Tomcat在日志JAR包共享情况下按webapp打印日志方案

Tomcat的多webapp要分日志打印的话，简单方案是把日志JAR包各放各webapp的lib目录，分别使用。但是这样的话，日志JAR包加载多份，资源有所浪费。

最好是日志JAR包共用，用其它的隔离机制实现。

万幸，log4j提供了一个叫LoggerRepository的API，可以做这个事情。

实现类图：

本例以使用slf4j打印为例说明。

其中org.apache.log4j.Logger和org.apache.log4j.LoggerRepository为log4j包中类。

org.slf4j.Logger为slf4j-api中类。

Log4jLoggerAdapter用于将log4j的Logger转换为slf4j的Logger，此类在slf4j包中已有，但其访问权限有限，构造函数无修饰符。需要注意。

LogService代码示意：

public class LogService
{    private org.apache.log4j.Logger logger;    private LoggerRepository loggerRepository;    /**     * Instantiates a new Oss log service.     *     * @param properties the properties     */    public LogService(Properties properties)
    {
        initEvn();        new PropertyConfigurator().doConfigure(properties, loggerRepository);
    }    /**     * Instantiates a new Oss log service.     *     * @param logFile the log file     */    public LogService(URL logFile)
    {
        initEvn();        new PropertyConfigurator().doConfigure(logFile, loggerRepository);
    }    private void initEvn()
    {        logger = new RootLogger(Level.ALL);        loggerRepository = new Hierarchy(logger);
    }    /**     * Gets logger.     *     * @param name the name     * @return the logger     */    public org.apache.log4j.Logger getLogger(String name)
    {        return loggerRepository.getLogger(name);
    }
}

MyLogFactory示例：

public final class MyLogFactory
{    private static final MyLogFactory FACTORY = new MyLogFactory();    private final Map<String, Map<String, Logger>> instances = new ConcurrentHashMap<String, Map<String, Logger>>();    private final static Map<String, LogService> SERVICES = new ConcurrentHashMap<String, LogService>();    private static final Map<String, String> APP_NAMES = new ConcurrentHashMap<String, String>();    /**     * Do configuration.     *     * @param propertiesFile the properties file     */    public static void doConfiguration(File propertiesFile)
    {        if (propertiesFile == null)
        {            return;
        }
        String serviceName = getAppName();
        LogService logService = SERVICES.get(serviceName);        if (logService == null)
        {            try            {
                logService = new LogService(propertiesFile.toURI().toURL());                SERVICES.put(serviceName, logService);
            }            catch (MalformedURLException e)
            {
                logService = new LogService(new Properties());                SERVICES.put(serviceName, logService);
            }
        }
    }    /**     * Do configuration.     *     * @param properties the properties     */    public static void doConfiguration(Properties properties)
    {        if (properties == null)
        {            return;
        }
        String serviceName = getAppName();
        LogService logService = SERVICES.get(serviceName);        if (logService == null)
        {
            logService = new LogService(properties);            SERVICES.put(serviceName, logService);
        }
    }    /**     * Gets log.     *     * @param arg0 the arg 0     * @return the log     */    public static Logger getLog(Class<?> arg0)
    {        return FACTORY.getInstance(arg0.getName());
    }    /**     * Gets logger.     *     * @param arg0 the arg 0     * @return the logger     */    public static Logger getLogger(Class<?> arg0)
    {        return FACTORY.getInstance(arg0.getName());
    }    /**     * Gets log.     *     * @param name the name     * @return the log     */    public static Logger getLog(String name)
    {        return FACTORY.getInstance(name);
    }    /**     * Gets security log.     *     * @return the security log     */    public static Logger getSecurityLog()
    {        return FACTORY.getInstance("securityLogger");
    }    /**     * Gets instance.     *     * @param name the name     * @return the instance     */    public Logger getInstance(String name)
    {
        String serviceName = getAppName();
        Map<String, Logger> logMap = instances.get(serviceName);        if (logMap == null)
        {
            logMap = new ConcurrentHashMap<String, Logger>();            instances.put(serviceName, logMap);
            Logger log = getLogByName(serviceName, name);
            logMap.put(name, log);            return log;
        }
        Logger log = logMap.get(name);        if (log == null)
        {
            log = getLogByName(serviceName, name);
            logMap.put(name, log);            return log;
        }        return log;
    }    private Logger getLogByName(String serviceName, String name)
    {
        LogService logService = SERVICES.get(serviceName);        if (null == logService)
        {            try            {
                File appRootDir = new File(getAppRoot(), "etc");
                File logProperties = new File(appRootDir, "log4j/log4j-app.properties");
                logService = new LogService(logProperties.toURI().toURL());                SERVICES.put(serviceName, logService);
            }            catch (MalformedURLException e)
            {
                logService = new LogService(new Properties());                SERVICES.put(serviceName, logService);
            }
        }
        org.apache.log4j.Logger log4jLogger = logService.getLogger(name);        return new Log4jLoggerAdapter(log4jLogger);
    }    public static String getLogHome()
    {
        ......
    }    private static String getProcessName()
    {
        ......        return ......;
    }    /**     * get app name     * @return the app name     */    public static String getAppName()
    {
        String clazzPath = "main";
        URL resourceUrl = Thread.currentThread().getContextClassLoader().getResource("/");        if (null != resourceUrl)
        {
            clazzPath = resourceUrl.getPath();
        }        if (!APP_NAMES.containsKey(clazzPath))
        {
            String appName = clazzPath.split("-")[1].split("/")[0];            APP_NAMES.put(clazzPath, appName);
        }        return APP_NAMES.get(clazzPath);
    }    private static String getAppRoot()
    {        return ... ...
    }
}

使用示例：

使用前，调用MyLogFactory.doConfiguration()将log4j.properties配置文件配置到相应webapp的logRepository中。

然后在业务类中使用Logger log = MyLogFactory.getLogger(A.class)获取日志对象，就可以正常使用了。