配置间隔时间，定时打印日志
接到个需求，通过log4j定时打印日志，需求描述如下：需要能够定时打印日志，时间间隔可配。说到定时，首先想到了DailyRollingFileAppender类，各种定时，根据datePattern，这个可以参考类SimpleDateFormat类，常见的一些定时设置如下：
'.'yyyy-MM: 每月 '.'yyyy-ww: 每周 '.'yyyy-MM-dd: 每天 '.'yyyy-MM-dd-a: 每天两次 '.'yyyy-MM-dd-HH: 每小时 '.'yyyy-MM-dd-HH-mm: 每分钟
通过观察发现没有n分钟类似的日期格式，因此，在DailyRollingFileAppender类基础上进行自定义类的编写。过程如下：
1）拷贝DailyRollingFileAppender类源码并并改名MinuteRollingAppender，为了在log4j.xml中配置，增加配置项intervalTime并添加set、get方法；
private int intervalTime = 10;
2）由于DailyRollingFileAppender类使用了RollingCalendar类来计算下一次间隔时间，而需要传递参数intervalTime，因此修改RollingCalendar类为内部类；由于其方法就是根据datePattern来计算下一次rollOver动作的时间，此时不需要其他的时间模式，修改方法如下：
public Date getNextCheckDate(Date now) { this.setTime(now); this.set(Calendar.SECOND, 0); this.set(Calendar.MILLISECOND, 0); this.add(Calendar.MINUTE, intervalTime); return getTime(); }
3）按照分钟可配时，时间模式就需要禁用了，将其改为static final，响应的去掉其get、set方法和MinuteRollingAppender构造函数中的datePattern参数
private static String DATEPATTERN = "'.'yyyy-MM-dd-HH-mm'.log'";
同样，服务于多种datePattern的方法computeCheckPeriod()也可以删除； 至此改造就完成了，成品类如下：
package net.csdn.blog; import java.io.File; import java.io.IOException; import java.io.InterruptedIOException; import java.text.SimpleDateFormat; import java.util.Calendar; import java.util.Date; import java.util.GregorianCalendar; import org.apache.log4j.FileAppender; import org.apache.log4j.Layout; import org.apache.log4j.helpers.LogLog; import org.apache.log4j.spi.LoggingEvent; /** * 按分钟可配置定时appender * * @author coder_xia * */ public class MinuteRollingAppender extends FileAppender { /** * The date pattern. By default, the pattern is set to "'.'yyyy-MM-dd" * meaning daily rollover. */ private static String DATEPATTERN = "'.'yyyy-MM-dd-HH-mm'.log'"; /** * 间隔时间，单位：分钟 */ private int intervalTime = 10; /** * 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(); /** * The default constructor does nothing. */ public MinuteRollingAppender() { } /** * Instantiate a <code>MinuteRollingAppender</code> and open the file * designated by <code>filename</code>. The opened filename will become the * ouput destination for this appender. */ public MinuteRollingAppender(Layout layout, String filename) throws IOException { super(layout, filename, true); activateOptions(); } /** * @return the intervalTime */ public int getIntervalTime() { return intervalTime; } /** * @param intervalTime * the intervalTime to set */ public void setIntervalTime(int intervalTime) { this.intervalTime = intervalTime; } @Override public void activateOptions() { super.activateOptions(); if (fileName != null) { now.setTime(System.currentTimeMillis()); sdf = new SimpleDateFormat(DATEPATTERN); File file = new File(fileName); scheduledFilename = fileName + sdf.format(new Date(file.lastModified())); } else { LogLog .error("Either File or DatePattern options are not set for appender [" + name + "]."); } } /** * Rollover the current file to a new file. */ void rollOver() throws IOException { 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 MinuteRollingAppender 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. * */ @Override 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 MinuteRollingAppender. 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; RollingCalendar() { super(); } public long getNextCheckMillis(Date now) { return getNextCheckDate(now).getTime(); } public Date getNextCheckDate(Date now) { this.setTime(now); this.set(Calendar.SECOND, 0); this.set(Calendar.MILLISECOND, 0); this.add(Calendar.MINUTE, intervalTime); return getTime(); } } }
测试配置文件如下：
<"1.0" encoding="UTF-8"?> <!DOCTYPE log4j:configuration SYSTEM "log4j.dtd"> <log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/"> <appender name="myFile"> <param name="File" value="log4jTest.log" /> <param name="Append" value="true" /> <param name="intervalTime" value="2"/> <layout> <param name="ConversionPattern" value="%p %d (%c:%L)- %m%n" /> </layout> </appender> <root> <priority value="debug"/> <appender-ref ref="myFile"/> </root> </log4j:configuration>
关于定时实现，还可以采用java提供的Timer实现，也就免去了每次记录日志时计算并且比较时间，区别其实就是自己起个线程与调用rollOver方法，实现如下：
package net.csdn.blog; import java.io.File; import java.io.IOException; import java.text.SimpleDateFormat; import java.util.Date; import java.util.Timer; import java.util.TimerTask; import org.apache.log4j.FileAppender; import org.apache.log4j.Layout; import org.apache.log4j.helpers.LogLog; public class TimerTaskRollingAppender extends FileAppender { /** * The date pattern. By default, the pattern is set to "'.'yyyy-MM-dd" * meaning daily rollover. */ private static final String DATEPATTERN = "'.'yyyy-MM-dd-HH-mm'.log'"; /** * 间隔时间，单位：分钟 */ private int intervalTime = 10; SimpleDateFormat sdf = new SimpleDateFormat(DATEPATTERN); /** * The default constructor does nothing. */ public TimerTaskRollingAppender() { } /** * Instantiate a <code>TimerTaskRollingAppender</code> and open the file * designated by <code>filename</code>. The opened filename will become the * ouput destination for this appender. */ public TimerTaskRollingAppender(Layout layout, String filename) throws IOException { super(layout, filename, true); activateOptions(); } /** * @return the intervalTime */ public int getIntervalTime() { return intervalTime; } /** * @param intervalTime * the intervalTime to set */ public void setIntervalTime(int intervalTime) { this.intervalTime = intervalTime; } @Override public void activateOptions() { super.activateOptions(); Timer timer = new Timer(); timer.schedule(new LogTimerTask(), 1000, intervalTime * 60000); } class LogTimerTask extends TimerTask { @Override public void run() { String datedFilename = fileName + sdf.format(new Date()); closeFile(); File target = new File(datedFilename); if (target.exists()) target.delete(); File file = new File(fileName); boolean result = file.renameTo(target); if (result) LogLog.debug(fileName + " -> " + datedFilename); else LogLog.error("Failed to rename [" + fileName + "] to [" + datedFilename + "]."); try { setFile(fileName, true, bufferedIO, bufferSize); } catch (IOException e) { errorHandler.error("setFile(" + fileName + ", true) call failed."); } } } }
不过，以上实现，存在2个问题：
1）并发
并发问题可能发生的一个地方在run()中调用closeFile();后，正好subAppend()方法写日志，此刻文件已关闭，则会报以下错误：
java.io.IOException: Stream closed at sun.nio.cs.StreamEncoder.ensureOpen(Unknown Source) at sun.nio.cs.StreamEncoder.write(Unknown Source) at sun.nio.cs.StreamEncoder.write(Unknown Source) at java.io.OutputStreamWriter.write(Unknown Source) at java.io.Writer.write(Unknown Source) .............................. 解决方法比较简单，直接让整个run()方法为同步的，加上synchronized关键字即可；不过目前楼主没有解决如果真要写，而且写的速度够快的情况下可能丢失日志的情况；
2）性能
使用Timer实现比较简单，但是Timer里面的任务如果执行时间太长，会独占Timer对象，使得后面的任务无法几时的执行，解决方法也比较简单，采用线程池版定时器类ScheduledExecutorService，实现如下：
/** * */ package net.csdn.blog; import java.io.File; import java.io.IOException; import java.text.SimpleDateFormat; import java.util.Date; import java.util.concurrent.Executors; import java.util.concurrent.TimeUnit; import org.apache.log4j.FileAppender; import org.apache.log4j.Layout; import org.apache.log4j.helpers.LogLog; /** * @author coder_xia * <p> * 采用ScheduledExecutorService实现定时配置打印日志 * <p> * */ public class ScheduledExecutorServiceAppender extends FileAppender { /** * The date pattern. By default, the pattern is set to "'.'yyyy-MM-dd" * meaning daily rollover. */ private static final String DATEPATTERN = "'.'yyyy-MM-dd-HH-mm'.log'"; /** * 间隔时间，单位：分钟 */ private int intervalTime = 10; SimpleDateFormat sdf = new SimpleDateFormat(DATEPATTERN); /** * The default constructor does nothing. */ public ScheduledExecutorServiceAppender() { } /** * Instantiate a <code>ScheduledExecutorServiceAppender</code> and open the * file designated by <code>filename</code>. The opened filename will become * the ouput destination for this appender. */ public ScheduledExecutorServiceAppender(Layout layout, String filename) throws IOException { super(layout, filename, true); activateOptions(); } /** * @return the intervalTime */ public int getIntervalTime() { return intervalTime; } /** * @param intervalTime * the intervalTime to set */ public void setIntervalTime(int intervalTime) { this.intervalTime = intervalTime; } @Override public void activateOptions() { super.activateOptions(); Executors.newSingleThreadScheduledExecutor().scheduleAtFixedRate( new LogTimerTask(), 1, intervalTime * 60000, TimeUnit.MILLISECONDS); } class LogTimerTask implements Runnable { @Override public void run() { String datedFilename = fileName + sdf.format(new Date()); closeFile(); File target = new File(datedFilename); if (target.exists()) target.delete(); File file = new File(fileName); boolean result = file.renameTo(target); if (result) LogLog.debug(fileName + " -> " + datedFilename); else LogLog.error("Failed to rename [" + fileName + "] to [" + datedFilename + "]."); try { setFile(fileName, true, bufferedIO, bufferSize); } catch (IOException e) { errorHandler.error("setFile(" + fileName + ", true) call failed."); } } } }
关于定时的实现，差不多就到这里了，采用的都默认是10分钟产生一个新的日志文件，在配置时可以自行设置，不过存在的一个隐患，万一配置的人不知道时间间隔是分钟，如果以为是秒，配了个600，又开了debug，产生上G的日志文件，这肯定是个灾难，下面的改造就是结合RollingFileAppender的最大大小和最多备份文件个数可配，再次进行完善，下次继续描述改造过程。
添加模块名配置
在前面讲到了log4j定时打印的定制类实现，就不讲指定大小和指定备份文件个数了，从RollingFileAppender类copy代码到前面的定制类中添加即可，唯一需要解决的是并发问题，即文件关闭rename文件时，发生了记录日志事件时，会报output stream closed的错误。
现在有这样一种应用场景，而且经常有：
1.项目包含有多个不同的工程；
2.同一工程包含不同的模块。
对第一种情况，可以通过配置log4j<catogery=“Test”>，再在产生Logger时使用类似如下方式：
Logger logger=Logger.getLogger("Test");
对第二种情况，我们希望能够将不同模块打印到同一个日志文件中，不过希望能够在日志中打印出模块名以便出问题时定位问题，因此便有了本文需要的在Appender类中添加配置ModuleName，下面开始改造，与定时打印不同，我们采用RollingFileAppender类为基类进行改造。
首先，添加配置项moduleName，并增加get、set方法；
由于继承自RollingFileAppender，所以只需要在subAppend()中格式化LoggingEvent中的数据，添加formatInfo方法格式化数据，代码略；
最终的成品类如下：
package net.csdn.blog; import org.apache.log4j.Category; import org.apache.log4j.RollingFileAppender; import org.apache.log4j.spi.LoggingEvent; /** * @author coder_xia * */ public class ModuleAppender extends RollingFileAppender { private String moduleName; /** * @return the moduleName */ public String getModuleName() { return moduleName; } /** * @param moduleName * the moduleName to set */ public void setModuleName(String moduleName) { this.moduleName = moduleName; } /** * 格式化打印内容 * * @param event * event * @return msg */ private String formatInfo(LoggingEvent event) { StringBuilder sb = new StringBuilder(); if (moduleName != null) { sb.append(moduleName).append("|"); sb.append(event.getMessage()); } return sb.toString(); } @Override public void subAppend(LoggingEvent event) { String msg = formatInfo(event); super.subAppend(new LoggingEvent(Category.class.getName(), event .getLogger(), event.getLevel(), msg, null)); } }
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