Java Mail IMAP 需要大量时间才能在邮箱中获取消息，25 秒才能获取 20 条消息

Question

有没有办法提高从 Javamail IMAP 服务器获取消息的性能？ 我找到了一些技巧，但无法提高性能。 此方法将从文件夹中获取大约 20 条消息，并将格式化的消息返回到 DTO，我尝试注释行以获取附件，并获取收件人，但它不会改变性能中的任何内容。

/**
 * Get all the emails that are inside the param folder
 *
 * @param folderId   folder to return the emails from the informed folder.
 * @param pageToken  pageToken to be used as pagination
 * @param maxResults maxResults to create a limit to the number of registers
 * @return {@link EmailsDTO} with all the messages
 */
public EmailsDTO getMessages(final String folderId, final String pageToken, final Integer maxResults) {
    final Properties properties = getServerInputProperties();
    final Session session = Session.getDefaultInstance(properties);
    try {
        final EmailsDTO emailsDTO = new EmailsDTO();
        final List<EmailDTO> emailDTOList = new ArrayList<>();

        // connects to the message store
        final Store store = session.getStore(IMAP);
        store.connect(email, password);

        // opens the folder to search the messages
        final Folder folder = store.getFolder(folderId);
        folder.open(Folder.READ_ONLY);

        //set a pagination used to get the results in JavaMail
        final int pageStart = nonNull(pageToken) ? Integer.valueOf(pageToken) : 1;
        final int pageEnd = (pageStart + maxResults) > folder.getMessageCount() ? folder.getMessageCount() : pageStart + maxResults;


        // fetches new messages from server, starts with 1
        final Message[] messages = folder.getMessages(pageStart, pageEnd);

        final FetchProfile fetchProfile  = new FetchProfile();
        fetchProfile.add(FetchProfile.Item.ENVELOPE);
        folder.fetch(messages, fetchProfile); // Load the profile of the messages in 1 fetch.

        for (final Message msg : messages) {
            final EmailDTO emailDTO = new EmailDTO();
            emailDTO.setId(msg.getHeader(MESSAGE_ID)[0]);
            emailDTO.setCc(this.parseAddresses(msg.getRecipients(Message.RecipientType.CC)));
            emailDTO.setTo(this.parseAddresses(msg.getRecipients(Message.RecipientType.TO)));
            emailDTO.setBcc(this.parseAddresses(msg.getRecipients(Message.RecipientType.BCC)));

            emailDTO.setFrom(this.getFrom(msg.getFrom()));
            emailDTO.setRead(msg.getFlags().contains(Flags.Flag.SEEN));
            emailDTO.setHasAttachments(this.hasAttachments(msg));
            emailDTO.setSubject(msg.getSubject());
            emailDTO.setMessage(this.getMessageContent(msg));

            emailDTO.setAttachments(this.getAttachements(msg));
            emailDTO.setDate(msg.getReceivedDate().toString());
            emailDTO.setParentFolder(msg.getFolder().getName());
            //TODO: see what need to put here emailDTO.setLabels();
            emailDTOList.add(emailDTO);
        }

        // disconnect
        folder.close(false);
        store.close();

        emailsDTO.setEstimatedNumberOfMessages(folder.getMessageCount());
        emailsDTO.setNextPageToken(String.valueOf(emailDTOList.size()));
        emailsDTO.setMessages(emailDTOList);
        return emailsDTO;
    } catch (final MessagingException | IOException e) {
        throw new RuntimeException(String.format("couldn't get messages from the folder with id: %s", folderId), e);
    }
}

Answer 1

在

for (final Message msg : messages)

中，将

messages

更改为

folder.getMessages()

。

messages

-> 多次加载

folder.getMessages()

-> 在一次 fetch 中加载，因为您在其中使用了 fetchProfile。

Answer 2

我不同意@Rose的回答。获取消息[]就可以了。