The Network Adapter Could Not Establish Connection

Issue 1:
  Connecting to database with jdbc thin driver the following error is reported:
 

java.sql.SQLException: Io exception: The Network Adapter could not establish the connection at
oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:111) at
oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:145) at
oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:254) at
oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:386) at
oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:413) at
oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:164)

The error can be caused by :

• A firewall between client and database server
• Database host does not exist in the etc/hosts file

Solution 1:  
   

1. Ensure that the database server host name exists in the etc/hosts file
2. Open the port used by java in the firewall

Issue 2:

      You implemented dataguard and your JDBC THIN client connections from your application server began failing shortly after. The class used to implement the JDBC driver is:
    oracle.jdbc.driver.OracleDriver

   Error message received:
java.sql.SQLException: Io exception: The Network Adapter could not establish the connection

As of JDBC 11g the oracle.jdbc.OracleConnection interface has been enhanced. For better visibility and clarity, all connection properties are defined as constants in this interface. The package oracle.jdbc.driver, which was deprecated in Oracle Database release 9.0.1, is desupported in this release. Code having references to this package will not compile and run. You can use package oracle.jdbc instead of this package.

Solution 2:

       To implement the solution, please execute the following steps:

      Change the JDBC connection driver class in your application server
     from:
          oracle.jdbc.driver.OracleDriver
    to
         oracle.jdbc.OracleDriver

Issue 3:

An application using the JDBC Thin Driver 10.2.0.1.0 cannot connect to the database server. At connection time, it fails with the following error:

java.sql.SQLException: Io exception: The Network Adapter could not establish the connection Error Code: 17002

If the NIC card of the server is configured to support IPv4 and IPv6, some services may start with IPv6. Any client application that tries to connect using IPv4 to the service that is running with IPv6 (or viceversa) will receive a connection refused error. If the java application is trying to connect to the database using JDBC then the client application may just hang or fail with an Io exception error.
The JDK used version is :  1.4.2.

Solution 3:

  

The java.net.preferIPv4Stack property allows Java applications to connect , and accept connections from, both IPv4 and IPv6 hosts. Setting this property to true indicates that JVM will use IPv4 sockets.

Here are two solutions :

1. Indicate to the java machine to use ip protocol used is V4.
   For this, launch the java machine where the jdbc application is running with the following parameter -Djava.net.preferIPv4Stack=true
   As example :
         java -Djava.net.preferIPv4Stack=true jdbcTest
   
2. Use the ORACLE OCI  JDBC driver.