RFR: 8314774: Optimize URLEncoder [v10]

[Claes Redestad]

On Tue, 5 Sep 2023 23:43:31 GMT, Glavo <duke at openjdk.org> wrote:

>> I mainly made these optimizations:
>> 
>> * Avoid allocating `StringBuilder` when there are no characters in the URL that need to be encoded;
>> * Implement a fast path for UTF-8.
>> 
>> In addition to improving performance, these optimizations also reduce temporary objects:
>> 
>> * It no longer allocates any object when there are no characters in the URL that need to be encoded;
>> * The initial size of StringBuilder is larger to avoid expansion as much as possible;
>> * For UTF-8, the temporary `CharArrayWriter`, strings and byte arrays are no longer needed.
>> 
>> The results of the `URLEncodeDecode` benchmark:
>> 
>> 
>> Before:
>> Benchmark                       (count)  (maxLength)  (mySeed)  Mode  Cnt  Score   Error  Units
>> URLEncodeDecode.testEncodeUTF8     1024         1024         3  avgt   15  5.587 ? 0.010  ms/op
>> 
>> After:
>> Benchmark                       (count)  (maxLength)  (mySeed)  Mode  Cnt  Score   Error  Units
>> URLEncodeDecode.testEncodeUTF8     1024         1024         3  avgt   15  3.582 ? 0.054  ms/op
>> 
>> 
>> I also updated the tests to add more test cases.
>
> Glavo has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove unused import

src/java.base/share/classes/java/net/URLEncoder.java line 140:

> 138:     }
> 139: 
> 140:     private static void encodeByte(StringBuilder out, byte b) {

This routine is basically 

out.append('%');
HexFormat.of().withUpperCase().toHexDigits(out, b);

If this doesn't perform as well (with or without `HexFormat.of().withUpperCase()` cached in a static field) then that might be worth looking into.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15354#discussion_r1317213624