java连接数据库的错误，请人指点

代码：
     package train.dao;import java.sql.*;public class ConnectionDB {
public static Connection getConn(){
Connection conn=null;
try {
Class.forName("oracle.jdbc.driver.OracleDriver");
conn=DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:orcl","system","admin");
System.out.println("123");
} catch (ClassNotFoundException e) {

// TODO Auto-generated catch block
e.printStackTrace();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return conn;
}
public static void  closeAll(Connection conn,Statement st,ResultSet rs){

try {
if(rs!=null)
rs.close();
if(st!=null)
st.close();
if(conn!=null)
conn.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public static void main(String[] args) {
ConnectionDB cd=new ConnectionDB();
Connection con=cd.getConn();
if(con==null){
System.out.println("连接失败");
}else{
System.out.println("连接成功");
}
}
}
异常：
      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 train.dao.ConnectionDB.getConn(ConnectionDB.java:10)
at train.dao.ConnectionDB.main(ConnectionDB.java:38)
连接失败
    
       发了几张贴，比较急，希望能有个符合的处理意见！