Sending Email (Java Servlet Programming)

Sometimes it's necessary, or just convenient, for a servlet to fire off an email message. For example, imagine a servlet that receives data from a user feedback form. The servlet might want to send the feedback data to a mailing list of interested parties. Or imagine a servlet that encounters an unexpected problem and knows to send an email page to its administrator asking for help.

13.2.1. Using sun.net.smtp.SmtpClient

For the purposes of this example, we'll demonstrate a servlet that uses the sun.net.smtp.SmtpClient class. It's conveniently provided with Sun's JDK and most JVMs descended from it, but we should warn you that it's unsupported and subject to change (though it hasn't changed since JDK 1.0). Using it is simple:

13.2.2. Emailing Form Data

Example 13-3 shows a servlet that emails the form data it receives to a mailing list. Notice the extensive use of the ParameterParser class.

Example 13-3. Sending mail from a servlet

import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;

import com.oreilly.servlet.ParameterParser;
import com.oreilly.servlet.ServletUtils;

import sun.net.smtp.SmtpClient;

public class MailServlet extends HttpServlet {

  static final String FROM = "MailServlet";
  static final String TO = "feedback-folks@attentive-company.com";

  public void doGet(HttpServletRequest req, HttpServletResponse res)
                               throws ServletException, IOException {
    res.setContentType("text/plain");
    PrintWriter out = res.getWriter();

    ParameterParser parser = new ParameterParser(req);
    String from = parser.getStringParameter("from", FROM);
    String to = parser.getStringParameter("to", TO);

    try {
      SmtpClient smtp = new SmtpClient();  // assume localhost
      smtp.from(from);
      smtp.to(to);
      PrintStream msg = smtp.startMessage();

      msg.println("To: " + to);  // so mailers will display the To: address
      msg.println("Subject: Customer feedback");
      msg.println();

      Enumeration enum = req.getParameterNames();
      while (enum.hasMoreElements()) {
        String name = (String)enum.nextElement();
        if (name.equals("to") || name.equals("from")) continue;  // Skip to/from
        String value = parser.getStringParameter(name, null);
        msg.println(name + " = " + value);
      }

      msg.println();
      msg.println("---");
      msg.println("Sent by " + HttpUtils.getRequestURL(req));

      smtp.closeServer();

      out.println("Thanks for the submission...");
    }
    catch (IOException e) {
      out.println("There was a problem handling the submission...");
      getServletContext().log(e, "There was a problem sending email");
    }
  }
}

This servlet first determines the "from" and "to" addresses for the message. The default values are set in the FROM and TO variables, although a submitted form can include (probably hidden) fields that specify alternate from and to addresses. The servlet then begins an SMTP email message. It connects to the local host and addresses the message. Next, it sets its headers and fills the body with the form data, ignoring the to and from variables. Finally, it sends the message and thanks the user for the submission. If there's a problem, it informs the user and logs the exception.

13.2. Sending Email

13.2.1. Using sun.net.smtp.SmtpClient

13.2.2. Emailing Form Data

Example 13-3. Sending mail from a servlet