廖雪峰Java13网络编程-2Email编程-2接收Email

## 1接收Email协议类型
接收Email：收件人通过MUA软件把邮件从MDA抓取到本地计算机的过程。

1.1 POP3

从MUA到MDA使用最广泛的是协议是POP3
* Post Office Protocol version 3，建立在tcp之上的协议
* 标准端口110
* 整个会话加密，加密端口995

1.2 IMAP

与POP3的区别：IMAP在本地的所有操作都会自动同步到服务器上，允许用户自己创建文件夹
* Internet Mail Access Protocol
* 标准端口143
* 加密端口993

2如何接收Email

• 使用Java Mail API，实现邮件的接收
• 无需关心POP3协议原理

    //创建session
    Session session = Session.getInstance(props, null);
    //创建Store对象，代表用户在邮件服务器上的整个存储
    Store store = new POP3SSLStore(session, url);
    //获取Folder对象，最常用的是收件箱INBOX
    Folder folder = store.getFolder("INBOX");
    //获取Message：返回收件箱所有的邮件，并循环处理message对象
    Message[] messages = folder.getMessages();
    for(Message message:messages){
        ...
    }

package com.feiyangedu.sample.pop3;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;

import javax.mail.Address;
import javax.mail.Authenticator;
import javax.mail.BodyPart;
import javax.mail.Flags;
import javax.mail.Folder;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Multipart;
import javax.mail.Part;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Store;
import javax.mail.URLName;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.MimeMessage.RecipientType;
import javax.mail.internet.MimeUtility;

import com.sun.mail.pop3.POP3SSLStore;

public class Pop3 {

	final String popHost;
	final String username;
	final String password;
	final boolean debug;

	public Pop3(String popHost, String username, String password) {
		this.popHost = popHost;
		this.username = username;
		this.password = password;
		this.debug = true;
	}

	public static void main(String[] args) throws Exception {
		Pop3 pop = new Pop3("pop.qq.com","123456789@qq.com","pop3授权码");//注意，不能用手机号，要用qq号
		Folder folder = null;
		Store store = null;
		try {
			store = pop.createSSLStore(); //获取到Store对象后，就可以获取Folder对象
			folder = store.getFolder("INBOX");
			folder.open(Folder.READ_WRITE);
			System.out.println("Total messages: " + folder.getMessageCount()); //邮件数量
			System.out.println("New messages: " + folder.getNewMessageCount()); //新邮件数量
			System.out.println("Unread messages: " + folder.getUnreadMessageCount()); //未读邮件数量
			System.out.println("Deleted messages: " + folder.getDeletedMessageCount()); //已删除的邮件数量
			Message[] messages = folder.getMessages();
			for (Message message : messages) {
				printMessage((MimeMessage) message);
			}
		} finally {
			if (folder != null) {
				try {
					folder.close(true);
				} catch (MessagingException e) {
					e.printStackTrace();
				}
			}
			if (store != null) {
				try {
					store.close();
				} catch (MessagingException e) {
					e.printStackTrace();
				}
			}
		}
	}
        //创建Store对象
	public Store createSSLStore() throws MessagingException {
		Properties props = new Properties();
		props.setProperty("mail.store.protocol", "pop3");
		props.setProperty("mail.pop3.port", "995"); // 主机端口号
		props.setProperty("mail.pop3.host", this.popHost);// POP3主机名
		// 启动SSL:
		props.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
		props.put("mail.smtp.socketFactory.port", "995");
		URLName url = new URLName("pop3", this.popHost, 995, "", this.username, this.password);
		Session session = Session.getInstance(props, null);
		session.setDebug(this.debug); // 显示调试信息
		Store store = new POP3SSLStore(session, url);
		store.connect(); //连接到服务器
		return store;
	}

	Session createTLSStore() {
		Properties props = new Properties();
		props.put("mail.smtp.host", this.popHost); // POP3主机名
		props.put("mail.smtp.port", "587"); // 主机端口号
		props.put("mail.smtp.auth", "true"); // 是否需要用户认证
		props.put("mail.smtp.starttls.enable", "true"); // 启用TLS加密
		Session session = Session.getInstance(props, new Authenticator() {
			protected PasswordAuthentication getPasswordAuthentication() {
				return new PasswordAuthentication(Pop3.this.username, Pop3.this.password);
			}
		});
		session.setDebug(this.debug); // 显示调试信息
		return session;
	}

	Session createInsecureStore() {
		Properties props = new Properties();
		props.put("mail.smtp.host", this.popHost); // POP3主机名
		props.put("mail.smtp.port", "25"); // 主机端口号
		props.put("mail.smtp.auth", "true"); // 是否需要用户认证
		Session session = Session.getInstance(props, new Authenticator() {
			protected PasswordAuthentication getPasswordAuthentication() {
				return new PasswordAuthentication(Pop3.this.username, Pop3.this.password);
			}
		});
		session.setDebug(this.debug); // 显示调试信息
		return session;
	}

	static void printMessage(MimeMessage msg) throws IOException, MessagingException {
		System.out.println("--------------------");
		System.out.println("Subject: " + MimeUtility.decodeText(msg.getSubject())); //邮件的主题
		System.out.println("From: " + getFrom(msg)); //发件人
		System.out.println("To: " + getTo(msg)); //收件人
		System.out.println("Sent: " + msg.getSentDate().toString()); //发送时间
		System.out.println("Seen: " + msg.getFlags().contains(Flags.Flag.SEEN)); //是否已读
		System.out.println("Priority: " + getPriority(msg)); //优先级
		System.out.println("Size: " + msg.getSize() / 1024 + "kb"); //邮件大小
		System.out.println("Body: " + getBody(msg)); //邮件正文
		System.out.println("--------------------");
		System.out.println();
	}

	static String getFrom(MimeMessage msg) throws IOException, MessagingException {
		Address[] froms = msg.getFrom();
		return addressToString(froms[0]);
	}

	static String getTo(MimeMessage msg) throws MessagingException, IOException {
		// 使用 msg.getAllRecipients() 获取所有收件人
		Address[] tos = msg.getRecipients(RecipientType.TO);
		List<String> list = new ArrayList<>();
		for (Address to : tos) {
			list.add(addressToString(to));
		}
		return String.join(", ", list);
	}

	static String addressToString(Address addr) throws IOException {
		InternetAddress address = (InternetAddress) addr;
		String personal = address.getPersonal();
		return personal == null ? address.getAddress()
				: (MimeUtility.decodeText(personal) + " <" + address.getAddress() + ">");
	}

	static String getPriority(MimeMessage msg) throws MessagingException {
		String priority = "Normal";
		String[] headers = msg.getHeader("X-Priority");
		if (headers != null) {
			String header = headers[0];
			if ("1".equals(header) || "high".equalsIgnoreCase(header)) {
				priority = "High";
			} else if ("5".equals(header) || "low".equalsIgnoreCase(header)) {
				priority = "Low";
			}
		}
		return priority;
	}

	static String getBody(Part part) throws MessagingException, IOException {
		if (part.isMimeType("text/*")) {//如果邮件的正文是text开头，是一个文本邮件或html邮件
			return part.getContent().toString();
		}
		if (part.isMimeType("multipart/*")) { //如果是以multipart开头，那么他是一个带附件的邮件，还需要递归的把附件的内容读出来
			Multipart multipart = (Multipart) part.getContent();
			for (int i = 0; i < multipart.getCount(); i++) {
				BodyPart bodyPart = multipart.getBodyPart(i);
				String body = getBody(bodyPart);
				if (!body.isEmpty()) {
					return body;
				}
			}
		}
		return "";
	}
}

3总结

Java接收Email：

• 用maven引入javamail依赖
• 确定POP3服务器信息：域名/端口/使用明文/SSL
• 调用相关API接收Email（无需关心底层TCP Socket连接）
• 设置debug模式可以查看通信详细内容（便于排查错误）