Io 异常: The Network Adapter could not establish the connection

今天遇到一个问题，jdbc连接oracle数据库查询数据时报错：

java.sql.SQLException: Io 异常: 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)
at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:34)
at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:752)
at java.sql.DriverManager.getConnection(DriverManager.java:582)
at java.sql.DriverManager.getConnection(DriverManager.java:185)
at net.yhte.db.DBUtil.getConnection(DBUtil.java:20)
at net.yhte.db.DBUtil.main(DBUtil.java:48)
Exception in thread "main" java.sql.SQLException: Io 异常: 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)
at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:34)
at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:752)
at java.sql.DriverManager.getConnection(DriverManager.java:582)
at java.sql.DriverManager.getConnection(DriverManager.java:185)
at net.yhte.db.DBUtil.getConnection(DBUtil.java:20)
at net.yhte.db.DBUtil.main(DBUtil.java:48)

代码如下：
package net.yhte.service;

import java.sql.Connection;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import net.yhte.db.DBUtil;

import net.yhte.db.insert.InsertDB;

public class CommService {

public static void main(String[] args) {

try {

Connection conn = DBUtil.getConnection();

String sql = "select min(id), max(id) from t_sentry_record t";

System.out.println(conn);

PreparedStatement pst = conn.prepareStatement(sql);

ResultSet rs = pst.executeQuery();

while(rs.next()){

System.out.println(rs.getLong(1));

}

} catch (Exception e) {

e.printStackTrace();

}

}

}

package net.yhte.db;

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.SQLException;

/**

* 获得和关闭数据库连接的工具类

* @author tarena

*

*/

public class DBUtil {

public static Connection getConnection() throws Exception{

Connection conn = null;

try {

Class.forName("oracle.jdbc.driver.OracleDriver");

conn = DriverManager.getConnection(

"jdbc:oracle:thin:@外网:1521:orcl",

"yhte","yhte");

//conn = DriverManager.getConnection(

// "jdbc:oracle:thin:@外网:1521/orcl",

// "yhte","yhte");

} catch (Exception e) {

e.printStackTrace();

throw e;

}

return conn;

}

public static void close(Connection conn){

if(conn !=null){

try {

conn.close();

} catch (SQLException e) {

e.printStackTrace();

}

}

}

/**

* @param args

* @throws Exception

*/

public static void main(String[] args) throws Exception {

// TODO Auto-generated method stub

System.out.println(getConnection());

}

}

从报错的信息中得知是连接数据库时出现问题，所以通过telnet命令查看端口是否开启或被占用，这时又出现了一个问题,oracle数据库装在双网卡的服务器上，telnet外网是可以通的，但是内网却不通，后来查资料说有可能数据库也要在内网的ip中添加监听；最后在jdbc连接Oracle数据库的字符串的IP还是选择了外网的IP。
jdbc:oracle:thin:@外网:1521:orcl
一开始认为是jdbc连接数据的jar包有问题，后来下了几个版本的jar包还是有问题，最后查找jdbc连接数据字符串格式将“jdbc:oracle:thin:@外网:1521:orcl”改成“jdbc:oracle:thin:@外网:1521/orcl”解决问题。