本篇内容主要讲解“怎么自定制LogManager实现程序完全自定义的logger”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“怎么自定制LogManager实现程序完全自定义的logger”吧!
引言
对tomcat熟悉的读者，有可能会注意到tomcat的启动脚本catalina.bat中也使用定制的LogManager，如下：
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"当tomcat的bin路径下存在tomcat-juli.jar文件(也就是存在定制的LogManager)时，那么会强制在JVM系统属性中指定org.apache.juli.ClassLoaderLogManager作为整个JVM的LogManager，以此来完成一些特殊操作。
websphere的启动脚本startServer.bat中也定义了自己的LogManager，如下：
java.util.logging.manager=com.ibm.ws.bootstrap.WsLogManager
怎么实现自定义的LogManager
首先要实现一个继承自java.util.logging.LogManager的类：
子类覆盖java.util.logging.LogManager的addLogger方法，在成功添加logger之后对logger做定制化操作，从代码中可以看出addLogger方法调用了子类的internalInitializeLogger方法，internalInitializeLogger方法中先清空logger的所有handler，然后再增加一个自定义的Handler
需要说明一下：internalInitializeLogger方法中的操作(给logger增设我们自定义的handler)是我们自定义LogManager的一大目的。
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 Loggerif (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;}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(); } 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; }}完成了定制的LogManager之后，在启动JVM的命令中增加系统属性便可
java -Djava.util.logging.manager=com.bes.logging.ServerLogManager
加上这个系统属性之后通过java.util.logging.Logger类获取的logger都是经过定制的LogManager作为初始化的，日志输出的时候便会使用上面的ServerFileHandler#publish()方法进行日志输出，并使用UniformLogFormatter对日志进行格式化。
到此，相信大家对“怎么自定制LogManager实现程序完全自定义的logger”有了更深的了解，不妨来实际操作一番吧！这里是编程网网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！
