如何使用Weld SE(CDI)异步创建Bean？

Great question! Let's break this down clearly for your JavaFX + AfterburnerFX + Weld SE setup:

First, the straight answer: Weld SE doesn't have a built-in, direct mechanism for asynchronous bean instantiation out of the box. CDI (and Weld as its reference implementation) is fundamentally designed around synchronous bean creation and injection, since the core spec assumes dependencies are ready when a bean is initialized. That said, there are several proven patterns to handle your slow-initializing dependency without freezing your dialog UI.

1. Use Provider<T> for Lazy + Async Instantiation #

CDI's javax.inject.Provider<T> is your go-to tool here. It lets you defer bean instantiation until you explicitly call get(), which you can run on a background thread to avoid blocking the JavaFX UI thread. This is perfect for heavy dependencies that don't need to be ready the second your dialog loads.

Example in your AfterburnerFX presenter:

import javax.inject.Inject;
import javax.inject.Provider;
import javafx.application.Platform;
import javafx.fxml.FXML;
import javafx.scene.control.Label;
import java.util.concurrent.CompletableFuture;

public class SlowDialogPresenter {
    @Inject
    private Provider<HeavyDependency> heavyDependencyProvider;
    
    @FXML
    private Label loadingStatus;

    public void initialize() {
        // Show loading state immediately to the user
        loadingStatus.setText("Preparing resources...");
        
        // Spin up a background thread to instantiate the heavy dependency
        CompletableFuture.supplyAsync(() -> heavyDependencyProvider.get())
            .thenAcceptAsync(heavyDep -> {
                // Update UI only on the JavaFX Application Thread
                loadingStatus.setText("Ready!");
                // Now use your fully initialized dependency for dialog logic
                heavyDep.executeCriticalWork();
            }, Platform::runLater)
            .exceptionally(ex -> {
                // Handle initialization failures gracefully on the UI thread
                Platform.runLater(() -> 
                    loadingStatus.setText("Failed to load: " + ex.getMessage())
                );
                return null;
            });
    }
}

Mark your heavy dependency with @Lazy (optional but recommended to ensure Weld doesn't instantiate it prematurely):

import jakarta.enterprise.context.Singleton;
import org.jboss.weld.context.ejb.Lazy;

@Lazy
@Singleton // Use @Dependent instead if you need a new instance each time
public class HeavyDependency {
    public HeavyDependency() {
        // Simulate slow initialization (e.g., connecting to a remote service)
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
    }

    public void executeCriticalWork() {
        // Your business logic here
    }
}

2. Preload the Dependency in the Background on App Startup #

If your heavy dependency is used across multiple dialogs or parts of the app, initialize it once in the background when your app launches. This way, it's already ready when the user opens the dialog.

In your JavaFX Application class:

import javafx.application.Application;
import javafx.stage.Stage;
import org.jboss.weld.environment.se.Weld;
import org.jboss.weld.environment.se.WeldContainer;
import java.util.concurrent.CompletableFuture;

public class MyApp extends Application {
    private static WeldContainer weldContainer;
    private static HeavyDependency preloadedHeavyDep;

    @Override
    public void init() throws Exception {
        // Initialize Weld SE
        weldContainer = new Weld().initialize();
        
        // Preload the heavy dependency in a background thread
        CompletableFuture.supplyAsync(() -> weldContainer.select(HeavyDependency.class).get())
            .thenAccept(dep -> preloadedHeavyDep = dep)
            .exceptionally(ex -> {
                System.err.println("Failed to preload dependency: " + ex.getMessage());
                return null;
            });
    }

    @Override
    public void start(Stage primaryStage) throws Exception {
        // Launch your main UI
        // ...
    }

    // Expose the preloaded dependency for easy access
    public static HeavyDependency getPreloadedHeavyDep() {
        return preloadedHeavyDep;
    }
}

Then in your dialog presenter, you can inject the singleton directly or fetch the preloaded instance—no wait time when the dialog opens.

3. Wrap the Dependency in an Async Factory #

Create a dedicated factory bean that encapsulates the asynchronous instantiation logic, returning a CompletableFuture<HeavyDependency> instead of the raw dependency. This keeps your presenter code clean and separates concerns.

import javax.inject.Inject;
import javax.inject.Provider;
import java.util.concurrent.CompletableFuture;

public class HeavyDependencyFactory {
    @Inject
    private Provider<HeavyDependency> heavyDepProvider;

    public CompletableFuture<HeavyDependency> createAsync() {
        return CompletableFuture.supplyAsync(heavyDepProvider::get);
    }
}

Then inject this factory into your presenter:

@Inject
private HeavyDependencyFactory heavyDepFactory;

public void initialize() {
    loadingStatus.setText("Loading...");
    heavyDepFactory.createAsync()
        .thenAcceptAsync(this::onDependencyReady, Platform::runLater)
        .exceptionally(this::handleLoadFailure);
}

private void onDependencyReady(HeavyDependency dep) {
    // Use the initialized dependency here
}

private Void handleLoadFailure(Throwable ex) {
    Platform.runLater(() -> loadingStatus.setText("Error: " + ex.getMessage()));
    return null;
}

Key Reminders for JavaFX + AfterburnerFX #

• Always update UI components on the JavaFX Application Thread (use Platform.runLater() for this, as shown in examples)—never modify UI elements from a background thread.
• AfterburnerFX presenters are initialized on the FX thread, so any slow operations here will freeze the UI—offloading dependency instantiation is critical.
• Choose the right scope for your heavy dependency: @Singleton for shared resources, @Dependent if you need a fresh instance each time.

内容的提问来源于stack exchange，提问作者Valya