Fix #21317: Replace colons with underscores in window filenames for Windows compatibility

[liferoad]

The default FilenamePolicy uses Instant.toString() for Beam Windows, which
produces ISO-8601 format (e.g., 2021-12-31T23:00:00.000Z) containing colons.
Colons are illegal characters in Windows file paths, causing
InvalidPathException when using TextIO.write().withWindowedWrites() on Windows.

This fix replaces colons with underscores in the window string format to
ensure cross-platform compatibility.

Fixes #21317

[gemini-code-assist]

Summary of Changes

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This pull request resolves a critical cross-platform compatibility issue where Beam's default filename policy generated windowed filenames containing colons. These colons are illegal characters in Windows file paths, leading to InvalidPathException when using TextIO.write().withWindowedWrites(). The change ensures that the generated filenames are valid on Windows by replacing colons with underscores, thereby preventing runtime errors and improving the robustness of Beam applications across different operating systems.

Highlights

• Windows Compatibility: Addressed an InvalidPathException on Windows by replacing colons with underscores in window filenames generated by DefaultFilenamePolicy.
• Filename Policy Update: Modified the windowToString method to ensure ISO-8601 formatted window strings are compatible with Windows file path restrictions.

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Changelog

• sdks/java/core/src/main/java/org/apache/beam/sdk/io/DefaultFilenamePolicy.java
  • Modified the windowToString method to replace colons with underscores in the start and end strings of IntervalWindow objects.

Activity

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