DailyRollingFileAppender Log examples<\/figcaption><\/figure><\/p>\nDefault date pattern is yyyy-MM-dd ie rolls every day. One downside of this appender is that old log file deletion does not happen automatically. Alternative is to implement your own custom appender.<\/p>\n
4. Custom Appender<\/h2>\n
Custom Appender can be created by extending AppenderSkeleton<\/code> class or AbstractAppender<\/code>. Typically we can write our own version of doAppend<\/code>. Our goal is to attach maxbackupindex capability to DailyRollingFileAppender<\/code>. So it is better to extend DailyRollingFileAppender<\/code> Class and provide our implementation.<\/p>\nCustom Appender
\n<\/em><\/span><\/p>\npackage org.apache.log4j;\r\n\r\nimport java.io.File;\r\nimport java.io.IOException;\r\nimport java.util.ArrayList;\r\nimport java.util.Arrays;\r\nimport java.util.List;\r\n\r\nimport org.apache.log4j.helpers.LogLog;\r\n\r\npublic class CustomAppender extends DailyRollingFileAppender {\r\n\r\n\tprivate int maxBackupIndex;\r\n\r\n\tpublic void setMaxBackupIndex(int maxBackupIndex) {\r\n\t\tthis.maxBackupIndex = maxBackupIndex;\r\n\t}\r\n\r\n\t@Override\r\n\tpublic void rollOver() throws IOException {\r\n\t\tsuper.rollOver();\r\n\t\tFile file = new File(fileName);\r\n\t\tList<String> files = new ArrayList<>();\r\n\t\tFile[] dirFiles = new File(file.getAbsolutePath()).getParentFile().listFiles();\r\n\t\tif (dirFiles != null && dirFiles.length > 0) {\r\n\t\t\tArrays.sort(dirFiles, (a, b) -> Long.compare(a.lastModified(), b.lastModified()));\r\n\t\t\tfor (File allFile : dirFiles) {\r\n\t\t\t\tif (allFile.getName().contains(fileName)) {\r\n\t\t\t\t\tfiles.add(allFile.getAbsolutePath());\r\n\t\t\t\t}\r\n\t\t\t}\r\n\t\t}\r\n\t\tif (files.size() > maxBackupIndex+1) {\r\n\t\t\tFile deleteFile = new File(files.get(0));\r\n\t\t\tLogLog.debug(\"delete result for\"+deleteFile.getAbsolutePath()+\" is \"+deleteFile.delete());\r\n\t\t\tfiles.remove(0);\r\n\t\t}\r\n\r\n\t}\r\n}\r\n<\/pre>\n\n- Line 1- Package declaration is log4j. We need it to override the
rollover<\/code> method as visibility cannot extend in another package<\/li>\n- Line 13- takes an option to control the maximum files to be backed up other than current file<\/li>\n
- Line 20,21- Override
rollover<\/code> method. Rollover gets called whenever a file needs to be rolledover. We call DailyRollingFileAppender<\/code>‘s method to finish its rollover process i.e. it renames the old file based on time and creates a new file with the filename specified<\/li>\n- Line 26 – Sort the file names by ascending order of created time.<\/li>\n
- Line 28,29 –\u00a0 Filter filenames containing our log file name. In a dedicated log folder, only our log files would be there and this step might be unnecessary. It is added as caution in case the specified folder contains other files.<\/li>\n
- Line 33,37 – delete the oldest log file and remove it from list<\/li>\n<\/ul>\n
This enhances Dailyrollingfileappender<\/code>. Typical use case would be to keep 20 days of log and delete the rest of them.<\/p>\nlog4j.properties<\/em><\/span><\/p>\nlog4j.rootLogger=INFO, fileLogger\r\nlog4j.appender.fileLogger.layout=org.apache.log4j.PatternLayout\r\nlog4j.appender.fileLogger.layout.ConversionPattern=%d [%t] %-5p (%F:%L) - %m%n\r\nlog4j.appender.fileLogger.File=example.log\r\nlog4j.appender.fileLogger=org.apache.log4j.CustomAppender\r\nlog4j.appender.fileLogger.datePattern='.'yyyy-MM-dd-HH-mm\r\n<\/pre>\nOnly change is to include our Custom appender. Date Pattern usage is similar to DailyRollingFileAppender<\/code> and that behaviour is extended in our custom class.<\/p>\n
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