Troostwijk Auction Scraper
A Java-based web scraper for Dutch auctions on Troostwijk Auctions with 100% free desktop/email notifications, SQLite persistence, and AI-powered object detection.
Features
- Auction Discovery: Automatically discovers active Dutch auctions
- Data Scraping: Fetches detailed lot information via Troostwijk's JSON API
- SQLite Storage: Persists auction data, lots, images, and detected objects
- Image Processing: Downloads and analyzes lot images using OpenCV YOLO object detection
- Free Notifications: Real-time notifications when:
- Bids change on monitored lots
- Auctions are closing soon (within 5 minutes)
- Via desktop notifications (Windows/macOS/Linux system tray) ✅
- Optionally via email (Gmail SMTP - free) ✅
Dependencies
All dependencies are managed via Maven (see pom.xml):
- jsoup 1.17.2 - HTML parsing and HTTP client
- Jackson 2.17.0 - JSON processing
- SQLite JDBC 3.45.1.0 - Database operations
- JavaMail 1.6.2 - Email notifications (free)
- OpenCV 4.9.0 - Image processing and object detection
Setup
1.. Notification Options (Choose One)
Option A: Desktop Notifications Only ⭐ (Recommended - Zero Setup)
Desktop notifications work out of the box on:
- Windows: System tray notifications
- macOS: Notification Center
- Linux: Desktop environment notifications (GNOME, KDE, etc.)
No configuration required! Just run with default settings:
export NOTIFICATION_CONFIG="desktop"
# Or simply don't set it - desktop is the default
Option B: Desktop + Email Notifications 📧 (Free Gmail)
- Enable 2-Factor Authentication in your Google Account
- Go to: Google Account → Security → 2-Step Verification → App passwords
- Generate an app password for "Mail"
- Set environment variable:
export NOTIFICATION_CONFIG="smtp:your.email@gmail.com:your_app_password:recipient@example.com"
Format: smtp:username:app_password:recipient_email
Example:
export NOTIFICATION_CONFIG="smtp:john.doe@gmail.com:abcd1234efgh5678:john.doe@gmail.com"
Note: This is completely free using Gmail's SMTP server. No paid services required!
2. OpenCV Native Libraries
Download and install OpenCV native libraries for your platform:
Windows:
# Download from https://opencv.org/releases/
# Extract and add to PATH or use:
java -Djava.library.path="C:\opencv\build\java\x64" -jar scraper.jar
Linux:
sudo apt-get install libopencv-dev
macOS:
brew install opencv
3. YOLO Model Files
Download YOLO model files for object detection:
mkdir models
cd models
# Download YOLOv4 config
wget https://raw.githubusercontent.com/AlexeyAB/darknet/master/cfg/yolov4.cfg
# Download YOLOv4 weights (245 MB)
wget https://github.com/AlexeyAB/darknet/releases/download/darknet_yolo_v3_optimal/yolov4.weights
# Download COCO class names
wget https://raw.githubusercontent.com/AlexeyAB/darknet/master/data/coco.names
Building
mvn clean package
This creates:
target/troostwijk-scraper-1.0-SNAPSHOT.jar- Regular JARtarget/troostwijk-scraper-1.0-SNAPSHOT-jar-with-dependencies.jar- Executable JAR with all dependencies
Running
Quick Start (Desktop Notifications Only)
java -Djava.library.path="/path/to/opencv/lib" \
-jar target/troostwijk-scraper-1.0-SNAPSHOT-jar-with-dependencies.jar
With Email Notifications
export NOTIFICATION_CONFIG="smtp:your@gmail.com:app_password:your@gmail.com"
java -Djava.library.path="/path/to/opencv/lib" \
-jar target/troostwijk-scraper-1.0-SNAPSHOT-jar-with-dependencies.jar
Using Maven
mvn exec:java -Dexec.mainClass="com.auction.scraper.TroostwijkScraper"
System Architecture & Integration Flow
┌─────────────────────────────────────────────────────────────────────────────┐
│ COMPLETE SYSTEM INTEGRATION DIAGRAM │
└─────────────────────────────────────────────────────────────────────────────┘
┌──────────────────────────────────────────────────────────────────────────────┐
│ PHASE 1: EXTERNAL SCRAPER (Python/Playwright) - ARCHITECTURE-TROOSTWIJK │
└──────────────────────────────────────────────────────────────────────────────┘
│
┌─────────────────────────────┼─────────────────────────────┐
▼ ▼ ▼
[Listing Pages] [Auction Pages] [Lot Pages]
/auctions?page=N /a/auction-id /l/lot-id
│ │ │
│ Extract URLs │ Parse __NEXT_DATA__ │ Parse __NEXT_DATA__
├────────────────────────────▶│ JSON │ JSON
│ │ │
│ ▼ ▼
│ ┌────────────────┐ ┌────────────────┐
│ │ INSERT auctions│ │ INSERT lots │
│ │ to SQLite │ │ INSERT images │
│ └────────────────┘ │ (URLs only) │
│ │ └────────────────┘
│ │ │
└─────────────────────────────┴────────────────────────────┘
▼
┌──────────────────┐
│ SQLITE DATABASE │
│ troostwijk.db │
└──────────────────┘
│
┌─────────────────┼─────────────────┐
▼ ▼ ▼
[auctions table] [lots table] [images table]
- auction_id - lot_id - id
- title - auction_id - lot_id
- location - title - url
- lots_count - current_bid - local_path
- closing_time - bid_count - downloaded=0
- closing_time
│
┌─────────────────────────────────────┴─────────────────────────────────────┐
│ PHASE 2: MONITORING & PROCESSING (Java) - THIS PROJECT │
└────────────────────────────────────────────────────────────────────────────┘
│
┌─────────────────┼─────────────────┐
▼ ▼ ▼
[TroostwijkMonitor] [DatabaseService] [ScraperDataAdapter]
│ │ │
│ Read lots │ Query lots │ Transform data
│ every hour │ Import images │ TEXT → INTEGER
│ │ │ "€123" → 123.0
└─────────────────┴─────────────────┘
│
┌─────────────────────────┼─────────────────────────┐
▼ ▼ ▼
[Bid Monitoring] [Image Processing] [Closing Alerts]
Check API every 1h Download images Check < 5 min
│ │ │
│ New bid? │ Process via │ Time critical?
├─[YES]──────────┐ │ ObjectDetection ├─[YES]────┐
│ │ │ │ │
▼ │ ▼ │ │
[Update current_bid] │ ┌──────────────────┐ │ │
in database │ │ YOLO Detection │ │ │
│ │ OpenCV DNN │ │ │
│ └──────────────────┘ │ │
│ │ │ │
│ │ Detect objects │ │
│ ├─[vehicle] │ │
│ ├─[furniture] │ │
│ ├─[machinery] │ │
│ │ │ │
│ ▼ │ │
│ [Save labels to DB] │ │
│ [Estimate value] │ │
│ │ │ │
│ │ │ │
└─────────┴───────────────────────┴──────────┘
│
┌───────────────────────────────────────────────┴────────────────────────────┐
│ PHASE 3: NOTIFICATION SYSTEM - USER INTERACTION TRIGGERS │
└────────────────────────────────────────────────────────────────────────────┘
│
┌─────────────────┴─────────────────┐
▼ ▼
[NotificationService] [User Decision Points]
│ │
┌───────────────────┼───────────────────┐ │
▼ ▼ ▼ │
[Desktop Notify] [Email Notify] [Priority Level] │
Windows/macOS/ Gmail SMTP 0=Normal │
Linux system (FREE) 1=High │
tray │
│ │ │ │
└───────────────────┴───────────────────┘ │
│ │
▼ ▼
┌──────────────────┐ ┌──────────────────┐
│ USER INTERACTION │ │ TRIGGER EVENTS: │
│ NOTIFICATIONS │ │ │
└──────────────────┘ └──────────────────┘
│ │
┌───────────────────┼───────────────────┐ │
▼ ▼ ▼ │
┌──────────────────┐ ┌──────────────────┐ ┌──────────────────┐ │
│ 1. BID CHANGE │ │ 2. OBJECT │ │ 3. CLOSING │ │
│ │ │ DETECTED │ │ ALERT │ │
│ "Nieuw bod op │ │ │ │ │ │
│ kavel 12345: │ │ "Lot contains: │ │ "Kavel 12345 │ │
│ €150 (was €125)"│ │ - Vehicle │ │ sluit binnen │ │
│ │ │ - Machinery │ │ 5 min." │ │
│ Priority: NORMAL │ │ Est: €5000" │ │ Priority: HIGH │ │
│ │ │ │ │ │ │
│ Action needed: │ │ Action needed: │ │ Action needed: │ │
│ ▸ Place bid? │ │ ▸ Review item? │ │ ▸ Place final │ │
│ ▸ Monitor? │ │ ▸ Confirm value? │ │ bid? │ │
│ ▸ Ignore? │ │ ▸ Add to watch? │ │ ▸ Let expire? │ │
└──────────────────┘ └──────────────────┘ └──────────────────┘ │
│ │ │ │
└───────────────────┴───────────────────┴─────────────┘
│
▼
┌─────────────────────────────────────────────────────────────────────────────┐
│ USER ACTIONS & EXCEPTIONS │
├─────────────────────────────────────────────────────────────────────────────┤
│ Additional interaction points: │
│ │
│ 4. VIEWING DAY QUESTIONS │
│ "Bezichtiging op [date] - kunt u aanwezig zijn?" │
│ Action: ▸ Confirm attendance ▸ Request alternative ▸ Decline │
│ │
│ 5. ITEM RECOGNITION CONFIRMATION │
│ "Detected: [object] - Is deze correcte identificatie?" │
│ Action: ▸ Confirm ▸ Correct label ▸ Add notes │
│ │
│ 6. VALUE ESTIMATE APPROVAL │
│ "Geschatte waarde: €X - Akkoord?" │
│ Action: ▸ Accept ▸ Adjust ▸ Request manual review │
│ │
│ 7. EXCEPTION HANDLING │
│ "Afwijkende sluitingstijd / locatiewijziging / special terms" │
│ Action: ▸ Acknowledge ▸ Update preferences ▸ Withdraw interest │
└─────────────────────────────────────────────────────────────────────────────┘
┌─────────────────────────────────────────────────────────────────────────────┐
│ OBJECT DETECTION & VALUE ESTIMATION PIPELINE │
└─────────────────────────────────────────────────────────────────────────────┘
[Downloaded Image] → [ImageProcessingService]
│ │
│ ▼
│ [ObjectDetectionService]
│ │
│ ├─ Load YOLO model
│ ├─ Run inference (416x416)
│ ├─ Post-process detections
│ │ (confidence > 0.5)
│ │
│ ▼
│ ┌──────────────────────┐
│ │ Detected Objects: │
│ │ - person │
│ │ - car │
│ │ - truck │
│ │ - furniture │
│ │ - machinery │
│ │ - electronics │
│ │ (80 COCO classes) │
│ └──────────────────────┘
│ │
│ ▼
│ [Value Estimation Logic]
│ (Future enhancement)
│ │
│ ├─ Match objects to auction categories
│ ├─ Historical price analysis
│ ├─ Condition assessment
│ ├─ Market trends
│ │
│ ▼
│ ┌──────────────────────┐
│ │ Estimated Value: │
│ │ €X - €Y range │
│ │ Confidence: 75% │
│ └──────────────────────┘
│ │
└──────────────────────┴─ [Save to DB]
│
▼
[Trigger notification if
value > threshold]
Integration Hooks & Timing
| Event | Frequency | Trigger | Notification Type | User Action Required |
|---|---|---|---|---|
| New auction discovered | On scrape | Scraper finds new auction | Desktop + Email (optional) | Review auction |
| Bid change detected | Every 1 hour | Monitor detects higher bid | Desktop + Email | Place counter-bid? |
| Closing soon (< 30 min) | When detected | Time-based check | Desktop + Email | Review lot |
| Closing imminent (< 5 min) | When detected | Time-based check | Desktop + Email (HIGH) | Final bid decision |
| Object detected | On image process | YOLO finds objects | Desktop + Email | Confirm identification |
| Value estimated | After detection | Estimation complete | Desktop + Email | Approve estimate |
| Viewing day scheduled | From lot metadata | Scraper extracts date | Desktop + Email | Confirm attendance |
| Exception/Change | On update | Scraper detects change | Desktop + Email (HIGH) | Acknowledge |
Project Structure
src/main/java/com/auction/
├── Main.java # Entry point
├── TroostwijkMonitor.java # Monitoring & orchestration
├── DatabaseService.java # SQLite operations
├── ScraperDataAdapter.java # Schema translation (TEXT→INT, €→float)
├── ImageProcessingService.java # Downloads & processes images
├── ObjectDetectionService.java # OpenCV YOLO detection
├── NotificationService.java # Desktop + Email notifications (FREE)
├── Lot.java # Domain model for auction lots
├── AuctionInfo.java # Domain model for auctions
└── Console.java # Logging utility
Configuration
Edit TroostwijkScraper.main() to customize:
- Database file:
troostwijk.db(SQLite database location) - YOLO paths: Model configuration and weights files
- Monitoring frequency: Default is every 1 hour
- Closing alerts: Default is 5 minutes before closing
Database Schema
The scraper creates three tables:
sales
sale_id(PRIMARY KEY)title,location,closing_time
lots
lot_id(PRIMARY KEY)sale_id,title,description,manufacturer,type,yearcategory,current_bid,currency,urlclosing_time,closing_notified
images
id(PRIMARY KEY)lot_id,url,local_path,labels(detected objects)
Notification Examples
Desktop Notification
![System Tray Notification]
🔔 Kavel bieding update
Nieuw bod op kavel 12345: €150.00 (was €125.00)
Email Notification
From: your.email@gmail.com
To: your.email@gmail.com
Subject: [Troostwijk] Kavel bieding update
Nieuw bod op kavel 12345: €150.00 (was €125.00)
High Priority Alerts (closing soon):
⚠️ Lot nearing closure
Kavel 12345 sluit binnen 5 min.
Why This Approach?
✅ 100% Free - No paid services (Twilio, Pushover, etc.) ✅ No External Dependencies - Desktop notifications built into Java ✅ Works Offline - Desktop notifications don't need internet ✅ Privacy First - Your data stays on your machine ✅ Cross-Platform - Windows, macOS, Linux supported ✅ Optional Email - Add Gmail notifications if you want
Troubleshooting
Desktop Notifications Not Showing
- Windows: Check if Java has notification permissions
- Linux: Ensure you have a desktop environment running (not headless)
- macOS: Check System Preferences → Notifications
Email Not Sending
- Verify 2FA is enabled in Google Account
- Confirm you're using an App Password (not your regular Gmail password)
- Check that "Less secure app access" is NOT needed (app passwords work with 2FA)
- Verify the SMTP format:
smtp:username:app_password:recipient
Notes
- Desktop notifications require a graphical environment (not headless servers)
- For headless servers, use email-only notifications
- Gmail SMTP is free and has generous limits (500 emails/day)
- OpenCV native libraries must match your platform architecture
- YOLO weights file is ~245 MB
License
This is example code for educational purposes.