SQLNestedException: Cannot create PoolableConnectionFactory (Io Exceptions: NL Exception was generated)

 

Because the program has been running normally for a long time, so the basic rule out code logic problems, check the configuration found that the JDBC connection string problem;
The original URL was written as:

jdbc:oracle:thin:@(DESCRIPTION =(DESCRIPTION =(ADDRESS_LIST =(ADDRESS = (PROTOCOL = TCP)(HOST = 127.0.0.1)(PORT = 1521))(ADDRESS = (PROTOCOL = TCP)(HOST = 127.0.0.1)(PORT = 1521))(LOAD_BALANCE = yes))(CONNECT_DATA =(SERVER = DEDICATED)(SERVICE_NAME = orcl)(FAILOVER_MODE =(TYPE = SELECT)(METHOD = BASIC)(RETRIES = 180)(DELAY = 5))))

Where, DESCRIPTION appears twice, which is incorrect, and the correct connection string should be:

jdbc:oracle:thin:@(DESCRIPTION =(ADDRESS_LIST =(ADDRESS = (PROTOCOL = TCP)(HOST = 127.0.0.1)(PORT = 1521))(ADDRESS = (PROTOCOL = TCP)(HOST = 127.0.0.1)(PORT = 1521))(LOAD_BALANCE = yes))(CONNECT_DATA =(SERVER = DEDICATED)(SERVICE_NAME = orcl)(FAILOVER_MODE =(TYPE = SELECT)(METHOD = BASIC)(RETRIES = 180)(DELAY = 5))))

Conclusion:
A JDBC connection string syntax error may result in Io exceptions: NL Exception was generated.