Avoid StringBuilder.append(Object) in ContentDisposition

[stsypanov]

The return type of expression (c == '"' && !escaped) ? "\\\"" : c is Object, which implies a call to StringBuilder.append(Object).

The implementation of the following means that lots of garbage objects are allocated as a result of String.valueOf().

@Override
public StringBuilder append(Object obj) {
    return append(String.valueOf(obj));
}

Instead of covariant append we can use exact signatures, i.e. one taking char and one taking String which allows us to avoid unnecessary allocations.

This benchmark demonstrates significant improvement even for filename of length = 10:

JDK 8

Benchmark                              (latin)  (length)  Mode  Cnt     Score     Error   Units
appendCovariant                           true        10  avgt   50   180.230 ±  10.346   ns/op
appendExact                               true        10  avgt   50    68.517 ±   1.479   ns/op

appendCovariant                          false        10  avgt   50   177.713 ±   4.438   ns/op
appendExact                              false        10  avgt   50    67.798 ±   1.364   ns/op

appendCovariant:·gc.alloc.rate.norm       true        10  avgt   50   688.000 ±   0.001    B/op
appendExact:·gc.alloc.rate.norm           true        10  avgt   50   112.000 ±   0.001    B/op

appendCovariant:·gc.alloc.rate.norm      false        10  avgt   50   816.000 ±   0.001    B/op
appendExact:·gc.alloc.rate.norm          false        10  avgt   50   112.000 ±   0.001    B/op

JDK 14

Benchmark                              (latin)  (length)  Mode  Cnt     Score     Error   Units
appendCovariant                           true        10  avgt   50   228.858 ±  18.627   ns/op
appendExact                               true        10  avgt   50    57.950 ±   2.660   ns/op

appendCovariant                          false        10  avgt   50   292.879 ±  12.408   ns/op
appendExact                              false        10  avgt   50    90.228 ±   2.277   ns/op

appendCovariant:·gc.alloc.rate.norm       true        10  avgt   50   688.026 ±   0.002    B/op
appendExact:·gc.alloc.rate.norm           true        10  avgt   50   112.004 ±   0.001    B/op

appendCovariant:·gc.alloc.rate.norm      false        10  avgt   50  1096.040 ±   0.002    B/op
appendExact:·gc.alloc.rate.norm          false        10  avgt   50   200.008 ±   0.001    B/op

[sbrannen]

This has been merged into master.

Thanks

[rstoyanchev]

Good catch!