Egge: New page: Occasionally something will go wrong in a program an log4j will send a mountain of emails. Here's a simple filtering class that can be used to prevent too many emails from being sent at o...

2007-11-06T22:25:32Z

New page: Occasionally something will go wrong in a program an log4j will send a mountain of emails. Here's a simple filtering class that can be used to prevent too many emails from being sent at o...

New page

Occasionally something will go wrong in a program an log4j will send a mountain of emails. Here's a simple filtering class that can be used to prevent too many emails from being sent at once.

<geshi lang="java5">
import java.util.LinkedList;

import org.apache.log4j.spi.LoggingEvent;
import org.apache.log4j.spi.TriggeringEventEvaluator;
/**
* This class is a filter for log4j to send at most four emails per hour.
* @author brianegge
*/
public class SlowDownSpamEvaluator implements TriggeringEventEvaluator {

private static final int MAX_MESSAGES_PER_HOUR = 4;
private final LinkedList queue = new LinkedList();
private final TriggeringEventEvaluator parent;

public SlowDownSpamEvaluator() {
parent = null;
}

public SlowDownSpamEvaluator(TriggeringEventEvaluator parent) {
this.parent = parent;
}

/**
* At most, {@value #MAX_MESSAGES_PER_HOUR} messages per hour will be triggered.
* @return Is this the triggering event?
*/
public boolean isTriggeringEvent(LoggingEvent event) {
long oneHourAgo = getTime() - 1000L * 60 * 60;
synchronized (queue) {
while(queue.size() > 0 && ((Long)queue.getLast()).longValue() <= oneHourAgo)
queue.removeLast();
if (queue.size() >= MAX_MESSAGES_PER_HOUR) { // we've sent more than four messages in the past hour
return false;
}
queue.addFirst(new Long(getTime()));
}
if (parent != null)
return parent.isTriggeringEvent(event);
return true;
}

/**
* subclasses can override this method for testing. <a href="http://joda-time.sourceforge.net/">
* Joda Time</a> provides good testing capabilities,
* but I don't want to add an external dependency.
*
* @return System.currentTimeMillis()
*/
protected long getTime() {
return System.currentTimeMillis();
}
}
</geshi>

And of course the test case.
<geshi lang="java5">
import org.apache.log4j.spi.LoggingEvent;
import org.apache.log4j.spi.TriggeringEventEvaluator;

import junit.framework.TestCase;

public class SlowDownSpamEvaluatorUnitTest extends TestCase implements TriggeringEventEvaluator {

int parent;
long offset;

public void testIsTriggeringEvent() {
TriggeringEventEvaluator evaluator = new SlowDownSpamEvaluator() {
protected long getTime() {
return super.getTime() + offset;
}
};
assertTrue(evaluator.isTriggeringEvent(null));
assertTrue(evaluator.isTriggeringEvent(null));
assertTrue(evaluator.isTriggeringEvent(null));
assertTrue(evaluator.isTriggeringEvent(null));
assertFalse(evaluator.isTriggeringEvent(null));
offset += 1000L * 60 * 60; // One hour
assertTrue(evaluator.isTriggeringEvent(null));
}

public void testParent() throws Exception {
TriggeringEventEvaluator evaluator = new SlowDownSpamEvaluator(this);
assertEquals(0, parent);
assertFalse(evaluator.isTriggeringEvent(null));
assertEquals(1, parent);
}

// we could use EasyMock, but since this is a small project, I'll create the stub in-line
public boolean isTriggeringEvent(LoggingEvent event) {
parent++;
return false;
}

}
</geshi>
[[Category:Java]]

SlowDownSpamEvaluator - Revision history

Egge: New page: Occasionally something will go wrong in a program an log4j will send a mountain of emails. Here's a simple filtering class that can be used to prevent too many emails from being sent at o...