SpanKindExtractor (instrumentation-api 1.1.0 API)

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.
```
@FunctionalInterface
public interface SpanKindExtractor<REQUEST>
```
Extractor or SpanKind. In most cases, the span kind will be constant for server or client requests, but you may need to implement a custom SpanKindExtractor if a framework can generate different kinds of spans, for example both HTTP and messaging spans.

Method Summary

All Methods Static Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`static <REQUEST> SpanKindExtractor<REQUEST>`	`alwaysClient()`	Returns a `SpanNameExtractor` which always returns `SpanKind.CLIENT`.
`static <REQUEST> SpanKindExtractor<REQUEST>`	`alwaysInternal()`	Returns a `SpanNameExtractor` which always returns `SpanKind.INTERNAL`.
`static <REQUEST> SpanKindExtractor<REQUEST>`	`alwaysServer()`	Returns a `SpanNameExtractor` which always returns `SpanKind.SERVER`.
`io.opentelemetry.api.trace.SpanKind`	`extract(REQUEST request)`	Returns the `SpanKind` corresponding to the `SpanKindExtractor`.

- Method Detail
  - alwaysInternal
```
static <REQUEST> SpanKindExtractor<REQUEST> alwaysInternal()
```
    Returns a SpanNameExtractor which always returns SpanKind.INTERNAL.
  - alwaysClient
```
static <REQUEST> SpanKindExtractor<REQUEST> alwaysClient()
```
    Returns a SpanNameExtractor which always returns SpanKind.CLIENT.
  - alwaysServer
```
static <REQUEST> SpanKindExtractor<REQUEST> alwaysServer()
```
    Returns a SpanNameExtractor which always returns SpanKind.SERVER.
  - extract
```
io.opentelemetry.api.trace.SpanKind extract(REQUEST request)
```
    Returns the SpanKind corresponding to the SpanKindExtractor.