连接数据库时提示如下错误提示：

Caused by: java.sql.SQLException: Io 异常: The Network Adapter could not establish the connection
at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:112)
at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:146)
at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:255)
at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:387)
at oracle.jdbc.driver.PhysicalConnection.(PhysicalConnection.java:439)at oracle.jdbc.driver.T4CConnection.(T4CConnection.java:165)at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:35)at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:801) ...68 more
请问问题出在哪儿，如何解决？