使用可执行JAR时指定Log4j2配置文件

Question

I am having trouble specifying the Log4j2 config file location when using an executable JAR file. It works fine if I separate all the JARs, but when I try to combine them into one executable JAR file, for some reason the log4j2.xml file isn't picked up from the command line.

I've tried these two methods of specifying the location:

java -Djava.libary.path=..\bin -cp ..\config -jar MyApplication.jar

java -Djava.libary.path=..\bin -Dlog4j.configurationFile=..\config\log4j2.xml -jar MyApplication.jar

Neither of those are working. I've also tried adding the directory containing the config file to the classpath in the JAR's manifest file:

Manifest-Version: 1.0
Ant-Version: Apache Ant 1.9.2
Created-By: 1.7.0_21-b11 (Oracle Corporation)
Main-Class: com.abc.MyApplication
Class-Path: ../config/

I haven't had success with this method either. Any ideas what I might be doing wrong?

Thanks in advance for any help!

---

EDIT

Ah, I believe I mistook the problem. Originally, this was the error I was seeing in the command line output:

ERROR StatusLogger No log4j2 configuration file found. Using default configuration: logging only errors to the console.

But at some point while I was changing things, the error message changed without my realizing it to this:

ERROR StatusLogger Log4j2 could not find a logging implementation. Please add log4j-core to the classpath. Using SimpleLogger to log to the console...

So what I figured out was that even though the executable JAR I was building was including the log4j-core-2.1.jar and log4j-api-2.1.jar JARs inside of it and in the MANIFEST file's classpath, there was a problem. The way I wrote my ant file to combine the libraries into the single JAR I was creating was successfully copying over the directories and class files, but was not copying over the other types for some reason, which are also obviously necessary (eg Log4j-config.xsd, Log4j-events.dtd, etc.).

To fix this, I changed the way I was merging the JARs in my Ant build file to this:

<jar destfile="${dist}/${jarName}" basedir="${classes}" 
    excludes=".svn">

    <!-- Merge this JAR with all the JARs in the lib directory, so that
    we are only creating one distribution JAR that includes all the
    libraries that you need. -->
    <fileset dir="${classes}" includes="**/*.class" />
    <zipgroupfileset dir="${lib}" includes="**/*.jar" />

    <!-- Specify the manifest file of the JAR -->
    <manifest>
        <attribute name="Main-Class" value="com.abc.MyApplication"/>
        <attribute name="Class-Path" value=". ${manifest.classpath}"/>
    </manifest>
</jar>

And that fixed the issue and copied over all files from the JARs into my newly created JAR.

Once this issue was resolved, the second of the commands I posted above worked for specifying the location of the configuration file. (As noted by @rewolf below, the first command won't work because the classpath specified in the MANIFEST of the JAR overrides any classpath specified on the command line.

Thanks for your responses, they definitely helped me get on the right path toward figuring out my mistakes.

Answer 1

Something that isn't explained very well/obviously in the Java documentation is that if you're using an executable Jar, it will only use the Class-Path as specified in the Manifest file. It will not listen to the -cp or --classpath arguments.

-Dlog4j.configurationFile=directory/file.xml

should definitely work though. I'm assuming you're running on Windows given your slash direction. Are you sure you are running it from the correct relative directory?

Update

I just tried it in Windows with no problems. I used the following manifest:

Manifest-Version: 1.0
Built-By: andrew.flower
Build-Jdk: 1.7.0_67
Class-Path: lib/log4j-api-2.1.jar lib/log4j-core-2.1.jar
Created-By: Apache Maven 3.2.3
Main-Class: com.andrew_flower.test.Log4jTest
Archiver-Version: Plexus Archiver

The Log4j2 jars are located in a lib/ directory and the log4j2.xml is in the conf/ directory. I executed the following command, and it found the config successfully.

java -Dlog4j.configurationFile=conf\log4j2.xml -jar log4j2test1-1.0-SNAPSHOT.jar

Answer 2

I solved the problem of specifying the location of log4j2 configuration in a runnable Jar that I created from Eclipse by including this in my java code:

System.setProperty("log4j.configurationFile", "resources/log4j2.xml");

I have a package and so I needed to specify the path to my "resources" folder (in my "src" folder in Eclipse):

System.setProperty("log4j.configurationFile", "com/company/app/resources/log4j2.xml");

Notice I didn't include "src" in my path and I think it's the path in the "bin" folder that's required: ie in my case "com/company/app/resources/log4j2.xml"

My configuration file looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration> 

<appenders>

<Console name="Console" target="SYSTEM_OUT">
  <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss.SSS} %-5level - %msg%n"/>  
</Console>

<RollingFile 
        name="RollingFile" 
        fileName="${sys:logFilename}"
        filePattern="${sys:logFilename}-%d{yyyy-MM-dd}-%i.log"> 
  <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %-5level - %msg%n"/>      
  <Policies>
    <SizeBasedTriggeringPolicy size="1 MB"/>
  </Policies>  
  <DefaultRolloverStrategy max="10"/> 
</RollingFile>

</appenders> 


<loggers>     
 <root level="all">
  <appender-ref ref="Console"/>      
  <appender-ref ref="RollingFile"/> 
 </root>    
</loggers>

Also notice I dynamically assign the rolling log file path + name "${sys:logFilename}" by including this in my java code:

System.setProperty("logFilename", "logs/myApp.log");

In order to get these 2 dynamic System.setProperty assignments to work they need to execute before the "getLogger" statement and so my java code looks like:

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

public class MyTestLoggingClass {

 public static Logger logger = null;

 ...................
 setUpLogging();
 ...............

 public static void setUpLogging() {
    System.setProperty("log4j.configurationFile",  "com/company/app/resources/log4j2.xml");
    System.setProperty("logFilename", "logs/myApp.log");

    logger = LogManager.getLogger(Logger.class.getName());  
 }

}

Having "logger" declared at the start of my class (but without invoking "getLogger" before my 2 System.setProperty statements) enables me to reference "logger" in other methods. I am obliged to initialise it though and so I chose "null" but then later update it with the "getLogger" statement - given this I can't make it "final" (can only assign it once) but can make it static - a constant class variable.

nb the 2 log4j2 jars I included in the build path are:

1. log4j-api-2.6.2.jar

2. log4j-core-2.6.2.jar

Answer 3

For others who may have this issue...

1. Make sure your -Dlog4j.configurationFile options occur before your '-jar' not after. Might seem obvious, but saw that mistake once.
2. Try treating the file location as a url and see if that works. Ie escape spaces with %20 etc. Also use 'file:// path ', replace backslashes with forwardslashes.
3. Windows paths can be written as file://c:/path/to/log4j2.xml

Hence if you have a log4j2.xml in your program folder for your exampleApp in C:\\Program Files\\ExampleApp then...

java.exe -Dlog4j.configurationFile=file://c:/program%20files/exampleapp/log4j2.xml -jar exampleApp.jar ... 

...should work

Answer 4

I had this issue with version 2.8 of Log4j2. This was gone when the respective Log4j2 jars were replaced with version 2.6 of Log4j2.