java - 使用 JavaMail 发送带有附件的邮件 - 写入 Multipart 时出现异常

Question

我想使用 JavaMail 发送带有附件的邮件，但遇到了难以理解的异常。

我的代码分为两部分。第一个是EmailSender类，负责管理用于发送邮件的邮件帐户和系统配置。第二个是 Mail 类，用于管理单个电子邮件。 (代码在文末)

创建 EmailSender 时，构造函数会使用 setServerHost() 方法自动从已知设置列表中搜索 SMTP 设置。

当 EmailSender 被要求发送 Email 时，EmailSender 会转换 Email< 字段中包含的信息 通过调用 Email 的 build() 方法转换为 MimeMessage；然后使用 JavaMail 的 Transport 类发送该邮件。

我使用的测试方法比较简单:

public static void sendMail(String subject, String body, String to, String urlAttachment) {
        System.out.printf("Username:\t");
        String username = readString();
        System.out.printf("Password:\t");
        String password = readString();

        EmailSender account = new EmailSender(username, password);
        Email mail = new Email(username, to, subject, body);
        mail.addAttachment(urlAttachment);
        account.sendMail(to, subject, body);
    }

我得到的错误较少。

javax.mail.MessagingException: IOException while sending message;
  nested exception is:
    java.io.IOException: Exception writing Multipart
    at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:1365)
    at mail.EmailSender.sendMail(EmailSender.java:104)
    at mail.EmailSender.sendMail(EmailSender.java:122)
    at Test.TestLibraries.sendMail(TestLibraries.java:134)
    at Test.TestLibraries.main(TestLibraries.java:51)
Caused by: java.io.IOException: Exception writing Multipart
    at com.sun.mail.handlers.multipart_mixed.writeTo(multipart_mixed.java:86)
    at javax.activation.ObjectDataContentHandler.writeTo(Unknown Source)
    at javax.activation.DataHandler.writeTo(Unknown Source)
    at javax.mail.internet.MimeBodyPart.writeTo(MimeBodyPart.java:1694)
    at javax.mail.internet.MimeMessage.writeTo(MimeMessage.java:1913)
    at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:1315)
    ... 4 more
Caused by: javax.mail.MessagingException: Empty multipart: multipart/mixed; 
    boundary="----=_Part_0_2129789493.1581503162040"
    at javax.mail.internet.MimeMultipart.writeTo(MimeMultipart.java:556)
    at com.sun.mail.handlers.multipart_mixed.writeTo(multipart_mixed.java:84)
    ... 9 more

问题是什么(以及如何解决)？

<小时/>

这是代码:

public class EmailSender {
    private String from;
    private String password;


    private String emailHost;
    private Properties properties = System.getProperties();
    private Session session;


    public static final int serverName = 0;
    public static final int serverPort = 1;
    public static final int serverAutentication = 2;
    public static final String[][] knownServerHostData = new String[][]
            {
                {   "smtp.mail.yahoo.com",  "587",  "SLL"       }           ,
                {   "smtp.mail.com",        "587",  "StartTLS"  }           ,
                {   "smtp.gmail.com",       "587",  ""          }           ,
                {   "out.virgilio.it",      "587",  ""          }
    };

    public EmailSender(String username, String password) {
        this.from = username;
        this.password = password;

        this.session = Session.getDefaultInstance(properties);

        this.setServerHost(password);
    }

    public boolean sendMail(String to, String subject, String body) {
        return sendMail(new Email(from, to, subject, body));
    }
    public boolean sendMail(Email email) {
        MimeMessage message = email.build(session);

        Transport transport = null;
        try {
            transport = session.getTransport("smtp");
            } catch (NoSuchProviderException e) {       e.printStackTrace();        closeTransport(transport);      }
        try {   
            transport.connect(emailHost, from, password);
            } catch (MessagingException e) {            e.printStackTrace();        closeTransport(transport);      }
        try {
            transport.sendMessage(message, message.getAllRecipients()); // <== THIS LINE RETURN EXCEPTION
            } catch (MessagingException e) {            e.printStackTrace();        closeTransport(transport);      }
        closeTransport(transport);

        return true;
    }

    private void closeTransport(Transport transport) {
        try {   transport.close();
            } catch (MessagingException e) {            e.printStackTrace();        }
    }

}

public class Email {

    private String sender;
    private Vector<String> recipients = new Vector<String>();
    private Vector<String> cc = new Vector<String>();
    private Vector<String> bcc = new Vector<String>();
    private String subject;
    private String body;
    private Vector<String> attachments = new Vector<String>();

    public Email(String from, String to, String subject, String body) {
        this.sender = from;
        this.recipients.add(to);
        this.subject = subject;
        this.body = body;
    }

    /** Returns a {@link MimeMessage} ready to be sent by an {@link EmailSender} with all the fields of {@code this} {@link Email}.
     * 
     * @return
     */
    public MimeMessage build(Session session) {
        MimeMessage message = new MimeMessage(session);

        // STEP 1 - Header

        // Sets the sender
        try {           message.setFrom(new InternetAddress(sender));
            } catch (AddressException e) {              e.printStackTrace();        }
              catch (MessagingException e) {            e.printStackTrace();        }

        // Sets the subject
        try {           message.setSubject(subject);
            } catch (MessagingException e) {            e.printStackTrace();        }

        // Adds the recipients one by one
        int i = 0;
        try {           
            for(i=0 ; i<recipients.size() ; i++)
                message.addRecipient(Message.RecipientType.TO, new InternetAddress(recipients.get(i)));
            } catch (MessagingException e) {            e.printStackTrace();    System.err.println("The " + i + "-th recipient gave error.");       }
        try {           
            for(i=0 ; i<cc.size() ; i++)
                message.addRecipient(Message.RecipientType.CC, new InternetAddress(cc.get(i)));
            } catch (MessagingException e) {            e.printStackTrace();    System.err.println("The " + i + "-th cc gave error.");      }
        try {
            for(i=0 ; i<bcc.size() ; i++)
                message.addRecipient(Message.RecipientType.BCC, new InternetAddress(bcc.get(i)));
            } catch (MessagingException e) {            e.printStackTrace();    System.err.println("The " + i + "-th bcc gave error.");     }



        // STEP 2 - Body

        // Adds the body
        MimeBodyPart messageBodyPart = new MimeBodyPart();
        Multipart multipart = new MimeMultipart();
        try {
            messageBodyPart.setContent(message, "text/plain; charset=" +
                    MimeUtility.quote("us-ascii", HeaderTokenizer.MIME));
            } catch (MessagingException e) {            e.printStackTrace();        }
        try {           message.setText(body);
            } catch (MessagingException e) {            e.printStackTrace();        }

        // Adds the attachments
        try {   
            for(i=0 ; i<attachments.size() ; i++)           // Preps the attachments
                attachFileToMessageMultipart(multipart, attachments.get(i));
            } catch (MessagingException e) {            e.printStackTrace();        System.err.println("The " + i + "-th attachment gave error.");      }
              catch (IOException e) {                   e.printStackTrace();        System.err.println("The " + i + "-th attachment gave error.");      }



        // STEP 3 - Appends the MimeMessage's body
        try {
            message.setContent(multipart);
            } catch (MessagingException e1) {           e1.printStackTrace();       }
        return message;
    }

    /** This method avoids compatibility problems between JavaMail 1.3 and JavaMail 1.4.
     * @throws MessagingException 
     * @throws IOException 
     * 
     */
    private static void attachFileToMessageMultipart(Multipart multipart, String fileUrl) throws MessagingException, IOException {
        File file = new File(fileUrl);
        if( ! file.isFile() )       
            throw new IOException("The specified url does not identify a file.");

        // JavaMail 1.3

        MimeBodyPart attachPart = new MimeBodyPart();

        DataSource source = new FileDataSource(fileUrl);
        attachPart.setDataHandler(new DataHandler(source));
        attachPart.setFileName(file.getName());

        multipart.addBodyPart(attachPart);
    }

<小时/> 编辑:阅读 Bill Shannon 的答案后，我编辑了我的方法 build()。当前版本是:

        MimeMessage message = new MimeMessage(session);

        System.out.println("\t Building mail.");


        // STEP 1 - Header

        // Sets the sender
        try {           message.setFrom(new InternetAddress(sender));
            } catch (AddressException e) {              e.printStackTrace();        }
              catch (MessagingException e) {            e.printStackTrace();        }

        // Sets the subject
        try {           message.setSubject(subject);
            } catch (MessagingException e) {            e.printStackTrace();        }

        System.out.println("\t\t Sender and subject set mail.");

        // Adds the recipients one by one
        int i = 0;
        try {           
            for(i=0 ; i<recipients.size() ; i++)
                message.addRecipient(Message.RecipientType.TO, new InternetAddress(recipients.get(i)));
            } catch (MessagingException e) {            e.printStackTrace();    System.err.println("The " + i + "-th recipient gave error.");       }
        try {           
            for(i=0 ; i<cc.size() ; i++)
                message.addRecipient(Message.RecipientType.CC, new InternetAddress(cc.get(i)));
            } catch (MessagingException e) {            e.printStackTrace();    System.err.println("The " + i + "-th cc gave error.");      }
        try {
            for(i=0 ; i<bcc.size() ; i++)
                message.addRecipient(Message.RecipientType.BCC, new InternetAddress(bcc.get(i)));
            } catch (MessagingException e) {            e.printStackTrace();    System.err.println("The " + i + "-th bcc gave error.");     }

        System.out.println("\t\t TO, CC, BCC fields setted.");


        // STEP 2 - Body

        // Adds the body
        MimeBodyPart messageBodyPart = new MimeBodyPart();
        Multipart multipart = new MimeMultipart();
        try {           
            messageBodyPart.setText(body);
            } catch (MessagingException e) {            e.printStackTrace();        }
        try {
            multipart.addBodyPart(messageBodyPart);
            } catch (IllegalWriteException e) {         e.printStackTrace();        }
              catch (MessagingException e) {            e.printStackTrace();        }

        //  try {
        //      messageBodyPart.setContent(message, "text/plain; charset=" +
        //              MimeUtility.quote("us-ascii", HeaderTokenizer.MIME));
        //      } catch (MessagingException e) {            e.printStackTrace();        }

        System.out.println("\t\t Body attached.");

        // Adds the attachments
        for(i=0 ; i<attachments.size() ; i++)           
            {
            // Creates a BodyPart representing the attachment
            try {   
                messageBodyPart.attachFile(attachments.get(i));
                } catch (MessagingException e) {            e.printStackTrace();        System.err.println("The " + i + "-th attachment gave error.");      }
                  catch (IOException e) {                   e.printStackTrace();        System.err.println("The " + i + "-th attachment gave error.");      }

            // Appends the BodyPart to the MultiPart
            try {
                multipart.addBodyPart(messageBodyPart);
                } catch (IllegalWriteException e) {         e.printStackTrace();        }
                  catch (MessagingException e) {            e.printStackTrace();        }
            }
        System.out.println("\t\t Files attached.");


        // STEP 3 - Appends the MimeMessage's body
        try {
            message.setContent(multipart);
            } catch (MessagingException e1) {           e1.printStackTrace();       }
        System.out.println("\t\t MimeMessage created.");
        return message;
    }

此版本不会出现异常，并且邮件已发送...但没有附件。

Answer 1

我不明白你想在这里做什么:

messageBodyPart.setContent(message, "text/plain; charset=" +
                MimeUtility.quote("us-ascii", HeaderTokenizer.MIME));

我确信您并不是想将 MimeMessage 对象本身添加为消息正文部分的内容。而且你永远不需要以这种方式使用 MimeUtility.quote 方法。

此声明:

message.setText(body);

将 MimeMessage 对象的全部内容设置为纯文本以正文字符串作为内容的文本消息。我不认为这就是你想要的。

你想要的是使用setText方法来设置内容messageBodyPart 对象到字符串主体。然后添加messageBodyPart对象到多部分对象。

之后，您可以将所有附件添加到多部分对象中。请注意，您可能想要使用 MimeBodyPart.atttachFile简化代码的方法。