发送电子邮件（Sending Email）

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2023-12-01

使用Java应用程序发送电子邮件非常简单，但首先应该在您的计算机上安装JavaMail API和Java Activation Framework (JAF) 。

您可以从Java的标准网站下载最新版本的JavaMail (Version 1.2) 。
您可以从Java的标准网站下载最新版本的JAF (Version 1.1.1) 。

下载并解压缩这些文件，在新创建的顶级目录中，您将找到两个应用程序的jar文件。您需要在CLASSPATH中添加mail.jar和activation.jar文件。

发送简单的电子邮件

以下是从您的计算机发送简单电子邮件的示例。假设您的localhost已连接到Internet并且足以发送电子邮件。

例子 (Example)

// File Name SendEmail.java
import java.util.*;
import javax.mail.*;
import javax.mail.internet.*;
import javax.activation.*;
public class SendEmail {
   public static void main(String [] args) {    
      // Recipient's email ID needs to be mentioned.
      String to = "abcd@gmail.com";
      // Sender's email ID needs to be mentioned
      String from = "web@gmail.com";
      // Assuming you are sending email from localhost
      String host = "localhost";
      // Get system properties
      Properties properties = System.getProperties();
      // Setup mail server
      properties.setProperty("mail.smtp.host", host);
      // Get the default Session object.
      Session session = Session.getDefaultInstance(properties);
      try {
         // Create a default MimeMessage object.
         MimeMessage message = new MimeMessage(session);
         // Set From: header field of the header.
         message.setFrom(new InternetAddress(from));
         // Set To: header field of the header.
         message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));
         // Set Subject: header field
         message.setSubject("This is the Subject Line!");
         // Now set the actual message
         message.setText("This is actual message");
         // Send message
         Transport.send(message);
         System.out.println("Sent message successfully....");
      } catch (MessagingException mex) {
         mex.printStackTrace();
      }
   }
}

编译并运行此程序以发送简单的电子邮件 -

输出 (Output)

$ java SendEmail
Sent message successfully....

如果要向多个收件人发送电子邮件，则可以使用以下方法指定多个电子邮件ID -

void addRecipients(Message.RecipientType type, Address[] addresses)
   throws MessagingException

以下是参数的说明 -

type - 将设置为TO，CC或BCC。这里CC表示碳复制，BCC表示黑碳复制。示例: Message.RecipientType.TO
addresses - 这是一个电子邮件ID数组。在指定电子邮件ID时，您需要使用InternetAddress（）方法。

发送HTML电子邮件

以下是从您的计算机发送HTML电子邮件的示例。这里假设您的localhost已连接到Internet并且足以发送电子邮件。

此示例与前一个示例非常相似，不同之处在于我们使用setContent（）方法设置第二个参数为“text/html”的内容，以指定HTML内容包含在消息中。

使用此示例，您可以发送与您喜欢的HTML内容一样大的内容。

例子 (Example)

// File Name SendHTMLEmail.java
import java.util.*;
import javax.mail.*;
import javax.mail.internet.*;
import javax.activation.*;
public class SendHTMLEmail {
   public static void main(String [] args) {
      // Recipient's email ID needs to be mentioned.
      String to = "abcd@gmail.com";
      // Sender's email ID needs to be mentioned
      String from = "web@gmail.com";
      // Assuming you are sending email from localhost
      String host = "localhost";
      // Get system properties
      Properties properties = System.getProperties();
      // Setup mail server
      properties.setProperty("mail.smtp.host", host);
      // Get the default Session object.
      Session session = Session.getDefaultInstance(properties);
      try {
         // Create a default MimeMessage object.
         MimeMessage message = new MimeMessage(session);
         // Set From: header field of the header.
         message.setFrom(new InternetAddress(from));
         // Set To: header field of the header.
         message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));
         // Set Subject: header field
         message.setSubject("This is the Subject Line!");
         // Send the actual HTML message, as big as you like
         message.setContent("<h1>This is actual message</h1>", "text/html");
         // Send message
         Transport.send(message);
         System.out.println("Sent message successfully....");
      } catch (MessagingException mex) {
         mex.printStackTrace();
      }
   }
}

编译并运行此程序以发送HTML电子邮件 -

输出 (Output)

$ java SendHTMLEmail
Sent message successfully....

通过电子邮件发送附件

以下是从您的计算机发送带附件的电子邮件的示例。这里假设您的localhost已连接到互联网并且足以发送电子邮件。

例子 (Example)

// File Name SendFileEmail.java
import java.util.*;
import javax.mail.*;
import javax.mail.internet.*;
import javax.activation.*;
public class SendFileEmail {
   public static void main(String [] args) {     
      // Recipient's email ID needs to be mentioned.
      String to = "abcd@gmail.com";
      // Sender's email ID needs to be mentioned
      String from = "web@gmail.com";
      // Assuming you are sending email from localhost
      String host = "localhost";
      // Get system properties
      Properties properties = System.getProperties();
      // Setup mail server
      properties.setProperty("mail.smtp.host", host);
      // Get the default Session object.
      Session session = Session.getDefaultInstance(properties);
      try {
         // Create a default MimeMessage object.
         MimeMessage message = new MimeMessage(session);
         // Set From: header field of the header.
         message.setFrom(new InternetAddress(from));
         // Set To: header field of the header.
         message.addRecipient(Message.RecipientType.TO,new InternetAddress(to));
         // Set Subject: header field
         message.setSubject("This is the Subject Line!");
         // Create the message part 
         BodyPart messageBodyPart = new MimeBodyPart();
         // Fill the message
         messageBodyPart.setText("This is message body");
         // Create a multipar message
         Multipart multipart = new MimeMultipart();
         // Set text message part
         multipart.addBodyPart(messageBodyPart);
         // Part two is attachment
         messageBodyPart = new MimeBodyPart();
         String filename = "file.txt";
         DataSource source = new FileDataSource(filename);
         messageBodyPart.setDataHandler(new DataHandler(source));
         messageBodyPart.setFileName(filename);
         multipart.addBodyPart(messageBodyPart);
         // Send the complete message parts
         message.setContent(multipart );
         // Send message
         Transport.send(message);
         System.out.println("Sent message successfully....");
      } catch (MessagingException mex) {
         mex.printStackTrace();
      }
   }
}

编译并运行此程序以发送HTML电子邮件 -

输出 (Output)

$ java SendFileEmail
Sent message successfully....

用户认证部分

如果需要向电子邮件服务器提供用户ID和密码以进行身份验证，则可以按如下方式设置这些属性 -

props.setProperty("mail.user", "myuser");
props.setProperty("mail.password", "mypwd");

其余的电子邮件发送机制将保持如上所述。