如何在EDT中运行Swing输入对话框并获取返回值？

Got it, let's break down how to solve this problem. The core issue is that Runnable.run() is a void method, so you can't directly return the input value from the EDT thread to your non-EDT trigger thread. Here's a clean, thread-safe way to capture that value:

Use an AtomicReference to Store the Result #

Since anonymous inner classes can only access variables that are final or effectively final, we need a mutable container that can hold the input value. AtomicReference is perfect here—it's thread-safe and works seamlessly with the EDT/non-EDT interaction.

Here's the complete code example:

import java.awt.EventQueue;
import java.util.concurrent.atomic.AtomicReference;
import javax.swing.JOptionPane;
import java.lang.reflect.InvocationTargetException;

// ... your existing chat app code ...

// In your non-EDT thread (server notification handler)
AtomicReference<String> usernameRef = new AtomicReference<>();

try {
    EventQueue.invokeAndWait(() -> {
        // This code runs safely on the EDT
        String username = JOptionPane.showInputDialog(null, "Choose your username:");
        usernameRef.set(username);
    });
} catch (InterruptedException | InvocationTargetException e) {
    // Handle exceptions appropriately (log, notify user, etc.)
    e.printStackTrace();
}

// Access the value from your non-EDT thread
String selectedUsername = usernameRef.get();
if (selectedUsername != null) {
    // User submitted a username, proceed with your chat logic
    System.out.println("User selected username: " + selectedUsername);
} else {
    // User canceled the dialog, handle this edge case
    System.out.println("User canceled username selection.");
}

Why This Works #

• AtomicReference<String> acts as a shared, thread-safe holder for the input value. We initialize it in the non-EDT thread, then the EDT thread sets its value once the user interacts with the dialog.
• EventQueue.invokeAndWait() blocks the non-EDT thread until the Runnable completes on the EDT, so once it returns, you can safely call usernameRef.get() to retrieve the value.
• We handle the checked exceptions thrown by invokeAndWait()—these occur if the waiting thread is interrupted, or if an error occurs inside the EDT-run code.

Critical Notes #

• Never call invokeAndWait() from the EDT itself—this will cause a deadlock, as the EDT will wait for itself to finish the task. Always confirm your trigger code runs on a non-EDT thread (like your server notification handler).
• If the user clicks "Cancel" or closes the dialog, JOptionPane.showInputDialog() returns null—make sure your code accounts for this to avoid null pointer exceptions or unexpected behavior.

内容的提问来源于stack exchange，提问作者Constantin Müller