Module jdk.dynalink
Package jdk.dynalink.beans

Interface MissingMemberHandlerFactory

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 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 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.
See Also:
BeansLinker(MissingMemberHandlerFactory)

  • Method Details

    • createMissingMemberHandler

      MethodHandle createMissingMemberHandler​(LinkRequest linkRequest, LinkerServices linkerServices) throws Exception
      Returns a method handle suitable for implementing missing member behavior for a particular link request. See the class description for details.
      Parameters:
      linkRequest - the current link request
      linkerServices - the current link services
      Returns:
      a method handle that can be invoked if the property, element, or method being addressed by an operation is missing. The return value can be null.
      Throws:
      Exception - if the operation fails for any reason. Please observe the class documentation notes for implementing exception-throwing missing member behavior.