前言

本文为JavaWeb基础邮件收发相关知识介绍~，Java全栈学习路线可参考：【Java全栈学习路线】最全的Java学习路线及知识清单，Java自学方向指引，内含最全Java全栈学习技术清单~

一、邮件的发送与接收原理

要在Internet上提供电子邮件功能，必须有专门的电子邮件服务器。电子邮箱(E-Mail地址)的获得需要在邮件服务器上进行申请。以QQ邮箱为例，需要从账户设置中开启POP3/SMTP服务。

用户连接上邮件服务器之后，要想给它发送一封电子邮件，需要遵循一定的通讯规则，SMTP协议就是用来定义这种通讯规则的。

用户若想从邮件服务器管理的电子邮箱当中接收一封电子邮件话，它连上邮件服务器后，也要遵循一定的通讯格式，POP3协议就是用来定义这种通讯格式的。

邮件的发送与接收过程：

场景假设xxx.@qq.com想给xxx.@sina.com发送邮件

首先，xxx.@qq.com通过smtp协议连接到qq邮箱的smtp服务器，并将邮件发送给smtp服务器，紧接着，QQ邮箱的smtp服务器将邮件转投给sina的smtp服务器

sina的smtp服务器将接收到的邮件存储到xxx.@sina.com的存储空间中，xxx.@sina.com通过POP3协议连接到sina的POP3服务器上收取邮件，POP3服务器从xxx.@sina.com账号的存储空间中取出邮件并将该邮件回送给xxx.@sina.com账户

二、发送简单文本邮件

使用Java发送 E-mail 需要通过JavaMail API和Java Activation Framework得到两个jar包：mail.jar，activation.jar。

代码实现：

public class SendMail {
    public static void main(String[] args) throws MessagingException, GeneralSecurityException {
        //1 准备步骤
        //1.1 创建一个配置文件保存并读取信息
        Properties properties = new Properties();
        //1.2 设置邮件服务器（这里使用了QQ邮箱）
        properties.setProperty("mail.host","smtp.qq.com");
        //1.3 设置发送使用的协议
        properties.setProperty("mail.transport.protocol","smtp");
        //1.4 设置用户是否需要验证
        properties.setProperty("mail.smtp.auth","true");
        //1.5 关于QQ邮箱，还要设置SSL加密，加上以下代码即可
        MailSSLSocketFactory sf = new MailSSLSocketFactory();
        sf.setTrustAllHosts(true);
        properties.put("mail.smtp.ssl.enable", "true");
        properties.put("mail.smtp.ssl.socketFactory", sf);
        //2 连接服务器
        //2.1 创建session会话对象
        Session session = Session.getDefaultInstance(properties, new Authenticator() {
            @Override
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication("553401298@qq.com", "jyyylkflmkyybcif");
            }
        });
        //开启Session的debug模式，这样就可以查看到程序发送Email的运行状态
        session.setDebug(true);
        //2.2 通过session对象获取Transport对象（需要抛出异常）
        Transport transport = session.getTransport();
        //2.3 连接服务器(需要抛出异常)
        transport.connect("smtp.qq.com","553401298@qq.com","jyyylkflmkyybcif");
        //3 发送邮件
        //3.1 创建用来发送邮件的对象(需要传入session)
        MimeMessage mimeMessage = new MimeMessage(session);
        //3.2 创建邮件发送人
        mimeMessage.setFrom(new InternetAddress("553401298@qq.com"));
        //3.3 创建邮件接收人(可以同时发送给很多人（添加抄送）)
        mimeMessage.setRecipients(Message.RecipientType.TO, new InternetAddress[]{new InternetAddress("553401298@qq.com")});
        //3.4 创建邮件主题
        mimeMessage.setSubject("LUCK");
        //3.5 创建邮件正文
        mimeMessage.setContent("GOOD LUCK","text/html;charset=utf-8");
        //3.6 发送邮件
        transport.sendMessage(mimeMessage,mimeMessage.getAllRecipients());
        //===================================================================
        //4 关闭连接
        transport.close();
    }
}

运行结果：

三、发送文本嵌入图片的邮件

代码实现：

public class SendImageEmail {
    public static void main(String[] args) throws GeneralSecurityException, MessagingException {
        //1.准备
        Properties properties = new Properties();
        properties.setProperty("mail.host","smtp.qq.com");
        properties.setProperty("mail.transport.protocol","smtp");
        properties.setProperty("mail.smtp.auth","true");
        MailSSLSocketFactory sf = new MailSSLSocketFactory();
        sf.setTrustAllHosts(true);
        properties.put("mail.smtp.ssl.enable", "true");
        properties.put("mail.smtp.ssl.socketFactory", sf);
        //2.连接服务器
        Session session = Session.getDefaultInstance(properties, new Authenticator() {
            @Override
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication("553401298@11.com", "jyyylkflmkyybcif");
            }
        });
        session.setDebug(true);
        Transport transport = session.getTransport();
        //连接服务器
        transport.connect("smtp.qq.com","553401298@qq.com","jyyylkflmkyybcif");
        //通过方法获取一个MimeMessage
        MimeMessage mimeMessage = setImgEmail(session);
        //设置发件人和收件人
        mimeMessage.setFrom(new InternetAddress("553401298@qq.com"));
        mimeMessage.setRecipients(Message.RecipientType.TO,new InternetAddress[]{new InternetAddress("553401298@qq.com")});
        //发送邮件
        transport.sendMessage(mimeMessage,mimeMessage.getAllRecipients());
        //关闭连接
        transport.close();
    }
    public static MimeMessage setImgEmail(Session session) throws MessagingException {
        //编写邮件内容
        //1.准备图片
        MimeBodyPart bodyPart = new MimeBodyPart();
        //2.将图片变为数据流
        //获取图片数据
        FileDataSource fileDataSource = new FileDataSource("src/resources/timg.jpg");
        //需要一个处理数据流的处理器来处理
        DataHandler dataHandler = new DataHandler(fileDataSource);
        //把图片数据放到邮件的正文中
        bodyPart.setDataHandler(dataHandler);
        //给图片设置一个名字
        bodyPart.setContentID("timg.jpg");
        //设置文本内容
        MimeBodyPart bodyPart2 = new MimeBodyPart();
        //给第二个邮件内容插入图片 通过图片ID插入
        bodyPart2.setContent("I need more space"+"<img src='cid:timg.jpg'>","text/html;charset=utf-8");
        //拼接邮件，描述关系
        MimeMultipart multipart = new MimeMultipart();
        multipart.addBodyPart(bodyPart);
        multipart.addBodyPart(bodyPart2);
        //描述邮件类型：related表示邮件为内嵌类型 mixed表示邮件为附件类型
        multipart.setSubType("related");
        MimeMessage mimeMessage = new MimeMessage(session);
        mimeMessage.setContent(multipart);
        //保存设置
        mimeMessage.setSubject("内嵌式邮件");
        mimeMessage.saveChanges();
        return mimeMessage;
    }
}

运行结果：

四、发送复杂邮件（文本嵌入图片，添加附件）

代码实现：

public class SendMail {
    public static void main(String[] args) throws MessagingException, GeneralSecurityException {
        //1 准备步骤
        //1.1 创建一个配置文件保存并读取信息
        Properties properties = new Properties();
        //1.2 设置邮件服务器（这里使用了QQ邮箱）
        properties.setProperty("mail.host","smtp.qq.com");
        //1.3 设置发送使用的协议
        properties.setProperty("mail.transport.protocol","smtp");
        //1.4 设置用户是否需要验证
        properties.setProperty("mail.smtp.auth","true");
        //1.5 关于QQ邮箱，还要设置SSL加密，加上以下代码即可
        MailSSLSocketFactory sf = new MailSSLSocketFactory();
        sf.setTrustAllHosts(true);
        properties.put("mail.smtp.ssl.enable", "true");
        properties.put("mail.smtp.ssl.socketFactory", sf);
        //2 连接服务器
        //2.1 创建session会话对象
        Session session = Session.getDefaultInstance(properties, new Authenticator() {
            @Override
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication("553401298@qq.com", "jyyylkflmkyybcif");
            }
        });
        //开启Session的debug模式，这样就可以查看到程序发送Email的运行状态
        session.setDebug(true);
        //2.2 通过session对象获取Transport对象（需要抛出异常）
        Transport transport = session.getTransport();
        //2.3 连接服务器(需要抛出异常)
        transport.connect("smtp.qq.com","553401298@qq.com","jyyylkflmkyybcif");
        //3 发送邮件
        //3.1 创建用来发送邮件的对象(需要传入session)
        MimeMessage mimeMessage = new MimeMessage(session);
        //3.2 创建邮件发送人
        mimeMessage.setFrom(new InternetAddress("553401298@qq.com"));
        //3.3 创建邮件接收人(可以同时发送给很多人（添加抄送）)
        mimeMessage.setRecipients(Message.RecipientType.TO, new InternetAddress[]{new InternetAddress("553401298@qq.com")});
        //3.4 创建邮件主题
        mimeMessage.setSubject("LUCK");
        //3.5 创建邮件正文
        mimeMessage.setContent("GOOD LUCK","text/html;charset=utf-8");
        //3.6 发送邮件
        transport.sendMessage(mimeMessage,mimeMessage.getAllRecipients());
        //===================================================================
        //4 关闭连接
        transport.close();
    }
}

运行结果：

五、发送注册提示邮件

实体类：

public class User {
    //实体类，用来封装用户信息
    private String username;
    private String password;
    private String email;
    public User(){
    }
    public User(String username, String password, String email) {
        this.username = username;
        this.password = password;
        this.email = email;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }
    @Override
    public String toString() {
        return "User{" +
                "username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", email='" + email + '\'' +
                '}';
    }
}

发送邮件工具类：

public class SendEmail extends Thread{
    //工具类，用来发送邮件
    //发件邮箱
    private String from = "553401298@qq.com";
    //邮箱的用户名
    private String username= "553401298@qq.com";
    //邮箱的授权码
    private String password = "jyyylkflmkyybcif";
    //邮箱服务器地址
    private String host = "smtp.qq.com";
    private User user;
    public SendEmail(User user){
        this.user=user;
    }
    @Override
    public void run() {
        try {
            Properties properties = new Properties();
            properties.setProperty("mail.host",host);
            properties.setProperty("mail.transport.protocol","smtp");
            properties.setProperty("mail.smtp.auth","true");
            MailSSLSocketFactory sf  = new MailSSLSocketFactory();
            sf.setTrustAllHosts(true);
            properties.put("mail.smtp.ssl.enable", "true");
            properties.put("mail.smtp.ssl.socketFactory", sf);
            Session session = Session.getDefaultInstance(properties, new Authenticator() {
                @Override
                protected PasswordAuthentication getPasswordAuthentication() {
                    return new PasswordAuthentication(username, password);
                }
            });
            Transport transport = session.getTransport();
            transport.connect(host,username,password);
            //通过MimeMessage设置邮件详情
            MimeMessage mimeMessage = new MimeMessage(session);
            mimeMessage.setFrom(new InternetAddress(from));
            mimeMessage.setRecipients(Message.RecipientType.TO, new InternetAddress[]{
    new InternetAddress(user.getEmail())});
            mimeMessage.setSubject("注册成功回执");
            mimeMessage.setContent("您已成功注册，您的用户名为："+user.getUsername()
                            +",密码为："+user.getPassword()
                            +",请您妥善保管。"
                    ,"text/html;charset=utf-8");
            //通过transport对象传输邮件
            transport.sendMessage(mimeMessage,mimeMessage.getAllRecipients());
            transport.close();
        } catch (GeneralSecurityException e) {
            e.printStackTrace();
        } catch (NoSuchProviderException e) {
            e.printStackTrace();
        } catch (MessagingException e) {
            e.printStackTrace();
        }
    }
}

servlet类：

public class RegisterServlet extends javax.servlet.http.HttpServlet{
    //servlet类用来获取前端数据，处理转发请求
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req,resp);
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //接收用户请求，封装为对象
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        String email = req.getParameter("email");
        User user = new User(username, password, email);
        //用户注册成功之后，给用户回执邮件
        //使用线程发送邮件，可以防止出现耗时，和网站注册人数过多的情况
        SendEmail sendEmail = new SendEmail(user);
        sendEmail.start();
        //提示用户查收注册回执邮件
        req.setAttribute("msg","注册成功，请查收回执邮件");
        req.getRequestDispatcher("info.jsp").forward(req,resp);
    }
}

web.xml：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
    <servlet>
        <servlet-name>RegisterServlet</servlet-name>
        <servlet-class>com.hooi.servlet.RegisterServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>RegisterServlet</servlet-name>
        <url-pattern>/rgs.do</url-pattern>
    </servlet-mapping>
</web-app>