Java 邮件发送

使用 Java 原生方法发送邮件感觉略显麻烦，于是学习了下 Java 发送邮件的方法，然后自己封装了一层流式风格的 `MailSender`:

MailSender

见：https://github.com/YouthLin/java-utils/tree/master/mail

package com.youthlin.utils.mail;

import net.markenwerk.utils.mail.dkim.DkimMessage;
import net.markenwerk.utils.mail.dkim.DkimSigner;

import javax.activation.DataHandler;
import javax.activation.FileDataSource;
import javax.mail.Address;
import javax.mail.Authenticator;
import javax.mail.BodyPart;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.AddressException;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeBodyPart;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.MimeMultipart;
import javax.mail.internet.MimeUtility;
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.UnsupportedEncodingException;
import java.io.InputStream;
import java.security.interfaces.RSAPrivateKey;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;

/**
 * SMTP 邮件发送工具.
 * <p>
 * Created by lin on 2017-01-23-023.
 * <p>
 * 示例:
 * <pre>
 * new MailSender()
 *      .start(new MailSender.SessionBuilder()
 *          .host("host")
 *          .auth("username", "password")
 *          .ssl(465)   // JDK 7 OK. JDK8 由于安全原因需要替换俩 jar 包
 *          .debug()    // 注释这行关闭调试信息的输出
 *          .toSession()
 *      )//Session 只能调用一次 start
 *      .from("email", "DisplayName")//发件人 email,name
 *      .to("to", "DisplayName")//收件人
 *      .cc("cc")//抄送
 *      .cc("another", "name")
 *      .bcc("bcc")//密送
 *      .subject("subject")//主题
 *      .text("content")//只能设置一次内容. 或[html("html content")][content("plain",false)][content("html",true);]
 *      .attachment("path/to/file", "cid")//内嵌附件
 *      .attachment("path/to/file")//普通附件
 *      .attachment(file)//普通附件
 *      .dkim(new File("D:/key.der"), "youthlin.com", "xxx.youthlin")//验证发信人身份
 *      .send();//发送
 * </pre>
 * <p>
 * 使用 DKIM 验证发信人身份：
 * <ol>
 * <li>使用 OpenSSL 生成密钥对, 或者在 http://dkimcore.org/tools/ 生成</li>
 * <li>再把 Base64 文本格式的私钥转换为 der 二进制证书:<br>
 * <code>openssl pkcs8 -topk8 -nocrypt -in key.pem -outform der -out key.der</code><br>
 * 其中 key.pem 是第一步生成的私钥, 以「-----BEGIN RSA PRIVATE KEY-----」开头的文件, key.der 是要保存的文件</li>
 * <li>把公钥部署到域名的 TXT 记录中, 格式可参加步骤 1 网址.(记录名：xxx._domainkey, 记录值：p=xxx的一串 不含「p=」和末尾冒号)</li>
 * <li>使用 dkim 方法验证自己的身份:<br>
 * <code>privateDERKey</code> 是 der 私钥, <code>domain</code> 是域名, <code>selector</code> 是记录名(xxx._domainkey中的xxx)</li>
 * </ol>
 * <p>
 * 注意：<br>
 * Gmail 对附件要求严格, 对于下列类型的附件(或包含这些文件类型的压缩文件), 即使使用 DKIM 认证仍然会被退信:<br>
 * <pre>
 * .ADE、.ADP、.BAT、.CHM、.CMD、.COM、.CPL、.EXE、.HTA、.INS、.ISP、
 * .JAR、.JS、.JSE、.LIB、.LNK、.MDE、.MSC、.MSI、.MSP、.MST、.PIF、
 * .SCR、.SCT、.SHB、.SYS、.VB、.VBE、.VBS、.VXD、.WSC、.WSF、.WSH</pre>
 * 详见<a href="https://support.google.com/mail/answer/6590">某些文件类型被阻止 - Gmail 帮助</a>
 */
@SuppressWarnings({"WeakerAccess", "SameParameterValue", "unused"})
public class MailSender {
    /**
     * Session 构造器.
     * Session 是与服务器通信的前提环境, 如 host username password 等在此设置.
     * <p>
     * 示例:
     * <pre>
     * new MailSender.SessionBuilder()
     *         .host("host")
     *         .auth("username", "password")
     *         .ssl(465)
     *         .toSession()
     * </pre>
     */
    public static class SessionBuilder {
        private final Properties props = new Properties();
        private Authenticator authenticator = null;

        public SessionBuilder host(String host) {
            props.put("mail.host", host);
            return this;
        }

        /**
         * 如果需要授权才能登录的服务器, 那么请提供账号和密码.
         */
        public SessionBuilder auth(final String username, final String password) {
            props.put("mail.smtp.auth", true);
            authenticator = new Authenticator() {
                @Override
                protected PasswordAuthentication getPasswordAuthentication() {
                    return new PasswordAuthentication(username, password);
                }
            };
            return this;
        }

        /**
         * 端口号，默认25
         */
        public SessionBuilder port(int port) {
            props.put("mail.smtp.port", port);
            return this;
        }

        /**
         * 需要 SSL 安全连接, 则请提供端口.
         * <p>
         * JDK8 不能使用 SSL, 需要替换 <code>JDK_HOME/jre/lib/security/</code> 下的两个 jar 包, 下载地址见下
         *
         * @see <a href="http://www.oracle.com/technetwork/java/javase/downloads/jce-7-download-432124.html">http://www.oracle.com/technetwork/java/javase/downloads/jce-7-download-432124.html</a>
         */
        public SessionBuilder ssl(int port) {
            props.put("mail.smtp.ssl.enable", true);//使用 SSL
            props.put("mail.smtp.socketFactory.port", port);
            return port(port);
        }

        /**
         * 是否开启 Debug 输出, 默认否.
         */
        public SessionBuilder debug(boolean debug) {
            props.put("mail.debug", Boolean.toString(debug));//必须要是 String 类型
            return this;
        }

        public SessionBuilder debug() {
            return debug(true);
        }

        public Session toSession() {
            return Session.getInstance(props, authenticator);
        }
    }

    //region //field
    private static final String default_charset = "UTF-8";//默认字符编码
    private final MimeMultipart content = new MimeMultipart();//邮件的所有内容(body+Attachment)
    private final BodyPart body = new MimeBodyPart();//body
    private final List<BodyPart> attachments = new ArrayList<BodyPart>();//attachments
    private boolean started = false;//是否已经设置 Session
    private boolean contentHasSet = false;//是否已经设置过内容
    private MimeMessage msg;//每次设置的 Message 主体
    private DkimSigner signer;//DKIM 邮件认证
    //endregion //field

    /**
     * 从 Session 构造 Message.
     *
     * @throws IllegalStateException 当已经调用过本方法再次调用时抛出
     */
    public MailSender start(Session session) {
        if (started) {
            throw new IllegalStateException("start() method already called.");
        }
        started = true;
        msg = new MimeMessage(session);
        return this;
    }

    public MailSender from(String email) throws MessagingException {
        msg.setFrom(new InternetAddress(email));
        return this;
    }

    public MailSender from(String email, String name) throws MessagingException {
        try {
            msg.setFrom(new InternetAddress(email, name, default_charset));
        } catch (UnsupportedEncodingException e) {
            from(email);
        }
        return this;
    }

    //region  //recipients
    public MailSender to(String email) throws MessagingException {
        return to(new String[]{email}, null);
    }

    public MailSender to(String email, String name) throws MessagingException {
        return to(new String[]{email}, new String[]{name});
    }

    public MailSender to(String[] emails) throws MessagingException {
        return to(emails, null);
    }

    public MailSender to(String[] emails, String[] names) throws MessagingException {
        return addRecipients(Message.RecipientType.TO, toAddresses(emails, names));
    }

    public MailSender cc(String email) throws MessagingException {
        return cc(new String[]{email}, null);
    }

    public MailSender cc(String email, String name) throws MessagingException {
        return cc(new String[]{email}, new String[]{name});
    }

    public MailSender cc(String[] emails) throws MessagingException {
        return cc(emails, null);
    }

    public MailSender cc(String[] emails, String[] names) throws MessagingException {
        return addRecipients(Message.RecipientType.CC, toAddresses(emails, names));
    }

    public MailSender bcc(String email) throws MessagingException {
        return bcc(new String[]{email}, null);
    }

    public MailSender bcc(String email, String name) throws MessagingException {
        return bcc(new String[]{email}, new String[]{name});
    }

    public MailSender bcc(String[] emails) throws MessagingException {
        return bcc(emails, null);
    }

    public MailSender bcc(String[] emails, String[] names) throws MessagingException {
        return addRecipients(Message.RecipientType.BCC, toAddresses(emails, names));

    }

    private Address[] toAddresses(String[] emails, String[] names) throws AddressException {
        int eLen = emails.length;
        Address[] addresses = new Address[eLen];
        if (names != null && names.length == eLen) {//email 和 name 能对上时
            try {
                for (int i = 0; i < eLen; i++) {
                    addresses[i] = new InternetAddress(emails[i], names[i], default_charset);
                }
                return addresses;
            } catch (UnsupportedEncodingException ignore) {
            }
        }
        for (int i = 0; i < eLen; i++) {//对不上 或 异常
            addresses[i] = new InternetAddress(emails[i]);
        }
        return addresses;
    }

    private MailSender addRecipients(Message.RecipientType type, Address[] addresses) throws MessagingException {
        msg.addRecipients(type, addresses);
        return this;
    }
    //endregion  //recipients

    public MailSender subject(String subject) throws MessagingException {
        msg.setSubject(subject);
        return this;
    }

    //region //content
    public MailSender html(String html) throws MessagingException {
        return content(html, true);
    }

    public MailSender text(String plain) throws MessagingException {
        return content(plain, false);
    }

    /**
     * 设置邮件内容.
     * <p>
     * 也可以使用 <code>html()</code> 或 <code>text()</code> 设置, 但只能设置一次内容, 否则将抛出异常.
     *
     * @throws IllegalStateException 当多次设置邮件内容时抛出.
     */
    public MailSender content(String content, boolean isHtml) throws MessagingException {
        if (contentHasSet) {
            throw new IllegalStateException("Content already set.");
        }
        contentHasSet = true;
        if (isHtml) {
            body.setContent(content, "text/html;charset=" + default_charset);
        } else {
            body.setContent(content, "text/plain;charset=" + default_charset);
        }
        return this;
    }
    //endregion //content

    //region //attachment

    /**
     * 带附件.
     * <p>
     * 在「附件」中显示.
     */
    public MailSender attachment(String pathToFile) throws MessagingException {
        return attachment(pathToFile, null);
    }

    /**
     * 带附件.
     * <p>
     * 没有设置 cid 则只在附件中显示，设置了 cid 则 对应 html 邮件内容. 如：&lt;img src="cid:img1"/>
     * Outlook - cid 只支持图片, 文件的 cid 在 a 标签 href 属性中不起作用，只在附件中显示
     * QQ      - cid 支持二进制文件，有 cid 的附件将不会在「附件」中显示
     */
    public MailSender attachment(String pathToFile, String cid) throws MessagingException {
        return attachment(new File(pathToFile), cid);
    }

    public MailSender attachment(File file) throws MessagingException {
        return attachment(file, null);
    }

    public MailSender attachment(File file, String cid) throws MessagingException {
        BodyPart attach = new MimeBodyPart();
        attach.setDataHandler(new DataHandler(new FileDataSource(file)));
        try {
            attach.setFileName(MimeUtility.encodeWord(file.getName(), default_charset, null));
        } catch (UnsupportedEncodingException ignore) {
        }
        if (cid != null) {
            attach.setHeader("Content-ID", cid);
        }
        attachments.add(attach);
        return this;
    }
    //endregion //attachment

    //region //dkim
    public MailSender dkim(File privateDERKey, String domain, String selector) {
        try {
            signer = new DkimSigner(domain, selector, privateDERKey);
        } catch (Exception e) {
            signer = null;
            e.printStackTrace();
        }
        return this;
    }

    public MailSender dkim(byte[] privateDERKey, String domain, String selector) {
        return dkim(new ByteArrayInputStream(privateDERKey), domain, selector);
    }

    public MailSender dkim(InputStream privateDERKey, String domain, String selector) {
        try {
            signer = new DkimSigner(domain, selector, privateDERKey);
        } catch (Exception e) {
            signer = null;
            e.printStackTrace();
        }
        return this;
    }

    public MailSender dkim(RSAPrivateKey privateKey, String domain, String selector) {
        signer = new DkimSigner(domain, selector, privateKey);
        return this;
    }
    //endregion

    public Message toMessage() throws MessagingException {
        content.removeBodyPart(body);//防止多次调用添加多次
        content.addBodyPart(body);//顺序：body 在 attachment 之前
        for (BodyPart attach : attachments) {
            content.removeBodyPart(attach);
            content.addBodyPart(attach);
        }
        msg.setContent(content);
        if (signer != null) {
            return new DkimMessage(msg, signer);
        }
        return msg;
    }

    public void send() throws MessagingException {
        Transport.send(toMessage(), msg.getAllRecipients());
    }
}

测试代码

public static void main(String[] args) throws javax.mail.MessagingException {
        new MailSender()
                .start(new MailSender.SessionBuilder()
                        .host("mail.qq.com")
                        .auth("[email protected]", "password")
                        //.ssl(465)// JDK 7 OK. JDK8 由于安全原因需要替换俩 jar 包
                        .debug()
                        .toSession()
                )//Session 只能调用一次 start
                .from("[email protected]")//发件人 email,name
                .to("[email protected]")//收件人
                .cc("[email protected]")//抄送
                .subject("测试邮件")//主题
                .html("<span style='color:blue;'>Hello</span>,<br>World!")//只能设置一次内容. 或[html("html content")][content("plain",false)][content("html",true);]
                .attachment("/path/to/attachment/file")
                //.dkim(new java.io.File("/path/to/rsa.der"), "domain", "selector")
                .send();//发送
}

说明

• SSL JDK8 不能使用 SSL, 会报异常，需要替换 `JDK_HOME/jre/lib/security/` 下的两个 jar 包, 下载地址：http://www.oracle.com/technetwork/java/javase/downloads/jce-7-download-432124.html
• 附件 `attachment(String pathToFile)` 直接作为附件，`attachment(String pathToFile, String cid)` 作为 *内嵌附件*, 在 HTML 可以使用 cid:xxx 引用，一般用于内嵌图片（`attachment(“/path/to/pic.png”, “pic”)`, `<img src=’cid:pic’/>`）
• DKIM 用于垃圾邮件反查，确定邮件的确是发送方发送的。
  你可以在 http://dkimcore.org/tools/ 生成一对密钥，公钥在 DNS 里设置 TXT 记录，私钥在发送邮件时使用 dkim() 方法带上，这样对方收到邮件时就会去你的域名下根据 selector 查 DNS TXT 记录从而确定邮件确实是域名所有者发送的。
  这里 dkim 依赖的是第三方包：

  <dependency>
    <groupId>net.markenwerk</groupId>
    <artifactId>utils-mail-dkim</artifactId>
    <version>1.1.7</version>
  </dependency>

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