如何基于一些会话信息自动装配Spring bean

Question

We are working on a multilingual Spring based web application (not Spring Boot).

Now we are searching for the "spring way" of doing the following.

1. user starts a http session with some parameters, eg a locale "de" and/or a country-code "DE" (the type of parameter isn't really important)
2. user works with application
3. at some point the user triggers an action that somewhere deep inside needs a "localized" functionality

Example (java pseudocode):

// service with functionality common for all users
@Service
class CommonService implements ICommonService
{
    // how to autowire a service based on some info in the actual HttpSession, eg. CustomServiceUK or CustomServiceDE
    @Autowired
    private ICustomService customServiceImpl;

    @Override
    public void doSomeAction(String param)
    {
        ... do some common stuff

        customResult = customServiceImpl.calculate(param);

        ... do some common stuff with custom result
    }
}

// custom service implementations
@Service("CustomServiceUK")
class CustomServiceUK implements ICustomService
{
    @Override
    public String calculate(String value)
    {
        ... execute logic on value for an "uk" user
    }
}

@Service("CustomServiceDE")
class CustomServiceDE implements ICustomService
{
    @Override
    public String calculate(String value)
    {
        ... execute logic on value for an "de" user
    }
}

How to inject a custom service based on some info in the actual HttpSession (eg CustomServiceUK or CustomServiceDE) into CommonService? What are our options to solve this issue? Is there something like a dynamic @Qualifier or some @Autowired Spring-Factory thing?

(the service implementation to use must not necessarily depend on the locale of the user but on some other piece of session/request information)

Answer 1

Thanks for your answers.

Actually we end up with the following solution which works for us.

We created an additional implementation of ICustomService with name CustomServiceProxy. This service has @Primary annotation to tell Spring that this component should be injected when no explicit qualifier is supplied. The service gets the sessionData and a Map with all Spring managed ICustomService-Components injected (Map-Key = Qualifier of the Component). Now when some method on CustomServiceProxy gets called, it generates the Map-Key based on the actual sessionData (eg language), lookup the ICustomService in the Map and delegates the call to this specific service.

// service with functionality common for all users
@Service
class CommonService implements ICommonService
{
    // because of @Primary an instance of CustomServiceProxy will be injected
    @Autowired
    private ICustomService customServiceImpl;

    @Override
    public void doSomeAction(String param)
    {
        ... do some common stuff

        customResult = customServiceImpl.calculate(param);

        ... do some common stuff with custom result
    }
}

// custom service implementations
@Service
@Primary
class CustomServiceProxy implements ICustomService
{
    private CustomData sessionData;
    private Map<String, ICustomService> services;

    @Autowired
    public CustomServiceProxy(CustomData sessionData, Map<String, ICustomService> services)
    {
        this.sessionData = sessionData;
        this.services = services;
    }

    @Override
    public String calculate(String value)
    {
        String serviceName = "CustomService" + sessionData.getLanguage().toUpperCase();
        ICustomService customService = services.get(serviceName);
        // handle missing service: throw exception or maybe switch to a default implementation
        Objects.requireNonNull(customService, "missing CustomService with name " + serviceName);
        return customService.calculate(value);
    }
}

@Service("CustomServiceUK")
class CustomServiceUK implements ICustomService
{
    @Override
    public String calculate(String value)
    {
        ... execute logic on value for an "uk" user
    }
}

@Service("CustomServiceDE")
class CustomServiceDE implements ICustomService
{
    @Override
    public String calculate(String value)
    {
        ... execute logic on value for an "de" user
    }
}