I'm not completely following your code example, but I think I have a basic
understanding of your problem and I think I may have had similar issues in
the past. You have an input parameter you want to pass down through your
call chain, and you have an output you want to return back up your call
chain. I don't think Guice really makes this anymore difficult, and it may
have some things you can leverage to make it easier.
How would you go about doing this if you weren't using Guice? If you're
wanting to pass parameters to objects via their constructor, well you are
delegating to Guice and your Guice modules to construct your object graph
so your options are slightly limited. If you are in the context of
receiving an HTTP request, you could use a @RequestScoped variable to store
the data, then access the @RequestScoped variable to construct the leaf
object. If you are not in the context of an HTTP request, but all the calls
are happening in the same thread, then you could use a ThreadLocal variable
to store the data. Or you could get fancy and implement a CustomScope,
although this is generally not recommended and you would likely need to
leverage ThreadLocal or some global/static mechanism to make it work
anyway. In any of these cases, you will likely need to delay the creation
of your leaf object until you've had a chance to set the input data (in
RequestScoped or ThreadLocal), you can do this by using a Guice Provider to
get an instance of the leaf object, then just make sure you call the
Provider sometime after the input data has been set.
Another (maybe too obvious?) solution, would be to just pass the input
parameter via a typical method invocation, and return the output through
the return. Is there a reason why you can't do that? You can separate
constructing your system from using it by using Guice to construct your
object graph, but then calling methods with parameters and return values to
pass values up and down the call stack.
On Saturday, March 30, 2013 11:21:36 AM UTC-5, caseybasichis wrote:
>
> Hi.
>
> So i realize this is a kind of circular dependency.
>
> How do you all go about taking a serial DI chain that takes an input and
> output?
>
> The only method i've been able to come up with is sticking a session scope
> object at the top of each chain so I can pass it a global value as an input
> for it to send down the chain. This seems like an awful practice.
>
> On Thursday, March 28, 2013 8:19:46 AM UTC-7, caseybasichis wrote:
>>
>> Hi,
>>
>> class E {
>> public:
>> E(D);
>> setLeafData(AData);
>> getE();
>> };
>>
>> class D {
>> public:
>> D(C)
>> ..
>>
>> class A {
>> public:
>> A();
>> setAData(AData)
>> getAData()
>> }
>>
>> myE = inject->E
>>
>> myE.setLeafData("blah")
>> myE.getE();
>>
>> Here is a basic idea. It's not Java, but the concept is a fundamental
>> question.
>>
>> On Thursday, March 28, 2013 7:52:05 AM UTC-7, Fred Faber wrote:
>>>
>>> Could you sketch a quick concrete example to show this in code real
>>> quick?
>>>
>>> On Thu, Mar 28, 2013 at 10:29 AM, caseybasichis <[email protected]>wrote:
>>>
>>>> Hi,
>>>>
>>>> I am struggling to understand how to give parameter information to leaf
>>>> nodes, from the root node in a DI setup similar to Guice.
>>>>
>>>> I have a class that takes a set of A's and generates E's.
>>>> (E(D(C(B(A)))))
>>>>
>>>> E is the injected, the rest are instantiated by the DI, A is an 'A
>>>> provider' or 'A factory'
>>>>
>>>> E is the interface, how can I get a path, or other const data from a
>>>> function in E to A, to start the function chain?
>>>>
>>>> In other words I have some simple data A, that gets processed through a
>>>> function chain, down to an E class which generates an E_Data object which
>>>> is then used in the root of my application.
>>>>
>>>> Do I string functions through E,D,C,B to get A's reference? That seems
>>>> wrong.
>>>>
>>>> Reversing the chain make the path simple A(B(C(D(E))))), but the only
>>>> way to get the output seems to be to attach a singleton to E like
>>>> A(B(C(D(E(SQL)))))).
>>>>
>>>> That seems like inversion-of-inversion of control, but it also seems
>>>> like a data manager could be made at the session scope that E could take
>>>> as
>>>> a constructor.
>>>>
>>>> What do I have flipped?
>>>>
>>>> Thanks,
>>>>
>>>> Casey
>>>>
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>>>>
>>>
>>>
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