neow3j: A Java Library to interact with NEO nodes

Neow3j is a Java library that aims to provide an easy and reliable integration to NEO nodes/clients.

By using neow3j, you will happily play with NEO and end up neow'ing around like Bongo Cat.

You can now focus on building Java/Android applications that use the functions provided by the NEO blockchain -- without being concerned on writing specific code to integrate with NEO nodes/clients.

Neow3j is an open-source project developed by the community and maintained by AxLabs.

Features

• Support to NEO node/client API version 2.9.* (100% implemented)
• Observable pattern to get info about past and upcoming NEO blocks
• Android support from API 24, which covers ~49% of all active Android devices (~1 billion devices)
• Passphrase-protected Private Key implementation (NEP-2)
• Wallet SDK implementation (NEP-6)
• Mnemonic utils implementation (BIP-39), compatible to NEO
• Multisig addresses
• Signing and sending raw transactions
• Sync and Async interface
• Retry on node errors
• Integration tests with the dotnet NEO VM

Upcoming Features/Enhancements

• Documentation on using neow3j with Android apps
• Observable pattern to get specific transactions
• Improve the response model: introduce purpose-specific objects rather than the current raw Java types
• Interacting with smart contracts
• Select best seed NEO node based on some metrics (e.g., latency)

Getting Started

Add the neow3j dependencies to your Java project -- either using Gradle or Maven:

Gradle

Java 8 & Android (min. API 24):

compile 'io.neow3j:core:1.0.11'

Maven

Java 8 & Android (min. API 24):

<dependency>
    <groupId>io.neow3j</groupId>
    <artifactId>core</artifactId>
    <version>1.0.11</version>
</dependency>

Examples

• Initialize Neow3j providing the JSON-RPC's endpoint of a NEO node/client:

Neow3j neow3j = Neow3j.build(new HttpService("http://seed1.ngd.network:10332"));

• Get all blocks starting from, e.g. 2889367, and subscribe to also get newly generated NEO blocks:

neow3j.catchUpToLatestAndSubscribeToNewBlocksObservable(new BlockParameterIndex(2889367), true)
        .subscribe((blockReqResult) -> {
            System.out.println("#######################################");
            System.out.println("blockIndex: " + blockReqResult.getBlock().getIndex());
            System.out.println("hashId: " + blockReqResult.getBlock().getHash());
            System.out.println("confirmations: " + blockReqResult.getBlock().getConfirmations());
            System.out.println("transactions: " + blockReqResult.getBlock().getTransactions());
        });

Or, you can just subscribe to the newly generated NEO blocks:

neow3j.catchUpToLatestAndSubscribeToNewBlocksObservable(BlockParameterName.LATEST, true)
        .subscribe((blockReqResult) -> {
            System.out.println("#######################################");
            System.out.println("blockIndex: " + blockReqResult.getBlock().getIndex());
            System.out.println("hashId: " + blockReqResult.getBlock().getHash());
            System.out.println("confirmations: " + blockReqResult.getBlock().getConfirmations());
            System.out.println("transactions: " + blockReqResult.getBlock().getTransactions());
        });

• Get the latest block index received by the NEO node:

NeoBlockCount blockCountReq = neow3j.getBlockCount().send();
System.out.println(blockCountReq.getBlockIndex());

• Validate whether an address is a valid NEO address:

NeoValidateAddress validateReq = neow3j.validateAddress("ARvMqz3hEFE4qBkHAaPNxALquNQtBbH12f").send();
System.out.println("isValid=" + validateReq.getValidation().isValid());

• Get info about NEO consensus nodes:

NeoGetValidators getValidatorsReq = neow3j.getValidators().send();
System.out.println(getValidatorsReq.getValidators());

• Create a key pair:

ECKeyPair ecKeyPair = Keys.createEcKeyPair();

• Create a key pair from WIF:

ECKeyPair ecKeyPair = ECKeyPair.create(WIF.getPrivateKeyFromWIF("Kx9xMQVipBYAAjSxYEoZVatdVQfhYHbMFWSYPinSgAVd1d4Qgbpf"));

• Generate the WIF based on a key pair:

String wif = ecKeyPair.exportAsWIF();

• Get the NEO address from a key pair:

String neoAddress = Keys.getAddress(ecKeyPair);

• Create a standard wallet (NEP-6):

WalletFile wallet = Wallet.createStandardWallet();

• Create a password-protected account (NEP-2) based on a key pair:

WalletFile.Account account = Wallet.createStandardAccount("myPassw0rd!@#", keyPair);

• Add a password-protected account (NEP-2) to a standard wallet (NEP-6):

wallet.addAccount(account);

• Get the plain key pair from a password-protected account within a wallet:

ECKeyPair ecKeyPair = Wallet.decryptStandard("myPassw0rd!@#", wallet, account);

• Also, if you want to create a wallet file (NEP-6), the class WalletUtils provide some easy to use methods.

Creates a wallet file, and adds an account based on the provided key pair and password:

String fileName = WalletUtils.generateWalletFile("myPassw0rd!@#", ecKeyPair, destinationDiretory);

Or, if you want to create a wallet file with a newly created account, you simply can call:

String fileName = WalletUtils.generateNewWalletFile("myPassw0rd!@#", destinationDiretory);

There's also the possibility to create a new BIP-39 compatible wallet (generating the mnemonic words):

Bip39Wallet bip39Wallet = WalletUtils.generateBip39Wallet("myPassw0rd!@#", destinationDirectory);
String mnemonicWords = bip39Wallet.getMnemonic();
System.out.println("mnemonic words: " + mnemonicWords);

And, load the credential based on the mnemonic words:

Credentials credentials = WalletUtils.loadBip39Credentials("myPassw0rd!@#", mnemonicWords);

• Build a raw transaction with a 2/3 multisig address:

ECKeyPair ecKeyPair1 = ECKeyPair.create(WIF.getPrivateKeyFromWIF("Kx9xMQVipBYAAjSxYEoZVatdVQfhYHbMFWSYPinSgAVd1d4Qgbpf"));
ECKeyPair ecKeyPair2 = ECKeyPair.create(WIF.getPrivateKeyFromWIF("KzbKux44feMetfqdA5Cze9FNAkydRmphoFKnK5TGDdEQ8Nv1poXV"));
ECKeyPair ecKeyPair3 = ECKeyPair.create(WIF.getPrivateKeyFromWIF("L3hxLFUsNDmkzW6QoLH2PGc2DqGG5Kj1gCVwmr7duWJ9FReYWnjU"));

String multiSigAddress = Keys.getMultiSigAddress(
                2,
                ecKeyPair1.getPublicKey(),
                ecKeyPair2.getPublicKey(),
                ecKeyPair3.getPublicKey()
);

RawVerificationScript verificationScript = Keys.getVerificationScriptFromPublicKey(
                2,
                ecKeyPair1.getPublicKey(),
                ecKeyPair2.getPublicKey(),
                ecKeyPair3.getPublicKey()
);

RawTransaction rawTx = RawTransaction.createContractTransaction(
                null,
                null,
                Arrays.asList(
                        new RawTransactionInput("9feac4774eb0f01ab5d6817c713144b7c020b98f257c30b1105062d434e6f254", 0)
                ),
                Arrays.asList(
                        new RawTransactionOutput(0, NEOAsset.HASH_ID, "100.0", "AK2nJJpJr6o664CWJKi1QRXjqeic2zRp8y"),
                        new RawTransactionOutput(1, NEOAsset.HASH_ID, "900.0", multiSigAddress)
                )
);

// serialize the base raw transaction
// Important: without scripts!
byte[] rawTxUnsignedArray = rawTx.toArray();

// add 2 signatures out of the 3 possible -- order here is important!
List<RawInvocationScript> rawInvocationScriptList = new ArrayList<>();
rawInvocationScriptList.add(new RawInvocationScript(Sign.signMessage(rawTxUnsignedArray, ecKeyPair1)));
rawInvocationScriptList.add(new RawInvocationScript(Sign.signMessage(rawTxUnsignedArray, ecKeyPair2)));

// give the invocation and verification script to the raw transaction:
rawTx.addScript(rawInvocationScriptList, verificationScript);

byte[] rawTxSignedArray = rawTx.toArray();
String rawTransactionHexString = Numeric.toHexStringNoPrefix(rawTxSignedArray);
System.out.println("rawTransactionHexString: " + rawTransactionHexString);

• Send the raw transaction (built in the example above) to a validator node:

NeoSendRawTransaction sendRawTransactionReq = neow3j.sendRawTransaction(rawTransactionHexString).send();
System.out.println(sendRawTransactionReq.getResult());

For more code snippets and examples, check the neow3j-examples repository.

Donate

Help the development of neow3j by donating to the following addresses:

Crypto	Address
NEO	AHb3PPUY6a36Gd6JXCkn8j8LKtbEUr3UfZ
ETH	0xe85EbabD96943655e2DcaC44d3F21DC75F403B2f
BTC	3L4br7KQ8DCJEZ77nBjJfrukWEdVRXoKiy

NEO JSON-RPC Support

Here you can find a complete list of all JSON-RPC methods supported by neow3j.

In summary, neow3j supports JSON-RPC API version 2.9.* and version 2.10.*.

Why "neow3j"?

This project is based on web3j, but focusing on NEO. That's why the suffix "w3j" was added to the "neo" name, forming "neow3j".

Well... then, it was simply natural to imagine Bongo Cat playing on NEO nodes and neow'ing instead of meow'ing, don't you think? :-)

Thanks and Credits

• This project was strongly based on web3j, a library originally developed by Conor Svensson, latest on this commit. We are really thankful for it. :-)
• NEO Global Development (NGD)