基于log4j-1.2.15.jar

分析log4j的實現原理

org.apache.log4j.Logger類

package org.apache.log4j;import org.apache.log4j.spi.LoggerFactory; import org.apache.log4j.spi.LoggerRepository;public class Logger extends Category {private static final String FQCN = Logger.class.getName();protected Logger(String name){super(name);}public static Logger getLogger(String name){return LogManager.getLogger(name);}//經常使用的方法public static Logger getLogger(Class clazz){return LogManager.getLogger(clazz.getName());}public static Logger getRootLogger(){return LogManager.getRootLogger();}public static Logger getLogger(String name, LoggerFactory factory){return LogManager.getLogger(name, factory);}public void trace(Object message){if (this.repository.isDisabled(5000)) {return;}if (Level.TRACE.isGreaterOrEqual(getEffectiveLevel()))forcedLog(FQCN, Level.TRACE, message, null);}public void trace(Object message, Throwable t){if (this.repository.isDisabled(5000)) {return;}if (Level.TRACE.isGreaterOrEqual(getEffectiveLevel()))forcedLog(FQCN, Level.TRACE, message, t);}public boolean isTraceEnabled(){if (this.repository.isDisabled(5000)) {return false;}return Level.TRACE.isGreaterOrEqual(getEffectiveLevel());} }

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下面是Logger的父類Category類，發現log4j也是大量使用Service Provider機制來完成工具類接口的設計

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package org.apache.log4j;import java.text.MessageFormat; import java.util.Enumeration; import java.util.MissingResourceException; import java.util.ResourceBundle; import java.util.Vector; import org.apache.log4j.helpers.AppenderAttachableImpl; import org.apache.log4j.helpers.NullEnumeration; import org.apache.log4j.spi.AppenderAttachable; import org.apache.log4j.spi.HierarchyEventListener; import org.apache.log4j.spi.LoggerRepository; import org.apache.log4j.spi.LoggingEvent;public class Categoryimplements AppenderAttachable {protected String name;protected volatile Level level;protected volatile Category parent;private static final String FQCN = Category.class.getName();protected ResourceBundle resourceBundle;protected LoggerRepository repository;AppenderAttachableImpl aai;protected boolean additive = true;protected Category(String name){this.name = name;}public synchronized void addAppender(Appender newAppender){if (this.aai == null) {this.aai = new AppenderAttachableImpl();}this.aai.addAppender(newAppender);this.repository.fireAddAppenderEvent(this, newAppender);}public void assertLog(boolean assertion, String msg){if (!assertion)error(msg);}public void callAppenders(LoggingEvent event){int writes = 0;for (Category c = this; c != null; c = c.parent){synchronized (c) {if (c.aai != null) {writes += c.aai.appendLoopOnAppenders(event);}if (!c.additive) {break;}}}if (writes == 0)this.repository.emitNoAppenderWarning(this);}synchronized void closeNestedAppenders(){Enumeration enumeration = getAllAppenders();if (enumeration != null)while (enumeration.hasMoreElements()) {Appender a = (Appender)enumeration.nextElement();if ((a instanceof AppenderAttachable))a.close();}}public void debug(Object message){if (this.repository.isDisabled(10000))return;if (Level.DEBUG.isGreaterOrEqual(getEffectiveLevel()))forcedLog(FQCN, Level.DEBUG, message, null);}public void debug(Object message, Throwable t){if (this.repository.isDisabled(10000))return;if (Level.DEBUG.isGreaterOrEqual(getEffectiveLevel()))forcedLog(FQCN, Level.DEBUG, message, t);}public void error(Object message){if (this.repository.isDisabled(40000))return;if (Level.ERROR.isGreaterOrEqual(getEffectiveLevel()))forcedLog(FQCN, Level.ERROR, message, null);}public void error(Object message, Throwable t){if (this.repository.isDisabled(40000))return;if (Level.ERROR.isGreaterOrEqual(getEffectiveLevel()))forcedLog(FQCN, Level.ERROR, message, t);}/** @deprecated */public static Logger exists(String name){return LogManager.exists(name);}public void fatal(Object message){if (this.repository.isDisabled(50000))return;if (Level.FATAL.isGreaterOrEqual(getEffectiveLevel()))forcedLog(FQCN, Level.FATAL, message, null);}public void fatal(Object message, Throwable t){if (this.repository.isDisabled(50000))return;if (Level.FATAL.isGreaterOrEqual(getEffectiveLevel()))forcedLog(FQCN, Level.FATAL, message, t);}protected void forcedLog(String fqcn, Priority level, Object message, Throwable t){callAppenders(new LoggingEvent(fqcn, this, level, message, t));}public boolean getAdditivity(){return this.additive;}public synchronized Enumeration getAllAppenders(){if (this.aai == null) {return NullEnumeration.getInstance();}return this.aai.getAllAppenders();}public synchronized Appender getAppender(String name){if ((this.aai == null) || (name == null)) {return null;}return this.aai.getAppender(name);}public Level getEffectiveLevel(){for (Category c = this; c != null; c = c.parent) {if (c.level != null)return c.level;}return null;}/** @deprecated */public Priority getChainedPriority(){for (Category c = this; c != null; c = c.parent) {if (c.level != null)return c.level;}return null;}/** @deprecated */public static Enumeration getCurrentCategories(){return LogManager.getCurrentLoggers();}/** @deprecated */public static LoggerRepository getDefaultHierarchy(){return LogManager.getLoggerRepository();}/** @deprecated */public LoggerRepository getHierarchy(){return this.repository;}public LoggerRepository getLoggerRepository(){return this.repository;}/** @deprecated */public static Category getInstance(String name){return LogManager.getLogger(name);}/** @deprecated */public static Category getInstance(Class clazz){return LogManager.getLogger(clazz);}public final String getName(){return this.name;}public final Category getParent(){return this.parent;}public final Level getLevel(){return this.level;}/** @deprecated */public final Level getPriority(){return this.level;}/** @deprecated */public static final Category getRoot(){return LogManager.getRootLogger();}public ResourceBundle getResourceBundle(){for (Category c = this; c != null; c = c.parent) {if (c.resourceBundle != null) {return c.resourceBundle;}}return null;}protected String getResourceBundleString(String key){ResourceBundle rb = getResourceBundle();if (rb == null){return null;}try{return rb.getString(key);}catch (MissingResourceException mre) {error("No resource is associated with key \"" + key + "\".");}return null;}public void info(Object message){if (this.repository.isDisabled(20000))return;if (Level.INFO.isGreaterOrEqual(getEffectiveLevel()))forcedLog(FQCN, Level.INFO, message, null);}public void info(Object message, Throwable t){if (this.repository.isDisabled(20000))return;if (Level.INFO.isGreaterOrEqual(getEffectiveLevel()))forcedLog(FQCN, Level.INFO, message, t);}public boolean isAttached(Appender appender){if ((appender == null) || (this.aai == null)) {return false;}return this.aai.isAttached(appender);}public boolean isDebugEnabled(){if (this.repository.isDisabled(10000))return false;return Level.DEBUG.isGreaterOrEqual(getEffectiveLevel());}public boolean isEnabledFor(Priority level){if (this.repository.isDisabled(level.level))return false;return level.isGreaterOrEqual(getEffectiveLevel());}public boolean isInfoEnabled(){if (this.repository.isDisabled(20000))return false;return Level.INFO.isGreaterOrEqual(getEffectiveLevel());}public void l7dlog(Priority priority, String key, Throwable t){if (this.repository.isDisabled(priority.level)) {return;}if (priority.isGreaterOrEqual(getEffectiveLevel())) {String msg = getResourceBundleString(key);if (msg == null) {msg = key;}forcedLog(FQCN, priority, msg, t);}}public void l7dlog(Priority priority, String key, Object[] params, Throwable t){if (this.repository.isDisabled(priority.level)) {return;}if (priority.isGreaterOrEqual(getEffectiveLevel())) {String pattern = getResourceBundleString(key);String msg;String msg;if (pattern == null)msg = key;elsemsg = MessageFormat.format(pattern, params);forcedLog(FQCN, priority, msg, t);}}public void log(Priority priority, Object message, Throwable t){if (this.repository.isDisabled(priority.level)) {return;}if (priority.isGreaterOrEqual(getEffectiveLevel()))forcedLog(FQCN, priority, message, t);}public void log(Priority priority, Object message){if (this.repository.isDisabled(priority.level)) {return;}if (priority.isGreaterOrEqual(getEffectiveLevel()))forcedLog(FQCN, priority, message, null);}public void log(String callerFQCN, Priority level, Object message, Throwable t){if (this.repository.isDisabled(level.level)) {return;}if (level.isGreaterOrEqual(getEffectiveLevel()))forcedLog(callerFQCN, level, message, t);}private void fireRemoveAppenderEvent(Appender appender){if (appender != null)if ((this.repository instanceof Hierarchy))((Hierarchy)this.repository).fireRemoveAppenderEvent(this, appender);else if ((this.repository instanceof HierarchyEventListener))((HierarchyEventListener)this.repository).removeAppenderEvent(this, appender);}public synchronized void removeAllAppenders(){if (this.aai != null) {Vector appenders = new Vector();for (Enumeration iter = this.aai.getAllAppenders(); iter.hasMoreElements(); ) {appenders.add(iter.nextElement());}this.aai.removeAllAppenders();for (Enumeration iter = appenders.elements(); iter.hasMoreElements(); ) {fireRemoveAppenderEvent((Appender)iter.nextElement());}this.aai = null;}}public synchronized void removeAppender(Appender appender){if ((appender == null) || (this.aai == null))return;boolean wasAttached = this.aai.isAttached(appender);this.aai.removeAppender(appender);if (wasAttached)fireRemoveAppenderEvent(appender);}public synchronized void removeAppender(String name){if ((name == null) || (this.aai == null)) return;Appender appender = this.aai.getAppender(name);this.aai.removeAppender(name);if (appender != null)fireRemoveAppenderEvent(appender);}public void setAdditivity(boolean additive){this.additive = additive;}final void setHierarchy(LoggerRepository repository){this.repository = repository;}public void setLevel(Level level){this.level = level;}/** @deprecated */public void setPriority(Priority priority){this.level = ((Level)priority);}public void setResourceBundle(ResourceBundle bundle){this.resourceBundle = bundle;}/** @deprecated */public static void shutdown(){LogManager.shutdown();}public void warn(Object message){if (this.repository.isDisabled(30000)) {return;}if (Level.WARN.isGreaterOrEqual(getEffectiveLevel()))forcedLog(FQCN, Level.WARN, message, null);}public void warn(Object message, Throwable t){if (this.repository.isDisabled(30000))return;if (Level.WARN.isGreaterOrEqual(getEffectiveLevel()))forcedLog(FQCN, Level.WARN, message, t);} }

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看一個普通Log4j使用的例子

package com.coderdream.log4j;import org.apache.log4j.Logger;public class HelloLog4j {private static Logger logger = Logger.getLogger(HelloLog4j.class);/*** @param args*/public static void main(String[] args) {// System.out.println("This is println message.");// 記錄debug級別的信息logger.debug("This is debug message.");// 記錄info級別的信息logger.info("This is info message.");// 記錄error級別的信息logger.error("This is error message.");} }

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?配置文件log4j.properties:

#可以設置級別：debug>info>error #debug：顯示debug、info、error #info：顯示info、error #error：只error log4j.rootLogger=debug,appender1 #log4j.rootLogger=info,appender1 #log4j.rootLogger=error,appender1 #輸出到控制臺 log4j.appender.appender1=org.apache.log4j.ConsoleAppender #樣式為TTCCLayout log4j.appender.appender1.layout=org.apache.log4j.TTCCLayout

結果

[main] DEBUG com.coderdream.log4j.HelloLog4j - This is debug message. [main] INFO com.coderdream.log4j.HelloLog4j - This is info message. [main] ERROR com.coderdream.log4j.HelloLog4j - This is error message.

　　

　　

轉載于:https://www.cnblogs.com/wuxinliulei/p/4934826.html

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