Javaメール送受信の全手法10選！初心者でも簡単マスター

import javax.mail.*;
import javax.mail.internet.*;

public class EmailSender {
    public static void main(String[] args) {
        String to = "recipient@example.com"; 
        String from = "sender@example.com"; 
        String host = "localhost"; 

        Properties properties = System.getProperties(); 
        properties.setProperty("mail.smtp.host", host); 

        Session session = Session.getDefaultInstance(properties); 

        try {
            MimeMessage message = new MimeMessage(session); 
            message.setFrom(new InternetAddress(from)); 
            message.addRecipient(Message.RecipientType.TO, new InternetAddress(to)); 
            message.setSubject("テストメール"); 
            message.setText("これはテストメールです。"); 

            Transport.send(message); 
            System.out.println("メール送信成功！");
        } catch (MessagingException mex) {
            mex.printStackTrace(); 
        }
    }
}

import java.util.Properties;
import javax.mail.*;

public class EmailReceiver {
    public static void main(String[] args) {
        String host = "pop3.example.com"; 
        String user = "user@example.com"; 
        String password = "password"; 

        try {
            Properties properties = new Properties();
            properties.put("mail.pop3.host", host);
            properties.put("mail.pop3.user", user);
            properties.put("mail.pop3.password", password);
            properties.put("mail.pop3.port", "110");

            Session session = Session.getDefaultInstance(properties);
            Store store = session.getStore("pop3");
            store.connect(host, user, password);

            Folder inbox = store.getFolder("INBOX");
            inbox.open(Folder.READ_ONLY);

            Message[] messages = inbox.getMessages();

            for (Message message : messages) {
                System.out.println("件名：" + message.getSubject());
                System.out.println("送信者：" + message.getFrom()[0]);
                System.out.println("本文：" + message.getContent().toString());
            }

            inbox.close(false);
            store.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

try {
    // メール送信のコード
} catch (MessagingException e) {
    // エラーメッセージをログに記録
    System.err.println("メール送信エラー: " + e.getMessage());
    // ユーザーに適切なエラーレスポンスを提示
    // ...
}

Properties properties = new Properties();
properties.put("mail.smtp.auth", "true");
properties.put("mail.smtp.starttls.enable", "true");
properties.put("mail.smtp.host", "smtp.gmail.com");
properties.put("mail.smtp.port", "587");

Session session = Session.getInstance(properties, new javax.mail.Authenticator() {
    protected PasswordAuthentication getPasswordAuthentication() {
        return new PasswordAuthentication("yourEmail@example.com", "yourEmailPassword");
    }
});

try {
    // セキュアなメール送信のコード
} catch (MessagingException e) {
    // エラーハンドリングのコード
    System.err.println("セキュリティエラー: " + e.getMessage());
}

import javax.mail.*;
import javax.mail.internet.*;

public class SendHTMLMail {
    public static void main(String[] args) {
        String to = "recipient@example.com";
        String from = "sender@example.com";
        String host = "localhost";

        Properties properties = System.getProperties();
        properties.setProperty("mail.smtp.host", host);

        Session session = Session.getDefaultInstance(properties);

        try {
            MimeMessage message = new MimeMessage(session);
            message.setFrom(new InternetAddress(from));
            message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));
            message.setSubject("Test HTML Mail");
            message.setContent("<h1>This is a test</h1><p>HTML mail content</p>", "text/html");

            Transport.send(message);
            System.out.println("Sent message successfully...");
        } catch (MessagingException mex) {
            mex.printStackTrace();
        }
    }
}

import java.util.Properties;
import javax.mail.*;
import javax.mail.internet.*;
import javax.activation.*;

public class SendAttachmentMail {
    public static void main(String[] args) {
        String to = "recipient@example.com";
        String from = "sender@example.com";
        String host = "localhost";

        Properties properties = System.getProperties();
        properties.setProperty("mail.smtp.host", host);

        Session session = Session.getDefaultInstance(properties);

        try {
            MimeMessage message = new MimeMessage(session);
            message.setFrom(new InternetAddress(from));
            message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));
            message.setSubject("Test Attachment Mail");

            BodyPart messageBodyPart = new MimeBodyPart();
            messageBodyPart.setText("This is message body");

            Multipart multipart = new MimeMultipart();
            multipart.addBodyPart(messageBodyPart);

            messageBodyPart = new MimeBodyPart();
            String filename = "path/to/file.txt";
            DataSource source = new FileDataSource(filename);
            messageBodyPart.setDataHandler(new DataHandler(source));
            messageBodyPart.setFileName(filename);
            multipart.addBodyPart(messageBodyPart);

            message.setContent(multipart);

            Transport.send(message);
            System.out.println("Sent message successfully...");
        } catch (MessagingException mex) {
            mex.printStackTrace();
        }
    }
}

import javax.mail.*;
import javax.mail.internet.*;

public class AutoReplySystem {
    public static void main(String[] args) {
        String host = "your.pop3.server";
        String user = "your.email@example.com";
        String password = "yourpassword";

        try {
            Properties properties = new Properties();
            properties.put("mail.pop3.host", host);
            properties.put("mail.pop3.port", "995");
            properties.put("mail.pop3.starttls.enable", "true");
            Session emailSession = Session.getDefaultInstance(properties);
            Store store = emailSession.getStore("pop3s");
            store.connect(host, user, password);

            Folder emailFolder = store.getFolder("INBOX");
            emailFolder.open(Folder.READ_ONLY);

            Message[] messages = emailFolder.getMessages();
            for (Message message : messages) {
                String subject = message.getSubject();
                if (subject.contains("特定のキーワード")) {
                    String replyMessage = "これは自動返信メッセージです。";
                    sendReply(message, replyMessage);
                }
            }

            emailFolder.close(false);
            store.close();

        } catch (NoSuchProviderException e) {
            e.printStackTrace();
        } catch (MessagingException e) {
            e.printStackTrace();
        }
    }

    public static void sendReply(Message receivedMessage, String replyMessageContent) {
        String to = "recipient@example.com";
        String from = "your.email@example.com";
        String host = "your.smtp.server";

        Properties properties = System.getProperties();
        properties.setProperty("mail.smtp.host", host);
        Session session = Session.getDefaultInstance(properties);

        try {
            MimeMessage message = new MimeMessage(session);
            message.setFrom(new InternetAddress(from));
            message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));
            message.setSubject("自動返信: " + receivedMessage.getSubject());
            message.setText(replyMessageContent);

            Transport.send(message);
            System.out.println("自動返信が送信されました。");
        } catch (MessagingException mex) {
            mex.printStackTrace();
        }
    }
}

import org.apache.commons.mail.EmailException;
import org.apache.commons.mail.SimpleEmail;

public class EmailAlertSystem {
    public static void main(String[] args) {
        SimpleEmail email = new SimpleEmail();
        email.setHostName("smtp.yourserver.com");
        email.setSmtpPort(587);
        email.setAuthentication("user", "password");

        try {
            email.setFrom("alert@yourdomain.com", "Alert System");
            email.addTo("recipient@domain.com");
            email.setSubject("System Alert");
            email.setMsg("This is a system alert message.");
            email.send();
            System.out.println("Email sent successfully.");
        } catch (EmailException e) {
            e.printStackTrace();
            System.out.println("Failed to send email.");
        }
    }
}

import java.util.Timer;
import java.util.TimerTask;
import javax.mail.*;
import javax.mail.internet.*;

public class EmailBatchProcessing {

    private static final String USERNAME = "your_email@example.com";
    private static final String PASSWORD = "your_email_password";
    private static final String RECIPIENT = "recipient_email@example.com";

    public static void main(String[] args) {
        Timer timer = new Timer();
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                sendEmail();
            }
        }, 0, 60000);  // 60000ミリ秒（1分）ごとにsendEmailメソッドを呼び出す
    }

    private static void sendEmail() {
        Properties properties = new Properties();
        properties.put("mail.smtp.auth", "true");
        properties.put("mail.smtp.starttls.enable", "true");
        properties.put("mail.smtp.host", "smtp.gmail.com");
        properties.put("mail.smtp.port", "587");

        Session session = Session.getInstance(properties, new Authenticator() {
            @Override
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(USERNAME, PASSWORD);
            }
        });

        try {
            Message message = new MimeMessage(session);
            message.setFrom(new InternetAddress(USERNAME));
            message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(RECIPIENT));
            message.setSubject("Automated Email");
            message.setText("This is an automated email sent every minute.");

            Transport.send(message);
            System.out.println("メールが正常に送信されました");
        } catch (MessagingException e) {
            e.printStackTrace();
            System.out.println("メール送信に失敗しました");
        }
    }
}

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class EmailLogAnalysis {
    public static void main(String[] args) {
        String filePath = "path/to/your/email/log.txt";
        String searchKeyword = "ERROR";

        try (BufferedReader br = new BufferedReader(new FileReader(filePath))) {
            String line;
            while ((line = br.readLine()) != null) {
                if (line.contains(searchKeyword)) {
                    System.out.println(line);
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}