How Tomcat Works（十）

本文接下来分析tomcat的日志记录器，日志记录器是用来记录消息的组件，在tomcat中，日志记录器需要与某个servlet容器相关连；在org.apache.catalina.logger包下，tomcat提供了几种不同类型的日志记录器。

tomcat中的日志记录器都必须实现org.apache.catalina.Logger接口

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);
}

通常，当传入的日志级别verbosity大于Logger被设置的级别时，message会被记录，否则被忽略

Logger接口共定义了五种日志级别，分别为FATAL ERROR WARNING INFORMATION DEBUG

Tomcat提供了三种类型的日志记录器，分别为SystemOutLogger、SystemErrLogger、FileLogger，在org.apache.catalina.logger包下，均继承自org.apache.catalina.logger.LoggerBase类

LoggerBase类实现了org.apache.catalina.Logger接口，在tomcat5中还实现了Lifecycle接口

LoggerBase类为抽象类，实现了Logger接口中除abstract void log(String msg)外的全部方法实现，所有的其他重载方法最终都会调用该方法（templet模式）,我们还可以调用setVerbosity()方法设置日志级别

具体日志类都比较简单，下面是SystemOutLogger类的实现

public class SystemOutLogger
    extends LoggerBase {
   
    protected static final String info =
        "org.apache.catalina.logger.SystemOutLogger/1.0";
   
    public void log(String msg) {

        System.out.println(msg);

    }
}

SystemErrLogger类

public class SystemErrLogger
    extends LoggerBase {
   
    protected static final String info =
        "org.apache.catalina.logger.SystemErrLogger/1.0";
   
    public void log(String msg) {

        System.err.println(msg);
    }
}

FileLogger类稍微复杂一点，将从servlet容器中接收到的消息写入到一个文件中（在tomcat4中，FileLogger类实现了Lifecycle接口）

public class FileLogger
    extends LoggerBase
    implements Lifecycle {
    protected LifecycleSupport lifecycle = new LifecycleSupport(this);
    private StringManager sm =
        StringManager.getManager(Constants.Package);

    private boolean started = false;

    private String suffix = ".log";

    private boolean timestamp = false;

    private PrintWriter writer = null;
    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);

        // 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);
            }
        }

    }

    private void close() {

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

    /**
     * Open the new log file for the date specified by <code>date</code>.
     */
    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;
        }

    }
  
    public void addLifecycleListener(LifecycleListener listener) {

        lifecycle.addLifecycleListener(listener);
    }

    public LifecycleListener[] findLifecycleListeners() {

        return lifecycle.findLifecycleListeners();
    }

    public void removeLifecycleListener(LifecycleListener listener) {

        lifecycle.removeLifecycleListener(listener);
    }

    public void start() throws LifecycleException {

        // Validate and update our current component state
        if (started)
            throw new LifecycleException
                (sm.getString("fileLogger.alreadyStarted"));
        lifecycle.fireLifecycleEvent(START_EVENT, null);
        started = true;
    }

    public void stop() throws LifecycleException {

        // Validate and update our current component state
        if (!started)
            throw new LifecycleException
                (sm.getString("fileLogger.notStarted"));
        lifecycle.fireLifecycleEvent(STOP_EVENT, null);
        started = false;
        close();
    }

}

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