TradeUp — P2P Marketplace Android App

A peer-to-peer marketplace Android application that connects local buyers and sellers for secondhand item transactions. Supports real-time chat, GPS-based search, price negotiation, and OAuth authentication.

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System Architecture

┌────────────────────┐     REST API      ┌─────────────────────┐
│   Android Client   │ ◄────────────────► │  Spring Boot Backend │
│   (Java, MVVM)     │                   │  + MySQL Database    │
│                    │   WebSocket       │                     │
│   Firebase FCM     │ ◄────────────────► │  Real-time Events   │
└────────────────────┘                   └─────────────────────┘

• Frontend: Android (Java), Min SDK 24, Target SDK 34
• Backend: Spring Boot + MySQL
• Real-time: Java-WebSocket for chat and live location updates
• Push Notifications: Firebase Cloud Messaging
• Auth: JWT + Refresh Token, Google OAuth 2.0

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Features

User Management

• Email/password registration with OTP email verification
• Google Sign-In (OAuth 2.0)
• JWT authentication with automatic refresh token handling
• Public user profiles with ratings, listing count, and join date
• Edit profile (avatar, bio, contact info)
• Account deactivation and permanent deletion

Product Listings

• Create listings with title, description, price, category (9 categories), condition, and up to 10 photos
• GPS auto-location with manual override
• Negotiable/fixed price toggle
• Product preview before publishing
• Status management: Available, Sold, Paused
• Per-listing analytics: views, likes, contact requests
• Edit and delete listings from personal dashboard

Search & Discovery

• Keyword search with 200ms debounce
• Filters: category, price range, condition, distance radius (1–100 km)
• Sort by: relevance, newest, price (ascending/descending), distance, popularity
• GPS-based proximity search with manual location entry
• Personalized recommendations based on browsing history
• Category browsing with featured and recently added sections

In-App Chat

• Real-time messaging via WebSocket
• Text, image, and emoji support
• Delivery status indicators: Sent, Delivered, Read, Failed
• Typing indicators and online/offline status
• Block and report functionality
• Firebase push notifications for new messages

Price Negotiation

• Buyers can make offers on negotiable listings
• Sellers can accept, reject, or counter-offer
• Offer status tracking: Pending, Accepted, Rejected, Countered, Expired

Transactions & Reviews

• Mark items as sold and track transaction history
• Payment method records: Cash, Bank Transfer, Digital Wallet
• Post-transaction ratings (1–5 stars) with optional written reviews
• Average rating displayed on seller profiles
• Review moderation for abuse filtering

Notifications

• Firebase Cloud Messaging for push notifications
• Events: new messages, offer updates, listing status changes
• In-app notification center with configurable preferences

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Tech Stack

Category	Library / Technology
Language	Java
UI	Material Design 3, ConstraintLayout, ViewPager2, RecyclerView
Navigation	Android Navigation Component (nav graph)
Networking	Retrofit 2.9.0, OkHttp 4.11.0 (logging interceptor), Gson 2.10.1
Real-time	Java-WebSocket 1.5.4
Auth	Google Sign-In (Play Services Auth 20.7.0), JWT
Push Notifications	Firebase Cloud Messaging (BOM 32.7.0), Firebase Analytics
Location & Maps	Google Play Services Location 21.0.1, Maps 18.2.0
Image Loading	Glide 4.16.0, ExifInterface 1.3.6
Permissions	Dexter 6.2.3
State Management	ViewModel 2.7.0, LiveData 2.7.0
Build System	Gradle (Kotlin DSL), Version Catalog (libs.versions.toml)

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Project Structure

app/src/main/
├── java/
│   ├── activities/
│   │   ├── LoginActivity.java          # Email/password + Google Sign-In
│   │   ├── RegisterActivity.java       # Account creation
│   │   ├── OtpVerificationActivity.java # Email OTP verification
│   │   ├── ForgotPasswordActivity.java
│   │   ├── MainActivity.java           # Container: bottom nav + FAB
│   │   ├── ProductDetailActivity.java  # View product, make offer
│   │   ├── ChatActivity.java           # Real-time one-on-one chat
│   │   ├── EditProfileActivity.java
│   │   ├── SettingsActivity.java
│   │   ├── MyListingsActivity.java     # Seller dashboard
│   │   ├── SavedItemsActivity.java
│   │   ├── UserProfileActivity.java    # Public profile view
│   │   ├── LocationPickerActivity.java # Map-based location selection
│   │   └── RealtimeLocationActivity.java
│   ├── fragments/
│   │   ├── HomeFragment.java           # Feed: recommendations, categories
│   │   ├── SearchFragment.java         # Search + advanced filters
│   │   ├── AddProductFragment.java     # Create/edit listing
│   │   ├── MessagesFragment.java       # Conversation list
│   │   ├── ProfileFragment.java        # User dashboard
│   │   ├── FilterBottomSheetDialogFragment.java
│   │   └── MakeOfferBottomSheetDialogFragment.java
│   ├── services/
│   │   └── RealtimeWebSocketService.java # Persistent WebSocket connection
│   └── utils/
│       └── SharedPrefsManager.java     # JWT token & user prefs storage
└── res/
    ├── navigation/main_nav_graph.xml
    ├── values/colors.xml       # 200+ semantic color tokens
    ├── values/dimens.xml       # 160+ dimension constants
    ├── values/styles.xml       # Material 3 component styles
    └── values/themes.xml       # Light/dark theme definitions

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Screens Overview

Screen	Description
Home	Personalized feed, category filters, nearby items
Search	Keyword search with price/distance/condition filters
Add Product	Multi-step listing creation with GPS and photo upload
Messages	Conversation list with unread indicators
Profile	User dashboard, listings, saved items, transaction history
Product Detail	Full listing view, offer panel, seller profile link
Chat	Real-time messaging with image and emoji support
Settings	Notifications, privacy (online status, location sharing), dark mode

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Getting Started

Prerequisites

• Android Studio Hedgehog (2023.1.1) or newer
• JDK 11+
• A running instance of the Spring Boot backend
• google-services.json placed in app/ (from Firebase Console)

Setup

git clone https://github.com/YaoMing-dev/Android_App.git
cd Android_App

1. Open the project in Android Studio
2. Add your google-services.json to app/
3. Configure the backend base URL in the Retrofit client
4. Configure OAuth credentials (Google Sign-In client ID)
5. Sync Gradle and run on an emulator or physical device (API 24+)

Required Permissions

INTERNET
ACCESS_NETWORK_STATE
ACCESS_FINE_LOCATION
ACCESS_COARSE_LOCATION
POST_NOTIFICATIONS
CAMERA
READ_EXTERNAL_STORAGE

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Security

• JWT access token + refresh token stored in SharedPreferences
• Automatic token refresh on expiry
• Google OAuth 2.0 for social login
• Email verification required on registration
• User blocking and content reporting
• Privacy controls: toggle online status and location sharing

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License

MIT © YaoMing-dev