Java

figure out how logger get the source method name

info in Logger
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package java.util.logging;

public class Logger {
	
    public void info(String msg) {
        if (Level.INFO.intValue() < levelValue) {
            return;
        }
        log(Level.INFO, msg);
  		}

    /**
     * Log a message, with no arguments.
     * <p>
     * If the logger is currently enabled for the given message
     * level then the given message is forwarded to all the
     * registered output Handler objects.
     * <p>
     * @param   level   One of the message level identifiers, e.g., SEVERE
     * @param   msg     The string message (or a key in the message catalog)
     */
    public void log(Level level, String msg) {
        if (level.intValue() < levelValue || levelValue == offValue) {
            return;
        }
        LogRecord lr = new LogRecord(level, msg);
        doLog(lr);
    }

LogRecord
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   public LogRecord(Level level, String msg) {
       // Make sure level isn't null, by calling random method.
       level.getClass();
       this.level = level;
       message = msg;
       // Assign a thread ID and a unique sequence number.
       sequenceNumber = globalSequenceNumber.getAndIncrement();
       threadID = defaultThreadID();
       millis = System.currentTimeMillis();
       needToInferCaller = true;
  	}


   public String getSourceClassName() {
       if (needToInferCaller) {
           inferCaller();
       }
       return sourceClassName;
   }

// 这里就是找出当前执行的类与方法的地方
   // Private method to infer the caller's class and method names
   private void inferCaller() {
       needToInferCaller = false;
       JavaLangAccess access = SharedSecrets.getJavaLangAccess();
       Throwable throwable = new Throwable();
       int depth = access.getStackTraceDepth(throwable);

       String logClassName = "java.util.logging.Logger";
       String plogClassName = "sun.util.logging.PlatformLogger";
       boolean lookingForLogger = true;
       for (int ix = 0; ix < depth; ix++) {
           // Calling getStackTraceElement directly prevents the VM
           // from paying the cost of building the entire stack frame.
           StackTraceElement frame =
               access.getStackTraceElement(throwable, ix);
           String cname = frame.getClassName();
           if (lookingForLogger) {
			// 跳过所有looger之前的栈帧
               // Skip all frames until we have found the first logger frame.
               if (cname.equals(logClassName) || cname.startsWith(plogClassName)) {
                   lookingForLogger = false;
               }
           } else {
               if (!cname.equals(logClassName) && !cname.startsWith(plogClassName)) {
				// 跳过反射调用
                   // skip reflection call
                   if (!cname.startsWith("java.lang.reflect.") && !cname.startsWith("sun.reflect.")) {
                      // We've found the relevant frame.
                      setSourceClassName(cname);
                      setSourceMethodName(frame.getMethodName());
                      return;
                   }
               }
           }
       }
       // We haven't found a suitable frame, so just punt.  This is
       // OK as we are only committed to making a "best effort" here.
   }