添加依赖

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-mail</artifactId>
        </dependency>

获取邮件附件代码

package com.example.emaildemo.email;

import javax.mail.*;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeUtility;
import javax.mail.search.*;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.util.*;

public class Pop3Mails {
    public static void main(String[] args) {
        Pop3Mails mail = new Pop3Mails();
        mail.read();
    }

    public void read() {
        Properties props = new Properties();
        try {
            final String SSL_FACTORY = "javax.net.ssl.SSLSocketFactory";
            props.setProperty("mail.pop3.socketFactory.class", SSL_FACTORY);
            props.setProperty("mail.pop3.socketFactory.fallback", "false");
            props.setProperty("mail.pop3.port", "995");
            props.setProperty("mail.pop3.socketFactory.port", "995");

            Session session = Session.getDefaultInstance(props, null);

            Store store = session.getStore("pop3");
            String user = "xxxx@gmail.com";
            // 如果为gmail需开通二次验证密码
            String password = "xxxxxx"; 
            store.connect("pop.gmail.com", user, password);

            Folder inbox = store.getFolder("inbox");
            inbox.open(Folder.READ_ONLY);

            LocalDateTime localDateTime = LocalDateTime.now().minusYears(1);

            ZoneId zoneId = ZoneId.systemDefault();
            ZonedDateTime zdt = localDateTime.atZone(zoneId);//Combines this date-time with a time-zone to create a  ZonedDateTime.
            Date start = Date.from(zdt.toInstant());
            Date now = new Date();
            SearchTerm comparisonTermGe = new SentDateTerm(ComparisonTerm.GE, start);
            SearchTerm comparisonTermLe = new SentDateTerm(ComparisonTerm.LE, now);
            //需要查询的邮件名
            String fromEmail = "xxxxxxxxxx@gmail.com";
            FromStringTerm fromStringTerm = new FromStringTerm(fromEmail);
            SearchTerm andTerm = new AndTerm(new SearchTerm[]{comparisonTermGe, comparisonTermLe});
            Message[] messages = inbox.search(andTerm); //根据设置好的条件获取message
            Message[] search = inbox.search(fromStringTerm, messages);
            for (int i = search.length - 1; i >= 0; i--) {
                Message message = search[i];
                Date date = message.getSentDate();
                System.out.println("Mail Subject:- " + message.getSubject());
                System.out.println("Mail Content Type:- " + message.getContentType());
                System.out.println("Mail Sent Date:- " + date);
                if (message.getContentType().startsWith("multipart/")) {
                    needProcessEmail(message);
                }
            }
            inbox.close(true);
            store.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /**
     * 文件拷贝，在用户进行附件下载的时候，可以把附件的InputStream传给用户进行下载
     *
     * @param is
     * @param os
     * @throws IOException
     */
    public static void copy(InputStream is, OutputStream os) throws IOException {
        byte[] bytes = new byte[1024];
        int len = 0;
        while ((len = is.read(bytes)) != -1) {
            os.write(bytes, 0, len);
        }
        if (os != null)
            os.close();
        if (is != null)
            is.close();
    }


    private boolean needProcessEmail(Message msg) throws Exception {
        System.out.println("needProcessEmail  > 当前邮件的标题" + msg.getSubject());
        // 1. 检查发件人邮箱是否包含在我们监控的邮箱列表里面
        String from = getFrom(msg);
        if (!isContainAttach((Part) msg)) {
            System.out.println("发件人满足要求但是附件为空，不满足我们监控的需求！");
            return false;
        }
        Map<String, InputStream> fileMap = new HashMap<>();
        getFileInputStream(msg, fileMap);
        if (fileMap.isEmpty()) {
            System.out.println("尽管邮件中有附件但是邮件中的附件却无一个满足要求！");
            return false;
        }
        System.out.println(fileMap);
        for (String s : fileMap.keySet()) {
            InputStream inputStream = fileMap.get(s);
            copy(inputStream, new FileOutputStream("D:\\" + s));

        }
        return true;
    }

    private String getFrom(Message msg) throws MessagingException {
        String from = "";
        InternetAddress[] addresses = (InternetAddress[]) msg.getFrom();
        if (null == addresses || addresses.length == 0) {
            System.out.println("无法获取发送人地址信息");
            return from;
        }
        Address address = addresses[0];
        System.out.println("件人地址json：" + address);
        String form = ((InternetAddress) address).getAddress();
        return form;
    }


    private void getFileInputStream(Part part, Map<String, InputStream> inputStreamMap) throws Exception {
        String fileName;
        if (part.isMimeType("multipart/*")) {
            Multipart mp = (Multipart) part.getContent();
            for (int i = 0; i < mp.getCount(); i++) {
                BodyPart mPart = mp.getBodyPart(i);
                String disposition = mPart.getDisposition();
                if ((disposition != null)
                        && ((disposition.equals(Part.ATTACHMENT)) || (disposition
                        .equals(Part.INLINE)))) {
                    fileName = mPart.getFileName();
                    if (fileName.toLowerCase().contains("gb2312")) {
                        fileName = MimeUtility.decodeText(fileName);
                    }
                    if (checkFileName(fileName)) {
                        inputStreamMap.put(fileName, mPart.getInputStream());
                    }
                } else if (mPart.isMimeType("multipart/*")) {
                    System.out.println("子邮件里面的附件");
                    getFileInputStream(mPart, inputStreamMap);
                } else {
                    fileName = mPart.getFileName();
                    if ((fileName != null)
                            && (fileName.toLowerCase().contains("GB2312"))) {
                        fileName = MimeUtility.decodeText(fileName);
                        if (checkFileName(fileName)) {
                            inputStreamMap.put(fileName, mPart.getInputStream());
                        }
                    }
                }
            }
        } else if (part.isMimeType("message/rfc822")) {
            getFileInputStream((Part) part.getContent(), inputStreamMap);
        }
    }


    private boolean checkFileName(String fileName) {
        return true;
    }

    private boolean isContainAttach(Part part) throws Exception {
        boolean attachFlag = false;
        // String contentType = part.getContentType();
        if (part.isMimeType("multipart/*")) {
            Multipart mp = (Multipart) part.getContent();
            for (int i = 0; i < mp.getCount(); i++) {
                BodyPart mPart = mp.getBodyPart(i);
                String disposition = mPart.getDisposition();
                if ((disposition != null)
                        && ((disposition.equals(Part.ATTACHMENT)) || (disposition
                        .equals(Part.INLINE)))) {
                    attachFlag = true;
                } else if (mPart.isMimeType("multipart/*")) {
                    attachFlag = isContainAttach((Part) mPart);
                } else {
                    String conType = mPart.getContentType();

                    if (conType.toLowerCase().contains("application")) {
                        attachFlag = true;
                    }
                    if (conType.toLowerCase().contains("name")) {
                        attachFlag = true;
                    }
                }
            }
        } else if (part.isMimeType("message/rfc822")) {
            attachFlag = isContainAttach((Part) part.getContent());
        }
        return attachFlag;
    }

}