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
GuardingDynamicLinker.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.