日志相关杂

记录一个点：

很多时候，生产环境的log4j appender会设置bufferIO。但是系统意外挂了就会丢失部分日志。通过下面的语句flush log4j的日志：

LogManager.shutdown();

或者：

public static void flushAllLogs()
{
    try
    {
        Set<FileAppender> flushedFileAppenders = new HashSet<FileAppender>();
        Enumeration currentLoggers = LogManager.getLoggerRepository().getCurrentLoggers();
        while(currentLoggers.hasMoreElements())
        {
            Object nextLogger = currentLoggers.nextElement();
            if(nextLogger instanceof Logger)
            {
                Logger currentLogger = (Logger) nextLogger;
                Enumeration allAppenders = currentLogger.getAllAppenders();
                while(allAppenders.hasMoreElements())
                {
                    Object nextElement = allAppenders.nextElement();
                    if(nextElement instanceof FileAppender)
                    {
                        FileAppender fileAppender = (FileAppender) nextElement;
                        if(!flushedFileAppenders.contains(fileAppender) && !fileAppender.getImmediateFlush())
                        {
                            flushedFileAppenders.add(fileAppender);
                            //log.info("Appender "+fileAppender.getName()+" is not doing immediateFlush ");
                            fileAppender.setImmediateFlush(true);
                            currentLogger.info("FLUSH");
                            fileAppender.setImmediateFlush(false);
                        }
                        else
                        {
                            //log.info("fileAppender"+fileAppender.getName()+" is doing immediateFlush");
                        }
                    }
                }
            }
        }
    }
    catch(RuntimeException e)
    {
        log.error("Failed flushing logs",e);
    }
}

PS：可能要增加一个java代码的钩子， 在系统关闭的时候触发。　　

        //增加关闭钩子
        Runtime.getRuntime().addShutdownHook(new Thread(){
            public void run(){
                     //STH TODO
            }
        });

//移除关闭钩子
Runtime.getRuntime().removeShutdownHook(hook);

其实是“参考” stackoverflow的：

http://stackoverflow.com/questions/3060240/how-do-you-flush-a-buffered-log4j-fileappender