RFR: 8340232: Optimize DataInputStream::readUTF

[ExE Boss]

On Sun, 8 Sep 2024 07:52:26 GMT, Shaojin Wen <swen at openjdk.org> wrote:

> Similar to ObjectInputStream, use JLA.countPositives and JLA.inflateBytesToChars to speed up readUTF

src/java.base/share/classes/java/io/DataInputStream.java line 602:

> 600:         int ascii = JLA.countPositives(bytearr, 0, utflen);
> 601:         if (ascii == utflen) {
> 602:             return new String(bytearr, 0, utflen, StandardCharsets.ISO_8859_1);

Maybe use `sun.nio.cs​.ISO_8859_1​.INSTANCE` instead in order to avoid initialising unused charsets:
Suggestion:

            return new String(bytearr, 0, utflen, ISO_8859_1.INSTANCE);

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PR Review Comment: https://git.openjdk.org/jdk/pull/20903#discussion_r1749167163