Can I skip/omit a log4j2 configurationFile that doesn't exist to fall back to an existing one?-CodePudding

I am running log4j2 logging in a java application with not the most flexibility in setup. We have an existing log4j2.xml configuration file in the classpath of our application that exists within an executable jar. I can modify the jar but not what calls it or is outside of it (I don't control the environment). I would like to add an optional overriding log4j2 configuration file outside of the jar. When it exists it overrides log4j2.xml, when it doesn't log4j2.xml is used. So I added this property to a log4j2.component.properties file:

log4j.configurationFile=../conf/log4j2-override.xml

When I create this optional file it works perfectly. When I don't create this file, log4j2 prints an error that the file cannot be found and then fails to fallback to the existing log4j2.xml file in the classpath. It doesn't seem to matter if I add the classpath-specific file to the configurationFile property. The configuration file is certainly available because if I remove the property completely it uses the configuration from the jar's classpath.

It's seems log4j2 has an error looking for the file and stops the automatic configuration sequence instead of continuing. Is there anyway for me to optionally override the default configuration xml file without requiring it be present outside the jar if I choose not to? I am hoping to specify this from within the jar file instead of requiring the way in which the jar is called to be changed based on the files existence.

CodePudding user response：

The log4j.configurationFile property allows you to specify a comma-separated list of configuration sources, which will be merged using a merge strategy (see DefaultMergeStrategy for the default rules). In your case you can use:

log4j.configurationFile=classpath:log4j2.xml,../conf/log4j2-override.cml

Missing files will be ignored and a warning will be sent to the status logger.

Log4j 2.13.x is affected by bug LOG4J2-2901, which stops the configuration process if a file is missing. Therefore make sure to use the latest version.

CodePudding user response：

Piotr's answer solved the immediate reason why the automatic configuration sequence wasn't working, but it still printed warning messages that didn't work for my use case. So here's an alternative approach that handles the constraints I have around environment (limiting modification to the jar file itself and no console output).

Basically just conditionally set the logger config file within the code itself. I have an application.properties file that unfortunately is not loaded into spring config so I really have to do this manually. You may be able to conditionally specify the log4j.configurationFile property from within a standard external spring application.properties file and not even use this code.

import java.io.File;
import org.apache.logging.log4j.core.LoggerContext;

Properties props = new EncryptableProperties(encryptor);

if (props.getProperty("log4j.configurationFile") != null) {
    LoggerContext loggerContext = (org.apache.logging.log4j.core.LoggerContext) LogManager.getContext(false);
    File file = new File(props.getProperty("log4j.configurationFile"));
    loggerContext.setConfigLocation(file.toURI());
}