Java 002：发邮件，及NoSuchAlgorithmException报错解决办法_java.security.nosuchalgorithmexception: suntls12rs

第1步：首先，项目要引入javax.mail库：

<!-- https://mvnrepository.com/artifact/com.sun.mail/javax.mail -->
<dependency>
    <groupId>com.sun.mail</groupId>
    <artifactId>javax.mail</artifactId>
    <version>1.6.2</version>
</dependency>

1.1 或者，你也可以直接下载这2个jar引入到你的java项目中：下载地址，当然你也可以去Maven仓库下载（javax.mail-1.6.2.jar和activation-1.1.1.jar）。

第2步：写代码，以下是我Hyb测试过（2023/5/12测试可行）可正常发邮件的代码：

import java.util.Properties;
import javax.mail.*;
import javax.mail.internet.*;
 
public final class EmailTest {
	public static void main(String[] args) throws Exception {
		final String subject = "邮件标题";
		final String content = "邮件内容";
 
		final Properties props = new Properties();
		props.put("mail.smtp.host", "smtp.126.com");
		props.put("mail.smtp.auth", "true");
		props.put("mail.smtp.starttls.enable", "true");
		props.put("mail.smtp.ssl.trust", "*");
 
		final String to = "收件人@126.com";
		final String from = "发件人@126.com";
		final String fromPwd = "发件邮箱的授权密码";
 
		final MimeMessage mm = new MimeMessage(Session.getInstance(props, new Authenticator() {
			protected PasswordAuthentication getPasswordAuthentication() {
				return new PasswordAuthentication(from, fromPwd);
			}
		})); // 创建MimeMessage
		mm.setFrom(new InternetAddress(from)); // 设置发件人、收件人、主题和消息内容
		mm.addRecipient(Message.RecipientType.TO, new InternetAddress(to));
		mm.setSubject(subject);
		mm.setText(content);
		Transport.send(mm); // 发送消息
	}
}

2.1 以上代码，你只需要将收件人、发件人、发件邮箱的授权密码 改成你的就可以了。

第3步：以上授权密码从哪来？这就需要你登录你的发件邮箱去设置、开启SMTP服务：

第4：以上发邮件的代码，发出的邮件内容是纯文本。如果要求邮件内容是html，下面代码可以做到：

import java.util.Properties;
import javax.mail.*;
import javax.mail.internet.*;
 
public final class EmailTest {
	public static void main(String[] args) throws Exception {
		final String subject = "邮件标题";
		final String content = "<font color=red>邮件内容</font>";
 
		final Properties props = new Properties();
		props.put("mail.smtp.host", "smtp.126.com");
		props.put("mail.smtp.auth", "true");
		props.put("mail.smtp.starttls.enable", "true");
		props.put("mail.smtp.ssl.trust", "*");
 
		final String to = "收件人@126.com";
		final String from = "发件人@126.com";
		final String fromPwd = "发件邮箱的授权密码";
 
		final MimeMultipart 正文和附件 = new MimeMultipart();
 
		final MimeBodyPart html = new MimeBodyPart();
		html.setContent(content, "text/html;charset=utf-8");
		正文和附件.addBodyPart(html);
 
		final MimeMessage mm = new MimeMessage(Session.getInstance(props, new Authenticator() {
			protected PasswordAuthentication getPasswordAuthentication() {
				return new PasswordAuthentication(from, fromPwd);
			}
		})); // 创建MimeMessage
		mm.setFrom(new InternetAddress(from)); // 设置发件人、收件人、主题和消息内容
		mm.addRecipient(Message.RecipientType.TO, new InternetAddress(to));
		mm.setSubject(subject);
		mm.setContent(正文和附件); // 设置发件内容
		Transport.send(mm); // 发送消息
	}
 
}

第5：如果要求邮件内容是html，且带图片，下面代码可以做到：

import java.util.Properties;
import javax.activation.DataHandler;
import javax.activation.FileDataSource;
import javax.mail.Authenticator;
import javax.mail.Message;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeBodyPart;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.MimeMultipart;
 
public final class EmailTest {
	public static void main(String[] args) throws Exception {
		final String subject = "邮件标题";
		final String content = "<font color=red>邮件内容</font>";
 
		final Properties props = new Properties();
		props.put("mail.smtp.host", "smtp.126.com");
		props.put("mail.smtp.auth", "true");
		props.put("mail.smtp.starttls.enable", "true");
		props.put("mail.smtp.ssl.trust", "*");
 
		final String to = "收件人@126.com";
		final String from = "发件人@126.com";
		final String fromPwd = "发件邮箱的授权密码";
 
		final MimeMultipart 正文和附件 = new MimeMultipart();
		正文和附件.setSubType("related"); //文本和图片内嵌成功
 
		final MimeBodyPart image = new MimeBodyPart();
		image.setDataHandler(new DataHandler(new FileDataSource("D:/aaa.png")));
		image.setContentID("a.png"); //设置图片id，这个非常重要。如果这个a.png跟下面的不一样，那这个图片就成邮件附件了
		正文和附件.addBodyPart(image);
 
		final MimeBodyPart html = new MimeBodyPart();
		html.setContent(content + "<br/><img src='cid:a.png'>", "text/html;charset=utf-8");
		正文和附件.addBodyPart(html);
 
		final MimeMessage mm = new MimeMessage(Session.getInstance(props, new Authenticator() {
			protected PasswordAuthentication getPasswordAuthentication() {
				return new PasswordAuthentication(from, fromPwd);
			}
		})); // 创建MimeMessage
		mm.setFrom(new InternetAddress(from)); // 设置发件人、收件人、主题和消息内容
		mm.addRecipient(Message.RecipientType.TO, new InternetAddress(to));
		mm.setSubject(subject);
		mm.setContent(正文和附件); // 设置发件内容
		Transport.send(mm); // 发送消息
	}
 
}

第6：如果要求邮件带附件，只要让上面代码setContentID("a.png")中，a.png不要被引用就可以了，当然网上还有其它办法，具体自己查查。反正以上3份代码，你copy后，改下收件人、发件人、发件邮箱授权密码，代码就可以成功运行的，本人Hyb测试多次没有问题。

第7：以上代码在eclipse中运行，没有一点问题。但如果脱离IDE环境，改成命令行部署的方式，就会报错。

7.1 命令行执行为：java -Djava.ext.dirs=D:/K/lib/ KxSnapshot 3600 1600 Z:/K/

      关于这条命令， 参数-Djava.ext.dirs指定了KxSnapshot.class依赖jar的存放目录。

7.2 但该命令在执行时会报错：NoSuchAlgorithmException: SunTls12RsaPremasterSecret KeyGenerator not available

javax.mail.MessagingException: Could not convert socket to TLS
	at com.sun.mail.smtp.SMTPTransport.startTLS(SMTPTransport.java:2155)
	at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:752)
	at javax.mail.Service.connect(Service.java:388)
	at javax.mail.Service.connect(Service.java:246)
	at javax.mail.Service.connect(Service.java:195)
	at javax.mail.Transport.send0(Transport.java:254)
	at javax.mail.Transport.send(Transport.java:124)
	at KxSnapshot.emailSend(KxSnapshot.java:897)
	at KxSnapshot.emailFindKDJ紫色连续2点升降(KxSnapshot.java:859)
	at KxSnapshot.main(KxSnapshot.java:105)
Caused by: javax.net.ssl.SSLKeyException: RSA premaster secret error
	at sun.security.ssl.RSAClientKeyExchange.<init>(Unknown Source)
	at sun.security.ssl.ClientHandshaker.serverHelloDone(Unknown Source)
	at sun.security.ssl.ClientHandshaker.processMessage(Unknown Source)
	at sun.security.ssl.Handshaker.processLoop(Unknown Source)
	at sun.security.ssl.Handshaker.process_record(Unknown Source)
	at sun.security.ssl.SSLSocketImpl.readRecord(Unknown Source)
	at sun.security.ssl.SSLSocketImpl.performInitialHandshake(Unknown Source)
	at sun.security.ssl.SSLSocketImpl.startHandshake(Unknown Source)
	at sun.security.ssl.SSLSocketImpl.startHandshake(Unknown Source)
	at com.sun.mail.util.SocketFetcher.configureSSLSocket(SocketFetcher.java:626)
	at com.sun.mail.util.SocketFetcher.startTLS(SocketFetcher.java:553)
	at com.sun.mail.smtp.SMTPTransport.startTLS(SMTPTransport.java:2150)
	... 9 more
Caused by: java.security.NoSuchAlgorithmException: SunTls12RsaPremasterSecret KeyGenerator not available
	at javax.crypto.KeyGenerator.<init>(KeyGenerator.java:169)
	at javax.crypto.KeyGenerator.getInstance(KeyGenerator.java:223)
	at sun.security.ssl.JsseJce.getKeyGenerator(Unknown Source)
	... 21 more

7.3 对于发邮件时报出NoSuchAlgorithmException，我Hyb实际的解决办法也简单：

      将jdk1.8.0_112/jre/lib/ext目录下的5个jar，copy到上面命令中的D:/K/lib/下。这5个jar是：

      ​​​​​​​localedata.jar , sunpkcs11.jar , sunmscapi.jar , sunjce_provider.jar , dnsns.jar