log4j 설정 파일 위치를 명시적으로 설정하고 싶을 때..

package org.springframework.util;

import java.io.File;
import java.io.FileNotFoundException;
import java.net.URL;

import org.apache.log4j.LogManager;
import org.apache.log4j.PropertyConfigurator;
import org.apache.log4j.xml.DOMConfigurator;

/**
 * Convenience class that features simple methods for custom log4j configuration.
 *
 * <p>Only needed for non-default log4j initialization, for example with a custom
 * config location or a refresh interval. By default, log4j will simply read its
 * configuration from a "log4j.properties" or "log4j.xml" file in the root of
 * the classpath.
 *
 * <p>For web environments, the analogous Log4jWebConfigurer class can be found
 * in the web package, reading in its configuration from context-params in
 * <code>web.xml</code>. In a J2EE web application, log4j is usually set up
 * via Log4jConfigListener or Log4jConfigServlet, delegating to
 * Log4jWebConfigurer underneath.
 *
 * @author Juergen Hoeller
 * @since 13.03.2003
 * @see org.springframework.web.util.Log4jWebConfigurer
 * @see org.springframework.web.util.Log4jConfigListener
 * @see org.springframework.web.util.Log4jConfigServlet
 */

public abstract class Log4jConfigurer {

    /** Pseudo URL prefix for loading from the class path: "classpath:" */
    public static final String CLASSPATH_URL_PREFIX = "classpath:";

    /** Extension that indicates a log4j XML config file: ".xml" */
    public static final String XML_FILE_EXTENSION = ".xml";

    /**
     * Initialize log4j from the given file location, with no config file refreshing.
     * Assumes an XML file in case of a ".xml" file extension, and a properties file
     * otherwise.
     * @param location the location of the config file: either a "classpath:" location
     * (e.g. "classpath:myLog4j.properties"), an absolute file URL
     * (e.g. "file:C:/log4j.properties), or a plain absolute path in the file system
     * (e.g. "C:/log4j.properties")
     * @throws FileNotFoundException if the location specifies an invalid file path
     */
    public static void initLogging(String location) throws FileNotFoundException {
        String resolvedLocation = SystemPropertyUtils.resolvePlaceholders(location);
        URL url = ResourceUtils.getURL(resolvedLocation);
        if (resolvedLocation.toLowerCase().endsWith(XML_FILE_EXTENSION)) {
            DOMConfigurator.configure(url);
        }
        else {
            PropertyConfigurator.configure(url);
        }
    }

    /**
     * Initialize log4j from the given location, with the given refresh interval
     * for the config file. Assumes an XML file in case of a ".xml" file extension,
     * and a properties file otherwise.
     * <p>Log4j's watchdog thread will asynchronously check whether the timestamp
     * of the config file has changed, using the given interval between checks.
     * A refresh interval of 1000 milliseconds (one second), which allows to
     * do on-demand log level changes with immediate effect, is not unfeasible.
     * <p><b>WARNING:</b> Log4j's watchdog thread does not terminate until VM shutdown;
     * in particular, it does not terminate on LogManager shutdown. Therefore, it is
     * recommended to <i>not</i> use config file refreshing in a production J2EE
     * environment; the watchdog thread would not stop on application shutdown there.
     * @param location the location of the config file: either a "classpath:" location
     * (e.g. "classpath:myLog4j.properties"), an absolute file URL
     * (e.g. "file:C:/log4j.properties), or a plain absolute path in the file system
     * (e.g. "C:/log4j.properties")
     * @param refreshInterval interval between config file refresh checks, in milliseconds
     * @throws FileNotFoundException if the location specifies an invalid file path
     */
    public static void initLogging(String location, long refreshInterval) throws FileNotFoundException {
        String resolvedLocation = SystemPropertyUtils.resolvePlaceholders(location);
        File file = ResourceUtils.getFile(resolvedLocation);
        if (!file.exists()) {
            throw new FileNotFoundException("Log4j config file [" + resolvedLocation + "] not found");
        }
        if (resolvedLocation.toLowerCase().endsWith(XML_FILE_EXTENSION)) {
            DOMConfigurator.configureAndWatch(file.getAbsolutePath(), refreshInterval);
        }
        else {
            PropertyConfigurator.configureAndWatch(file.getAbsolutePath(), refreshInterval);
        }
    }

    /**
     * Shut down log4j, properly releasing all file locks.
     * <p>This isn't strictly necessary, but recommended for shutting down
     * log4j in a scenario where the host VM stays alive (for example, when
     * shutting down an application in a J2EE environment).
     */
    public static void shutdownLogging() {
        LogManager.shutdown();
    }

    /**
     * Set the specified system property to the current working directory.
     * <p>This can be used e.g. for test environments, for applications that leverage
     * Log4jWebConfigurer's "webAppRootKey" support in a web environment.
     * @param key system property key to use, as expected in Log4j configuration
     * (for example: "demo.root", used as "${demo.root}/WEB-INF/demo.log")
     * @see org.springframework.web.util.Log4jWebConfigurer
     */
    public static void setWorkingDirSystemProperty(String key) {
        System.setProperty(key, new File("").getAbsolutePath());
    }

}