7.1 Tomcat学习（日志记录器Logger）

日志记录器是一个组件，必须和某个servlet容器关联才能使用。

package org.apache.catalina;import java.beans.PropertyChangeListener;public interface Logger {    //日志记录器可以记录5种类型的日志，用int型整数表示等级，    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();//获取与日志记录器向关联的容器    public void setContainer(Container container);//设置与日志记录器向关联的容器    public String getInfo();    public int getVerbosity();//获取日志级别    public void setVerbosity(int verbosity);//设置日志级别    public void addPropertyChangeListener(PropertyChangeListener listener);

    //有5种记录日志的方式    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);}

Tomcat4种日志记录器的UML图：

LoggerBase是一个抽象类，实现了Logger接口除public void log(String message);以外的全部方法，因此，需要其子类实现抽象方法public abstract void log(String msg)。

SystemOutLogger、SystemErrorLogger、FileLogger3个类都由Tmocat提供。

1、SystemOutLogger类

package org.apache.catalina.logger;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);//将每条日志消息传递给System.out.println()，并输出    }}

2、SystemErrLogger

package org.apache.catalina.logger;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);//将日志信息输出到标准错误    }}

3、FileLogger类（代码太长就不贴出来了）
FileLogger继承LoggerBase类，并且实现Lifecycle接口

FileLogger类中几个比较重要的方法：

public void log(String msg) {        Timestamp ts = new Timestamp(System.currentTimeMillis());//获取当前系统时间，并把该时间作为时间戳保存到变量ts中，Timestamp是java.util.Date的廋包装        String tsString = ts.toString().substring(0, 19);        String tsDate = tsString.substring(0, 10);        if (!date.equals(tsDate)) {//首次执行程序时，date=""            synchronized (this) {                if (!date.equals(tsDate)) {                    close();                    date = tsDate;                    open();//在指定目录创建一个日志文件                }            }        }        // Log this message, timestamped if necessary        if (writer != null) {            if (timestamp) {                writer.println(tsString + " " + msg);//有时间戳，使用PrintWriter写入日志            } else {                writer.println(msg);//无时间戳，使用PrintWriter写入日志            }        }    }

private void open() {        File dir = new File(directory);        if (!dir.isAbsolute())            dir = new File(System.getProperty("catalina.base"), directory);        dir.mkdirs();        try {            String pathname = dir.getAbsolutePath() + File.separator +                prefix + date + suffix;            writer = new PrintWriter(new FileWriter(pathname, true), true);        } catch (IOException e) {            writer = null;        }    }

程序执行过程：

// ------ add logger --------    System.setProperty("catalina.base", System.getProperty("user.dir"));    FileLogger logger = new FileLogger();//新建一个FileLogger实例    logger.setPrefix("FileLog_");    logger.setSuffix(".txt");    logger.setTimestamp(true);    logger.setDirectory("WebRoot");    context.setLogger(logger);//并将这个实例和容器关联

public synchronized void start() throws LifecycleException {    log("starting Context");//容器启动时，调用log(String message) 方法，添加日志    if (started)      throw new LifecycleException("SimpleContext has already started");    lifecycle.fireLifecycleEvent(BEFORE_START_EVENT, null);    started = true;    try {      if ((loader != null) && (loader instanceof Lifecycle))        ((Lifecycle) loader).start();      Container children[] = findChildren();      for (int i = 0; i < children.length; i++) {        if (children[i] instanceof Lifecycle)          ((Lifecycle) children[i]).start();      }      if (pipeline instanceof Lifecycle)        ((Lifecycle) pipeline).start();      lifecycle.fireLifecycleEvent(START_EVENT, null);    }    catch (Exception e) {      e.printStackTrace();    }    lifecycle.fireLifecycleEvent(AFTER_START_EVENT, null);    log("Context started");  }

private void log(String message) {    Logger logger = this.getLogger();    if (logger!=null)      logger.log(message);//调用和容器关联的日志记录器的log（String message）方法，将日志写入指定文件中  }