ojdbc6.jar连接Oracle11g报错，怎么解决？

java.sql.SQLRecoverableException: IO 错误: The Network Adapter could not establish the connection
at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:419)
at oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:536)
at oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:228)
at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:32)
at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:521)
at java.sql.DriverManager.getConnection(DriverManager.java:664)
at java.sql.DriverManager.getConnection(DriverManager.java:247)
at DbUtil.main(DbUtil.java:27)
Caused by: oracle.net.ns.NetException: The Network Adapter could not establish the connection
at oracle.net.nt.ConnStrategy.execute(ConnStrategy.java:375)
at oracle.net.resolver.AddrResolution.resolveAndExecute(AddrResolution.java:422)
at oracle.net.ns.NSProtocol.establishConnection(NSProtocol.java:678)
at oracle.net.ns.NSProtocol.connect(NSProtocol.java:238)
at oracle.jdbc.driver.T4CConnection.connect(T4CConnection.java:1054)
at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:308)
... 7 more
Caused by: java.net.ConnectException: Connection refused: connect
at java.net.DualStackPlainSocketImpl.waitForConnect(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:85)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at oracle.net.nt.TcpNTAdapter.connect(TcpNTAdapter.java:209)
at oracle.net.nt.ConnOption.connect(ConnOption.java:123)
at oracle.net.nt.ConnStrategy.execute(ConnStrategy.java:353)
... 12 more