> We need a String format solution with good performance. String Template was
> once expected, but it has been removed. j.u.Formatter is powerful, but its
> performance is not good enough.
>
> This PR implements a subset of j.u.Formatter capabilities. The performance is
> good enough that it is a fastpath for commonly used functions. When the
> supported functions are exceeded, it will fall back to using j.u.Formatter.
>
> The performance of this implementation is good enough, the fastpath has low
> detection cost, There is no noticeable performance degradation when falling
> back to j.u.Formatter via fastpath.
>
> Below is a comparison of String.format and concat-based and StringBuilder:
>
> * benchmark java code
>
> public class StringFormat {
> @Benchmark
> public String stringIntFormat() {
> return "%s %d".formatted(s, i);
> }
>
> @Benchmark
> public String stringIntConcat() {
> return s + " " + i;
> }
>
> @Benchmark
> public String stringIntStringBuilder() {
> return new StringBuilder(s).append(" ").append(i).toString();
> }
> }
>
>
> * benchmark number on macbook m1 pro
>
> Benchmark Mode Cnt Score Error Units
> StringFormat.stringIntConcat avgt 15 6.541 ? 0.056 ns/op
> StringFormat.stringIntFormat avgt 15 17.399 ? 0.133 ns/op
> StringFormat.stringIntStringBuilder avgt 15 8.004 ? 0.063 ns/op
>
>
> From the above data, we can see that the implementation of fastpath reduces
> the performance difference between String.format and StringBuilder from 10
> times to 2~3 times.
>
> The implementation of fastpath supports the following four specifiers, which
> can appear at most twice and support a width of 1 to 9.
>
> d
> x
> X
> s
>
> If necessary, we can add a few more.
>
>
> Below is a comparison of performance numbers running on a MacBook M1, showing
> a significant performance improvement.
>
> -Benchmark Mode Cnt Score Error Units
> (baseline)
> -StringFormat.complexFormat avgt 15 895.954 ? 52.541 ns/op
> -StringFormat.decimalFormat avgt 15 277.420 ? 18.254 ns/op
> -StringFormat.stringFormat avgt 15 66.787 ? 2.715 ns/op
> -StringFormat.stringIntFormat avgt 15 81.046 ? 1.879 ns/op
> -StringFormat.widthStringFormat avgt 15 38.897 ? 0.114 ns/op
> -StringFormat.widthStringIntFormat avgt 15 109.841 ? 1.028 ns/op
>
> +Benchmark Mode Cnt Score Error Units
> (current f925339e93fdf7a281462554ce5d73139bd0f0cd)
> +StringFormat.complexF...
Shaojin Wen has updated the pull request incrementally with one additional
commit since the last revision:
private method & field
-------------
Changes:
- all: https://git.openjdk.org/jdk/pull/19956/files
- new: https://git.openjdk.org/jdk/pull/19956/files/5bcbb358..39ef5815
Webrevs:
- full: https://webrevs.openjdk.org/?repo=jdk&pr=19956&range=04
- incr: https://webrevs.openjdk.org/?repo=jdk&pr=19956&range=03-04
Stats: 9 lines in 1 file changed: 0 ins; 0 del; 9 mod
Patch: https://git.openjdk.org/jdk/pull/19956.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/19956/head:pull/19956
PR: https://git.openjdk.org/jdk/pull/19956
