使用ManagedProperty有条件地注入bean

Question

I have a controller with the following properties:

@ManagedProperty(value="#{remoteApplication}")
private transient ProcessService applicationService;

@ManagedProperty(value="#{remoteSystem}")
private transient SystemService systemService;

@ManagedProperty(value="#{remoteFileSystem}")
private transient FileSystemService fileSystemService;

I would like to inject beans conditionally, according to a property file telling if the services shall be local or remote.

Example provided hereabove is for remote, and for local, would be:

@ManagedProperty(value="#{localApplication}")
private transient ProcessService applicationService;

@ManagedProperty(value="#{localSystem}")
private transient SystemService systemService;

@ManagedProperty(value="#{localFileSystem}")
private transient FileSystemService fileSystemService;

Is there any way to do this with JSF (maybe using ValueExpression as specified in ManagedProperty documentation ) ? Or do I have to use CDI ?

Many thanks in advance for your suggestions!

Kind regards,

Zim

Answer 1

You can do it with just JSF, even a CDI integration could help you dividing it in proper layers. Take a look at this JSF solution, using an application scoped bean which manages the configuration. The scope of the Bean can be anyone you need. Being your Service classes @ManagedBean :

@ManagedBean
@ApplicationScoped
public class LocalProcessService implements ProcessService {

    public LocalProcessService() {
        System.out.println("Local service created");
    }

}

@ManagedBean
@ApplicationScoped
public class RemoteProcessService implements ProcessService {

    public RemoteProcessService() {
        System.out.println("Remote service created");
    }

}

Then, implement a Configuration Bean which reads the file you want and stores a flag with the read value. I use a Random function for testing purpose:

@ManagedBean(eager = true)
@ApplicationScoped
public class PropertiesBean {

    private boolean localConfig = false;

    public PropertiesBean() {
        // Read your config file here and determine wether it is local
        //or remote configuration
        if (new Random().nextInt(2) == 1) {
            localConfig = true;
        }
    }

    public boolean isLocalConfig() {
        return localConfig;
    }

}

Once you've got it, in your view controller make the injection depending on that flag value, using a ternary operator:

@ManagedBean
@ViewScoped
public class Bean {

    @ManagedProperty(value = "#{propertiesBean.localConfig ? localProcessService : remoteProcessService}")
    protected ProcessService processService;

    public void setProcessService(ProcessService processService) {
        this.processService = processService;
    }

}

Alternativelly, you could store the service reference directly in your PropertiesBean , in order not to have to evaluate that flag value in your managed beans. Just evaluate the EL expression you need into the context (see the reference).

See also:

• Get JSF managed bean by name in any Servlet related class