How tomcat works（深入剖析tomcat） Logger

Posted 2020-12-21 danzz

How tomcat works （7）日志记录器

总体概述

顾名思义，这一章将的是tomcat的日志记录器组件，比较简单，tomcat提供了几种类型不同的日志记录器，但是所有的日志记录器都需要实现Logger接口，Logger的定义如下

Logger

public interface Logger {
	//日志级别
    public static final int FATAL = Integer.MIN_VALUE;

    public static final int ERROR = 1;

    public static final int WARNING = 2;

    public static final int INFORMATION = 3;

    public static final int DEBUG = 4;

    public Container getContainer();

    //与container绑定
    public void setContainer(Container container);

    public String getInfo();

    public int getVerbosity();

    //设置日志级别
    public void setVerbosity(int verbosity);

    public void addPropertyChangeListener(PropertyChangeListener listener);
	
    //重载了log方法，不同的logger实现实现了不同的log方法
    public void log(String message);

    public void log(Exception exception, String msg);

    public void log(String message, Throwable throwable);
	
    //这两个log方法都接收一个verbosity参数，如果该参数的级别数字比该日志记录器的级别数字小，才会记录
    //该日志，好比说DEBUG级别的日志记录器可以记录所有级别的日志
    public void log(String message, int verbosity);

    public void log(String message, Throwable throwable, int verbosity);

    public void removePropertyChangeListener(PropertyChangeListener listener);


}

tomcat提供了三种具体实现，FileLogger、SystemErrLogger、SystemOutLogger，这三者与Logger的UML图如下：

LoggerBase为抽象类，它实现了除了log(String msg)之外的所有方法，而具体的实现类则根据自己的特点实现了不同的log(String msg)方法，此外LoggerBase的默认日志级别是ERROR

protected int verbosity = ERROR;

可以调用setVerbosity(int verbosity)来设置

下面来看，三个不同的log方法的实现

SystemOutLogger类

public void log(String msg) {

        System.out.println(msg);

    }

SystemErrLogger类

public void log(String msg) {

        System.err.println(msg);

}

FileLogger类

public void log(String msg) {

        // Construct the timestamp we will use, if requested
        Timestamp ts = new Timestamp(System.currentTimeMillis());
    	//ts.toString()返回的日期格式如下：yyyy-mm-dd hh：mm：ss.fffffffff
    	//fffffffff表示纳秒，substring(0,19)去除掉后面纳秒数
        String tsString = ts.toString().substring(0, 19);
    	//以天为单位
        String tsDate = tsString.substring(0, 10);

        // If the date has changed, switch log files
    	//如果day发生了变化，换一个文件重新记录
        if (!date.equals(tsDate)) {
            synchronized (this) {
                if (!date.equals(tsDate)) {
                    close();
                    date = tsDate;
                    open();
                }
            }
        }

        // Log this message, timestamped if necessary
        if (writer != null) {
            if (timestamp) {
                writer.println(tsString + " " + msg);
            } else {
                writer.println(msg);
            }
        }

}

private void close() {

        if (writer == null)
            return;
        writer.flush();
        writer.close();
        writer = null;
        date = "";

}

private void open() {

    // Create the directory if necessary
    File dir = new File(directory);
    if (!dir.isAbsolute())
        dir = new File(System.getProperty("catalina.base"), directory);
    dir.mkdirs();

    // Open the current log file
    try {
        String pathname = dir.getAbsolutePath() + File.separator +
            prefix + date + suffix;
        writer = new PrintWriter(new FileWriter(pathname, true), true);
    } catch (IOException e) {
        writer = null;
    }

}

应用程序

直接看看Bootstrap即可

// ------ add logger --------
System.setProperty("catalina.base", "D:\tomcat\HowTomcatWorks");
FileLogger logger = new FileLogger();
logger.setPrefix("FileLog_");
logger.setSuffix(".txt");
logger.setTimestamp(true);
logger.setDirectory("webroot");
context.setLogger(logger);