如何使用Java下载Outlook邮件中的多个附件？

你遇到的报错核心来自4个问题：

• 文件名未解码：报错信息里的=?utf-8?B?QW5udWxhdGlvbiAtIEF2ZW5hbnQgZGUgcsOpc2lsaWF0aW9uLlBERg==?=是符合MIME标准的编码后文件名，直接作为系统文件名使用会触发路径语法错误
• 路径拼接错误：你的保存路径写了"Y:\\pdf\\" + File.separator，等于重复拼接了路径分隔符，部分系统会识别为非法路径
• 未处理文件名非法字符：Windows系统不允许文件名包含/:*?"<>|等字符，如果附件名带这些字符也会报错
• 未校验保存目录存在性：如果Y盘下的pdf目录不存在，也会触发文件找不到异常

第一步：调整Session配置，开启自动文件名解码 #

在Properties配置中新增如下配置，让Java Mail优先自动处理文件名解码：

props.put("mail.mime.decodefilename", "true");

第二步：手动解码文件名+清洗非法字符 #

需要导入javax.mail.internet.MimeUtility工具类，对获取到的文件名做解码和非法字符清洗

第三步：修正路径拼接逻辑 #

使用File构造方法拼接路径，避免手动拼接分隔符出错

第四步：提前校验保存目录是否存在，不存在则创建 #

package Email_Attachment;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.nio.file.Files;
import java.util.Properties;

import javax.mail.Address;
import javax.mail.Flags;
import javax.mail.Folder;
import javax.mail.Session;
import javax.mail.Store;
import javax.mail.internet.MimeBodyPart;
import javax.mail.internet.MimeUtility;
import javax.mail.search.FlagTerm;

import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Multipart;
import javax.mail.NoSuchProviderException;
import javax.mail.Part;
import javax.mail.PasswordAuthentication;
public class test  {

   public static void main(String[]args)throws Exception,FileNotFoundException {
         Properties props = System.getProperties();
       props.setProperty("mail.store.protocol", "imap");
       props.setProperty("mail.imap.ssl.enable", "true");
       props.setProperty("mail.imap.partialfetch", "false");
       props.put("mail.mime.base64.ignoreerrors", "true");
       // 新增配置：自动解码文件名
       props.put("mail.mime.decodefilename", "true");
       Session mailSession = Session.getDefaultInstance(props, new javax.mail.Authenticator(){
                  protected PasswordAuthentication getPasswordAuthentication() {
                      return new PasswordAuthentication("username", "password");
                  }
          });
       mailSession.setDebug(true);
       // 提前校验保存目录，不存在则创建
       File saveDir = new File("Y:\\pdf\\");
       if (!saveDir.exists()) {
           Files.createDirectories(saveDir.toPath());
       }
       try {
      Store store = mailSession.getStore("imap");
       store.connect( "outlook.office365.com","username", "password");
       Folder folderInbox = store.getFolder("INBOX");
       folderInbox.open(Folder.READ_ONLY);
       Message[] messages = folderInbox.search(new FlagTerm(new Flags(Flags.Flag.SEEN), false));
       for (int i = 0; i < messages.length; i++) {
           Message message = messages[i];
           Address[] fromAddress = message.getFrom();
           String from = fromAddress[0].toString();
           String subject = message.getSubject();
           String sentDate = message.getSentDate().toString();
           String contentType = message.getContentType();
           String messageContent = "";
           String attachFiles = "";
           if (contentType.contains("multipart")) {
               Multipart multiPart = (Multipart) message.getContent();
               int numberOfParts = multiPart.getCount();
               for (int partCount = 0; partCount < numberOfParts; partCount++) {
                   MimeBodyPart part = (MimeBodyPart) multiPart.getBodyPart(partCount);
                   if (Part.ATTACHMENT.equalsIgnoreCase(part.getDisposition())) {
                       // 解码文件名+清洗非法字符
                       String fileName = MimeUtility.decodeText(part.getFileName());
                       // 替换Windows文件名非法字符
                       fileName = fileName.replaceAll("[\\\\/:*?\"<>|]", "_");
                       attachFiles += fileName + ", ";
                       // 修正路径拼接，直接用File构造方法避免分隔符错误
                       part.saveFile(new File(saveDir, fileName));
                   } else {
                       messageContent = part.getContent().toString();
                   }
               }
               if (attachFiles.length() > 1) {
                   attachFiles = attachFiles.substring(0, attachFiles.length() - 2);
               }
           } else if (contentType.contains("text/plain") || contentType.contains("text/html")) {
               Object content = message.getContent();
               if (content != null) {
                   messageContent = content.toString();
               }
           }
           System.out.println("Message #" + (i + 1) + ":");
           System.out.println("\t From: " + from);
           System.out.println("\t Subject: " + subject);
           System.out.println("\t Sent Date: " + sentDate);
           System.out.println("\t Message: " + messageContent);
           System.out.println("\t Attachments: " + attachFiles);
       }
       folderInbox.close(false);
       store.close();
   } catch (NoSuchProviderException ex) {
       System.out.println("No provider for imap.");
       ex.printStackTrace();
   } catch (MessagingException ex) {
       System.out.println("Could not connect to the message store");
       ex.printStackTrace();
   } catch (IOException ex) {
       ex.printStackTrace();
   }
 }}

额外说明 #

原代码的异常捕获里错误打印了No provider for pop3，已经同步修正为imap协议的对应提示。

内容的提问来源于stack exchange，提问作者ANU PRAKASH