修改DailyRollingFileAppender类及其父类源码，解决以日期作为日志文件名时，当天的文件没有日期后缀

题记------学习别人的精髓，并加以总结，消化吸收，这就是提高！！！　

　  DailyRollingFileAppender生成的文件是不带时间戳的，必须在某个时间点后，才对原来文件加上时间戳进行重命名，这样就有很大的问题，当天的日志，没有时间戳，而且如果在log4j.properties配置文件路径采用log4j.appender.dailyFile.File=E:/logs/log_或者log4j.appender.dailyFile.File=${webapp.root}/WEB-INF/logs/log_这种命名方式的，那么恭喜你，你生成的日志文件连后缀名都没有，想打开还得自己加后缀名，比如.log,.xml什么的总之很不方便。在此处说句题外话，就是解释下什么是${webapp.root}，这个说简单点就是你项目运行环境的绝对路径，一般在web.xml中如果我们不配置webAppRootKey默认的缺省值就是${webapp.root}，不过本人还是建议大家配置一下webAppRootKey，这样在同一服务器下运行多个项目就没冲突了。

　　log4j真的是一款很强大的日志开源框架，免费且好用，当然也会略有瑕疵，如果项目允许，我建议小伙伴们还是采用logback框架吧，这个框架不仅效率高，而且还规避了本文谈及的一系列问题，更关键的是如果你会用log4j那么学会使用logback简直是小kiss，废话不多说，这次主要是重新了log4j的两个类，FileAppender及其子类DailyRollingFileAppender，由于篇幅太多我就不一一赘述代码改动了，同志们如果想知道改了哪些，可以采用代码比对工具Beyond Compare 4，下载地址http://download.csdn.net/download/gongxun344/9982938，附apache-log4j-1.2.17源码地址http://download.csdn.net/download/gongxun344/9982916。话不多说，上本人修改后的源码：

 1、修改FileAppender类 

// Decompiled by DJ v3.12.12.100 Copyright 2015 Atanas Neshkov  Date: 2017-09-16 21:34:52
// Home Page:  http://www.neshkov.com/dj.html - Check often for new version!
// Decompiler options: packimports(3) 
// Source File Name:   FileAppender.java

package com.gongli.log;

import java.io.*;
import java.util.Date;
import java.text.SimpleDateFormat;

import org.apache.log4j.Layout;
import com.gongli.log.WriterAppender;
import org.apache.log4j.helpers.LogLog;
import org.apache.log4j.helpers.QuietWriter;

// Referenced classes of package org.apache.log4j:
//            WriterAppender, Layout

public class FileAppender extends WriterAppender
{
    private String datePattern = "yyyy-MM-dd";

    public FileAppender()
    {
        fileAppend = true;
        fileName = null;
        bufferedIO = false;
        bufferSize = 8192;
    }

    public FileAppender(Layout layout, String filename, boolean append, boolean bufferedIO, int bufferSize)
        throws IOException
    {
        fileAppend = true;
        fileName = null;
        this.bufferedIO = false;
        this.bufferSize = 8192;
        this.layout = layout;
        setFile(filename, append, bufferedIO, bufferSize);
    }

    public FileAppender(Layout layout, String filename, boolean append)
        throws IOException
    {
        fileAppend = true;
        fileName = null;
        bufferedIO = false;
        bufferSize = 8192;
        this.layout = layout;
        setFile(filename, append, false, bufferSize);
    }

    public FileAppender(Layout layout, String filename)
        throws IOException
    {
        this(layout, filename, true);
    }

    public void setFile(String file)
    {
        String val = file.trim();
        fileName = val;
    }

    public boolean getAppend()
    {
        return fileAppend;
    }

    public String getFile()
    {
        return fileName;
    }

    public void activateOptions()
    {
        SimpleDateFormat sdf = new SimpleDateFormat(datePattern);    
        Date now =  new Date();
        now.setTime(System.currentTimeMillis());
        //System.out.println(fileName.substring(fileName.lastIndexOf("_")+1,fileName.length())+"-+"); 
        fileName=fileName+sdf.format(now)+".log";
        //System.out.println(fileName+"-+");
        if(fileName != null)
        {
            try
            {
                setFile(fileName, fileAppend, bufferedIO, bufferSize);
            }
            catch(IOException e)
            {
                errorHandler.error("setFile(" + fileName + "," + fileAppend + ") call failed.", e, 4);
            }
        } else
        {
            LogLog.warn("File option not set for appender [" + name + "].");
            LogLog.warn("Are you using FileAppender instead of ConsoleAppender?");
        }
    }

    protected void closeFile()
    {
        if(qw != null)
            try
            {
                qw.close();
            }
            catch(IOException e)
            {
                if(e instanceof InterruptedIOException)
                    Thread.currentThread().interrupt();
                LogLog.error("Could not close " + qw, e);
            }
    }

    public boolean getBufferedIO()
    {
        return bufferedIO;
    }

    public int getBufferSize()
    {
        return bufferSize;
    }

    public void setAppend(boolean flag)
    {
        fileAppend = flag;
    }

    public void setBufferedIO(boolean bufferedIO)
    {
        this.bufferedIO = bufferedIO;
        if(bufferedIO)
            immediateFlush = false;
    }

    public void setBufferSize(int bufferSize)
    {
        this.bufferSize = bufferSize;
    }

    public synchronized void setFile(String fileName, boolean append, boolean bufferedIO, int bufferSize)
        throws IOException
    {
        System.out.println("--==--"+fileName);
        LogLog.debug("setFile called: " + fileName + ", " + append);
        if(bufferedIO)
            setImmediateFlush(false);
        reset();
        FileOutputStream ostream = null;
        try
        {
            ostream = new FileOutputStream(fileName, append);
        }
        catch(FileNotFoundException ex)
        {
            String parentName = (new File(fileName)).getParent();
            if(parentName != null)
            {
                File parentDir = new File(parentName);
                if(!parentDir.exists() && parentDir.mkdirs())
                    ostream = new FileOutputStream(fileName, append);
                else
                    throw ex;
            } else
            {
                throw ex;
            }
        }
        Writer fw = createWriter(ostream);
        if(bufferedIO)
            fw = new BufferedWriter(fw, bufferSize);
        setQWForFiles(fw);
        this.fileName = fileName;
        fileAppend = append;
        this.bufferedIO = bufferedIO;
        this.bufferSize = bufferSize;
        writeHeader();
        LogLog.debug("setFile ended");
    }

    protected void setQWForFiles(Writer writer)
    {
        qw = new QuietWriter(writer, errorHandler);
    }

    protected void reset()
    {
        closeFile();
        fileName = null;
        super.reset();
    }

    protected boolean fileAppend;
    protected String fileName;
    protected boolean bufferedIO;
    protected int bufferSize;
}

 2、修改DailyRollingFileAppender类 

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */



package com.gongli.log;

import java.io.IOException;
import java.io.File;
import java.io.InterruptedIOException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.Calendar;
import java.util.TimeZone;
import java.util.Locale;

import org.apache.log4j.Layout;
import org.apache.log4j.helpers.LogLog;
import org.apache.log4j.spi.LoggingEvent;

/**
   DailyRollingFileAppender extends {@link FileAppender} so that the
   underlying file is rolled over at a user chosen frequency.
   
   DailyRollingFileAppender has been observed to exhibit 
   synchronization issues and data loss.  The log4j extras
   companion includes alternatives which should be considered
   for new deployments and which are discussed in the documentation
   for org.apache.log4j.rolling.RollingFileAppender.

   <p>The rolling schedule is specified by the <b>DatePattern</b>
   option. This pattern should follow the {@link SimpleDateFormat}
   conventions. In particular, you <em>must</em> escape literal text
   within a pair of single quotes. A formatted version of the date
   pattern is used as the suffix for the rolled file name.

   <p>For example, if the <b>File</b> option is set to
   <code>/foo/bar.log</code> and the <b>DatePattern</b> set to
   <code>'.'yyyy-MM-dd</code>, on 2001-02-16 at midnight, the logging
   file <code>/foo/bar.log</code> will be copied to
   <code>/foo/bar.log.2001-02-16</code> and logging for 2001-02-17
   will continue in <code>/foo/bar.log</code> until it rolls over
   the next day.

   <p>Is is possible to specify monthly, weekly, half-daily, daily,
   hourly, or minutely rollover schedules.

   <p><table border="1" cellpadding="2">
   <tr>
   <th>DatePattern</th>
   <th>Rollover schedule</th>
   <th>Example</th>

   <tr>
   <td><code>'.'yyyy-MM</code>
   <td>Rollover at the beginning of each month</td>

   <td>At midnight of May 31st, 2002 <code>/foo/bar.log</code> will be
   copied to <code>/foo/bar.log.2002-05</code>. Logging for the month
   of June will be output to <code>/foo/bar.log</code> until it is
   also rolled over the next month.

   <tr>
   <td><code>'.'yyyy-ww</code>

   <td>Rollover at the first day of each week. The first day of the
   week depends on the locale.</td>

   <td>Assuming the first day of the week is Sunday, on Saturday
   midnight, June 9th 2002, the file <i>/foo/bar.log</i> will be
   copied to <i>/foo/bar.log.2002-23</i>.  Logging for the 24th week
   of 2002 will be output to <code>/foo/bar.log</code> until it is
   rolled over the next week.

   <tr>
   <td><code>'.'yyyy-MM-dd</code>

   <td>Rollover at midnight each day.</td>

   <td>At midnight, on March 8th, 2002, <code>/foo/bar.log</code> will
   be copied to <code>/foo/bar.log.2002-03-08</code>. Logging for the
   9th day of March will be output to <code>/foo/bar.log</code> until
   it is rolled over the next day.

   <tr>
   <td><code>'.'yyyy-MM-dd-a</code>

   <td>Rollover at midnight and midday of each day.</td>

   <td>At noon, on March 9th, 2002, <code>/foo/bar.log</code> will be
   copied to <code>/foo/bar.log.2002-03-09-AM</code>. Logging for the
   afternoon of the 9th will be output to <code>/foo/bar.log</code>
   until it is rolled over at midnight.

   <tr>
   <td><code>'.'yyyy-MM-dd-HH</code>

   <td>Rollover at the top of every hour.</td>

   <td>At approximately 11:00.000 o'clock on March 9th, 2002,
   <code>/foo/bar.log</code> will be copied to
   <code>/foo/bar.log.2002-03-09-10</code>. Logging for the 11th hour
   of the 9th of March will be output to <code>/foo/bar.log</code>
   until it is rolled over at the beginning of the next hour.


   <tr>
   <td><code>'.'yyyy-MM-dd-HH-mm</code>

   <td>Rollover at the beginning of every minute.</td>

   <td>At approximately 11:23,000, on March 9th, 2001,
   <code>/foo/bar.log</code> will be copied to
   <code>/foo/bar.log.2001-03-09-10-22</code>. Logging for the minute
   of 11:23 (9th of March) will be output to
   <code>/foo/bar.log</code> until it is rolled over the next minute.

   </table>

   <p>Do not use the colon ":" character in anywhere in the
   <b>DatePattern</b> option. The text before the colon is interpeted
   as the protocol specificaion of a URL which is probably not what
   you want.


   @author Eirik Lygre
   @author Ceki G&uuml;lc&uuml;*/
public class DailyRollingFileAppender extends FileAppender {


  // The code assumes that the following constants are in a increasing
  // sequence.
  static final int TOP_OF_TROUBLE=-1;
  static final int TOP_OF_MINUTE = 0;
  static final int TOP_OF_HOUR   = 1;
  static final int HALF_DAY      = 2;
  static final int TOP_OF_DAY    = 3;
  static final int TOP_OF_WEEK   = 4;
  static final int TOP_OF_MONTH  = 5;


  /**
     The date pattern. By default, the pattern is set to
     "'.'yyyy-MM-dd" meaning daily rollover.
   */
  private String datePattern = "'.'yyyy-MM-dd";

  /**
     The log file will be renamed to the value of the
     scheduledFilename variable when the next interval is entered. For
     example, if the rollover period is one hour, the log file will be
     renamed to the value of "scheduledFilename" at the beginning of
     the next hour. 

     The precise time when a rollover occurs depends on logging
     activity. 
  */
  private String scheduledFilename;

  /**
     The next time we estimate a rollover should occur. */
  private long nextCheck = System.currentTimeMillis () - 1;

  Date now = new Date();

  SimpleDateFormat sdf;

  RollingCalendar rc = new RollingCalendar();

  int checkPeriod = TOP_OF_TROUBLE;

  // The gmtTimeZone is used only in computeCheckPeriod() method.
  static final TimeZone gmtTimeZone = TimeZone.getTimeZone("GMT");


  /**
     The default constructor does nothing. */
  public DailyRollingFileAppender() {
  }

  /**
    Instantiate a <code>DailyRollingFileAppender</code> and open the
    file designated by <code>filename</code>. The opened filename will
    become the ouput destination for this appender.

    */
  public DailyRollingFileAppender (Layout layout, String filename,
                   String datePattern) throws IOException {
    super(layout, filename, true);
    this.datePattern = datePattern;
    activateOptions();
  }

  /**
     The <b>DatePattern</b> takes a string in the same format as
     expected by {@link SimpleDateFormat}. This options determines the
     rollover schedule.
   */
  public void setDatePattern(String pattern) {
    datePattern = pattern;
  }

  /** Returns the value of the <b>DatePattern</b> option. */
  public String getDatePattern() {
    return datePattern;
  }

  public void activateOptions() {
    super.activateOptions();
    if(datePattern != null && fileName != null) {
      now.setTime(System.currentTimeMillis());
      sdf = new SimpleDateFormat(datePattern);
      int type = computeCheckPeriod();
      printPeriodicity(type);
      rc.setType(type);
      File file = new File(fileName);
      //System.out.println(fileName+"+++___===");
     // if("".equals(fileName.substring(fileName.lastIndexOf("_")+1,fileName.length()))){
          scheduledFilename = fileName+sdf.format(new Date(file.lastModified()));
      //}else{
         //scheduledFilename = fileName;
      //}
      //System.out.println(scheduledFilename+"+++___===");
    } else {
      LogLog.error("Either File or DatePattern options are not set for appender ["
           +name+"].");
    }
  }

  void printPeriodicity(int type) {
    switch(type) {
    case TOP_OF_MINUTE:
      LogLog.debug("Appender ["+name+"] to be rolled every minute.");
      break;
    case TOP_OF_HOUR:
      LogLog.debug("Appender ["+name
           +"] to be rolled on top of every hour.");
      break;
    case HALF_DAY:
      LogLog.debug("Appender ["+name
           +"] to be rolled at midday and midnight.");
      break;
    case TOP_OF_DAY:
      LogLog.debug("Appender ["+name
           +"] to be rolled at midnight.");
      break;
    case TOP_OF_WEEK:
      LogLog.debug("Appender ["+name
           +"] to be rolled at start of week.");
      break;
    case TOP_OF_MONTH:
      LogLog.debug("Appender ["+name
           +"] to be rolled at start of every month.");
      break;
    default:
      LogLog.warn("Unknown periodicity for appender ["+name+"].");
    }
  }


  // This method computes the roll over period by looping over the
  // periods, starting with the shortest, and stopping when the r0 is
  // different from from r1, where r0 is the epoch formatted according
  // the datePattern (supplied by the user) and r1 is the
  // epoch+nextMillis(i) formatted according to datePattern. All date
  // formatting is done in GMT and not local format because the test
  // logic is based on comparisons relative to 1970-01-01 00:00:00
  // GMT (the epoch).

  int computeCheckPeriod() {
    RollingCalendar rollingCalendar = new RollingCalendar(gmtTimeZone, Locale.getDefault());
    // set sate to 1970-01-01 00:00:00 GMT
    Date epoch = new Date(0);
    if(datePattern != null) {
      for(int i = TOP_OF_MINUTE; i <= TOP_OF_MONTH; i++) {
    SimpleDateFormat simpleDateFormat = new SimpleDateFormat(datePattern);
    simpleDateFormat.setTimeZone(gmtTimeZone); // do all date formatting in GMT
    String r0 = simpleDateFormat.format(epoch);
    rollingCalendar.setType(i);
    Date next = new Date(rollingCalendar.getNextCheckMillis(epoch));
    String r1 =  simpleDateFormat.format(next);
    //System.out.println("Type = "+i+", r0 = "+r0+", r1 = "+r1);
    if(r0 != null && r1 != null && !r0.equals(r1)) {
      return i;
    }
      }
    }
    return TOP_OF_TROUBLE; // Deliberately head for trouble...
  }

  /**
     Rollover the current file to a new file.这个第二天生成前一天以日期命名的方法没用了
  */
//  void rollOver() throws IOException {
//
//    /* Compute filename, but only if datePattern is specified */
//    if (datePattern == null) {
//      errorHandler.error("Missing DatePattern option in rollOver().");
//      return;
//    }
//
//    String datedFilename = fileName+sdf.format(now);
//    // It is too early to roll over because we are still within the
//    // bounds of the current interval. Rollover will occur once the
//    // next interval is reached.
//    if (scheduledFilename.equals(datedFilename)) {
//      return;
//    }
//
//    // close current file, and rename it to datedFilename
//    this.closeFile();
//
//    File target  = new File(scheduledFilename);
//    if (target.exists()) {
//      target.delete();
//    }
//
//    File file = new File(fileName);
//    boolean result = file.renameTo(target);
//    if(result) {
//      LogLog.debug(fileName +" -> "+ scheduledFilename);
//    } else {
//      LogLog.error("Failed to rename ["+fileName+"] to ["+scheduledFilename+"].");
//    }
//
//    try {
//      // This will also close the file. This is OK since multiple
//      // close operations are safe.
//      this.setFile(fileName, true, this.bufferedIO, this.bufferSize);
//    }
//    catch(IOException e) {
//      errorHandler.error("setFile("+fileName+", true) call failed.");
//    }
//    scheduledFilename = datedFilename;
//  }

  /**
   * This method differentiates DailyRollingFileAppender from its
   * super class.
   *
   * <p>Before actually logging, this method will check whether it is
   * time to do a rollover. If it is, it will schedule the next
   * rollover time and then rollover.
   * */
//  protected void subAppend(LoggingEvent event) {
//    long n = System.currentTimeMillis();
//    if (n >= nextCheck) {
//      now.setTime(n);
//      nextCheck = rc.getNextCheckMillis(now);
//      try {
//    rollOver();
//      }
//      catch(IOException ioe) {
//          if (ioe instanceof InterruptedIOException) {
//              Thread.currentThread().interrupt();
//          }
//          LogLog.error("rollOver() failed.", ioe);
//      }
//    }
//    super.subAppend(event);
//   }
}

/**
 *  RollingCalendar is a helper class to DailyRollingFileAppender.
 *  Given a periodicity type and the current time, it computes the
 *  start of the next interval.  
 * */
class RollingCalendar extends GregorianCalendar {
  private static final long serialVersionUID = -3560331770601814177L;

  int type = DailyRollingFileAppender.TOP_OF_TROUBLE;

  RollingCalendar() {
    super();
  }  

  RollingCalendar(TimeZone tz, Locale locale) {
    super(tz, locale);
  }  

  void setType(int type) {
    this.type = type;
  }

  public long getNextCheckMillis(Date now) {
    return getNextCheckDate(now).getTime();
  }

  public Date getNextCheckDate(Date now) {
    this.setTime(now);

    switch(type) {
    case DailyRollingFileAppender.TOP_OF_MINUTE:
    this.set(Calendar.SECOND, 0);
    this.set(Calendar.MILLISECOND, 0);
    this.add(Calendar.MINUTE, 1);
    break;
    case DailyRollingFileAppender.TOP_OF_HOUR:
    this.set(Calendar.MINUTE, 0);
    this.set(Calendar.SECOND, 0);
    this.set(Calendar.MILLISECOND, 0);
    this.add(Calendar.HOUR_OF_DAY, 1);
    break;
    case DailyRollingFileAppender.HALF_DAY:
    this.set(Calendar.MINUTE, 0);
    this.set(Calendar.SECOND, 0);
    this.set(Calendar.MILLISECOND, 0);
    int hour = get(Calendar.HOUR_OF_DAY);
    if(hour < 12) {
      this.set(Calendar.HOUR_OF_DAY, 12);
    } else {
      this.set(Calendar.HOUR_OF_DAY, 0);
      this.add(Calendar.DAY_OF_MONTH, 1);
    }
    break;
    case DailyRollingFileAppender.TOP_OF_DAY:
    this.set(Calendar.HOUR_OF_DAY, 0);
    this.set(Calendar.MINUTE, 0);
    this.set(Calendar.SECOND, 0);
    this.set(Calendar.MILLISECOND, 0);
    this.add(Calendar.DATE, 1);
    break;
    case DailyRollingFileAppender.TOP_OF_WEEK:
    this.set(Calendar.DAY_OF_WEEK, getFirstDayOfWeek());
    this.set(Calendar.HOUR_OF_DAY, 0);
    this.set(Calendar.MINUTE, 0);
    this.set(Calendar.SECOND, 0);
    this.set(Calendar.MILLISECOND, 0);
    this.add(Calendar.WEEK_OF_YEAR, 1);
    break;
    case DailyRollingFileAppender.TOP_OF_MONTH:
    this.set(Calendar.DATE, 1);
    this.set(Calendar.HOUR_OF_DAY, 0);
    this.set(Calendar.MINUTE, 0);
    this.set(Calendar.SECOND, 0);
    this.set(Calendar.MILLISECOND, 0);
    this.add(Calendar.MONTH, 1);
    break;
    default:
    throw new IllegalStateException("Unknown periodicity type.");
    }
    return getTime();
  }
}

 3、log4j.properties配置

#the destination is file
log4j.appender.dailyFile=com.gongli.log.DailyRollingFileAppender
log4j.appender.dailyFile.File=E:/logs/log_
#log4j.appender.dailyFile.DatePattern=yyyy-MM-dd'.log'这个千万别配置了，我在源码里面修改过，生成日志时时间戳会自动附加上的
log4j.appender.dailyFile.layout=org.apache.log4j.PatternLayout
log4j.appender.dailyFile.layout.ConversionPattern=%d{HH:mm:ss} %5p%6.6r - %m%n