java.sql.SQLRecoverableException: IO Error: The Network Adapter could not establish the connection hostname

You got the following error when you run your program

java.sql.SQLRecoverableException: IO Error: The Network Adapter could not establish the connection
        at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:673)
        at oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:715)
        at oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:385)
        at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:30)
        at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:564)
        at java.sql.DriverManager.getConnection(DriverManager.java:664)
        at java.sql.DriverManager.getConnection(DriverManager.java:247)
        ...
Caused by: oracle.net.ns.NetException: The Network Adapter could not establish the connection
        at oracle.net.nt.ConnStrategy.execute(ConnStrategy.java:445)
        at oracle.net.resolver.AddrResolution.resolveAndExecute(AddrResolution.java:464)
        at oracle.net.ns.NSProtocol.establishConnection(NSProtocol.java:594)
        at oracle.net.ns.NSProtocol.connect(NSProtocol.java:229)
        at oracle.jdbc.driver.T4CConnection.connect(T4CConnection.java:1360)
        at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:486)
        ... 9 more
Caused by: java.net.ConnectException: Connection refused (Connection refused)
        at java.net.PlainSocketImpl.socketConnect(Native Method)
        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.SocksSocketImpl.connect(SocksSocketImpl.java:392)
        at java.net.Socket.connect(Socket.java:589)
        at oracle.net.nt.TcpNTAdapter.connect(TcpNTAdapter.java:162)
        at oracle.net.nt.ConnOption.connect(ConnOption.java:133)
        at oracle.net.nt.ConnStrategy.execute(ConnStrategy.java:411)
        ... 14 more


Check the followings are correct:

1. the database URL
2. the database port
3. username and password are correct and granted the privilege for the operation
4. the host name is correct in the listener.ora and tnsnames.ora files. They are located at $ORACLE_HOME/netowrk/admin.
5. Check if the listener is running using the command: lsnrctl START

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