java - Using log4j to send email reports via the SMTPAppender

Question

I'm trying to use log4j to send emailable reports that contain the logging statements from a background process. I want one email sent for each process run, not one email for each logging statement. I've looked at the SMTPAppender, but don't see a way to manually send the report when the process completes. I believe the TriggeringEventEvaluator may be the key, but one issue I'm running into is how to get a handle to the TriggeringEventEvaluator instance. I'm stuck using log4j 1.2.14 and the SMTPAppender.getEvaluator() method was introduced in 1.2.15. Any thoughts? Am I even on the right track? Does the SMTPAppender.close() method come into play here?

I want to be able to do this:

log.info(message1);
log.info(message2);
log.info(message3);
log.sendMail();

After thinking about this some more, I think I need to clarify what I'm hoping to accomplish. I'm trying to capture the logging from running a quartz job and send the resulting log as an email. The quartz job makes a bunch of service method calls into various services. I want the to include any logging those service methods perform as well as the logging of the quartz jobs itself. I was thinking I could do something like the following for capturing all the logging, but it isn't working.

// at the beginning of quartz job
Logger logger = Logger.getRootLogger();
StringWriter sw = new StringWriter();
WriterAppender wa = new WriterAppender(new SimpleLayout(), sw);
logger.addAppender(wa);

// at the end of the quartz job 
String report = sw.toString();

Answer 1

You shouldn't use any of log4j's methods, you should configure it properly instead.

First of all, define in your log4j.properties file your appender properly:

#CONFIGURE SMTP
log4j.appender.email=org.apache.log4j.net.SMTPAppender
log4j.appender.email.SMTPHost=mail.mydomain.com
[email protected]
log4j.appender.email.SMTPPassword=mypw
[email protected]
[email protected]
log4j.appender.email.Subject=Log of messages
log4j.appender.email.BufferSize=1
log4j.appender.email.EvaluatorClass=TriggerLogEvent
log4j.appender.email.layout=org.apache.log4j.PatternLayout
log4j.appender.email.layout.ConversionPattern=%m

Note: code taken from this post. More information can be obtained in SMTPAppender API.

Next, make a special class that will be used just for sending email. Example:

package com.foo.mailer;
import org.apache.log4j.Logger;

public class Mailer {
   private static final Logger logger = Logger.getLogger(Mailer.class);

   public void logMail(String mailString) {
      logger.info(mailString);
   }
}

Next, put in log4j.properties configuration for this class:

# INFO level will be logged
log4j.logger.com.foo.mailer = INFO, email
# turn off additivity
log4j.additivity.com.foo.mailer = false

Now, whenever you want to send an email using log4j, put this in your code:

new Mailer().logMail("This mail should be sent");

Disclaimer: I haven't tested any of this code.