How tomcat works（深入剖析tomcat）（7） Logger

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)

log(String msg)

protected int verbosity = ERROR;

可以调用

setVerbosity(int verbosity)

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);