创建与 Oracle的SQL模型连接时出错：The Network Adapter could not establish the connection

1.具体异常信息：
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.<init>(PhysicalConnection.java:414)
at oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:165)
at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:35)
at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:801)
at org.eclipse.datatools.connectivity.drivers.jdbc.JDBCConnection.createConnection(JDBCConnection.java:214)
at org.eclipse.datatools.connectivity.DriverConnectionBase.internalCreateConnection(DriverConnectionBase.java:105)
at org.eclipse.datatools.connectivity.DriverConnectionBase.open(DriverConnectionBase.java:54)
at org.eclipse.datatools.connectivity.drivers.jdbc.JDBCConnection.open(JDBCConnection.java:73)
at org.eclipse.datatools.enablement.internal.oracle.JDBCOracleConnectionFactory.createConnection(JDBCOracleConnectionFactory.java:27)
at org.eclipse.datatools.connectivity.internal.ConnectionFactoryProvider.createConnection(ConnectionFactoryProvider.java:83)
at org.eclipse.datatools.connectivity.internal.ConnectionProfile.createConnection(ConnectionProfile.java:359)
at org.eclipse.datatools.connectivity.sqm.internal.core.connection.ConnectionInfoImpl.initializeJDBCConnection(ConnectionInfoImpl.java:705)
at org.eclipse.datatools.connectivity.sqm.internal.core.connection.ConnectionInfoImpl.<init>(ConnectionInfoImpl.java:690)
at org.eclipse.datatools.connectivity.sqm.internal.core.connection.ConnectionFactory.createConnection(ConnectionFactory.java:38)
at org.eclipse.datatools.connectivity.sqm.core.SQMConnectionFactory.createConnection(SQMConnectionFactory.java:45)
at org.eclipse.datatools.connectivity.sqm.internal.core.connection.ConnectionFactory.createConnection(ConnectionFactory.java:59)
at org.eclipse.datatools.connectivity.internal.ConnectionFactoryAdapterProvider.createConnection(ConnectionFactoryAdapterProvider.java:114)
at org.eclipse.datatools.connectivity.internal.ManagedConnection.createConnection(ManagedConnection.java:163)
at org.eclipse.datatools.connectivity.internal.CreateConnectionJob.run(CreateConnectionJob.java:56)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:54)
2.说明：
     远程服务器监听器正常开启；
     plsql可以登录进去；
     jdbc偶尔能够连接正常，所以url,用户名和密码不会错误；
所以，这个问题怎么解决，求各位帮助解答，谢谢