Switching injected implementations based on runtime parameters

[tew88]

Hi,

An approximation of my problem as follows:

Based upon a value that I will parse from an incoming request, I wish to inject one of two implementations of my interface.  Where is this logic best placed?

More specifically:

public interface NetworkCommunicator {

    public void sendCommandToNetwork(Command command, NetworkElement recipient);

}

--

public class OldNetworkCommunicatorImpl implements NetworkCommunicator {

    @Override

    public void sendCommandToNetwork(Command command, NetworkElement recipient) {

        ...

    }

}

--

public class NewNetworkCommunicatorImpl implements NetworkCommunicator {

    @Override

    public void sendCommandToNetwork(Command command, NetworkElement recipient) {

        ...

    }

}

--

public class NetworkCommandIssuer {

    private final NetworkCommunicator networkCommunicator;

    @Inject

    public NetworkCommandIssuer(final NetworkCommunicator networkCommunicator) {

        this.networkCommunicator = networkCommunicator;

    }

}

--

Based on some arbitrary mapping, I'd like to wire up my NetworkCommandIssuer to use my NewNetworkCommunicatorImpl implementation instead of my OldNetworkCommunicatorImpl implementation.  This will change from request to request.  So, where should I define this behaviour?

I'm new to Guice and DI in general, so please assume as little as possible in your responses!

Thanks in advance,

tew88

[Martin Grajcar]

I had a similar. Just

bind(NetworkCommunicator.class)

    .toProvider(NetworkCommunicator.class);

Inject all needed information into your provider and let it take the decision. 

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[Tom Wadeson]

Hi Martin,

Thanks for the reply.

Could I trouble you for a minimal example of what that provider might look like?

Cheers,
tew88

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[Martin Grajcar]

On Tue, Sep 9, 2014 at 12:26 AM, Tom Wadeson <tom...@gmail.com> wrote:

Hi Martin,

Thanks for the reply.

Could I trouble you for a minimal example of what that provider might look like?

A running example (needs Lombok, but that's trivial to resolve):

https://dl.dropboxusercontent.com/u/4971686/published/maaartin/misc/Tew88.java

Regards,

Martin.

[Tom Wadeson]

Thanks very much, Martin.  Just what I needed!  :)

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