@FunctionalInterface public interface MissingMemberHandlerFactory

A factory for creating method handles for linking missing member behavior in BeansLinker. BeansLinker links these method handles into guarded invocations for link requests specifying GET_* and SET_* StandardOperations when it is either certain or possible that the requested member (property, method, or element) is missing. They will be linked both for named and unnamed operations. The implementer must ensure that the parameter types of the returned method handle match the parameter types of the call site described in the link request. The return types can differ, though, to allow DynamicLinkerFactory.setPrelinkTransformer(jdk.dynalink.linker.GuardedInvocationTransformer) late return type transformations}. It is allowed to return null for a method handle if the default behavior is sufficient.

Default missing member behavior

When a BeansLinker is configured without a missing member handler factory, or the factory returns null for a particular handler creation invocation, the default behavior is used. The default behavior is to return null from BeansLinker.getGuardedInvocation(LinkRequest, LinkerServices) when it can be determined at link time that the linked operation will never address an existing member. This lets the DynamicLinker attempt the next linker if there is one, or ultimately fail the link request with NoSuchDynamicMethodException. For other cases (typically all unnamed member operations as well as most named operations on collection elements) BeansLinker will produce a conditional linkage that will return null when invoked at runtime with a name that does not match any member for getters and silently ignore the passed values for setters.

Implementing exception-throwing behavior

Note that if the language-specific behavior for an operation on a missing member is to throw an exception then the factory should produce a method handle that throws the exception when invoked, and must not throw an exception itself, as the linkage for the missing member is often conditional.