春季：如何動態獲取bean實現？

Question

假設我們有接口：

public interface IAuthentication { }

和兩個實現：

public class LdapAuthentication implements IAuthentication {}

public class DbAuthentication implements IAuthentication {}

最后，我們有一個負責處理身份驗證的bean。 該bean應該使用上面顯示的一種實現（基於db中指定的配置）。

@Service
public class AuthenticationService {
    public boolean authenticate(...) {
        boolean useDb = ...;   //got from db
        //my problem here
        //how to get right implementation: either LdapAuthentication or DbAuthentication?
        IAuthentication auth = ...;
        return auth.authenticate(...);
    }
}

題：
如何獲得正確的實施？

Answer 1

如果參數值不變：

@Service
public class AuthenticationService {

    private IAuthentication auth;

    @PostConstruct
    protected void init() {
        boolean useDb = ...;   //got from db
        this.auth = ...; //choose correct one
    }
    public boolean authenticate(...) {        
        return auth.authenticate(...);
    }
}

如果參數是動態的

@Service
public class AuthenticationService {

    @Autowired
    private ApplicationContext сontext;

    public boolean authenticate(...) { 
        boolean useDb = ...;   //got from db
        IAuthentication auth = context.getBean(useDb ? DbAuthentication.class : LdapAuthentication.class);       
        return auth.authenticate(...);
    }
}