本文Tags: Velocity
之前有问过这个奇怪的问题，日志一直报错：
log4j:ERROR Attempted to append to closed appender named [null].
原来是velocity的bug，目前为止所有release都有这个bug (velocity的网站上说1.5版会fix这个bug)
> Key: VELOCITY-193
> URL: http://issues.apache.org/jira/browse/VELOCITY-193
> Project: Velocity
> Type: Bug
When creating and then releasing to garbage collection multiple VelocityEngine instances, the
instances are apparently not closing out or otherwise letting go of their logger instances. As a
result, code that needs to create and destroy several VelocityEngine instances will eventually choke and die. This happens with either Avalon Logkit or Log4j, although the exact nature of the choking differs. This test program isolates the problem:
import org.apache.velocity.app.VelocityEngine;
public class IsolateVelocityBug {
static public void main( String[] args ) {
int repCount = Integer.parseInt( args[0] );
for( int i = 0; i < repCount; i++ ) {
System.out.println( "Test repetition " + i + "..." );
try {
final VelocityEngine velocityEngine = new VelocityEngine();
velocityEngine.init();
} catch( Exception e ) {
throw new Error( e );
}
}
}
}
Run the program with an integer command-line argument specifying the number of times to cycle through the loop, and make sure velocity-1.3.1.jar, commons-collections.jar, and either an Avalon Logkit or Log4j JAR are on your classpath. (I tested with logkit-1.0.1.jar and log4j-1.1.3.jar.) What *should* happen is that the program completes its specified number of loops, doing nothing but writing “Test repetition” over and over with an incrementing number. What *does* happen, at least on my machine, depends on which logging package is provided for Velocity.
Using Avalon Logkit 1.0.1, the program runs fine for 252 iterations; on the 253nd, it aborts with
the following message:
“PANIC : Error configuring AvalonLogSystem : java.io.FileNotFoundException: /Users/ibeatty/
Development/javaDev/VelocityBugIsolator/velocity.log (Too many open files)”
Using Log4j 1.1.3, the program runs fine for only one iteration; on the second and any subsequent iterations, it continues but prints out a whole mess of
“log4j:ERROR Attempted to append to closed appender named [null].
log4j:WARN Not allowed to write to a closed appender.”
That happens for as long as I care to let it run (95 iterations, with something over 800 lines of
such errors per iteration by the end).
To me, it sure looks like Velocity is leaving dangling loggers behind as VelocityEngine instances
are created and discarded, and that the two logging systems respond differently to this but both have problems.
Why, might you ask, should anyone care about making many VelocityEngine instances? I ran into it when developing a major web app using JUnit to build comprehensive test suites. To run
independently, every test has to start from scratch, which means getting its own VelocityEngine.
Many tests means many instances, and the logging problem kicks in. Running JUnit test suites
within Intellij IDEA and using Log4j, the ERROR/WARN messages were more than a nuicanse;
eventually, I’d start getting out-of-memory errors, too. These went away when I changed the tests to use a shared VelocityEngine instance (which caused its own set of problems).
Using binary download of Velocity 1.3.1, which claims to have been created on 2003-04-01.
I find it hard to believe nobody else has tripped over this before, so maybe it’s sensitive to the OS or something. It happened whether I compiled the test code with Javac or Jikes. Using Java
1.4.1_01.
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