发送电子邮件

使用 Servlet 发送一封电子邮件是非常简单的，但是开始之前你必须在你的计算机上安装 JavaMail API 和 Java Activation Framework(JAF)。

你可以从 Java 标准网站下载最新版本的 JavaMail版本 1.2
你可以从 Java 标准网站下载最新版本的 JAF版本 1.1.1

下载并解压缩这些文件，在新创建的顶级目录中你会发现这两个应用程序的一些 jar 文件。你需要把 mail.jar 和 activation.jar 文件添加到你的 CLASSPATH 中。

发送一封简单的电子邮件

这是从你的计算机上发送一封简单的电子邮件的实例。这里假设你的本地主机已连接到互联网并可以发送电子邮件。同时确保来自 Java Email API 包和 JAF 包的所有的 jar 文件在 CLASSPATH 中是可用的。

// File Name SendEmail.java
import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.mail.*;
import javax.mail.internet.*;
import javax.activation.*;
public class SendEmail extends HttpServlet{  
  public void doGet(HttpServletRequest request,
                    HttpServletResponse response)
            throws ServletException, IOException
  {
      // 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);      
      // Set response content type
      response.setContentType("text/html");
      PrintWriter out = response.getWriter();
      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);
         String title = "Send Email";
         String res = "Sent message successfully....";
         String docType =
         "<!doctype html public \"-//w3c//dtd html 4.0 " +
         "transitional//en\">\n";
         out.println(docType +
         "<html>\n" +
         "<head><title>" + title + "</title></head>\n" +
         "<body bgcolor=\"#f0f0f0\">\n" +
         "<h1 align=\"center\">" + title + "</h1>\n" +
         "<p align=\"center\">" + res + "</p>\n" +
         "</body></html>");
      }catch (MessagingException mex) {
         mex.printStackTrace();
      }
   }
}

现在让我们来编译上述 servlet 并在 web.xml 文件中创建以下条目：

....
 <servlet>
     <servlet-name>SendEmail</servlet-name>
     <servlet-class>SendEmail</servlet-class>
 </servlet> 
 <servlet-mapping>
     <servlet-name>SendEmail</servlet-name>
     <url-pattern>/SendEmail</url-pattern>
 </servlet-mapping>
....

现在使用 URL http://localhost:8080/SendEmail 来调用这个 servlet。这将会给给定的电子邮件 ID abcd@gmail.com 发送一封电子邮件并将显示如下所示的响应：

Send Email

Sent message successfully....

如果你想把一封电子邮件发送给多个收件人，那么使用下面的方法来指定多个电子邮件 ID：

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

这里是对参数的描述：

type：这将被设置为 TO、CC 或 BCC。这里 CC 代表抄送且 BCC 代表密件抄送。例如 Message.RecipientType.TO。
addresses：这是电子邮件 ID 的数组。当指定电子邮件 ID 时，你需要使用 InternetAddress() 方法。

发送一封 HTML 电子邮件

这个例子将从你的计算机上发送一封 HTML 电子邮件。这里假设你的本地主机已连接到互联网且可以发送电子邮件。同时确保来自 Java Email API 包和 JAF 包的所有的 jar 文件在 CLASSPATH 中都是可用的。

这个例子与上一个例子非常相似，除了在这里我们使用的是 setContent() 方法来设置内容，它的第二个参数为 “text/html” 用来指定 HTML 内容是包含在消息中的。

使用这个实例，你可以发送内容大小不限的 HTML 内容。

// File Name SendEmail.java
import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.mail.*;
import javax.mail.internet.*;
import javax.activation.*;
public class SendEmail extends HttpServlet{   
  public void doGet(HttpServletRequest request,
                    HttpServletResponse response)
            throws ServletException, IOException
  {
      // 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);    
      // Set response content type
      response.setContentType("text/html");
      PrintWriter out = response.getWriter();
      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);
         String title = "Send Email";
         String res = "Sent message successfully....";
         String docType =
         "<!doctype html public \"-//w3c//dtd html 4.0 " +
         "transitional//en\">\n";
         out.println(docType +
         "<html>\n" +
         "<head><title>" + title + "</title></head>\n" +
         "<body bgcolor=\"#f0f0f0\">\n" +
         "<h1 align=\"center\">" + title + "</h1>\n" +
         "<p align=\"center\">" + res + "</p>\n" +
         "</body></html>");
      }catch (MessagingException mex) {
         mex.printStackTrace();
      }
   }
}

编译并运行上述 servlet 来在给定的电子邮件 ID 上发送 HTML 消息。

在电子邮件中发送附件

这里的例子将从你的计算机上发送一封带有附件的电子邮件。这里假设你的本地主机已连接到互联网并能够发送电子邮件。同时确保来自 Java Email API 包和 JAF 包的所有的 jar 文件在 CLASSPATH 中都是可用的。

// File Name SendEmail.java
import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.mail.*;
import javax.mail.internet.*;
import javax.activation.*; 
public class SendEmail extends HttpServlet{    
  public void doGet(HttpServletRequest request,
                    HttpServletResponse response)
            throws ServletException, IOException
  {
      // 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);   
      // Set response content type
      response.setContentType("text/html");
      PrintWriter out = response.getWriter();
       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);
         String title = "Send Email";
         String res = "Sent message successfully....";
         String docType =
         "<!doctype html public \"-//w3c//dtd html 4.0 " +
         "transitional//en\">\n";
         out.println(docType +
         "<html>\n" +
         "<head><title>" + title + "</title></head>\n" +
         "<body bgcolor=\"#f0f0f0\">\n" +
         "<h1 align=\"center\">" + title + "</h1>\n" +
         "<p align=\"center\">" + res + "</p>\n" +
         "</body></html>");
      }catch (MessagingException mex) {
         mex.printStackTrace();
      }
   }
}

编译并运行上面的 servlet 来在给定的电子邮件 ID 上发送附件文件和消息。

用户身份认证部分

如果需要向电子邮件服务器提供用户 ID 和密码来进行身份认证，那么你可以设置如下所示的属性：

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

电子邮件发送机制的其余部分与上面解释的一致。