Crossmint Wallet Java Demo

Java console app demonstrating Crossmint wallet operations with EVM keypair signer.

What it does

1. Generate EVM keypair using web3j
2. Create smart wallet via Crossmint API with external wallet signer
3. Fund wallet with test USDC tokens
4. Create USDC transfer transaction
5. Sign the transaction message hash with EVM keypair
6. Approve transaction with signature
7. Poll transaction status until completion

Project Structure

src/
├── Main.java              # Main demo orchestrator
├── services/
│   ├── KeypairService.java    # EVM keypair generation and signing
│   └── CrossmintService.java  # Crossmint API client
└── utils/
    ├── Config.java            # Configuration management
    └── Logger.java             # Logging utilities

Setup

Prerequisites

• Java 17+ (tested with Java 21)
• Gradle (or use the included wrapper)

Environment

Create a .env file in the project root and add your api key:

# Crossmint API Configuration
CROSSMINT_API_KEY=your_crossmint_api_key_here
CROSSMINT_BASE_URL=https://staging.crossmint.com

# Network Configuration
NETWORK=base-sepolia

# Logging Configuration
LOG_LEVEL=info

# Demo Configuration
DEMO_RECIPIENT_ADDRESS=0x6671f7552df0fbAF762Bd40aEd1cA3ec670d6161
DEMO_AMOUNT_USDC=1
FUND_AMOUNT=10

Run

./gradlew run

API Endpoints Used

1. Create Wallet

• POST /api/2025-06-09/wallets

2. Fund Wallet

• POST /api/v1-alpha2/wallets/{walletLocator}/balances

3. Create Transaction

• POST /api/2025-06-09/wallets/{walletLocator}/tokens/{chain}:usdc/transfers

4. Approve Transaction

• POST /api/2025-06-09/wallets/{walletLocator}/transactions/{transactionId}/approvals

5. Get Transaction Status

• GET /api/2025-06-09/wallets/{walletLocator}/transactions/{transactionId}

Dependencies

• web3j: EVM keypair generation and message signing
• OkHttp: HTTP client for API calls
• Jackson: JSON processing
• dotenv-java: Environment variable loading
• SLF4J: Logging

Integration Notes

• Replace CROSSMINT_API_KEY with your actual Crossmint API key
• The demo uses base-sepolia testnet by default
• It uses USDXM (crossmint's test usdc) instead of USDC to be able to fund via API