GH-42101: [Java] Create File for Output Validation in FileRoundtrip

[llama90]

Rationale for this change

Enhance the logic to ensure that the output directory and file are created if they do not exist. While the input directory and file are mandatory, the output directory and file might not exist.

What changes are included in this PR?

• Create file if output directory or file does not exist.
• Add unit tests
  • Test with different directories to validate creation of non-existent directory
  • Test for non-existent input file

Are these changes tested?

Yes. Additional unit tests have been added.

Are there any user-facing changes?

Maybe. Yes.

• GitHub Issue: [Java] Enhance the FileRoundtrip about Creating File #42101

[github-actions]

⚠️ GitHub issue #42101 has been automatically assigned in GitHub to PR creator.

[llama90]

If this PR is merged, changes will be needed to make it compatible with JUnit 5.

When using JUnit 5's @TempDir annotation, it was found that the logic works with non-existent files, causing IllegalArgumentException with the message input file not found.

This seems to be due to differences in behavior between JUnit 4's @TemporaryFolder and JUnit 5's @TempDir annotations.

[vibhatha]

Overall LGTM! Let's check the CIs.

[lidavidm]

Hmm, why does the output file need to exist?

[llama90]

In JUnit 4, there was an annotation called @TemporaryFolder, but in JUnit 5, it's changed to @TempDir. This means that the way temporary files are created has changed too.

So, just changing the annotation in the old test code wasn't enough to make the tests pass. I had to add some code to create the output file using createNewFile() to make the tests work.

arrow/java/tools/src/test/java/org/apache/arrow/tools/TestFileRoundtrip.java

Lines 55 to 59 in 298786a

	if (!testOutFile.exists()) {
	if (!testOutFile.createNewFile()) {
	throw new IOException("Failed to create file: " + testOutFile);
	}
	}

While working with the FileRoundtrip class, I thought of two ways to handle this (you can check the link for details). The input is always needed, but the output path or file might not always exist (especially if it's different from the input path).

So, I added some code to create the output path or file if they don't exist, before the rest of the logic runs.

If you think there are better ways to do this or if something's unclear, I'd appreciate your advice.

Here’s the link explaining why this change was needed.

• GH-42092: [Java] Update Unit Tests for Tools Module #42093 (comment)

[lidavidm]

Er, but again...I can see why the output directory needs to exist, but why does the output file have to exist?

[llama90]

Aha! You are right. We don't need to create the file in validateFile. This is because the run method executes try (FileOutputStream fileOutputStream = new FileOutputStream(outFile);.

[llama90]

I removed it.

[lidavidm]

What is actually being tested here? A 0-length input file?

[llama90]

No.

In JUnit 5, I want to check for IllegalArgumentException and input file not found errors.

The code I wrote still works with JUnit 4 logic, so the tests don't write the input (writeInput(testInFile, allocator)). Because the file exists, I can see these exceptions happening.

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 6 benchmarking runs that have been run so far on merge-commit 02f461f.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 16 possible false positives for unstable benchmarks that are known to sometimes produce them.