how tomcat works讀書筆記 七 日志記錄器

大家可以松一口氣了,這個元件比較簡單,這一節和前面幾節想比,也簡單的多。

Logger接口

Tomcat中的日志記錄器都必須實作org.apache.catalina.Logger接口。

package org.apache.catalina;

import java.beans.PropertyChangeListener;

public interface Logger {
    
    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();
    public void setContainer(Container container);
    public String getInfo();
    public int getVerbosity();
    public void setVerbosity(int verbosity);
    public void addPropertyChangeListener(PropertyChangeListener listener);

    public void log(String message);
    public void log(Exception exception, String msg);
    public void log(String message, Throwable throwable);
    public void log(String message, int verbosity);
    public void log(String message, Throwable throwable, int verbosity);
    public void removePropertyChangeListener(PropertyChangeListener listener);
}      

Logger定義了五種日志記錄基本,當我們在調用log(String message, int verbosity)方法記錄日志的時候,隻有傳進來的verbosity小于等于系統的預設值才會記錄。話說大家知道Integer.MIN_VALUE等于多少嗎?大概負的21億左右吧。setVerbosity與getVerbosity是幹什麼的還需要我說麼?

Tomcat的日志記錄器

LoggerBase類(抽象類)

它實作了Logger接口中除log(String message)方法外的其餘方法;

在類中預設了日志記錄級别為

protected int verbosity = ERROR;      

但是我們可以通過setVerbosity(int verbosity)來重新設定記錄級别;

看看定義的接受日志級别的兩個log方法

public void log(String message, int verbosity) {
    if (this.verbosity >= verbosity)
        log(message);
}
public void log(String message, Throwable throwable, int verbosity) {
    if (this.verbosity >= verbosity)
        log(message, throwable);
}      

SystemOutLogger類

看名字就知道,資訊最後輸出到控制台。

SysteErrLogger類

看名字就知道,它是錯誤輸出,資訊仍在控制台,不過是紅色的。

FileLogger類

看名字就知道,它是吧資訊輸出的檔案裡。

不過具體的來說,裡面還是有點說頭的,慢慢來。

首先FileLogger還實作了Lifecycle接口,是以它可以像其他元件一樣被父元件所啟動。

在本節中FileLogger的start與stop方法其實隻是改變了布爾值started而已,沒有做其他的,另一方面,FileLogger的start與stop方法也并沒有被調用!

現在我們就看看怎麼給檔案裡寫資訊。

public void log(String msg) {

        // Construct the timestamp we will use, if requested
        Timestamp ts = new Timestamp(System.currentTimeMillis());
        String tsString = ts.toString().substring(0, 19);
        String tsDate = tsString.substring(0, 10);
        System.out.println("tsString   "+tsString); //tsString   2014-10-20 15:25:27
        System.out.println("ts   "+ts);            //ts   2014-10-20 15:25:27.406
        System.out.println("tsDate   "+tsDate);        //tsDate   2014-10-20

        // If the date has changed, switch log files
        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);
            }
        }
    }      

File預設是每一天一個新的檔案,檔案内格式就是日期+具體資訊(如果timestamp為true的話);

那close(),open()方法和writer屬性又是什麼呢?

private void open() {

        // Create the directory if necessary
        File dir = new File(directory);
        if (!dir.isAbsolute())
            dir = new File(System.getProperty("catalina.base"), directory);  //至于catalina.base是什麼 一會再說
        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;
        }

    }      

先檢查給定的目錄是否存在,如果不存在建立一個;接着根據字首,時間,字尾設定檔案名;根據檔案名填充writer對象。

private void close() {

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

FileLogger中的date代表的就是目前的時間,當然關閉後為空。

應用程式

Bootstrap類

...
    System.setProperty("catalina.base", System.getProperty("user.dir"));
    FileLogger logger = new FileLogger();
    logger.setPrefix("FileLog_");
    logger.setSuffix(".txt");
    logger.setTimestamp(true);
    logger.setDirectory("webroot");
    context.setLogger(logger);
....      

SimpleContext類

public synchronized void start() throws LifecycleException {
    log("starting Context");
    ........
    lifecycle.fireLifecycleEvent(AFTER_START_EVENT, null);
    log("Context started");
  }
private void log(String message) {
    Logger logger = this.getLogger();
    if (logger!=null)
      logger.log(message);
  }      

運作後在項目的webroot目錄下就可以看到FileLog_2014-10-20.txt檔案;

每次運作,在檔案中都會多出如下的内容

2014-10-20 14:34:21 HttpConnector Opening server socket on all host IP addresses

2014-10-20 14:34:22 HttpConnector[8080] Starting background thread

2014-10-20 14:34:22 HttpProcessor[8080][0] Starting background thread

2014-10-20 14:34:22 HttpProcessor[8080][1] Starting background thread

2014-10-20 14:34:22 HttpProcessor[8080][2] Starting background thread

2014-10-20 14:34:22 HttpProcessor[8080][3] Starting background thread

2014-10-20 14:34:22 HttpProcessor[8080][4] Starting background thread

2014-10-20 14:34:22 starting Context