Benutzerbenachrichtigungen implementieren

What are User Notifications?

Core Notification System

Crafting a Notification Model

Server-Side Notification Creation

public class Notification {
  private String id;
  private String recipientId;
  private String senderId;
  private String message;
  private String type;
  private long timestamp;
  private boolean isRead;

  // Constructor
  public Notification(String recipientId, String senderId, String message, String type) {
    this.id = java.util.UUID.randomUUID().toString();
    this.recipientId = recipientId;
    this.senderId = senderId;
    this.message = message;
    this.type = type;
    this.timestamp = System.currentTimeMillis();
    this.isRead = false;
  }

  // Getters (and setters if needed)
  public String getId() { return id; }
  public String getRecipientId() { return recipientId; }
  public String getSenderId() { return senderId; }
  public String getMessage() { return message; }
  public String getType() { return type; }
  public long getTimestamp() { return timestamp; }
  public boolean isRead() { return isRead; }
  public void setRead(boolean read) { isRead = read; }

  @Override
  public String toString() {
    return "Notification [recipient=" + recipientId + ", msg='" + message + "']";
  }
}

Directing User Notifications

Pushing Notifications (Server Concept)

public class Notification {
  private String recipientId;
  private String message;
  private long timestamp;

  public Notification(String recipientId, String message) {
    this.recipientId = recipientId;
    this.message = message;
    this.timestamp = System.currentTimeMillis();
  }

  public String getRecipientId() { return recipientId; }
  public String getMessage() { return message; }
  public long getTimestamp() { return timestamp; }

  @Override
  public String toString() {
    return "Notification [to=" + recipientId + ", msg='" + message + "']";
  }

  public static void main(String[] args) {
    // This simulates creating and conceptually sending a notification
    String userId = "user123";
    String notificationMessage = "You have a new message!";
    Notification newNotification = new Notification(userId, notificationMessage);

    System.out.println("Created notification: " + newNotification);
    System.out.println("Spring's SimpMessagingTemplate would then send this to /user/" + userId + "/queue/notifications");
    System.out.println("Client-side would receive this via their WebSocket subscription.");
  }
}

Client Listens for Updates

Client-Side Subscription (JS)

// Assume 'stompClient' is already connected to WebSocket
// and authenticated.

// Function to handle incoming notifications
function onNotificationReceived(notification) {
  console.log("Received notification:", notification.body);
  // Parse JSON body, e.g., JSON.parse(notification.body)
  // Then update UI to display the notification
  displayNotification(JSON.parse(notification.body));
}

// Function to display notification in UI
function displayNotification(notifObj) {
    const notifArea = document.getElementById("notificationArea");
    const newNotif = document.createElement("div");
    newNotif.innerHTML = `<b>${notifObj.message}</b> 
                              <small>(${new Date(notifObj.timestamp).toLocaleTimeString()})</small>`;
    notifArea.prepend(newNotif);
}

// Subscribe to the user's private notification queue
stompClient.subscribe('/user/queue/notifications', onNotificationReceived);

console.log("Subscribed to /user/queue/notifications");
// In a real app, you'd have a 'connect' function first.
// Example: stompClient.connect({}, frame => { ... subscribe here ... });

Marking Notifications as Read

Notification Delivery Check

Recap: Building Notifiers