JavaMail 郵件接收完整解析：MimeMessage 遞迴解析、附件下載、編碼處理

JavaMail 處理郵件接收最棘手在於 MIME 結構複雜：多層 multipart/*、巢狀 message/rfc822、編碼參雜。本文提供生產級 PraseMimeMessage 工具類，完整實現發件人/收件人/主題/日期/正文/附件/已讀狀態/回執/Message-ID 解析與附件存檔。

核心架構

• 輸入：javax.mail.internet.MimeMessage
• 遞迴解析 Part 介面（MimeMessage、BodyPart 皆實作）
• 依 Content-Type 分派處理邏輯

關鍵解析邏輯：getMailContent(Part)

public void getMailContent(Part part) throws Exception {
    String ct = part.getContentType();
    boolean hasName = ct.indexOf("name") != -1;
    
    if (part.isMimeType("text/plain") && !hasName) {
        bodytext.append((String) part.getContent());
    } else if (part.isMimeType("text/html") && !hasName) {
        bodytext.append((String) part.getContent());
    } else if (part.isMimeType("multipart/*")) {
        Multipart mp = (Multipart) part.getContent();
        for (int i=0; i

public boolean isContainAttach(Part part) { ... }  // 遞迴檢查 disposition 或 application/name

public void saveAttachMent(Part part) { ... }  // 遞迴處理 multipart、message/rfc822
// 關鍵：decodeText() 處理 GB2312 等編碼檔名
// 儲存：BufferedInputStream → BufferedOutputStream 逐位元組寫入

Properties props = new Properties();
Session session = Session.getDefaultInstance(props, null);
Store store = session.getStore("pop3");
store.connect("pop.mail.yahoo.com.cn", "username", "password");
Folder folder = store.getFolder("INBOX");
folder.open(Folder.READ_ONLY);
Message[] msgs = folder.getMessages();

PraseMimeMessage pmm = null;
for (int i=0; i