On 29/06/2025 17:03, wenshao wrote:
BufferedWriter -> OutputStreamWriter -> StreamEncoder

In this call chain, BufferedWriter has a char[] buffer, and StreamEncoder has a ByteBuffer. There are two layers of cache here, or the BufferedWriter layer can be removed.

LATIN1 (byte[]) -> UTF16 (char[]) -> UTF8 (byte[])

And when charset is UTF8, if the content of write(String) is LATIN1, a conversion from LATIN1 to UTF16 and then to LATIN1 will occur here.

We can improve BufferedWriter. When the parameter Writer instanceof OutputStreamWriter is passed in, remove the cache and call it directly. In addition, improve write(String) in StreamEncoder to avoid unnecessary encoding conversion.

I see you've already proposed a PR. Most of this code goes back to JDK 1.4 so we need to be very careful, any changes will require a lot of Reviewer cycles.

Have you surveyed the tests to ensure that there are good tests with different charsets and usage patterns? I think we need to be confidence in the tests before touching anything.

-Alan

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