安装依赖

前三个是接收邮件用的,其他的酌情安装(java世界坑太多了,本以为装第一个依赖就够了,结果给你各种出错)
implementation 'jakarta.mail:jakarta.mail-api:2.1.2'
implementation 'jakarta.activation:jakarta.activation-api:2.1.2'
implementation 'org.eclipse.angus:jakarta.mail:1.0.0'

implementation 'org.yaml:snakeyaml:2.0'
annotationProcessor 'org.projectlombok:lombok'

配置文件

resources目录下,config/mail-config.yml

recive:
    protocol: "pop3"
    host: "pop3.163.com"
    port: "110"
    username: "abc@163.com"
    password: "ASDFSFSDFSDFDSF"
    baseDir: "C:\\Users\\{user}\\Desktop"

这里用了网易邮箱,使用pop3协议, baseDir是存放附件的目录

示例代码

import jakarta.mail.*;
import jakarta.mail.internet.*;
import jakarta.activation.*;
import lombok.extern.slf4j.Slf4j;
import org.yaml.snakeyaml.Yaml;

import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Map;
import java.util.Properties;

/**
* @param
* @param null
* @author aloha
* @description TODO
* @createTime 
* @return
* @return null
*/
@Slf4j
public class MailRecive {
private String protocol;
private String host;
private String port;
private String username;
private String password;
private String baseDir;  //存储附件的目录

public void mailRecive() throws Exception {
    Yaml yaml = new Yaml();
    try (InputStream in = MailRecive.class.getClassLoader().getResourceAsStream("config/mail-config.yml")) {
        Map config = (Map<String, Object>) yaml.load(in);
        Map<String, String> recive = (Map<String, String>) config.get("recive");
        protocol = recive.get("protocol");
        host = recive.get("host");
        port = recive.get("port");
        username = recive.get("username");
        password = recive.get("password");
        baseDir = recive.get("baseDir");

    } catch (Exception e) {
        log.error("读取邮件配置文件{}", e);
    }
    // 准备连接服务器的会话信息
    Properties props = new Properties();
    props.setProperty("mail.store.protocol", protocol);  //协议 ,如"imap"
    props.setProperty("mail.host", host);      //主机 ,如 imap.163.com
    props.setProperty("mail.port", port);    //端口 ,如 143

    // 创建Session实例对象
    Session session = Session.getInstance(props);

    // 创建IMAP协议的Store对象
    Store store = session.getStore(protocol);

    // 连接邮件服务器
    store.connect(username, password);

    // 获得收件箱
    Folder folder = store.getFolder("INBOX");

    // 打开收件箱
    folder.open(Folder.READ_ONLY);  //打开方式,只读:Folder.READ_ONLY 或1. 读写:Folder.READ_WRITE  或2
    //   folder.open(1);  //打开方式,只读: 1. 读写: 2
    //邮件数
    // folder.getMessageCount();  //邮件总数,等同于msgs.length
    // folder.getUnreadMessageCount() //未读邮件数
    // folder.getNewMessageCount()  //新邮件数
    // folder.getDeletedMessageCount()  //已删除邮件数

    // 获得收件箱的邮件列表,遍历每封邮件,并下载附件到指定目录,测试邮箱只有一封邮件
    Message[] msgs = folder.getMessages();

    for (Message msg : msgs) {
//            log.debug("标题:{}", msg.getSubject());
//            log.debug("内容:{}", msg.getContent()); //内容目前没拿到,官网上不去,后面需要再说jakarta.mail.internet.MimeMultipart@3bbc39f8
//            log.debug("邮件类型:{}", msg.getContentType().toString());  //multipart/mixed
//            log.debug("文件名:{}", msg.getFileName());  //null
//            log.debug("对方发送时间:{}", msg.getSentDate().toString());
////            log.debug("接收时间:{}", msg.getReceivedDate().toString()); 可能为null
//            log.debug("getDataHandler:{}", msg.getDataHandler());
////            log.debug("getFrom:{}",msg.getFrom());  //发件人,=?gb18030?B?0e6yxcvJ?= <abc@qq.com>
        MimeMessage message = (MimeMessage) msg;
        Multipart multipart = (Multipart) message.getContent();

        for (int j = 0; j < multipart.getCount(); j++) {
            BodyPart bodyPart = multipart.getBodyPart(j);
            //如果是附件,写入到指定位置
            if (bodyPart.isMimeType("application/octet-stream")) { //"text/plain","text/html"
                DataSource source = bodyPart.getDataHandler().getDataSource();
                String fileDir=baseDir+"\\" + source.getName();  //拼接附件名
                try (InputStream in = source.getInputStream();OutputStream out = new FileOutputStream(fileDir)){
                    byte[] bytes = new byte[1024];
                    while (in.read(bytes) != -1){
                        out.write(bytes);
                    }
                }catch (Exception e){
                    log.error("获取邮件getInputStream或 创建写入流错误,{}",e);
                }
            }
        }
    }
    // 关闭资源
    folder.close(false);
    store.close();
}

// 执行
public static void main(String[] args) {
    MailRecive server = new MailRecive();
    try {
        server.mailRecive();
    } catch (Exception e) {
        log.warn("邮件服务异常:{}", e);
    }
}

}