RFR: 8259699: Reduce char[] copying in URLEncoder.encode(String, Charset)

[Сергей Цыпанов]

Instead of allocating a copy of underlying array via `CharArrayWriter.toCharArray()` and passing it to constructor of String
String str = new String(charArrayWriter.toCharArray());
we could call `toString()` method
String str = charArrayWriter.toString();
decoding existing char[] without making a copy. This slightly speeds up the method reducing at the same time memory consumption for decoding URLs with non-latin symbols:
@State(Scope.Thread)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@Fork(jvmArgsAppend = {"-Xms2g", "-Xmx2g"})
public class UrlEncoderBenchmark {
  private static final Charset charset = Charset.defaultCharset();
  private static final String utf8Url = "https://ru.wikipedia.org/wiki/Организация_Объединённых_Наций"; // UN

  @Benchmark
  public String encodeUtf8() {
    return URLEncoder.encode(utf8Url, charset);
  }
}
The benchmark on my maching give the following output:
before
Benchmark                                                        Mode  Cnt     Score    Error   Units
UrlEncoderBenchmark.encodeUtf8                                   avgt  100  1166.378 ±  8.411   ns/op
UrlEncoderBenchmark.encodeUtf8:·gc.alloc.rate                    avgt  100   932.944 ±  6.393  MB/sec
UrlEncoderBenchmark.encodeUtf8:·gc.alloc.rate.norm               avgt  100  1712.193 ±  0.005    B/op
UrlEncoderBenchmark.encodeUtf8:·gc.churn.G1_Eden_Space           avgt  100   929.221 ± 24.268  MB/sec
UrlEncoderBenchmark.encodeUtf8:·gc.churn.G1_Eden_Space.norm      avgt  100  1705.444 ± 43.235    B/op
UrlEncoderBenchmark.encodeUtf8:·gc.churn.G1_Survivor_Space       avgt  100     0.006 ±  0.001  MB/sec
UrlEncoderBenchmark.encodeUtf8:·gc.churn.G1_Survivor_Space.norm  avgt  100     0.011 ±  0.002    B/op
UrlEncoderBenchmark.encodeUtf8:·gc.count                         avgt  100   652.000           counts
UrlEncoderBenchmark.encodeUtf8:·gc.time                          avgt  100   334.000               ms

after
Benchmark                                                        Mode  Cnt     Score    Error   Units
UrlEncoderBenchmark.encodeUtf8                                   avgt  100  1058.851 ±  6.006   ns/op
UrlEncoderBenchmark.encodeUtf8:·gc.alloc.rate                    avgt  100   931.489 ±  5.182  MB/sec
UrlEncoderBenchmark.encodeUtf8:·gc.alloc.rate.norm               avgt  100  1552.176 ±  0.005    B/op
UrlEncoderBenchmark.encodeUtf8:·gc.churn.G1_Eden_Space           avgt  100   933.491 ± 24.164  MB/sec
UrlEncoderBenchmark.encodeUtf8:·gc.churn.G1_Eden_Space.norm      avgt  100  1555.488 ± 39.204    B/op
UrlEncoderBenchmark.encodeUtf8:·gc.churn.G1_Survivor_Space       avgt  100     0.006 ±  0.001  MB/sec
UrlEncoderBenchmark.encodeUtf8:·gc.churn.G1_Survivor_Space.norm  avgt  100     0.010 ±  0.002    B/op
UrlEncoderBenchmark.encodeUtf8:·gc.count                         avgt  100   655.000           counts
UrlEncoderBenchmark.encodeUtf8:·gc.time                          avgt  100   333.000               ms

-------------

Commit messages:
 - Merge branch 'master' into enc
 - Improve URLEncoder.encode(String, Charset)

Changes: https://git.openjdk.java.net/jdk/pull/1598/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1598&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8259699
  Stats: 8 lines in 1 file changed: 0 ins; 0 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1598.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1598/head:pull/1598

PR: https://git.openjdk.java.net/jdk/pull/1598