Load Log4j2 configuration file programmatically

Question

I want to load Log4j2 XML configuration file programmatically from my application.

Tried this:

ConfigurationSource source = new ConfigurationSource();
source.setLocation(logConfigurationFile);
Configurator.initialize(null, source);

and this:

ConfigurationSource source = new ConfigurationSource();
source.setLocation(logConfigurationFile);
ConfigurationFactory factory = (ConfigurationFactory) XMLConfigurationFactory.getInstance().getConfiguration(source);
ConfigurationFactory.setConfigurationFactory(factory);

But nothing works yet.

Answer 1

If you are using a Servlet 3.0 Web Application you can use the Log4jServletContextListener and do the following:

Write a custom LogContextListener which extends from Log4jServletContextListener, set it up in your web.xml and disable auto initialization:

<listener>
    <listener-class>com.example.LogContextListener</listener-class>
</listener>
<context-param>
    <param-name>isLog4jAutoInitializationDisabled</param-name>
    <param-value>true</param-value>
</context-param>

In your custom LogContextListener overwrite contextInitialized and set the config location

public void contextInitialized(ServletContextEvent event) { 
    /* Some logic to calculate where the config file is saved. For 
     * example you can read an environment variable.
     */
    String pathToConfigFile = ... + "/log4j2.xml";
    Configurator.initialize(null, pathToConfigFile);
    super.contextInitialized(event);
}

The advantage over configuring the location directly in the web.xml is that you can compute the path based on some additional information and access the log4j2.xml even if its outside of your classpath.

Answer 2

If you have a single main entry point, this code snippet might save you some trouble. The set property call must fire before any loggers are created. This approach works with files on the classpath.

public class TestProcess {
    static {
        System.setProperty("log4j.configurationFile", "log4j-alternate.xml");
    }

    private static final Logger log = LoggerFactory.getLogger(TestProcess.class);

}

Answer 3

Found the answer myself. Someone might find it useful.

ConfigurationSource source = new ConfigurationSource();
source.setLocation(logConfigurationFile);
source.setFile(new File(logConfigurationFile));
source.setInputStream(new FileInputStream(logConfigurationFile));
Configurator.initialize(null, source);

Answer 4

For the newest version of log4j, here is what should work for loading an external log4j2.xml:

String log4jConfigFile = System.getProperty("user.dir") + File.separator + "log4j2.xml";
ConfigurationSource source = new ConfigurationSource(new FileInputStream(log4jConfigFile));
Configurator.initialize(null, source);

Answer 5

final URL log4j = Resources.getResource("log4j2-test.xml");
LoggerContext.getContext(false)
  .start(new XmlConfiguration(new ConfigurationSource(
    Resources.asByteSource(log4j).openStream(),
    log4j)));

Answer 6

Below worked for me, Log4j2 with SLF4J wrapper:

Solution 1:

public class MyClass {

    static {
        try {
            InputStream inputStream = new FileInputStream("C:/path/to/log4j2.xml");
            ConfigurationSource source = new ConfigurationSource(inputStream);
            Configurator.initialize(null, source);
        } catch (Exception ex) {
            // Handle here
        }
    }

    private static final Logger LOGGER = LoggerFactory.getLogger(MyClass.class); // LogManager if not using SLF4J

    public void doSomething() {
        LOGGER.info(...)
    }

}

Solution 2:

static {
    File log4j2File = new File("C:/path/to/log4j2.xml");
    System.setProperty("log4j2.configurationFile", log4j2File.toURI().toString());
}

Need toURI() to follow File URI Scheme format, else it throws MalformedURLException.

Sources:

• Proper format for log4j2.xml RollingFile configuration
• https://github.com/jprante/elasticsearch-jdbc/issues/562
• https://www.codeproject.com/Questions/190269/MalformedURLException-unknown-protocol-c-How-to-ha
• https://coderanch.com/t/633544/open-source/java-net-MalformedURLException-initialize-log