synchronized (s.lock()) {
   // Print our stack trace
// 1. 先打印 当前异常对象this的 异常栈。
   s.println(this);
   StackTraceElement[] trace = getOurStackTrace();
   for (StackTraceElement traceElement : trace)
    s.println("\tat " + traceElement);

   // Print suppressed exceptions, if any
   for (Throwable se : getSuppressed())
    se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu);
   // Print cause, if any
// 2. 打印 异常原因链
   Throwable ourCause = getCause();
   if (ourCause != null)
    ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu);
  }

public static String getStackTrace(Throwable t) {
  StringWriter sw = new StringWriter();
  PrintWriter pw = new PrintWriter(sw);
  try {
    t.printStackTrace(pw);
    return sw.toString();
  } finally {
    pw.close();
  }
}

org.apache.commons.lang3.exception.ExceptionUtils.getStackTrace(e);