code: public static String[] getClassPathsInSystemProperty() {
          if (classPathsInSystemProperty == null) {
              synchronized (ClassPathUtil.class) {
                  if (classPathsInSystemProperty == null) {
                      String classPathAll = System.getProperty("java.class.path");
                      classPathsInSystemProperty = classPathAll.split(System.getProperty("path.separator"));
                  }
              }
          }
          return classPathsInSystemProperty;
      }
docs: <p>
  Get class path from System.getProperty("java.class.path").
  </p>
  If run in jar(java -jar ....jar), this class path is just running jar file,
  more class path can't get from system properties, must get from "Class-Path" in manifest file.
  
  @return all class path string array.