🧠 Jot – A Modern Java SDK for Polkadot

Jot is a clean, modular SDK built from the ground up for developers working with Polkadot and Substrate-based chains.

⚡️ Everything you need to build real Substrate connected apps in Java — no outdated libs, no workarounds.

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✨ Features

✅ Custom SCALE encoding/decoding
✅ Runtime metadata parsing (v14+)
✅ Full transaction construction & signing
✅ Substrate JSON-RPC (HTTP + WSS)
✅ SS58 address encoding/decoding
✅ Cryptographic signing via sr25519 and ed25519
✅ Fee estimation
✅ Multisig transactions
✅ Batched extrinsics
✅ Persistent wallet file abstraction

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📦 Technology Stack

• Java 21+
• Maven (multi-module)

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🔧 Getting Started

Requires Java 21+ and Maven or Gradle.

Import via Maven

<dependency>
  <groupId>com.method5</groupId>
  <artifactId>jot</artifactId>
  <version>1.0.1</version>
</dependency>

Gradle (Kotlin DSL):

implementation("com.method5:jot:1.0.1")

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🧰 Modules

Module	Description
jot	SCALE codec, metadata, crypto, rpc, signing, extrinsics, etc.
jot-examples	50+ ready-to-run usage examples
jot-docs	Jot SDK API docs

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🚀 Usage Examples

🛡️ Create or Load Wallet

// Load wallet from file
Wallet wallet = Wallet.fromFile(new File("wallet.key"));

// or load from mnemonic
wallet = Wallet.fromMnemonic("gesture rather obey video awake marine ...");
System.out.println(wallet.getAddress());

// or create new
wallet = Wallet.generate();
wallet.saveToFile(new File("wallet.key"));
System.out.println(wallet.getAddress());

💸 Send a Transfer (Balances.transferKeepAlive)

try (PolkadotRpcClient rpc = new PolkadotRpcClient(new String[] { ExampleConstants.RPC_SERVER }, 10000)) {
    String to = "15..."; // destination address
    BigInteger amount = BigInteger.ONE; // 1 DOT
    
    // Build call data for Balances.transferKeepAlive
    byte[] callData = BalancesPallet.transferKeepAlive(
        rpc.getResolver(),
        to,
        amount
    );
    
    // Create and sign extrinsic
    byte[] extrinsic = ExtrinsicSigner.signAndBuild(rpc,
        wallet.getSigner(),
        callData
    );
    
    // Submit extrinsic to RPC
    String hash = AuthorRpc.submitExtrinsic(rpc, extrinsic);
    
    System.out.println("Extrinsic hash: "+ hash);
}

🛠️ Decode a Signed Extrinsic

String hex = "0x..."; // signed extrinsic hex
DecodedExtrinsic decoded = ExtrinsicDecoder.decode(hex, chain);

System.out.println(decoded);

📥 Subscribe to finalized blocks

// Subscribe to finalized blocks
Subscription<BlockHeader> subscription = new Subscription<>(
    SubscriptionType.FINALIZED_HEAD,
    rpc,
    header -> {
        System.out.println("New head: " + header);
    }
);

// Unsubscribe
subscription.unsubscribe();

🔍 Query wallet balance

// Account
AccountId account = AccountId.fromSS58("13UVJyLnbVp9RBZYFwFGyDvVd1y27Tt8tkntv6Q7JVPhFsTB");

// Query balance
AccountInfo accountInfo = StorageQuery.getAccountInfo(rpc, account);

System.out.println("Free balance: " + accountInfo.getFree());
System.out.println("Reserved balance: " + accountInfo.getReserved());
System.out.println("Frozen balance: " + accountInfo.getFrozen());

⏱️ Submit extrinsic and wait for result

// Build call data for System.remark
byte[] callData = SystemPallet.remark(
    client.getResolver(),
    "test".getBytes(StandardCharsets.UTF_8) // remark
);

// Create and sign extrinsic
byte[] extrinsic = ExtrinsicSigner.signAndBuild(client,
    wallet.getSigner(),
    callData
);

// Submit to RPC and wait for result
ExtrinsicResult result = client.submitAndWaitForExtrinsic(extrinsic, PolkadotWsClient.Confirmation.BEST, 10000);

// Result
System.out.println("Successful: " + result.isSuccess());

// Individual events related to extrinsic
System.out.println("Events: " + Arrays.toString(result.getEvents()));

// Failure reason (if it failed)
if (!result.isSuccess()) {
    System.err.println("Failed because: " + result.getError().toHuman());
}

👉 For full setup instructions, see Quick Start Guide.

👉 API reference: Javadoc.

👉 See jot-examples module for 50+ ready to run examples.

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📄 License

This project is licensed under the Apache License 2.0.

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Built with ❤️ to bring Polkadot to the Java ecosystem.