關于log4j

2019-11-11 01:40:26

字體：大中小

來源：轉載

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Log4j 是如何獲取類名、函數名、行數的

見 org.apache.log4j.spi.LocationInfo.LocationInfo(Throwable t, String fqnOfCallingClass)

源碼分析

Object[] noArgs = null; // 獲取函數調用棧 Object[] elements = (Object[]) getStackTraceMethod.invoke(t, noArgs); String PRevClass = NA; for(int i = elements.length - 1; i >= 0; i--) { String thisClass = (String) getClassNameMethod.invoke(elements[i], noArgs); // 判斷當前調用的類是否為 Category if(fqnOfCallingClass.equals(thisClass)) { int caller = i + 1; if (caller < elements.length) { className = prevClass; methodName = (String) getMethodNameMethod.invoke(elements[caller], noArgs); fileName = (String) getFileNameMethod.invoke(elements[caller], noArgs); if (fileName == null) { fileName = NA; } int line = ((Integer) getLineNumberMethod.invoke(elements[caller], noArgs)).intValue(); if (line < 0) { lineNumber = NA; } else { lineNumber = String.valueOf(line); } StringBuffer buf = new StringBuffer(); buf.append(className); buf.append("."); buf.append(methodName); buf.append("("); buf.append(fileName); buf.append(":"); buf.append(lineNumber); buf.append(")"); this.fullInfo = buf.toString(); } return; } prevClass = thisClass; }

函數調用棧

org.apache.log4j.spi.LoggingEvent.getLocationInformation(LoggingEvent.java:253)↓org.apache.log4j.helpers.PatternParser$LocationPatternConverter.convert(PatternParser.java:500)↓org.apache.log4j.helpers.PatternConverter.format(PatternConverter.java:65)↓org.apache.log4j.PatternLayout.format(PatternLayout.java:506)↓org.apache.log4j.WriterAppender.subAppend(WriterAppender.java:310)↓org.apache.log4j.WriterAppender.append(WriterAppender.java:162)↓org.apache.log4j.AppenderSkeleton.doAppend(AppenderSkeleton.java:251)↓org.apache.log4j.helpers.AppenderAttachableImpl.appendLoopOnAppenders(AppenderAttachableImpl.java:66)↓org.apache.log4j.Category.callAppenders(Category.java:206)↓xxx.xxx.Main(args:line)

從函數調用棧從下往上開始查找 Category ，若當前調用類為 Category，則上層就是 Main 方法的調用信息。

如何手動獲取 `函數調用信息`（類名、函數名、行號）

// 指定 fqnOfCategoryClass 為 LoggingEvent.class.getName()LoggingEvent event = new LoggingEvent(LoggingEvent.class.getName(), logger, Level.DEBUG, "i am message", null);// 然后手動獲取 LocationInfo，這時函數調用棧的倒數第二層就是// org.apache.log4j.spi.LoggingEvent.getLocationInformation(:line)// 此時的 line 就是下面這行代碼的行號LocationInfo info = event.getLocationInformation();

上面獲取的行號只是 event.getLocationInformation() 的行數，所以要想獲得自己想要的行號，必須對以上操作進行包裝。

獻上一個包裝的 Logger

maven

wrapper Logger

注意觀察 FQCN 的使用

import org.apache.log4j.Level;import org.apache.log4j.spi.LoggingEvent;/** * wrapper org.apache.log4j.Logger * * @author Jinpeng Cui * */public class Logger { public static final boolean enable = true; private static final String FQCN = Logger.class.getName(); private static org.apache.log4j.Logger proxy; public Logger(final String clazzName) { proxy = org.apache.log4j.Logger.getLogger(clazzName); } public static Logger getLogger(final Class<?> clazz) { return new Logger(clazz.getName()); } public void error(String message) { if (isErrorEnable()) { forceLog(Level.ERROR, message); } } public void info(String message) { if (isInfoEnabled()) { forceLog(Level.INFO, message); } } public void debug(String message) { if (isDebugEnabled()) { forceLog(Level.DEBUG, message); } } private void forceLog(Level level, String message) { proxy.callAppenders(new LoggingEvent(FQCN, proxy, level, message, null)); } public boolean isErrorEnable() { return enable && proxy.isEnabledFor(Level.ERROR); } public boolean isInfoEnabled() { return enable && proxy.isEnabledFor(Level.INFO); } public boolean isDebugEnabled() { return enable && proxy.isEnabledFor(Level.DEBUG); }}

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