[Enhancement]Optimize some codestyles and fix some warnings

[Mrhorse99]

Before Creating the Enhancement Request

• I have confirmed that this should be classified as an enhancement rather than a bug/feature.

Summary

The issue include some optimization for the code style and simplify some code.

Motivation

It make some changes to optimize the code a bit.

Describe the Solution You'd Like

The main optimizations are threefold:
Simplify the code：

Use the forEach function to replace the stream method in order to avoid the price on creating and destroying the stream object：

fix the potential npe problem：
if somwhere doesn't check the file as a directory , the files may be null and the length function may cause the npe problem.

Describe Alternatives You've Considered

The code may be enough for the optimization

Additional Context

No response