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Reporting Application Errors by Email Reporting Application Errors by Email

by Sean C. Sullivan

It is common practice for server-side applications to log messages to files on the server's file system. These logs are a vital source of information for system administrators and the application development team. If a user calls to report an error in the application, the developers can review the log files to determine what is happening in the application.

When your team has to support a mission-critical application, you can't afford to wait for users to tell you that the application is having problems. You need to be able to detect problems as soon as they occur. A simple and inexpensive solution is to implement an email notification system. The notification system will generate an email message whenever the application detects an error. If you are already using a standard logging framework like log4j, you can easily configure the logging system to broadcast error messages via email. In this article, we describe how to set up email notification for the two most widely used Java logging frameworks: log4j and java.util.logging.

log4j and java.util.logging

Let's start by reviewing the features and capabilities of log4j and java.util.logging. These logging frameworks provide the ability to categorize log messages, control over which messages will be logged, configurable message formatting, and configurable output destinations. The following table summarizes the core features of each logging framework.

  log4j java.util.logging
Manager class org.apache.log4j.LogManager java.util.logging.LogManager
Logger objects org.apache.log4j.Logger java.util.logging.Logger
Named loggers Supported Supported
Logging levels

Levels are declared in the org.apache.log4j.Level class. log4j has five pre-defined levels:

  1. FATAL
  2. ERROR
  3. WARN
  4. INFO
  5. DEBUG

Levels are declared in the java.util.logging.Level class. There are seven pre-defined levels:

  3. INFO
  5. FINE
  6. FINER
Log event object org.apache.log4j.spi.LoggingEvent java.util.logging.LogRecord
Output destinations Appender classes. These classes implement the org.apache.log4j.Appender interface. Handler classes. These classes extend java.util.logging.Handler.
Output message filtering Filter classes. These classes extend org.apache.log4j.spi.Filter. Filter classes. These classes must implement the java.util.logging.Filter interface.
Output message formatting Layout classes extend org.apache.log4j.Layout. Formatter classes extend java.util.logging.Formatter.
Programmatic configuration Supported Supported
Property file configuration Supported Supported
XML configuration Supported. The XML configuration file must comply with log4j.dtd. Not supported
Email notification SMTPAppender class SMTPHandler class (third-party extension)

If you are using java.util.logging, your application primarily uses the java.util.logging.Logger class to create log messages. This simple program demonstrates how to create a FINE-level message and a SEVERE-level message with the java.util.logging.Logger class:

import java.util.logging.*;
public class JDKLoggingExample
    private static final Logger log =
    public static void main(String[] args)
            log.fine("This is a fine message.");
            int i = Integer.parseInt("Hello world");
        catch (java.lang.Exception ex)
            log.log(Level.SEVERE, "Caught an exception", ex);

log4j has a similar approach. An application uses log4j's org.apache.log4j.Logger class to produce log messages. The following program demonstrates how to produce a DEBUG-level message and an ERROR-level message via log4j's Logger class.

import org.apache.log4j.*;

public class Log4jExample

    private static final Logger log = 

    public static void main(String[] args)
            log.debug("This is a debug message.");
            int i = Integer.parseInt("Hello world");
        catch (java.lang.Exception ex)
            log.error("Caught an exception", ex);

Appenders and Handlers

Both log4j and java.util.logging are capable of dispatching log messages to multiple destinations. log4j accomplishes this task by routing log messages through appender objects. Similarly, java.util.logging routes messages through handler objects. log4j users will typically configure a list of appenders in the log4j.xml file; java.util.logging users will typically configure a list of handlers in the logging.properties file.

log4j provides the SMTPAppender class so that applications can broadcast errors to an SMTP mail server. java.util.logging applications accomplish the same task with the SMTPHandler class.

Let's take a closer look at the SMTPAppender and the SMTPHandler.

log4j's SMTPAppender

The log4j JAR includes the org.apache.log4j.net.SMTPAppender class. With proper configuration, log4j will route error messages to the SMTPAppender. The SMTPAppender is then responsible for constructing an email message. The appender employs the JavaMail API to send the email message to an SMTP server.

Figure 1 illustrates the relationship between the log4j Logger, the SMTPAppender, and the SMTP server.

Figure 1
Figure 1. log4j Logger and SMTPAppender

The SMTPAppender makes it easy to broadcast application errors to your entire support team. Figure 2 shows an example email message from the SMTPAppender class.

Figure 2
Figure 2. An email message from the SMTPAppender

Next, we'll discuss how to configure log4j and how to enable the SMTPAppender.

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