无法创建池的初始连接

Question

嗨，我收到以下错误消息。当我们遇到以下错误时，请有人帮助我：

    2019-12-02 19:31:25.176 ERROR 1 --- [           main] o.a.tomcat.jdbc.pool.ConnectionPool      :  Unable to create initial connections of pool.
java.sql.SQLException: Driver:oracle.jdbc.OracleDriver@6b7906b3 returned null for URL:
        at org.apache.tomcat.jdbc.pool.PooledConnection.connectUsingDriver(PooledConnection.java:338) ~[tomcat-jdbc-9.0.21.jar!/:na]
        at org.apache.tomcat.jdbc.pool.PooledConnection.connect(PooledConnection.java:212) ~[tomcat-jdbc-9.0.21.jar!/:na]
        at org.apache.tomcat.jdbc.pool.ConnectionPool.createConnection(ConnectionPool.java:744) [tomcat-jdbc-9.0.21.jar!/:na]
        at org.apache.tomcat.jdbc.pool.ConnectionPool.borrowConnection(ConnectionPool.java:676) [tomcat-jdbc-9.0.21.jar!/:na]
        at org.apache.tomcat.jdbc.pool.ConnectionPool.init(ConnectionPool.java:483) [tomcat-jdbc-9.0.21.jar!/:na]
        at org.apache.tomcat.jdbc.pool.ConnectionPool.<init>(ConnectionPool.java:154) [tomcat-jdbc-9.0.21.jar!/:na]