commons.logging1.1.1源代码研究（3）-- 日志器Log接口，SimpleLog实现

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Log接口的定义如下：

package org.apache.commons.logging;public interface Log { // ----------------------------------------------------- Logging Properties /** * Is debug logging currently enabled? * * Call this method to prevent having to perform expensive operations * (for example, <code>String</code> concatenation) * when the log level is more than debug. * * @return true if debug is enabled in the underlying logger. */ public boolean isDebugEnabled(); /** * Is error logging currently enabled? * * Call this method to prevent having to perform expensive operations * (for example, <code>String</code> concatenation) * when the log level is more than error. * * @return true if error is enabled in the underlying logger. */ public boolean isErrorEnabled(); /** * Is fatal logging currently enabled? * * Call this method to prevent having to perform expensive operations * (for example, <code>String</code> concatenation) * when the log level is more than fatal. * * @return true if fatal is enabled in the underlying logger. */ public boolean isFatalEnabled(); /** * Is info logging currently enabled? * * Call this method to prevent having to perform expensive operations * (for example, <code>String</code> concatenation) * when the log level is more than info. * * @return true if info is enabled in the underlying logger. */ public boolean isInfoEnabled(); /** * Is trace logging currently enabled? * * Call this method to prevent having to perform expensive operations * (for example, <code>String</code> concatenation) * when the log level is more than trace. * * @return true if trace is enabled in the underlying logger. */ public boolean isTraceEnabled(); /** * Is warn logging currently enabled? * * Call this method to prevent having to perform expensive operations * (for example, <code>String</code> concatenation) * when the log level is more than warn. * * @return true if warn is enabled in the underlying logger. */ public boolean isWarnEnabled(); // -------------------------------------------------------- Logging Methods /** * Log a message with trace log level. * * @param message log this message */ public void trace(Object message); /** * Log an error with trace log level. * * @param message log this message * @param t log this cause */ public void trace(Object message, Throwable t); /** * Log a message with debug log level. * * @param message log this message */ public void debug(Object message); /** * Log an error with debug log level. * * @param message log this message * @param t log this cause */ public void debug(Object message, Throwable t); /** * Log a message with info log level. * * @param message log this message */ public void info(Object message); /** * Log an error with info log level. * * @param message log this message * @param t log this cause */ public void info(Object message, Throwable t); /** * Log a message with warn log level. * * @param message log this message */ public void warn(Object message); /** * Log an error with warn log level. * * @param message log this message * @param t log this cause */ public void warn(Object message, Throwable t); /** * Log a message with error log level. * * @param message log this message */ public void error(Object message); /** * Log an error with error log level. * * @param message log this message * @param t log this cause */ public void error(Object message, Throwable t); /** * Log a message with fatal log level. * * @param message log this message */ public void fatal(Object message); /** * Log an error with fatal log level. * * @param message log this message * @param t log this cause */ public void fatal(Object message, Throwable t);}

其中主要的方法有：

is<Level>Enabled() -- 是否某个层次的日志开启

<Level>(Object message) -- 记录日志消息

<Level>(Object message, Throwable t) -- 记录日志消息和异常

其中<Level>指trace,debug,info,wran,error,fatal

SimpleLog实现：

simplelog.properties必须放在根路径下，是配置文件

配置前缀：“org.apache.commons.logging.simplelog.”

showlogname -- 是否显示日志名（true/false ）

showShortLogname -- 是否显示短日志名（true /false）

showdatetime -- 是否显示时间（true/false ）

dateTimeFormat -- 日期格式（默认为yyyy/MM/dd HH:mm:ss:SSS zzz）

defaultlog -- 指定默认日志的层次（info,debug等）

log.<类的完全路径名> -- 指定某一类的日志的层次

比如：org.apache.commons.logging.simplelog.log.Test.TestClass=debug
org.apache.commons.logging.simplelog.log.Test.TestA=info

那么Test.TestClass类的日志层次为debug；而Test.TestA的日志层次为info

SimpleLog一些重要代码分析：

（1）构造函数

public SimpleLog(String name) { logName = name; // Set initial log level // Used to be: set default log level to ERROR // IMHO it should be lower, but at least info ( costin ). setLevel(SimpleLog.LOG_LEVEL_INFO); // Set log level from properties String lvl = getStringProperty(systemPrefix + "log." + logName); int i = String.valueOf(name).lastIndexOf("."); while(null == lvl && i > -1) { name = name.substring(0,i); lvl = getStringProperty(systemPrefix + "log." + name); i = String.valueOf(name).lastIndexOf("."); } if(null == lvl) { lvl = getStringProperty(systemPrefix + "defaultlog"); } if("all".equalsIgnoreCase(lvl)) { setLevel(SimpleLog.LOG_LEVEL_ALL); } else if("trace".equalsIgnoreCase(lvl)) { setLevel(SimpleLog.LOG_LEVEL_TRACE); } else if("debug".equalsIgnoreCase(lvl)) { setLevel(SimpleLog.LOG_LEVEL_DEBUG); } else if("info".equalsIgnoreCase(lvl)) { setLevel(SimpleLog.LOG_LEVEL_INFO); } else if("warn".equalsIgnoreCase(lvl)) { setLevel(SimpleLog.LOG_LEVEL_WARN); } else if("error".equalsIgnoreCase(lvl)) { setLevel(SimpleLog.LOG_LEVEL_ERROR); } else if("fatal".equalsIgnoreCase(lvl)) { setLevel(SimpleLog.LOG_LEVEL_FATAL); } else if("off".equalsIgnoreCase(lvl)) { setLevel(SimpleLog.LOG_LEVEL_OFF); } }

其中while循环处实现了日志器层次的继承性，即：

（1）如果没有设置，则黙认为info

（2）如果对某一类明确了日志层次，如：org.apache.commons.logging.simplelog.log.Test.TestA(Test.TestA类)，则使用这个明确的日志层次；如果没明确，则向上寻找org.apache.commons.logging.simplelog.log.Test；如果还没找到，则找org.apache.commons.logging.simplelog.defaultlog

（2）日志函数

protected void log(int type, Object message, Throwable t) { // Use a string buffer for better performance StringBuffer buf = new StringBuffer(); // Append date-time if so configured if(showDateTime) { Date now = new Date(); String dateText; synchronized(dateFormatter) { dateText = dateFormatter.format(now); } buf.append(dateText); buf.append(" "); } // Append a readable representation of the log level switch(type) { case SimpleLog.LOG_LEVEL_TRACE: buf.append("[TRACE] "); break; case SimpleLog.LOG_LEVEL_DEBUG: buf.append("[DEBUG] "); break; case SimpleLog.LOG_LEVEL_INFO: buf.append("[INFO] "); break; case SimpleLog.LOG_LEVEL_WARN: buf.append("[WARN] "); break; case SimpleLog.LOG_LEVEL_ERROR: buf.append("[ERROR] "); break; case SimpleLog.LOG_LEVEL_FATAL: buf.append("[FATAL] "); break; } // Append the name of the log instance if so configured if( showShortName) { if( shortLogName==null ) { // Cut all but the last component of the name for both styles shortLogName = logName.substring(logName.lastIndexOf(".") + 1); shortLogName = shortLogName.substring(shortLogName.lastIndexOf("/") + 1); } buf.append(String.valueOf(shortLogName)).append(" - "); } else if(showLogName) { buf.append(String.valueOf(logName)).append(" - "); } // Append the message buf.append(String.valueOf(message)); // Append stack trace if not null if(t != null) { buf.append(" <"); buf.append(t.toString()); buf.append(">"); java.io.StringWriter sw= new java.io.StringWriter(1024); java.io.PrintWriter pw= new java.io.PrintWriter(sw); t.printStackTrace(pw); pw.close(); buf.append(sw.toString()); } // Print to the appropriate destination write(buf); }

这段代码很简单，要注意的是：

showlogname 显示的是完全的类名（包括包名）；showShortLogname只显示类名

注意：SimpleDateFormat不是线程安全的，在多线程中必须同步

Date formats are not synchronized.
* It is recommended to create separate format instances for each thread.
* If multiple threads access a format concurrently, it must be synchronized

（3）具体的日志方法

public final void fatal(Object message, Throwable t) { if (isLevelEnabled(SimpleLog.LOG_LEVEL_FATAL)) { log(SimpleLog.LOG_LEVEL_FATAL, message, t); } }

先判断是否这个层次的日志开启，然后调用写日志方法

（4）得到资源的方法

private static InputStream getResourceAsStream(final String name) { return (InputStream)AccessController.doPrivileged( new PrivilegedAction() { public Object run() { ClassLoader threadCL = getContextClassLoader(); if (threadCL != null) { return threadCL.getResourceAsStream(name); } else { return ClassLoader.getSystemResourceAsStream(name); } } }); }

AccessController的doPrivileged方法给了其中的代码“特权”，从而不用checkPermissions.

以下得到ClassLoader

private static ClassLoader getContextClassLoader() { ClassLoader classLoader = null; if (classLoader == null) { try { // Are we running on a JDK 1.2 or later system? Method method = Thread.class.getMethod("getContextClassLoader", (Class[]) null); // Get the thread context class loader (if there is one) try { classLoader = (ClassLoader)method.invoke(Thread.currentThread(), (Class[]) null); } catch (IllegalAccessException e) { ; // ignore } catch (InvocationTargetException e) { /** * InvocationTargetException is thrown by 'invoke' when * the method being invoked (getContextClassLoader) throws * an exception. * * getContextClassLoader() throws SecurityException when * the context class loader isn't an ancestor of the * calling class's class loader, or if security * permissions are restricted. * * In the first case (not related), we want to ignore and * keep going. We cannot help but also ignore the second * with the logic below, but other calls elsewhere (to * obtain a class loader) will trigger this exception where * we can make a distinction. */ if (e.getTargetException() instanceof SecurityException) { ; // ignore } else { // Capture 'e.getTargetException()' exception for details // alternate: log 'e.getTargetException()', and pass back 'e'. throw new LogConfigurationException ("Unexpected InvocationTargetException", e.getTargetException()); } } } catch (NoSuchMethodException e) { // Assume we are running on JDK 1.1 ; // ignore } } if (classLoader == null) { classLoader = SimpleLog.class.getClassLoader(); } // Return the selected class loader return classLoader; }

以下是Thread类的getContextClassLoader()方法，可能会报SecurityException

public ClassLoader getContextClassLoader() {if (contextClassLoader == null) return null;SecurityManager sm = System.getSecurityManager();if (sm != null) { ClassLoader ccl = ClassLoader.getCallerClassLoader(); if (ccl != null && ccl != contextClassLoader && !contextClassLoader.isAncestor(ccl)) {sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION); }}return contextClassLoader;