执行查询到数据库后无法连接到SMTP服务器

Question

My program is initially connecting to databse server and executing a query and then trying to send an e-mail through smtp server.

The query is executing successfully but the program is unable to connect to smtp server.

If I'm commenting databse connection code mail sending code is executing properly.

And one more case If i'm wrting mail sending code first and then databse execution code after program is working properly.

The question is how I can send a mail after executing database queries in the same program.

Here is my code.

package com.ravi;

import java.util.Properties;
import java.sql.*;

import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;

public class TestMail {

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

        DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());
        Connection con = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:xe","system","****");
        Statement stmt = con.createStatement();
        ResultSet rs = stmt.executeQuery("select * from emp");
        while(rs.next()){
            System.out.println(rs.getString("eno"));
            System.out.println(rs.getString("ename"));
        }
        rs.close();
        stmt.close();
        con.close();
        //System.exit(1);


        String to = "****@***.co.in";//change accordingly  
        String from = "*****@***.co.in";//change accordingly  
        String host = "***.***.co.in";//or IP address  

       //Get the session object  
        Properties properties = System.getProperties();  
        properties.setProperty("mail.smtp.host", host); 
        properties.setProperty("java.net.preferIPv4Stack", "true");
        Session session = Session.getDefaultInstance(properties);  

       //compose the message  
        try{  
           MimeMessage message = new MimeMessage(session);  
           message.setFrom(new InternetAddress(from));  
           message.addRecipient(Message.RecipientType.TO,new InternetAddress(to));  
           message.setSubject("Ping");  
           message.setText("Hello, this is example of sending email  ");  

           // Send message  
           Transport.send(message);  
           System.out.println("message sent successfully....");  

        }catch (MessagingException mex) {mex.printStackTrace();}  

}

}

Stack trace

javax.mail.MessagingException: Could not connect to SMTP host: ***.***.co.in, port: 25;
  nested exception is:
    java.net.SocketException: Network is unreachable: connect
    at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1961)
    at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:654)
    at javax.mail.Service.connect(Service.java:295)
    at javax.mail.Service.connect(Service.java:176)
    at javax.mail.Service.connect(Service.java:125)
    at javax.mail.Transport.send0(Transport.java:194)
    at javax.mail.Transport.send(Transport.java:124)
    at com.ravi.TestMail.main(TestMail.java:50)
Caused by: java.net.SocketException: Network is unreachable: connect
    at java.net.DualStackPlainSocketImpl.connect0(Native Method)
    at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source)
    at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source)
    at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source)
    at java.net.AbstractPlainSocketImpl.connect(Unknown Source)
    at java.net.PlainSocketImpl.connect(Unknown Source)
    at java.net.SocksSocketImpl.connect(Unknown Source)
    at java.net.Socket.connect(Unknown Source)
    at java.net.Socket.connect(Unknown Source)
    at com.sun.mail.util.SocketFetcher.createSocket(SocketFetcher.java:321)
    at com.sun.mail.util.SocketFetcher.getSocket(SocketFetcher.java:237)
    at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1927)
    ... 7 more

Answer 1

May not be the best but below code does the work.

I'm creating session before i'm getting the databse connection.

I moved creating Session code before the database connection code.

import java.util.Properties;
import java.sql.*;

import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;

public class TestMail {

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


    String to = "****@***.co.in";//change accordingly  
    String from = "*****@***.co.in";//change accordingly  
    String host = "***.***.co.in";//or IP address  

   //Get the session object  
    Properties properties = System.getProperties();  
    properties.setProperty("mail.smtp.host", host); 
    properties.setProperty("java.net.preferIPv4Stack", "true");
    Session session = Session.getDefaultInstance(properties);  



    DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());
    Connection con = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:xe","system","****");
    Statement stmt = con.createStatement();
    ResultSet rs = stmt.executeQuery("select * from emp");
    while(rs.next()){
        System.out.println(rs.getString("eno"));
        System.out.println(rs.getString("ename"));
    }
    rs.close();
    stmt.close();
    con.close();
    //System.exit(1);



   //compose the message  
    try{  
       MimeMessage message = new MimeMessage(session);  
       message.setFrom(new InternetAddress(from));  
       message.addRecipient(Message.RecipientType.TO,new InternetAddress(to));  
       message.setSubject("Ping");  
       message.setText("Hello, this is example of sending email  ");  

       // Send message  
       Transport.send(message);  
       System.out.println("message sent successfully....");  

    }catch (MessagingException mex) {mex.printStackTrace();}  

}