Why is Logback SMTPAppender only sending 1 email?

Question

Here's a snippet containing my Logback SMTPAppender:

<appender name="logManager-smtpAppender" class="ch.qos.logback.classic.net.SMTPAppender">
    <filter class="ch.qos.logback.classic.filter.LevelFilter">
        <level>WARN</level>
        <onMatch>ACCEPT</onMatch>
        <onMismatch>NEUTRAL</onMismatch>
    </filter>
    <filter class="ch.qos.logback.classic.filter.LevelFilter">
        <level>ERROR</level>
        <onMatch>ACCEPT</onMatch>
        <onMismatch>DENY</onMismatch>
    </filter>

    <asynchronousSending>false</asynchronousSending>

    <smtpHost>my.smtp.host</smtpHost>
    <to>[email protected]</to>
    <from>[email protected]</from>
    <username>my_smtp_user</username>
    <password>my_smtp_password</password>
    <subject>%logger{20} - %m</subject>
    <layout class="ch.qos.logback.classic.html.HTMLLayout"/>
    <cyclicBufferTracker class="ch.qos.logback.core.spi.CyclicBufferTracker">
        <bufferSize>1</bufferSize>
    </cyclicBufferTracker>
</appender>

When the following Java executes:

logger.warn("This is a warning.");
logger.error("This is an error.");

I only get 1 email. By setting bufferSize to 1 I would have expected to get 2 different emails with 1 single log message in each of them. What's going on?

Wobbling

Answer 1

As Ceki has already mentioned that SMTPAPpender trigges emails on events of level ERROR. To get all your logs in one mail, You can increase the buffersize

10

Here by increasing bufferSize to 10, You will get last 10 messages logged by your error.

Check below link : https://github.com/abdulwaheed18/Slf4jTutorial/blob/master/src/com/waheed/tutorial8/Application8.java https://github.com/abdulwaheed18/Slf4jTutorial/blob/master/sample8.xml

Whimsical

Thanks @Whimsical (and +1 for the code samples). One thing I'm still not getting though is: what happens if I increase my bufferSize to 10, and then log, say, 12 ERROR messages? Will I get 1 email with 10 log messages? If so, what happens to the last 2 messages (10 + 2 = 12)? Thanks again! – Wobbling

Yes, If you set bufferSize value as 10, you will only get last 10 messages. Mostly we use SMTPAppender to notify admin/Ops that something has gone wrong in your Application. So as soon as it encountered ERROR log, it will send you a mail with numbers of logs you have set. Per ERROR log you will get one mail. – Whimsical

Thanks again (and +1!) I'm sorry though, not trying to be a pest here, but I'm still not understanding what would happen to the last 2 log messages. Say I have code that fires 12 logger.error("...") messages in a row, and bufferSize is set to 10. Like you said, I would get 1 email with 10 ERROR messages in it. But what happens to the last 2 ERROR logs? Thanks again for all your help so far! – Wobbling

I guess you are confused here. As I said per ERROR message you will get one mail. So for 12 errors, You will get 12 mails in your inbox. As soon as first logger.error encountered it will send one mail. On second error log you will get another mail. bufferSize set to 10 means the 10 messages get logged before error message. – Whimsical

Answer 2

Triggering of outgoing email is computed by an "evaluator". By default SMTPAppender comes with OnErrorEvaluator which triggers emails on events of level ERROR or higher. Thus, by default SMTPAppender will send out an email on the second message (of level ERROR) and not the first (WARN). To trigger outgoing messages on WARN, write your own evaluator. Here is the code:

public class OnWarnEvaluator extends EventEvaluatorBase<ILoggingEvent> {

 public boolean evaluate(ILoggingEvent event) throws NullPointerException,
           EvaluationException {
   return event.getLevel().levelInt >= Level.WARN_INT;
 }
}

Chronicle

Is it possible to describe/configure such an evaluator or sg. equivalent declaratively in log4j.xml (for Log4J 2.1)? I would like to get one e-mail per INFO and ERROR log message each. – Tunicle

Answer 3

To trigger outgoing messages at WARN without adding new source files, you could add the Janino dependency and its evaluator:

<appender name="EMAIL" class="ch.qos.logback.classic.net.SMTPAppender">

    <evaluator class="ch.qos.logback.classic.boolex.JaninoEventEvaluator">
        <expression>return level >= WARN;</expression>
    </evaluator>
    ...
</appender>

Christmastide