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This article focuses on "how to customize the LogManager program to achieve completely custom logger", interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Next let the editor to take you to learn "how to customize the LogManager implementation program completely custom logger" bar!

Introduction

Readers familiar with tomcat may notice that custom LogManager is also used in tomcat's startup script catalina.bat, as follows:

If not exist "% CATALINA_HOME%\ bin\ tomcat-juli.jar" goto noJuliset JAVA_OPTS=%JAVA_OPTS%-Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager-Djava.util.logging.config.file= "% CATALINA_BASE%\ conf\ logging.properties"

When the tomcat-juli.jar file exists under the bin path of the tomcat (that is, there is a custom LogManager), some special operations are performed by forcing org.apache.juli.ClassLoaderLogManager to be specified as the LogManager of the entire JVM in the JVM system properties.

Websphere's startup script startServer.bat also defines its own LogManager, as follows:

Java.util.logging.manager=com.ibm.ws.bootstrap.WsLogManager

How to implement custom LogManager

The first step is to implement a class that inherits from java.util.logging.LogManager:

The subclass overrides the addLogger method of java.util.logging.LogManager, and customizes the logger after successfully adding logger. You can see from the code that the addLogger method calls the internalInitializeLogger method of the subclass. The internalInitializeLogger method first empties all the handler of the logger, and then adds a custom Handler.

Need to be clear: the operation in the internalInitializeLogger method (to add our custom handler to logger) is one of the major purposes of our custom LogManager.

Package com.bes.logging;import java.util.logging.Handler;import java.util.logging.Level;import java.util.logging.LogManager;import java.util.logging.Logger;public class ServerLogManager extends LogManager {private static ServerFileHandler handlerSingleton; private static ServerLogManager thisInstance; private Object lockObj = new Object (); public ServerLogManager () {super () } public static synchronized ServerLogManager getInstance () {if (thisInstance = = null) {thisInstance = new ServerLogManager ();} return thisInstance;} public boolean addLogger (Logger logger) {boolean result = super.addLogger (logger) / / initialize Logger if (logger.getResourceBundleName () = = null) {try {Logger newLogger = Logger.getLogger (logger.getName (), getLoggerResourceBundleName (logger.getName (); assert (logger = = newLogger) } catch (Throwable ex) {/ / ex.printStackTrace ();}} synchronized (lockObj) {internalInitializeLogger (logger);} return result } / * Internal Method to initialize a list of unitialized loggers. * / private void internalInitializeLogger (final Logger logger) {/ / Explicitly remove all handlers. Handler [] h = logger.getHandlers (); for (int I = 0; I

< h.length; i++) { logger.removeHandler(h[i]); } logger.addHandler(getServerFileHandler()); logger.setUseParentHandlers(false); logger.setLevel(Level.FINEST);// only for test } private static synchronized Handler getServerFileHandler() { if (handlerSingleton == null) { try { handlerSingleton = ServerFileHandler.getInstance(); handlerSingleton.setLevel(Level.ALL); } catch (Exception e) { e.printStackTrace(); } } return handlerSingleton; } public String getLoggerResourceBundleName(String loggerName) { String result = loggerName + "." + "LogStrings"; return result; }}自定义的LogManager中使用到的ServerFileHandler 如下： 该ServerFileHandler是一个把logger日志输出到文件中的handler，可以通过com.bes.instanceRoot系统属性来指定日志文件跟路径；其次，ServerFileHandler也指定了自己的UniformLogFormatter；最后是需要覆盖父类的publish方法，覆盖的publish方法在做真正的日志输入之前会检查日志文件是否存在，然后就是创建一个和日志文件对应的输出流，把该输出流设置为ServerFileHandler的输出流以至日志输出的时候能输出到文件中。另外，WrapperStream仅仅是一个流包装类。 这里也需要说一下：ServerFileHandler构造方法中的setFormatter(new UniformLogFormatter());操作是我们自定义LogManager的第二大目的。 package com.bes.logging;import java.io.BufferedOutputStream;import java.io.File;import java.io.FileOutputStream;import java.io.IOException;import java.io.OutputStream;import java.util.logging.LogRecord;import java.util.logging.StreamHandler;public class ServerFileHandler extends StreamHandler { private WrapperStream wrappedStream; private String absoluteFileName = null; static final String LOG_FILENAME_PREFIX = "server"; static final String LOG_FILENAME_SUFFIX = ".log"; private String logFileName = LOG_FILENAME_PREFIX + LOG_FILENAME_SUFFIX; public static final ServerFileHandler thisInstance = new ServerFileHandler(); public static synchronized ServerFileHandler getInstance() { return thisInstance; } protected ServerFileHandler() { try { setFormatter(new UniformLogFormatter()); } catch (Exception e) { e.printStackTrace(); } } public synchronized void publish(LogRecord record) { if (wrappedStream == null) { try { absoluteFileName = createFileName(); openFile(absoluteFileName); } catch (Exception e) { throw new RuntimeException( "Serious Error Couldn't open Log File" + e); } } super.publish(record); flush(); } public String createFileName() { String instDir = ""; instDir = System.getProperty("com.bes.instanceRoot"); if(instDir == null || "".equals(instDir)){ instDir = "."; } return instDir + "/" + getLogFileName(); } /** * Creates the file and initialized WrapperStream and passes it on to * Superclass (java.util.logging.StreamHandler). */ private void openFile(String fileName) throws IOException { File file = new File(fileName); if(!file.exists()){ if(file.getParentFile() != null && !file.getParentFile().exists()){ file.getParentFile().mkdir(); } file.createNewFile(); } FileOutputStream fout = new FileOutputStream(fileName, true); BufferedOutputStream bout = new BufferedOutputStream(fout); wrappedStream = new WrapperStream(bout, file.length()); setOutputStream(wrappedStream); } private class WrapperStream extends OutputStream { OutputStream out; long written; WrapperStream(OutputStream out, long written) { this.out = out; this.written = written; } public void write(int b) throws IOException { out.write(b); written++; } public void write(byte buff[]) throws IOException { out.write(buff); written += buff.length; } public void write(byte buff[], int off, int len) throws IOException { out.write(buff, off, len); written += len; } public void flush() throws IOException { out.flush(); } public void close() throws IOException { out.close(); } } protected String getLogFileName() { return logFileName; }}实现Formatter 之前已经提到过，使用logger日志输出的时候，handler会自动调用自己的formatter对日志做format，然后输出格式化之后的日志。自定义的Formatter只需要覆盖public String format(LogRecord record)便可。这个类本身很简单，就是日志输出时自动增加指定格式的时间，加上分隔符，对日志进行国际化处理等操作。 需要注意的是类中对ResourceBundle做了缓存以提高效率。 package com.bes.logging;import java.text.MessageFormat;import java.text.SimpleDateFormat;import java.util.Date;import java.util.HashMap;import java.util.ResourceBundle;import java.util.logging.Formatter;import java.util.logging.LogManager;import java.util.logging.LogRecord;public class UniformLogFormatter extends Formatter { private Date date = new Date(); private HashMap loggerResourceBundleTable; private LogManager logManager; private static final char FIELD_SEPARATOR = '|'; private static final String CRLF = System.getProperty("line.separator"); private static final SimpleDateFormat dateFormatter = new SimpleDateFormat( "yyyy-MM-dd'T'HH:mm:ss.SSSZ"); public UniformLogFormatter() { super(); loggerResourceBundleTable = new HashMap(); logManager = LogManager.getLogManager(); } public String format(LogRecord record) { return uniformLogFormat(record); } private String uniformLogFormat(LogRecord record) { try { String logMessage = record.getMessage(); int msgLength = 150; // typical length of log record if (logMessage != null) msgLength += logMessage.length(); StringBuilder recordBuffer = new StringBuilder(msgLength); // add date to log date.setTime(record.getMillis()); recordBuffer.append(dateFormatter.format(date)).append( FIELD_SEPARATOR); // add log level and logger name to log recordBuffer.append(record.getLevel()).append(FIELD_SEPARATOR); recordBuffer.append(record.getLoggerName()).append(FIELD_SEPARATOR); if (logMessage == null) { logMessage = "The log message is null."; } if (logMessage.indexOf("{0}") >

= 0) {try {logMessage = java.text.MessageFormat.format (logMessage, record.getParameters ());} catch (Exception e) {/ / e.printStackTrace ();}} else {ResourceBundle rb = getResourceBundle (record.getLoggerName ()) If (rb! = null) {try {logMessage = MessageFormat.format (rb.getString (logMessage), record.getParameters ());} catch (java.util.MissingResourceException e) {} recordBuffer.append (logMessage); recordBuffer.append (CRLF); return recordBuffer.toString () } catch (Exception ex) {return "Log error occurred on msg:" + record.getMessage () + ":" + ex;}} private synchronized ResourceBundle getResourceBundle (String loggerName) {if (loggerName = = null) {return null;} ResourceBundle rb = (ResourceBundle) loggerResourceBundleTable. Get (loggerName); if (rb = = null) {rb = logManager.getLogger (loggerName). GetResourceBundle () LoggerResourceBundleTable.put (loggerName, rb);} return rb;}}

After you have completed the customized LogManager, you can add system properties to the command that starts JVM.

Java-Djava.util.logging.manager=com.bes.logging.ServerLogManager

After adding this system attribute, the logger obtained through the java.util.logging.Logger class is initialized by a custom LogManager. When the log is output, the ServerFileHandler#publish () method above will be used for log output, and UniformLogFormatter will be used to format the log.

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