multipart/alternative getContent()抛出IOException:无内容

MimeMultipart multipart = (MimeMultipart) message.getContent();
int count = multipart.getCount();
for (int i = 0; i < count; i++) {
    BodyPart bodyPart = multipart.getBodyPart(i);
    if (bodyPart.isMimeType("text/plain")) {
        // 处理纯文本内容
        String text = (String) bodyPart.getContent();
        System.out.println("纯文本内容：" + text);
    } else if (bodyPart.isMimeType("text/html")) {
        // 处理HTML内容
        String html = (String) bodyPart.getContent();
        System.out.println("HTML内容：" + html);
    }
}