#52 NPE during application start if log4j2 is in the classpath and the script engine logger is on debug

[Harald Kraemer]

Hey,

I just stumbled across a silly issue. If I have log4j2 in the classpath, and put specific loggers on debug, the system crashes.

Reproduction should be simple:
- Create a project
- add luaj 3.0.1 to the classpath
- add log4j2-core version 2.6.2 to the classpath
- add log4j2-api version 2.6.2 to the classpath
- create a small log4j2.xml as follows:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="DEBUG">
  <Appenders>
    <Console name="Console" target="SYSTEM_OUT">
      <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
    </Console>
  </Appenders>
  <Loggers>
    <Root level="DEBUG">
      <AppenderRef ref="Console"/>
    </Root>
  </Loggers>
</Configuration>

Create a java class as follows:

import org.apache.logging.log4j.LogManager;

public class LuaCrashRepro {
    public static void main(String[] args) {
        LogManager.getLogger("A");
    }
}

This will result in a crash as follows:

Exception in thread "main" java.lang.NullPointerException
    at org.luaj.vm2.script.LuaScriptEngineFactory.getParameter(Unknown Source)
    at org.apache.logging.log4j.core.script.ScriptManager.<init>(ScriptManager.java:62)
    at org.apache.logging.log4j.core.config.AbstractConfiguration.initialize(AbstractConfiguration.java:201)
    at org.apache.logging.log4j.core.config.AbstractConfiguration.start(AbstractConfiguration.java:231)
    at org.apache.logging.log4j.core.LoggerContext.setConfiguration(LoggerContext.java:496)
    at org.apache.logging.log4j.core.LoggerContext.reconfigure(LoggerContext.java:566)
    at org.apache.logging.log4j.core.LoggerContext.reconfigure(LoggerContext.java:582)
    at org.apache.logging.log4j.core.LoggerContext.start(LoggerContext.java:217)
    at org.apache.logging.log4j.core.impl.Log4jContextFactory.getContext(Log4jContextFactory.java:242)
    at org.apache.logging.log4j.core.impl.Log4jContextFactory.getContext(Log4jContextFactory.java:45)
    at org.apache.logging.log4j.LogManager.getContext(LogManager.java:174)
    at org.apache.logging.log4j.LogManager.getLogger(LogManager.java:618)
    at org.subquark.engine.LuaCrashRepro.main(LuaCrashRepro.java:7)

As far as I can see, the problem is rather simple:

• The log4j ScriptManager requests the parmeter "THREADING" from the LuaScriptEngine here: https://git-wip-us.apache.org/repos/asf?p=logging-log4j2.git;a=blob;f=log4j-core/src/main/java/org/apache/logging/log4j/core/script/ScriptManager.java;h=62b82c2902940c77d0eccab70ee0ec8d2b57b910;hb=3058278956c4b9474ef0da4e7aef46e484f9cc29#l62
• The LuaScriptEngine initializes the THREADING parameter as null in the constructor in line 72. http://luaj.cvs.sourceforge.net/viewvc/luaj/luaj-vm/src/jse/org/luaj/vm2/script/LuaScriptEngine.java?revision=1.20&view=markup#l72
• The LuaScriptEngineFactory implements "get" as get(foo).toString(), which fails if get(foo) returns null. http://luaj.cvs.sourceforge.net/viewvc/luaj/luaj-vm/src/jse/org/luaj/vm2/script/LuaScriptEngineFactory.java?view=markup#l92

I think the best fix here would be to use Objects.toString in getParameter, if don't need to support Java 7.

Regards,
Tetha

[Niket Arora]

we are facing the same issue. is there any resolution to this?