Play Framework

perf: cache Scala default-method probe in Binder.bind (PF-103)

Binder.bind probes for Scala-style $default$N helper methods on every
parameter bind via Class.getDeclaredMethod. In Java-only Play apps the
lookup always misses, so each bind throws NoSuchMethodException — a JDK
exception with a full stack walk and a StackTraceElement allocation. A
3-parameter action under load produces three throws per request. Pure
control-flow overhead with no observable behavioural effect.

Replace the per-call probe with a ConcurrentHashMap cache keyed by
declaring-class-name + method-name + parameter-index. The first lookup
resolves reflectively and stores either the resolved Method or a static
sentinel for the negative case; every subsequent lookup is a single map
read. The sentinel is a private no-op method on Binder reached via
class-init-time reflection, so a cache hit allocates nothing.

Behaviour preserved: Scala apps still resolve the real helper on the
first probe and cache it; Java apps cache the sentinel and skip the
throw on every subsequent call. The primitive-default fall-through is
unchanged. No public API surface changes — the cache + sentinel are
package-private only so tests can verify population.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>