Returns a new CompletionStage that, when this stage completes
normally, is executed using the supplied Executor, with this
stage's result as the argument to the supplied function.
See the {@link CompletionStage} documentation for rules
covering exceptional completion.
@param fn the function to use to compute the value of the
returned CompletionStage
@param executor the executor to use for asynchronous execution
@param (U) the function's return type
@return the new CompletionStage
Returns a new CompletionStage that, when this stage completes normally, is executed using the supplied Executor, with this stage's result as the argument to the supplied function.
See the {@link CompletionStage} documentation for rules covering exceptional completion.
@param fn the function to use to compute the value of the returned CompletionStage @param executor the executor to use for asynchronous execution @param (U) the function's return type @return the new CompletionStage