log4j提供了标准的日志输出，简单配置即可记录日志（参考Spring Boot入门：使用AOP实现拦截器 8、日志记录），但使用默认Appender记录日志时，有时并不能满足我们的需求，这时我们可以自定义log4j日志输出格式。

下面我们实现按日期记录日志，日志达到指定大小后重命名保存为新文件。

首先新建GlobalRollingFileAppender继承RollingFileAppender

import org.apache.log4j.RollingFileAppender;import org.apache.log4j.helpers.CountingQuietWriter;import org.apache.log4j.helpers.LogLog;import org.apache.log4j.spi.LoggingEvent;import java.io.File;import java.io.IOException;import java.io.InterruptedIOException;import java.text.SimpleDateFormat;import java.util.Date;public class GlobalRollingFileAppender extends RollingFileAppender {    private long nextRollover = 0L;  private static SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMdd");  public void rollOver() {        if (qw != null) {            long size = ((CountingQuietWriter) qw).getCount();      LogLog.debug("rolling over count=" + size);      nextRollover = size + maxFileSize;    }        LogLog.debug("maxBackupIndex=" + maxBackupIndex);    boolean renameSucceeded = true;    if (maxBackupIndex > 0) {            File file;      File target;      for (int i = maxBackupIndex - 1; i >= 1 && renameSucceeded; i--) {                file = new File(genFileName(fileName, i));        if (file.exists()) {                    target = new File(genFileName(fileName, i + 1));          LogLog.debug("Renaming file " + file + " to " + target);          renameSucceeded = file.renameTo(target);        }            }            if (renameSucceeded) {                target = new File(genFileName(fileName, 1));        this.closeFile();        file = new File(fileName);        LogLog.debug("Renaming file " + file + " to " + target);        renameSucceeded = file.renameTo(target);        if (!renameSucceeded) {                    try {                        this.setFile(fileName, true, bufferedIO, bufferSize);          } catch (IOException e) {                        if (e instanceof InterruptedIOException) {                            Thread.currentThread().interrupt();            }                        LogLog.error("setFile(" + fileName + ", true) call failed.", e);          }                }            }        }        if (renameSucceeded) {            try {                this.setFile(fileName, false, bufferedIO, bufferSize);        nextRollover = 0L;      } catch (IOException e) {                if (e instanceof InterruptedIOException) {                    Thread.currentThread().interrupt();        }                LogLog.error("setFile(" + fileName + ", false) call failed.", e);      }        }    }    private String genFileName(String name, int index) {        String fileName;    if (index > 0) {            String num = index < 10 ? "0" + index : String.valueOf(index);      fileName = name.replace(".log", "") + "_" + num + ".log";    } else {            fileName = name;    }        return fileName;  }    protected void subAppend(LoggingEvent event) {        boolean flag = false;    String fileNameNow = fileName.substring(fileName.lastIndexOf("/"));    String fileNameDate = simpleDateFormat.format(new Date());    if (!fileNameNow.contains(fileNameDate)) {            flag = true;      int tag = fileNameNow.indexOf("_");      fileName = fileName.replace(fileNameNow.substring(tag + 1, tag + 9), fileNameDate);    }        if (fileName != null && qw != null) {            long size = ((CountingQuietWriter) qw).getCount();      if (flag) {                size = 0L;      }            if ((size >= maxFileSize && size >= nextRollover) || flag) {                rollOver();      }        }        super.subAppend(event);  }    public void setFile(String file) {        fileName = file.trim().replace(".log", "") +                "_" + simpleDateFormat.format(new Date()) + ".log";  }}

然后我们将log4j.properties日志输出appender设为GlobalRollingFileAppender ，即log4j.appender.logInfo=cn.wbnull.springbootdemo.boot.GlobalRollingFileAppender

log4j.rootLogger=debug,Console,logInfo,logError,logDebuglog4j.category.org.springframework=debug,Console,logInfo,logError,logDebug##输出到控制台log4j.appender.Console=org.apache.log4j.ConsoleAppenderlog4j.appender.Console.Target=System.outlog4j.appender.Console.layout=org.apache.log4j.PatternLayoutlog4j.appender.Console.layout.ConversionPattern=[%p][%d{yyyy-MM-dd HH:mm:ss,SSS}][%C.%M(%F:%L)] || %m%n##输出到文件log4j.appender.logInfo=cn.wbnull.springbootdemo.boot.GlobalRollingFileAppenderlog4j.appender.logInfo.File=./logs/log.loglog4j.appender.logInfo.Append=truelog4j.appender.logInfo.Threshold=INFOlog4j.appender.logInfo.MaxFileSize=2048KBlog4j.appender.logInfo.MaxBackupIndex=1024log4j.appender.logInfo.layout=org.apache.log4j.PatternLayoutlog4j.appender.logInfo.layout.ConversionPattern=[%p][%d{yyyy-MM-dd HH:mm:ss,SSS}][%C.%M(%F:%L)] || %m%n##错误日志单独记录log4j.appender.logError=cn.wbnull.springbootdemo.boot.GlobalRollingFileAppenderlog4j.appender.logError.File=./logs/error.loglog4j.appender.logError.Append=truelog4j.appender.logError.Threshold=ERRORlog4j.appender.logError.MaxFileSize=2048KBlog4j.appender.logError.MaxBackupIndex=1024log4j.appender.logError.layout=org.apache.log4j.PatternLayoutlog4j.appender.logError.layout.ConversionPattern=[%p][%d{yyyy-MM-dd HH:mm:ss,SSS}][%C.%M(%F:%L)] || %m%n##Debug日志单独记录log4j.appender.logDebug=cn.wbnull.springbootdemo.boot.GlobalRollingFileAppenderlog4j.appender.logDebug.File=./logs/debug.loglog4j.appender.logDebug.Append=truelog4j.appender.logDebug.Threshold=DEBUGlog4j.appender.logDebug.MaxFileSize=2048KBlog4j.appender.logDebug.MaxBackupIndex=1024log4j.appender.logDebug.layout=org.apache.log4j.PatternLayoutlog4j.appender.logDebug.filter.infoFilter=org.apache.log4j.varia.LevelRangeFilterlog4j.appender.logDebug.filter.infoFilter.LevelMin=DEBUGlog4j.appender.logDebug.filter.infoFilter.LevelMax=DEBUGlog4j.appender.logDebug.layout.ConversionPattern=[%p][%d{yyyy-MM-dd HH:mm:ss,SSS}][%C.%M(%F:%L)] || %m%n

GitHub：https://github.com/dkbnull/SpringBootDemo

CSDN：https://blog.csdn.net/dkbnull/article/details/84558062

本篇文章来源于微信公众号: 程序员null