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Thinking in Java
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Example: Sending email to report log messages

You can actually have one of your logging handlers send you an email so that you can be automatically notified of important problems. The following example uses the JavaMail API to develop a mail user agent to send an email.

The JavaMail API is a set of classes that interface to the underlying mailing protocol (IMAP, POP, SMTP). You can devise a notification mechanism on some exceptional condition in the running code by registering an additional Handler to send an email.

// {RunByHand} Must be connected to the Internet
// {Depends: mail.jar,activation.jar}
import java.util.logging.*;
import java.util.Properties;
import javax.mail.*;
import javax.mail.internet.*;

public class EmailLogger {
  private static Logger logger =
  public static void main(String[] args) throws Exception {
    Handler conHdlr = new ConsoleHandler();
    conHdlr.setFormatter(new Formatter() {
      public String format(LogRecord record) {
        return record.getLevel() + "  :  "
          + record.getSourceClassName() + ":"
          + record.getSourceMethodName() + ":"
          + record.getMessage() + "\n";
      new FileHandler("EmailLoggerOutput.xml"));
    logger.addHandler(new MailingHandler());
      "Testing Multiple Handlers", "SendMailTrue");

// A handler that sends mail messages
class MailingHandler extends Handler {
  public void publish(LogRecord record) {
    Object[] params = record.getParameters();
    if(params == null) return;
    // Send mail only if the parameter is true
    if(params[0].equals("SendMailTrue")) {
      new MailInfo("[email protected]",
        new String[] { "[email protected]" },
        "", "Test Subject",
        "Test Content").sendMail();
  public void close() {}
  public void flush() {}

class MailInfo {
  private String fromAddr;
  private String[] toAddr;
  private String serverAddr;
  private String subject;
  private String message;
  public MailInfo(String from, String[] to,
    String server, String subject, String message) {
    fromAddr = from;
    toAddr = to;
    serverAddr = server;
    this.subject = subject;
    this.message = message;
  public void sendMail() {
    try {
      Properties prop = new Properties();
      prop.put("", serverAddr);
      Session session =
        Session.getDefaultInstance(prop, null);
      // Create a message
      Message mimeMsg = new MimeMessage(session);
      // Set the from and to address
      Address addressFrom = new InternetAddress(fromAddr);
      Address[] to = new InternetAddress[toAddr.length];
      for(int i = 0; i < toAddr.length; i++)
        to[i] = new InternetAddress(toAddr[i]);
    } catch (Exception e) {
      throw new RuntimeException(e);
} ///:~

MailingHandler is one of the Handlers registered with the logger. To send an email, the MailingHandler uses the MailInfo object. When a logging message is sent with an additional parameter of “SendMailTrue,” the MailingHandler sends an email.

The MailInfo object contains the necessary state information, such as the to address, from address, and the subject information required to send an email. This state information is provided to the MailInfo object through the constructor when it is instantiated.

To send an email you must first establish a Session with the Simple Mail Transfer Protocol (SMTP) server. This is done by passing the address of the server inside a Properties object, in a property named You establish a session by calling Session.getDefaultInstance( ), passing it the Properties object as the first argument. The second argument is an instance of Authenticator that may be used for authenticating the user. Passing a null value for the Authenticator argument specifies no authentication. If the debugging flag in the Properties object is set, information regarding the communication between the SMTP server and the program will be printed.

MimeMessage is an abstraction of an Internet email message that extends the class Message. It constructs a message that complies with the MIME (Multipurpose Internet Mail Extensions) format. A MimeMessage is constructed by passing it an instance of Session. You may set the from and to addresses by creating an instance of InternetAddress class (a subclass of Address). You send the message using the static call Transport.send( ) from the abstract class Transport. An implementation of Transport uses a specific protocol (generally SMTP) to communicate with the server to send the message.
Thinking in Java
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   Reproduced courtesy of Bruce Eckel, MindView, Inc. Design by Interspire