private static String determineJarType(Path jarPath) throws IOException {
    try (JarFile jarFile = new JarFile(jarPath.toFile())) {
      if (jarFile.getEntry("BOOT-INF") != null) {
        return SPRING_BOOT;
      }
      return STANDARD;
    }
  }
Determines whether the jar is a spring boot or standard jar.

@param jarPath path to the jar
@return the jar type
@throws IOException if I/O error occurs when opening the file
jib-cli/src/main/java/com/google/cloud/tools/jib/cli/ArtifactProcessors.java