Java Mail 下载附件 Office 365 缓慢

Question

我正在阅读 office 365 邮件帐户的收件箱并下载它的附件(txt 文件)。它适用于小于 2 MB 的小文件，但当我尝试处理 20 MB 的文件时，它真的很慢。我在两台不同的机器(Linux 和 Windows)上测试代码，速度是一样的，真​​的很慢。

String user = "mail@mail.com";
String password = "mypassword";
try{

    boolean foundSites = false;

    // Get a Properties object
    Properties properties = new Properties();

    properties.put("mail.imaps.host", host);
    properties.put("mail.imaps.port", port);
    properties.put("mail.imaps.starttls.enable", SSL);
    //properties.put("mail.imap.fetchsize", "1000000");
    Session emailSession = Session.getDefaultInstance(properties);

    //create the POP3 store object and connect with the pop server
    Store store = emailSession.getStore("imaps");
    store.connect(host, user, password);

    //create the folder object and open it
    Folder emailFolder = store.getFolder("INBOX");
    emailFolder.open(Folder.READ_ONLY);

    // retrieve the messages from the folder in an array and print it
    Message[] messages = emailFolder.getMessages();
    System.out.println("messages.length---" + messages.length);

    LocalDateTime now = LocalDateTime.now();
    int year = now.getYear();
    int month = now.getMonthValue();
    int day = now.getDayOfMonth();

    for (int i = messages.length - 1; i >= 0; i--) {
    Message message = messages[i];


    Calendar cal = Calendar.getInstance();
    cal.setTime(message.getReceivedDate());
    int yearMessage = cal.get(Calendar.YEAR);
    int monthMessage = cal.get(Calendar.MONTH) + 1;
    int dayMessage = cal.get(Calendar.DAY_OF_MONTH);



    if(year == yearMessage && month == monthMessage && day == dayMessage)
    {
        //The real code is doing this with 20 Subjects (20 emails)
        if(message.getSubject().equalsIgnoreCase("Integration - Site Info") && foundSites != true)
        {
            System.out.println("found Integration - Site Info");

            Multipart multipart = (Multipart) message.getContent();
            List<File> attachments = new ArrayList<>();
            for (int j = 0; j < multipart.getCount(); j++) {
                BodyPart bodyPart = multipart.getBodyPart(j);
                if(Part.ATTACHMENT.equalsIgnoreCase(bodyPart.getDisposition()))
                {
                    InputStream is = bodyPart.getInputStream();
                    File f = new File("./attachments/"
                            + "sites_"+Integer.toString(day)+"-"+Integer.toString(month)+"-"+Integer.toString(year)+".csv");
                    FileOutputStream fos = new FileOutputStream(f);
                    byte[] buf = new byte[4096];
                    int bytesRead;
                    while((bytesRead = is.read(buf))!=-1) {
                        fos.write(buf, 0, bytesRead);
                    }
                    fos.close();
                    attachments.add(f);
                    foundSites = true;
                    break;
                }


            }
        }
    }

    if(foundSites)
    {
        break;
    }
} catch (Exception e) {
    System.out.println(e);  
}

我可以创建线程，但还有其他选择吗？

只是一个旁注: 我用 python 尝试代码，速度显着提高。

==================================== 更新 1:

我对 saveFile 方法进行了更改，代码简化了很多，但仍然是每秒 10 KB 的相同下载速度。

MimeBodyPart bodyPart = (MimeBodyPart) multipart.getBodyPart(j);
if(Part.ATTACHMENT.equalsIgnoreCase(bodyPart.getDisposition()))
{
    bodyPart.saveFile("./attachments/"
        + "sites_"+Integer.toString(day)+"-"+Integer.toString(month)+"-"+Integer.toString(year)+".csv");

我也使用了探查器，结果是:

Answer 1

修复这些 common mistakes .

使用 MimeBodyPart.saveFile 简化您的代码保存附件。

由于您使用的是“imaps”协议(protocol)而不是“imap”协议(protocol)，请将 mail.imaps.fetchsize 属性设置为足够大的值，以便在不使用更多内存的情况下获得所需的性能比你想用的。或者，如果您不关心使用多少内存并且确信自己总是有足够的内存，则将 mail.imaps.partialfetch 设置为 false。