RFR: 8340232: Optimize DataInputStream::readUTF

[Chen Liang]

On Sun, 8 Sep 2024 10:05:35 GMT, ExE Boss <duke 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);

We should use `StandardCharsets` as in most other standard usages. This method is not on bootstrap path, so readability is more important.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20903#discussion_r1749203988