Java 中的电子邮件服务引发 "out of memory" 错误

Question

我是运行后台电子邮件服务（在命令提示符下），它旨在保留运行并从队列 table 中提取记录进行处理。

这是我的 Email.java:

public class Email {


    MySqlConnect con=new MySqlConnect();
    public PreparedStatement preparedStatement = null;

    public Connection con1 = con.connect();

    public Email() throws Exception {


    }

    //pick up queue and send email
    public void email() throws Exception {


        try{

            while(true) {
                String sql = "SELECT id,subject,recipient,content FROM emailqueue WHERE status='Pending' ";
                PreparedStatement statement = con1.prepareStatement(sql);
                ResultSet rs = statement.executeQuery();

                while (rs.next()) {

                    String subject = rs.getString("subject");

                    String recipient = rs.getString("recipient");

                    String content = rs.getString("content");

                    String id = rs.getString("id");

                    sendEmail(recipient, subject, content, id);


                }

            }


        }catch(Exception e){

            e.printStackTrace();

        }
        con1.close();
        Thread.sleep(2000);

    }


//Schedule a service for picking email
    public void schedule(){

        Thread service;
        service = new Thread(new Runnable() {

            public void run() {
                try {

                    System.out.println("Email service is ready");
                    email();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });

        service.start();


    }



    public void sendEmail(String recipient, String subject, String content,String id) {
        try {

            //final String fromEmail = "lordjesus0371@gmail.com"; //requires valid gmail id
            // final String password = "htasia123"; // correct password for gmail id
          //  InitialContext ctx = new InitialContext();


            String host = get_attributevalue("MAIL_SERVER");
            String port = get_attributevalue("MAIL_PORT");
            final String senderaddress = get_attributevalue("SENDER_ADDRESS");
            final String password = get_attributevalue("MAIL_PASSWORD");



            System.out.println("Please Wait, sending email...");




            /*Setup mail server */

            Properties props = new Properties();

            props.put("mail.smtp.host", host); //SMTP Host
            props.put("mail.smtp.port", port); //TLS Port
            props.put("mail.smtp.auth", "true"); //enable authentication
            props.put("mail.smtp.starttls.enable", "true"); //enable STARTTLS





            //create Authenticator object to pass in Session.getInstance argument
            Authenticator auth = new Authenticator() {
                //override the getPasswordAuthentication method
                protected PasswordAuthentication getPasswordAuthentication() {
                    return new PasswordAuthentication(senderaddress, password);
                }
            };
            Session session = Session.getInstance(props, auth);


            session.setDebug(true);


            // Define message
            MimeMessage message = new MimeMessage(session);
            // Set From: header field of the header.
            message.setFrom(new InternetAddress(senderaddress));
            message.addRecipients(Message.RecipientType.TO, InternetAddress.parse(recipient));
            // Set Subject: header field
            message.setSubject(subject);

            // Now set the actual message
            message.setText(content);


            Transport.send(message);

            delivered(id);
            System.out.print("Email sent");



        } catch (Exception e) {
            System.out.println(e.getMessage());
            try{
                error(id);
            } catch (SQLException e1) {
                e1.printStackTrace();
            }

        }


    }

在我的 Main 方法中：

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



        Email runEmailService=new Email();

        runEmailService.schedule();



    }

它能够很好地获取记录并处理电子邮件，但一段时间后它会抛出：

Exception in thread "Thread-1" java.lang.OutOfMemoryError: Java heap space

Exception: java.lang.OutOfMemoryError thrown from the UncaughtExceptionHandler in thread "Thread-1"

程序停止运行。

有没有办法防止这种情况发生，让我的程序保持运行？

Answer 1

语句和结果集资源可能尚未释放，并保存在内存中，因为您没有关闭它们。

考虑在 while(rs.next()) 循环后关闭它们：

rs.close(); 
statement.close();

请注意，您可以使用 "try with reousrces" 让事情自行关闭：

try (PreparedStatement statement = con1.prepareStatement(sql); ResultSet rs = statement.executeQuery())

比照。 Java 7 Automatic Resource Management JDBC (try-with-resources statement)

public void email() throws Exception {

    String sql = "SELECT id,subject,recipient,content FROM emailqueue WHERE status='Pending' ";

    while (true) {

        try (PreparedStatement statement = con1.prepareStatement(sql); ResultSet rs = statement.executeQuery()) {

            while (rs.next()) {

                String subject = rs.getString("subject");

                String recipient = rs.getString("recipient");

                String content = rs.getString("content");

                String id = rs.getString("id");

                sendEmail(recipient, subject, content, id);

            }

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

    con1.close();
    Thread.sleep(2000);

}

Java 中的电子邮件服务引发 "out of memory" 错误

Email service in Java throws an "out of memory" error

java

jdbc

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