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Getting Started

What's new?​

In caver-java 1.5.0, we adopt Common Architecture. Common Architecture is a new software architecture for kaia development environment, which is shared by all kaia SDKs (caver-js/caver-java). It is designed for your streamlined development experience and ease of extensibility to other programming languages.

As caver-java is updated to 1.5.0, the APIs used in 1.4.0 are deprecated except for some APIs.

The APIs newly provided in caver-java 1.5.0 are as follows.

caver.account​

caver.account is a package used to update AccountKey, which could be one or more public keys (AccountKeyPublic, AccountKeyWeightedMultiSig, and AccountKeyRoleBased) or a special type of keys (AccountKeyLegacy and AccountKeyFail), for a kaia account.

  • caver.account replaces caver.tx.account in caver-java 1.4.0

caver.wallet​

caver.wallet is a package that manages Keyring instances in in-memory wallet. A Keyring is an instance that stores the address of a kaia account and its private key(s), and it is used when the address of this account signs a transaction. caver.wallet accepts all types of Keyring (SingleKeyring, MultipleKeyring, and RoleBasedKeyring) and manages them with their kaia account address.

  • caver.wallet replaces caver.crypto in caver-java 1.4.0
  • caver.wallet.KeyStore replaces caver.wallet.WalletFile in caver-java 1.4.0

caver.transaction​

caver.transaction is a package that provides functionality related to Transaction.

  • caver.transaction replaces caver.tx in caver-java 1.4.0

caver.rpc​

caver.rpc is a package that provides functionality related to rpc call with kaia Node.

  • caver.rpc.klay and caver.rpc.net replaces Klay, Net interfaces in caver-java 1.4.0, respectively

caver.util​

caver.utils provides utility functions.

caver.contract​

caver.contract is a package that makes it easy to handle smart contracts in kaia. With caver.contract, you can deploy smart contracts and execute them by calling their functions. caver.contract first converts smart contract functions and events from ABI(Application Binary Interface), calls those functions, and obtains the event information.

Prerequisites ​

Adding a Repository ​

A library repository should be added before using IPFS. Please add the following repository first.

maven


<repositories>
<repository>
<id>jitpack.io</id>
<url>https://jitpack.io</url>
</repository>
</repositories>

gradle


allprojects {
repositories {
...
maven { url 'https://jitpack.io' }
}
}

Adding a Dependency ​

maven


<dependency>
<groupId>com.klaytn.caver</groupId>
<artifactId>core</artifactId>
<version>1.5.0</version>
</dependency>

gradle


implementation 'com.klaytn.caver:core:1.5.0'

If you want to use Android dependency, just append -android at the end of the version string. (e.g. 1.0.1-android)

If you want to see details of the JSON-RPC requests and responses, please include LOGBack dependency in your project. Below is a Gradle build file example. You can add the dependency to Maven as well. Since caver-java uses the SLF4J logging facade, you can switch to your preferred logging framework instead of LOGBack.


implementation "ch.qos.logback:logback-classic:1.2.3"

Note: In the central repository, the RC, Android, and Java versions are listed together. If you use wildcards to get a version, you may be using a version that is not appropriate for your platform.

Command-line Tool ​

The command-line tool allows you to generate Solidity smart contract function wrappers from the command line.

Installation (Homebrew)

Java 1.8+ is required to install this.


$ brew tap klaytn/klaytn
$ brew install caver-java

After installation you can run command 'caver-java' like below:


$ caver-java solidity generate -b <smart-contract>.bin -a <smart-contract>.abi -o <outputPath> -p <packagePath>

Installation (Other)

Currently, we do not support other package managers. As another solution, we provide a method to build the CLI below.

  • Download or fork caver-java.

  • Do task 'shadowDistZip' in the console module using Gradle. As a result, console/build/distributions/console-shadow-{version}.zip is generated.


    $ ./gradlew :console:shadowDistZip

  • Unzip the zip file in the build directory


    $ unzip ./console/build/distributions/console-shadow-{version}.zip

  • Execute the binary file to run the command-line tool like below. You can find a shell script file for macOS users and a batch file for Window users.


    $ ./console/build/distributions/console-shadow-{version}/bin/caver-java

Sending KAIA at a glance​

This section describes a simple example of using a keystore file to send KAIA with a value transfer transaction. The keystore file can be exported from  Kaia Wallet. If you need KAIA for testing, you can get test KAIA from the Kaia Faucet.

노트

When developing, it's best practice to use an account that isn't associated with any real funds. A good way to do this is to make a new browser profile (on Chrome, Brave, Firefox, etc) and install Kaia Wallet on that browser, and never send this wallet money.


public void sendingKLAY() throws IOException, CipherException, TransactionException {
Caver caver = new Caver(Caver.BAOBAB_URL);
//Read keystore json file.
File file = new File("./keystore.json");
//Decrypt keystore.
ObjectMapper objectMapper = ObjectMapperFactory.getObjectMapper();
KeyStore keyStore = objectMapper.readValue(file, KeyStore.class);
AbstractKeyring keyring = caver.wallet.keyring.decrypt(keyStore, "password");
//Add to caver wallet.
caver.wallet.add(keyring);
BigInteger value = new BigInteger(caver.utils.convertToPeb(BigDecimal.ONE, "KLAY"));
//Create a value transfer transaction
ValueTransfer valueTransfer = caver.transaction.valueTransfer.create(
TxPropertyBuilder.valueTransfer()
.setFrom(keyring.getAddress())
.setTo("0x8084fed6b1847448c24692470fc3b2ed87f9eb47")
.setValue(value)
.setGas(BigInteger.valueOf(25000))
);
//Sign to the transaction
valueTransfer.sign(keyring);
//Send a transaction to the kaia blockchain platform (kaia)
Bytes32 result = caver.rpc.klay.sendRawTransaction(valueTransfer.getRawTransaction()).send();
if(result.hasError()) {
throw new RuntimeException(result.getError().getMessage());
}
//Check transaction receipt.
TransactionReceiptProcessor transactionReceiptProcessor = new PollingTransactionReceiptProcessor(caver, 1000, 15);
TransactionReceipt.TransactionReceiptData transactionReceipt = transactionReceiptProcessor.waitForTransactionReceipt(result.getResult());
}

Starting with caver-java ​

Connecting to a kaia Node ​

If you are running an EN, you can connect it to your own node by changing the host and port like below:


Caver caver = new Caver("http://your.en.url:8551/");

Managing Keyrings ​

Keyring is a structure that contains the address of the kaia account and the private key(s).

Keyring can be classified into three types depending on the type of key being stored: SingleKeyring to store one address and one private key, MultipleKeyring to store one address and multiple private keys, and RoleBasedKeyring to store one address and one or more private keys for each role.

SingleKeyring defines key property inside, and this key stores one private key.

MultipleKeyring defines keys property inside, and this keys is implemented as an array to store multiple private keys.

The keys property defined in RoleBasedKeyring is implemented as a List object having 3 arrays of private key(s) as its elements (empty keys will look like [ [], [], [] ]) and so that it can include multiple keys for each role. The first element of the array is filled with the private key(s) to be used for roleTransactionKey, the second element the private key(s) to be used for roleAccountUpdateKey, and the third element the private key(s) to be used for roleFeePayerKey.

Creating a Keyring ​

Generating a SingleKeyring ​

You can randomly generate a single keyring as shown below.


SingleKeyring keyring = caver.wallet.keyring.generate();

Creating a SingleKeyring from private key ​

Also, if you own a specific private key, you can use it to create a keyring as shown below.


String privateKey = "0x{private key in hex}";
SingleKeyring keyring = caver.wallet.keyring.createFromPrivateKey(privateKey);

Creating a SingleKeyring with a private key and an address ​

If your private key for your kaia account is decoupled from the address, you can create a keyring using the given address and the given private key like below.


String address = "0x{address in hex}";
String privateKey = "0x{private key in hex}";
SingleKeyring keyring = caver.wallet.keyring.createWithSingleKey(address, privateKey);

Also, you can derive SingleKeyring instance from kaia wallet key.


String klaytnWalletKey = "0x{private key}0x{type}0x{address in hex}";
SingleKeyring keyring = caver.wallet.keyring.createFromKlaytnWalletKey(klaytnWalletKey);

Creating a MultipleKeyring with multiple private keys ​

If you want to use multiple private keys, you can create a MultipleKeyring using an address and multiple private keys. The below examples show how to create a MultipleKeyring with multiple private keys.


String address = "0x{address in hex}";
String[] privateKeyArray = new String[] {"0x{private key#1}", "0x{private key#2}", "0x{private key#3}"};
MultipleKeyring multipleKeyring = caver.wallet.keyring.createWithMultipleKey(address, privateKeyArray);

Creating a RoleBasedKeyring with private keys ​

To use different private key(s) for each role, caver.wallet.keyring.createWithRoleBasedKey is used. Each array element represents a role described in RoleBasedKeyring. The example below shows how to create a RoleBasedKeyring instance from different keys for each role.


String address = "0x{address in hex}";
String[][] privateKeyArr = new String[][] {
//roleTransactionKey
{
"0x{privateKey in hex}",
"0x{privateKey in hex}",
"0x{privateKey in hex}",
},
//roleAccountUpdateKey
{
"0x{privateKey in hex}",
"0x{privateKey in hex}",
"0x{privateKey in hex}",
},
//roleFeePayerKey
{
"0x{privateKey in hex}",
"0x{privateKey in hex}",
"0x{privateKey in hex}",
},
};
RoleBasedKeyring keyring = caver.wallet.keyring.createWithRoleBasedKey(address, Arrays.asList(privateKeyArr));

Adding Keyrings to caver-java from a keystore json string.​

You can use a keyring more easily by adding it to the in-memory wallet provided by caver-java. The following examples illustrate how to add a keyring to caver.wallet using a keystore JSON file string generated by Kaia Wallet.


Caver caver = new Caver(Caver.MAINNET_URL);
String password = "password";
String keyStoreJsonString = "{\n" +
" \"version\": 4,\n" +
" \"id\": \"9c12de05-0153-41c7-a8b7-849472eb5de7\",\n" +
" \"address\": \"0xc02cec4d0346bf4124deeb55c5216a4138a40a8c\",\n" +
" \"keyring\": [\n" +
" {\n" +
" \"ciphertext\": \"eacf496cea5e80eca291251b3743bf93cdbcf7072efc3a74efeaf518e2796b15\",\n" +
" \"cipherparams\": {\n" +
" \"iv\": \"d688a4319342e872cefcf51aef3ec2da\"\n" +
" },\n" +
" \"cipher\": \"aes-128-ctr\",\n" +
" \"kdf\": \"scrypt\",\n" +
" \"kdfparams\": {\n" +
" \"dklen\": 32,\n" +
" \"salt\": \"c3cee502c7157e0faa42386c6d666116ffcdf093c345166c502e23bc34e6ba40\",\n" +
" \"n\": 4096,\n" +
" \"r\": 8,\n" +
" \"p\": 1\n" +
" },\n" +
" \"mac\": \"4b49574f3d3356fa0d04f73e07d5a2a6bbfdd185bedfa31f37f347bc98f2ef26\"\n" +
" }\n" +
" ]\n" +
"}";
SingleKeyring decrypt = (SingleKeyring)caver.wallet.keyring.decrypt(keyStoreJsonString, password);
System.out.println("Decrypted address : " + decrypt.getAddress());
System.out.println("Decrypted key : " + decrypt.getKey().getPrivateKey());
SingleKeyring addedKeyring = (SingleKeyring)caver.wallet.add(decrypt);
System.out.println("address : " + addedKeyring.getAddress());
System.out.println("key : " + addedKeyring.getKey().getPrivateKey());


Decrypted address : 0xc02cec4d0346bf4124deeb55c5216a4138a40a8c
Decrypted key : 0x93c90135ae69669e416ba5997d9274f8c8bd60748761fc421e415602d68a13a5
address : 0xc02cec4d0346bf4124deeb55c5216a4138a40a8c
key : 0x93c90135ae69669e416ba5997d9274f8c8bd60748761fc421e415602d68a13a5

Looking at the output above, you can query your keyring from caver.wallet after adding it to caver.wallet.

If you have an address and private key(s) to use, you can easily create a keyring and add it directly to caver.wallet via caver.wallet.newKeyring.


Caver caver = new Caver(Caver.MAINNET_URL);
// Add to wallet with an address and a private key
AbstractKeyring addedSingleKeyring = caver.wallet.newKeyring("0x{address in hex}", "0x{private key1}");
// Add to wallet with an address and private keys
String[] privateKeyArr = new String[] {
"0x{privateKey in hex}",
"0x{privateKey in hex}",
"0x{privateKey in hex}",
};
AbstractKeyring addedMultipleKeyring = caver.wallet.newKeyring('0x{address in hex}', privateKeyArr);
// Add to wallet with an address and private keys defined by each roles
String[][] privateKeyArr = new String[][] {
//roleTransactionKey
{
"0x{privateKey in hex}",
"0x{privateKey in hex}",
"0x{privateKey in hex}",
},
//roleAccountUpdateKey
{
"0x{privateKey in hex}",
"0x{privateKey in hex}",
"0x{privateKey in hex}",
},
//roleFeePayerKey
{
"0x{privateKey in hex}",
"0x{privateKey in hex}",
"0x{privateKey in hex}",
},
};
AbstractKeyring addedRoleBased = caver.wallet.newKeyring('0x{address in hex}', Arrays.asList(privateKeyArr))

When caver.wallet.newKeyring is executed with a private key, a Keyring instance with one private key is created and added to caver.wallet. For multiple private keys, a Keyring instance with multiple private keys is created and added to caver.wallet. When passing a 2D string array including one or more private keys for each role as an element, a Keyring instance that contains the different private key(s) for each role is created and also added to the caver.wallet.

caver.wallet.add or caver.wallet.newKeyring returns a Keyring instance after adding it to caver.wallet.

Sending a Transaction ​

This section will show you how to send KAIA using caver-java on the Baobab network.

Getting KAIA via Baobab Faucet ​

If you need KAIA for testing, you can get Baobab testnet KAIA from the Kaia Wallet. Log in to the kaia Wallet using the private key or the keystore file and receive Baobab testnet KAIA via the faucet for testing.

Sending a Value Transfer Transaction ​

You can use a caver-java wallet to generate a signature of a transaction. You have to go through two steps below to send the transaction to the network.

  1. Sign a transaction
    • If the keyring you want to use is added to caver.wallet, you can use caver.wallet.sign function to sign.
    • If you manage the keyring separately without adding it to caver.wallet, you can sign the transaction through transaction.sign function.
  2. Send the RLP-encoded string of the signed transaction to the kaia via caver.rpc.klay.sendRawTransaction.

Note: The sender should have enough number of KAIA to be transferred and also to pay the transaction fee.

Sign a transaction​

Before sending a transaction to kaia, you should sign a transaction first.

Below is an example of how to sign a transaction if a keyring is added to the caver.wallet.


Caver caver = new Caver(Caver.MAINNET_URL);
// Add a keyring to caver.wallet
SingleKeyring keyring = caver.wallet.keyring.createFromPrivateKey("privateKey");
caver.wallet.add(keyring);
// Create a value transfer transaction
ValueTransfer valueTransfer = caver.transaction.valueTransfer.create(
TxPropertyBuilder.valueTransfer()
.setFrom(keyring.getAddress())
.setTo("0x176ff0344de49c04be577a3512b6991507647f72")
.setValue(BigInteger.valueOf(1))
.setGas(BigInteger.valueOf(30000))
);
// Sign the transaction via caver.wallet.sign
caver.wallet.sign(keyring.getAddress(), valueTransfer);
String rlpEncoded = valueTransfer.getRLPEncoding();
System.out.println("RLP-encoded string: " + rlpEncoded)

The above code adds a keyring to caver.wallet, creates a transaction, and signs the transaction through caver.wallet.sign.

Running the above code gives you the following result. When the above code is executed, the RLP-encoded string of the transaction is shown below. (The RLP-encoded string output you got could be different from the string output shown below.)


RLP-encoded string: 0x08f87e808505d21dba0082753094176ff0344de49c04be577a3512b6991507647f720194ade4883d092e2a972d70637ca7de9ab5166894a2f847f845824e44a0e1ec99789157e5cb6bc691935c204a23aaa3dc049efafca106992a5d5db2d179a0511c421d5e508fdb335b6048ca7aa84560a53a5881d531644ff178b6aa4c0a41

Send the RLP-encoded string of the signed transaction to the kaia​

Now you can send a signed transaction to the network like below. If you want to run the below example, replace "rlpEncoding" with the value of rlpEncoded in the code above.


public String sendRawTransaction() {
Caver caver = new Caver(Caver.BAOBAB_URL);
String rlpEncoding = "rlpEncoding";
String txHash = null;
try {
// Send the transaction using `caver.rpc.klay.sendRawTransaction`.
Bytes32 sendResult = caver.rpc.klay.sendRawTransaction(rlpEncoding).send();
if(sendResult.hasError()) {
//do something to handle error
}
txHash = sendResult.getResult();
} catch (IOException e) {
// do something to handle exception
}
return txHash;
}

If you want to sign a transaction and send it to the network without caver.wallet, see the example below.


Caver caver = new Caver(Caver.MAINNET_URL);
// Add a keyring to caver.wallet
SingleKeyring keyring = caver.wallet.keyring.createFromPrivateKey("privateKey");
caver.wallet.add(keyring);
// Create a value transfer transaction
ValueTransfer valueTransfer = caver.transaction.valueTransfer.create(
TxPropertyBuilder.valueTransfer()
.setFrom(keyring.getAddress())
.setTo("0x176ff0344de49c04be577a3512b6991507647f72")
.setValue(BigInteger.valueOf(1))
.setGas(BigInteger.valueOf(30000))
);
// Sign the transaction via transaction.sign
valueTransfer.sign(keyring);
String rlpEncoded = valueTransfer.getRLPEncoding();
try {
// Send the transaction using `caver.rpc.klay.sendRawTransaction`.
Bytes32 sendResult = caver.rpc.klay.sendRawTransaction(rlpEncoded).send();
if(sendResult.hasError()) {
//do something to handle error
}
String txHash = sendResult.getResult();
System.out.println("Transaction Hash : " + txHash);
} catch (IOException e) {
// do something to handle exception
}

When the above code is executed, the transaction hash (txHash) is printed like the example below.


Transaction Hash : 0x43e8ab1a2365ad598448b4402c1cfce6a71b3a103fce3a69905613e50b978113

Checking Receipts ​

You can use the TransactionReceiptProcessor to get the receipt of the transaction when you transfer the transaction to the kaia by caver.rpc.klay.sendRawTransaction.

The following example shows how to get a receipt using PollingTransactionReceiptProcessor.


Caver caver = new Caver(Caver.BAOBAB_URL);
String txHash = "0x40552efbba23347d36f6f5aaba6b9aeb6602e004df62c1988d9b7b1f036e676a";
//Sleep duration - 1000ms
//Attempts count - 15
TransactionReceiptProcessor receiptProcessor = new PollingTransactionReceiptProcessor(caver, 1000, 15);
try {
TransactionReceipt.TransactionReceiptData receiptData = receiptProcessor.waitForTransactionReceipt(txHash);
} catch (IOException | TransactionException e) {
// do something to handle error.
}

As described in the example above, you can get the result of sending a transaction through TransactionReceiptProcessor. The transactionHash field is defined inside the receipt object.

You can use caver.rpc.klay.getTransactionReceipt RPC call with txHash string to query the receipt of a transaction at any time from the network after the transaction is included in a block. The example below shows how to get a receipt using the caver.rpc.klay.getTransactionReceipt RPC call.


Caver caver = new Caver(Caver.BAOBAB_URL);
String txHash = "0x40552efbba23347d36f6f5aaba6b9aeb6602e004df62c1988d9b7b1f036e676a";
try {
TransactionReceipt receipt = caver.rpc.klay.getTransactionReceipt(txHash).send();
if(receipt.hasError()) {
// do something to handle error
}
TransactionReceipt.TransactionReceiptData receiptData = receipt.getResult();
} catch (IOException e) {
// do something to handle exception.
}

The result of the transaction can be found through the status of the receipt. For the details of the return values, see caver.rpc.klay.getTransactionReceipt. If a transaction is failed, you can check more about the error in txError of the receipt. For more information about txError, see txError: Detailed Information of Transaction Failures.

Executing Other Transaction Types ​

Kaia provides various transaction types for extensibility and performance. For more information, see Transactions. This section describes some examples that can be used with caver-java.

Fee Delegation ​

Kaia provides Fee Delegation feature. Here's an example of making a RLP-encoded transaction when you are a sender of this kind of transaction:


Caver caver = new Caver(Caver.BAOBAB_URL);
SingleKeyring senderKeyring = caver.wallet.keyring.createFromPrivateKey("0x{privateKey}");
caver.wallet.add(senderKeyring);
FeeDelegatedValueTransfer feeDelegatedValueTransfer = caver.transaction.feeDelegatedValueTransfer.create(
TxPropertyBuilder.feeDelegatedValueTransfer()
.setFrom(senderKeyring.getAddress())
.setTo("0x176ff0344de49c04be577a3512b6991507647f72")
.setValue(BigInteger.valueOf(1))
.setGas(BigInteger.valueOf(30000))
);
caver.wallet.sign(senderKeyring.getAddress(), feeDelegatedValueTransfer);
String rlpEncoded = feeDelegatedValueTransfer.getRLPEncoding();
System.out.println(rlpEncoded);

When the above code is executed, the RLP-encoded string will be printed. (The RLP-encoded string output you got could be different from the string output shown below.)


0x09f884028505d21dba0082c35094176ff0344de49c04be577a3512b6991507647f720594f5a9079f311f9ec55170af351627aff0c5d2e287f847f845824e43a0f4b53dbd4c915cb73b9c7fa17e22106ee9640155a06ab4a7ed8661f846d2a5cca035b5bba6a26d4ccd20c65e8f31cce265c193f1c874806f9fae6b0ee9df0addf080c4c3018080

The fee payer can send the transaction to the kaia after attaching the feePayerSignatures to the RLP-encoded string (rawTransaction) signed by the transaction sender. If caver.wallet also has the fee payer's keyring, the fee payer's signature can be injected into feeDelegatedTx by calling caver.wallet.signAsFeePayer(feePayer.address, feeDelegatedTx). Otherwise, the fee payer has to create a feeDelegatedTx from the RLP-encoded string signed by the sender and add the fee payer's sign onto it, as illustrated below. If you want to run the below example, replace 0x{RLP-encoded string} with the value of rlpEncoded above.


Caver caver = new Caver(Caver.BAOBAB_URL);
SingleKeyring feePayerKeyring = caver.wallet.keyring.createFromPrivateKey("0x{privateKey}");
caver.wallet.add(feePayerKeyring);
String rlpEncoded = "0x{RLP-encoded string}";
FeeDelegatedValueTransfer feeDelegatedValueTransfer = caver.transaction.feeDelegatedValueTransfer.decode(rlpEncoded);
feeDelegatedValueTransfer.setFeePayer(feePayerKeyring.getAddress());
feeDelegatedValueTransfer.setKlaytnCall(caver.rpc.klay);
caver.wallet.signAsFeePayer(feePayerKeyring.getAddress(), feeDelegatedValueTransfer);
System.out.println(feeDelegatedValueTransfer.getRLPEncoding());

When the above code is executed, the RLP-encoded string including the sender's signatures and fee payer's signatures is printed like below. (The output you got could be different from the string output shown below.)


0x09f8dc028505d21dba0082c35094176ff0344de49c04be577a3512b6991507647f720594f5a9079f311f9ec55170af351627aff0c5d2e287f847f845824e43a0f4b53dbd4c915cb73b9c7fa17e22106ee9640155a06ab4a7ed8661f846d2a5cca035b5bba6a26d4ccd20c65e8f31cce265c193f1c874806f9fae6b0ee9df0addf09417e7531b40ad5d7b5fa7b4ec78df64ce1cb36d24f847f845824e44a0921b7c3be69db96ce14134b306c2ada423613cb66ecc6697ee8067983c268b6ea07b86b255d1c781781315d85d7904226fb2101eb9498c4a03f3fbd30ba3ec5b79

The transaction is now signed by both the sender and the fee payer, and it can now be sent over the network. Replace 0x{RLP-encoded string} with the RLP-encoded string output of the example code above.


Caver caver = new Caver(Caver.BAOBAB_URL);
TransactionReceiptProcessor receiptProcessor = new PollingTransactionReceiptProcessor(caver, 1000, 15);
String rlpEncoded = "0x{RLP-encoded string}";
try {
// Send the transaction using `caver.rpc.klay.sendRawTransaction`.
Bytes32 sendResult = caver.rpc.klay.sendRawTransaction(rlpEncoding).send();
if(sendResult.hasError()) {
//do something to handle error
}
String txHash = sendResult.getResult();
TransactionReceipt.TransactionReceiptData receiptData = receiptProcessor.waitForTransactionReceipt(txHash);
} catch (IOException | TransactionException e) {
// do something to handle exception.
}

The result of the transaction can be found through the status of the receipt. For the details of the return values, see caver.rpc.klay.getTransactionReceipt. If a transaction is failed, you can check more about the error in txError of the receipt. For more information about txError, see txError: Detailed Information of Transaction Failures.

Account Update ​

If you want to change the private key(s) for your kaia account, there are 3 important things you need to remember:

  1. Kaia validates every transaction you send to it.
  2. The validation requires your public keys which exactly corresponds to your private key(s).
  3. Thus, changing your private key(s) into the new one(s) is always be preceded by changing your old public key(s) to the new one(s). The new public key(s) must be derived from the new private key(s).

Keeping the 3 things above in your mind, you can change your private key(s) by following the steps below:

  1. Prepare the new private key(s) to create a new keyring.
  2. Create a keyring by its type (Single keyring, Multiple keyring, or Role-based keyring) you need.
  3. Generate an Account instance from the new keyring. This Account instance holds the new public key(s) for your kaia account.
  4. Send AccountUpdate transaction including Account instance to kaia.
  5. Finally, replace your old keyring to the new one that was created in Step 2.

Please check Account Update for the details.

To change your AccountKey, you must provide an Account instance for the account field in the input argument object of caver.transaction.type.AccountUpdate. An Account instance contains the address of the kaia account and the AccountKey to be updated.

The code below is an example code that changes the private key(s) you use for your kaia account along with changing AccountKey of your kaia account to AccountKeyPublic. Don't forget to prepare your new private key(s).


Caver caver = new Caver(Caver.DEFAULT_URL);
SingleKeyring senderKeyring = caver.wallet.keyring.createFromPrivateKey("0x2359d1ae7317c01532a58b01452476b796a3ac713336e97d8d3c9651cc0aecc3");
caver.wallet.add(senderKeyring);
String newPrivateKey = caver.wallet.keyring.generateSingleKey();
SingleKeyring newKeyring = caver.wallet.keyring.create(senderKeyring.getAddress(), newPrivateKey);
Account account = newKeyring.toAccount();
AccountUpdate accountUpdate = caver.transaction.accountUpdate.create(
TxPropertyBuilder.accountUpdate()
.setFrom(senderKeyring.getAddress())
.setAccount(account)
.setGas(BigInteger.valueOf(50000))
);
try {
caver.wallet.sign(senderKeyring.getAddress(), accountUpdate);
String rlpEncoded = accountUpdate.getRLPEncoding();
Bytes32 sendResult = caver.rpc.klay.sendRawTransaction(rlpEncoded).send();
if(sendResult.hasError()) {
//do something to handle error
throw new TransactionException(sendResult.getError().getMessage());
}
String txHash = sendResult.getResult();
TransactionReceiptProcessor receiptProcessor = new PollingTransactionReceiptProcessor(caver, 1000, 15);
TransactionReceipt.TransactionReceiptData receiptData = receiptProcessor.waitForTransactionReceipt(txHash);
} catch (IOException | TransactionException e) {
// do something to handle exception.
e.printStackTrace();
}
senderKeyring = (SingleKeyring)caver.wallet.updateKeyring(newKeyring);

If the above code is executed successfully, you are no longer able to use the old private key(s) to sign any transaction with the old keyring. So you must update the old keyring with the newKeyring through caver.wallet.updateKeyring(newKeyring). Once it is updated, the signing will be done by the newly updated private key(s).

Here comes how to update AccountKey of your kaia account with multiple AccountKeys? The example below explains how to create an Account instance with multiple private keys that what you want to use (You can create an Account instance with multiple public keys via caver.account.create). Same again, after feeding the account instance created to the account field inside the transaction object, the left rest of the updating process is just the same as the above example.

First, let's create an Account instance to update with AccountKeyWeightedMultiSig. For AccountKeyWeightedMultiSig, a threshold and a weight for each key must be defined. To do this, use caver.account.weightedMultiSigOptions. The first parameter is the threshold, and the second parameter is an array containing the weight for each key.


// Create an account instance with three private keys using AccountKeyWeightedMultiSig
String[] privateKeyArr = caver.wallet.keyring.generateMultipleKeys(3);
MultipleKeyring multipleKeyring = caver.wallet.keyring.createWithMultipleKey(sender.getAddress(), privateKeyArr);
// threshold = 3, the weights of the three keys = [1, 2, 1]
BigInteger threshold = BigInteger.valueOf(3);
BigInteger[] weightedArr = new BigInteger[] {BigInteger.valueOf(1), BigInteger.valueOf(2), BigInteger.valueOf(1)};
WeightedMultiSigOptions options = new WeightedMultiSigOptions(threshold, Arrays.asList(weightedArr));
Account account = multipleKeyring.toAccount(options)

Now let's update AccountKey using AccountKeyRoleBased. AccountKeyRoleBased is an AccountKey type that defines the key to use for each role.


// Create an account instance with roles using AccountKeyRoleBased. In the account instance created, each role has a public key that corresponds to one private key.
List<String[]> newPrivateKeyArr = caver.wallet.keyring.generateRolBasedKeys(new int[] {1,1,1});
RoleBasedKeyring newKeyring = caver.wallet.keyring.createWithRoleBasedKey(senderKeyring.getAddress(), newPrivateKeyArr);
const account = newKeyring.toAccount()

The AccountKeyRoleBased above is an example of using one public key for each role. As you can see from the code above, each of them corresponds to one private key. If you want to use multiple private keys for each role, caver.account.weightedMultiSigOptions must be defined for each role as shown below.


// Create an account instance with [3, 2, 3] keys for each role using AccountKeyRoleBased
List<String[]> newPrivateKeyArr = caver.wallet.keyring.generateRolBasedKeys(new int[] {3, 2, 3});
RoleBasedKeyring newKeyring = caver.wallet.keyring.createWithRoleBasedKey(senderKeyring.getAddress(), newPrivateKeyArr);
WeightedMultiSigOptions[] options = new WeightedMultiSigOptions[] {
new WeightedMultiSigOptions(BigInteger.valueOf(4), Arrays.asList(BigInteger.valueOf(2), BigInteger.valueOf(2), BigInteger.valueOf(4))),
new WeightedMultiSigOptions(BigInteger.valueOf(2), Arrays.asList(BigInteger.valueOf(1), BigInteger.valueOf(1))),
new WeightedMultiSigOptions(BigInteger.valueOf(3), Arrays.asList(BigInteger.valueOf(1), BigInteger.valueOf(1), BigInteger.valueOf(1))),
};
Account account = newKeyring.toAccount(Arrays.asList(options));

If you want to update AccountKey to AccountKeyLegacy or accountKeyFail, create an Account instance as shown below and assign it to the account field of the transaction. The rest of the update process is same to that of other AccountKey.


// Create an account with AccountKeyLegacy
Account account = caver.account.createWithAccountKeyLegacy(keyringToUpdate.address);
// Create an account with AccountKeyFail
Account account = caver.account.createWithAccountKeyFail(keyringToUpdate.address)

Smart Contract ​

The Contract class in caver.contract package makes it easy to interact with smart contracts on kaia. All functions of a smart contract automatically converted and stored inside contract instance, when its low-level ABI is given. This allows you to interact with a smart contract like you handle a contract instance in Java.

We begin our explanation of dealing with a smart contract in Java by writing a simple solidity example code below. Create a 'test.sol' file and write down the example below.


pragma solidity ^0.5.6;
contract KVstore {
mapping(string=>string) store;
function get(string memory key) public view returns (string memory) {
return store[key];
}
function set(string memory key, string memory value) public {
store[key] = value;
}
}

Then, compile this smart contract to get its bytecode and ABI.


> solc --abi --bin ./test.sol
======= ./test.sol:KVstore =======
Binary:
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
Contract JSON ABI
[{"constant":true,"inputs":[{"name":"key","type":"string"}],"name":"get","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"key","type":"string"},{"name":"value","type":"string"}],"name":"set","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"}]

NOTE: To compile a smart contract, you must have a solidity compiler installed. To compile the above program, you need to install solc:0.5.6.

To deploy a smart contract by its type, you can use caver-java classes described below:

  • Contract class in the caver.contract package when the sender or the fee payer of a smart contract transaction pays the fee
  • SmartContractDeploy class in the caver.transaction package when the sender of a smart contract transaction pays the fee
  • feeDelegatedSmartContractDeploy class in the caver.transaction package when the fee payer of a smart contract transaction pays the fee
  • feeDelegatedSmartContractDeployWithRatio class in the caver.transaction package when the fee payer of a smart contract transaction pays the fee

Here is an example of exploiting Contract class in caver.contract package. You can create a contract instance like below from the bytecode and ABI you get after compiling the smart contract.


private static final String ABIJson = "[{\"constant\":true,\"inputs\":[{\"name\":\"key\",\"type\":\"string\"}],\"name\":\"get\",\"outputs\":[{\"name\":\"\",\"type\":\"string\"}],\"payable\":false,\"stateMutability\":\"view\",\"type\":\"function\"},{\"constant\":false,\"inputs\":[{\"name\":\"key\",\"type\":\"string\"},{\"name\":\"value\",\"type\":\"string\"}],\"name\":\"set\",\"outputs\":[],\"payable\":false,\"stateMutability\":\"nonpayable\",\"type\":\"function\"}]\n";
public void createContractInstance() {
Caver caver = new Caver(Caver.DEFAULT_URL);
try {
Contract contract = caver.contract.create(ABIJson);
contract.getMethods().forEach((name, method) ->{
System.out.println(method.getType() + " " + caver.abi.buildFunctionString(method));
});
System.out.println("ContractAddress : " + contract.getContractAddress());
} catch (IOException e) {
//handle exception..
}
}

Running the code above gives you the following result.


function set(string,string)
function get(string)
ContractAddress : null

Looking at the output above, you can see that the contract instance owns the smart contract method. And since it hasn't been deployed yet, you can see that the result of contract.getContractAddress() is output as null.

If this contract was already deployed and you knew the contract address where this contract was deployed at, pass the contract address as the third parameter of the constructor of the contract instance as below.


private static final String ABIJson = "[{\"constant\":true,\"inputs\":[{\"name\":\"key\",\"type\":\"string\"}],\"name\":\"get\",\"outputs\":[{\"name\":\"\",\"type\":\"string\"}],\"payable\":false,\"stateMutability\":\"view\",\"type\":\"function\"},{\"constant\":false,\"inputs\":[{\"name\":\"key\",\"type\":\"string\"},{\"name\":\"value\",\"type\":\"string\"}],\"name\":\"set\",\"outputs\":[],\"payable\":false,\"stateMutability\":\"nonpayable\",\"type\":\"function\"}]\n";
@Test
public void loadContract() {
Caver caver = new Caver(Caver.DEFAULT_URL);
String contractAddress = "0x3466D49256b0982E1f240b64e097FF04f99Ed4b9";
try {
Contract contract = caver.contract.create(ABIJson, contractAddress);
contract.getMethods().forEach((name, method) ->{
System.out.println(method.getType() + " " + ABI.buildFunctionString(method));
});
System.out.println("ContractAddress : " + contract.getContractAddress());
} catch (IOException e) {
//handle exception..
}
}

Running the code above gives you the following result.


function set(string,string)
function get(string)
ContractAddress : 0x3466D49256b0982E1f240b64e097FF04f99Ed4b9

A contract instance stores its contract address as contractAddress property when it was created. The address can be accessed through getter / setter function (getContractAddress() / setContractAddress()).

Once a contract instance is created, you can deploy the smart contract by passing its bytecode and constructor's arguments (when needed for deploying) as the example below.

Note that the deploy() method of the contract instance sends transactions for contract deployment and contract execution. For sending transactions, it uses Keyrings in caver.wallet to sign them. The keyring to be used must have been added to caver.wallet before signing.


private static final String byteCode = "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";
private static final String ABIJson = "[{\"constant\":true,\"inputs\":[{\"name\":\"key\",\"type\":\"string\"}],\"name\":\"get\",\"outputs\":[{\"name\":\"\",\"type\":\"string\"}],\"payable\":false,\"stateMutability\":\"view\",\"type\":\"function\"},{\"constant\":false,\"inputs\":[{\"name\":\"key\",\"type\":\"string\"},{\"name\":\"value\",\"type\":\"string\"}],\"name\":\"set\",\"outputs\":[],\"payable\":false,\"stateMutability\":\"nonpayable\",\"type\":\"function\"}]\n";
public void deployContract() {
Caver caver = new Caver(Caver.DEFAULT_URL);
SingleKeyring deployer = caver.wallet.keyring.createFromPrivateKey("0x{private key}");
caver.wallet.add(deployer);
try {
Contract contract = caver.contract.create(ABIJson);
SendOptions sendOptions = new SendOptions();
sendOptions.setFrom(deployer.getAddress());
sendOptions.setGas(BigInteger.valueOf(4000000));
Contract newContract = contract.deploy(sendOptions, byteCode);
System.out.println("Contract address : " + newContract.getContractAddress());
} catch (IOException | TransactionException | ClassNotFoundException | NoSuchMethodException | InvocationTargetException | InstantiationException | IllegalAccessException e) {
//handle exception..
}
}

In the code above, the deployer deploys the contract to the kaia and returns the deployed contract instance.


ContractAddress : 0x3466D49256b0982E1f240b64e097FF04f99Ed4b9

A smart contract can be deployed using one of the following classes, depending on the type of contract deploying transaction:

  • Contract class in the caver.contract package when the sender or the fee payer of a smart contract transaction pays the fee
  • SmartContractDeploy class in the caver.transaction package when the sender of a smart contract transaction pays the fee
  • feeDelegatedSmartContractDeploy class in the caver.transaction package when the fee payer of a smart contract transaction pays the fee
  • feeDelegatedSmartContractDeployWithRatio class in the caver.transaction package when the fee payer of a smart contract transaction pays the fee

To deploy a smart contract through a fee-delegated transaction, define the feeDelegation and feePayer fields in the SendOptions class like the example below.


private static final String byteCode = "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";
private static final String ABIJson = "[{\"constant\":true,\"inputs\":[{\"name\":\"key\",\"type\":\"string\"}],\"name\":\"get\",\"outputs\":[{\"name\":\"\",\"type\":\"string\"}],\"payable\":false,\"stateMutability\":\"view\",\"type\":\"function\"},{\"constant\":false,\"inputs\":[{\"name\":\"key\",\"type\":\"string\"},{\"name\":\"value\",\"type\":\"string\"}],\"name\":\"set\",\"outputs\":[],\"payable\":false,\"stateMutability\":\"nonpayable\",\"type\":\"function\"}]\n";
public void deployContractWithFeeDelegation() {
Caver caver = new Caver(Caver.DEFAULT_URL);
SingleKeyring deployer = caver.wallet.keyring.createFromPrivateKey("0x{private key}");
caver.wallet.add(deployer);
SingleKeyring feePayer = caver.wallet.keyring.createFromPrivateKey("0x{private key}");
caver.wallet.add(feePayer);
try {
Contract contract = caver.contract.create(ABIJson);
SendOptions sendOptionsForDeployment = new SendOptions();
sendOptionsForDeployment.setFrom(sender.getAddress());
sendOptionsForDeployment.setGas(BigInteger.valueOf(1000000));
sendOptionsForDeployment.setFeeDelegation(true);
sendOptionsForDeployment.setFeePayer(feePayer.getAddress());
contract.deploy(sendOptionsForDeployment, byteCode);
System.out.println("The address of deployed smart contract:" + contract.getContractAddress());
} catch (IOException | TransactionException | ClassNotFoundException | NoSuchMethodException | InvocationTargetException | InstantiationException | IllegalAccessException e) {
//handle exception..
}
}

If you want to send a transaction with sender and feePayer signed seperately when deploying a smart contract through caver.contract, refer to the code below.


private static final String byteCode = "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";
private static final String ABIJson = "[{\"constant\":true,\"inputs\":[{\"name\":\"key\",\"type\":\"string\"}],\"name\":\"get\",\"outputs\":[{\"name\":\"\",\"type\":\"string\"}],\"payable\":false,\"stateMutability\":\"view\",\"type\":\"function\"},{\"constant\":false,\"inputs\":[{\"name\":\"key\",\"type\":\"string\"},{\"name\":\"value\",\"type\":\"string\"}],\"name\":\"set\",\"outputs\":[],\"payable\":false,\"stateMutability\":\"nonpayable\",\"type\":\"function\"}]\n";
public void deployContractWithFeeDelegation() {
Caver caver = new Caver(Caver.DEFAULT_URL);
SingleKeyring deployer = caver.wallet.keyring.createFromPrivateKey("0x{private key}");
caver.wallet.add(deployer);
SingleKeyring feePayer = caver.wallet.keyring.createFromPrivateKey("0x{private key}");
caver.wallet.add(feePayer);
try {
Contract contract = caver.contract.create(ABIJson);
SendOptions sendOptionsForDeployment = new SendOptions();
sendOptionsForDeployment.setFrom(sender.getAddress());
sendOptionsForDeployment.setGas(BigInteger.valueOf(1000000));
sendOptionsForDeployment.setFeeDelegation(true);
sendOptionsForDeployment.setFeePayer(feePayer.getAddress());
AbstractTransaction signedTx = contract.sign(sendOptionsForSigning, "constructor", byteCode);
caver.wallet.signAsFeePayer(feePayer.getAddress(), (AbstractFeeDelegatedTransaction)signedTx);
Bytes32 txHash = caver.rpc.klay.sendRawTransaction(signedTx).send();
TransactionReceiptProcessor receiptProcessor = new PollingTransactionReceiptProcessor(caver, 1000, 15);
TransactionReceipt.TransactionReceiptData receiptData = receiptProcessor.waitForTransactionReceipt(txHash.getResult());
System.out.println("The address of deployed smart contract:" + receiptData.getContractAddress());
} catch (IOException | TransactionException | ClassNotFoundException | NoSuchMethodException | InvocationTargetException | InstantiationException | IllegalAccessException e) {
//handle exception..
}
}

To execute a smart contract's function by its type, you can use caver-java classes described below:

  • Contract class in the caver.contract package when the sender of a smart contract transaction pays the fee
  • SmartContractExecution class in the caver.transaction package when the sender of a smart contract transaction pays the fee
  • FeeDelegatedSmartContractExecution class in the caver.transaction package when the fee payer of a smart contract transaction pays the fee
  • FeeDelegatedSmartContractExecutionWithRatio class in the caver.transaction package when the fee payer of a smart contract transaction pays the fee

To show how to execute a function in a smart contract, here we send a contract execution transaction that puts a string "testValue" as the input parameter of the contract function set in the example code below.


private static final String ABIJson = "[{\"constant\":true,\"inputs\":[{\"name\":\"key\",\"type\":\"string\"}],\"name\":\"get\",\"outputs\":[{\"name\":\"\",\"type\":\"string\"}],\"payable\":false,\"stateMutability\":\"view\",\"type\":\"function\"},{\"constant\":false,\"inputs\":[{\"name\":\"key\",\"type\":\"string\"},{\"name\":\"value\",\"type\":\"string\"}],\"name\":\"set\",\"outputs\":[],\"payable\":false,\"stateMutability\":\"nonpayable\",\"type\":\"function\"}]\n";
public void executeContractFunction() {
Caver caver = new Caver(Caver.DEFAULT_URL);
SingleKeyring executor = caver.wallet.keyring.createFromPrivateKey("0x{private key}");
caver.wallet.add(executor);
try {
Contract contract = caver.contract.create(ABIJson, "0x{address in hex}");
SendOptions sendOptions = new SendOptions();
sendOptions.setFrom(executor.getAddress());
sendOptions.setGas(BigInteger.valueOf(4000000));
TransactionReceipt.TransactionReceiptData receipt = contract.send(sendOptions, "set", "test", "testValue");
} catch (IOException | TransactionException | ClassNotFoundException | NoSuchMethodException | InvocationTargetException | InstantiationException | IllegalAccessException e) {
//handle exception..
}
}

To execute a smart contract's function through a fee-delegated transaction, define the feeDelegation and feePayer fields in the SendOptions class like the example below.


private static final String ABIJson = "[{\"constant\":true,\"inputs\":[{\"name\":\"key\",\"type\":\"string\"}],\"name\":\"get\",\"outputs\":[{\"name\":\"\",\"type\":\"string\"}],\"payable\":false,\"stateMutability\":\"view\",\"type\":\"function\"},{\"constant\":false,\"inputs\":[{\"name\":\"key\",\"type\":\"string\"},{\"name\":\"value\",\"type\":\"string\"}],\"name\":\"set\",\"outputs\":[],\"payable\":false,\"stateMutability\":\"nonpayable\",\"type\":\"function\"}]\n";
public void executeContractWithFeeDelegation() {
Caver caver = new Caver(Caver.DEFAULT_URL);
SingleKeyring executor = caver.wallet.keyring.createFromPrivateKey("0x{private key}");
caver.wallet.add(executor);
SingleKeyring feePayer = caver.wallet.keyring.createFromPrivateKey("0x{private key}");
caver.wallet.add(feePayer);
try {
Contract contract = caver.contract.create(ABIJson, "0x{address in hex}");
SendOptions sendOptionsForExecution = new SendOptions();
sendOptionsForExecution.setFrom(executor.getAddress());
sendOptionsForExecution.setGas(BigInteger.valueOf(4000000));
sendOptionsForExecuted.setFeeDelegation(true);
sendOptionsForExecuted.setFeePayer(feePayer.getAddress());
TransactionReceipt.TransactionReceiptData receipt = contract.send(sendOptions, "set", "test", "testValue");
} catch (Exception e) {
//handle exception..
}
}

If you want to send a transaction with sender and feePayer signed separately when executing a smart contract through caver.contract, refer to the code below:


private static final String ABIJson = "[{\"constant\":true,\"inputs\":[{\"name\":\"key\",\"type\":\"string\"}],\"name\":\"get\",\"outputs\":[{\"name\":\"\",\"type\":\"string\"}],\"payable\":false,\"stateMutability\":\"view\",\"type\":\"function\"},{\"constant\":false,\"inputs\":[{\"name\":\"key\",\"type\":\"string\"},{\"name\":\"value\",\"type\":\"string\"}],\"name\":\"set\",\"outputs\":[],\"payable\":false,\"stateMutability\":\"nonpayable\",\"type\":\"function\"}]\n";
public void executeContractWithFeeDelegation() {
Caver caver = new Caver(Caver.DEFAULT_URL);
SingleKeyring executor = caver.wallet.keyring.createFromPrivateKey("0x{private key}");
caver.wallet.add(executor);
SingleKeyring feePayer = caver.wallet.keyring.createFromPrivateKey("0x{private key}");
caver.wallet.add(feePayer);
try {
Contract contract = caver.contract.create(ABIJson, "0x{address in hex}");
SendOptions sendOptionsForExecution = new SendOptions();
sendOptionsForExecution.setFrom(executor.getAddress());
sendOptionsForExecution.setGas(BigInteger.valueOf(4000000));
sendOptionsForExecuted.setFeeDelegation(true);
sendOptionsForExecuted.setFeePayer(feePayer.getAddress());
AbstractTransaction executionTx = contract.sign(sendOptionsForExecution, "set", "test", "testValue");
caver.wallet.signAsFeePayer(feePayer.getAddress(), (AbstractFeeDelegatedTransaction)executionTx);
Bytes32 txHash_executed = caver.rpc.klay.sendRawTransaction(executionTx).send();
TransactionReceiptProcessor receiptProcessor = new PollingTransactionReceiptProcessor(caver, 1000, 15);
TransactionReceipt.TransactionReceiptData receiptData = receiptProcessor.waitForTransactionReceipt(txHash_executed.getResult());
} catch (Exception e) {
//handle exception..
}
}

To load a contract instance and call one of its functions (not sending a transaction but just a call): the below example shows calling a get function in a contract.


private static final String ABIJson = "[{\"constant\":true,\"inputs\":[{\"name\":\"key\",\"type\":\"string\"}],\"name\":\"get\",\"outputs\":[{\"name\":\"\",\"type\":\"string\"}],\"payable\":false,\"stateMutability\":\"view\",\"type\":\"function\"},{\"constant\":false,\"inputs\":[{\"name\":\"key\",\"type\":\"string\"},{\"name\":\"value\",\"type\":\"string\"}],\"name\":\"set\",\"outputs\":[],\"payable\":false,\"stateMutability\":\"nonpayable\",\"type\":\"function\"}]\n";
public void callContractFunction() {
Caver caver = new Caver(Caver.DEFAULT_URL);
try {
Contract contract = caver.contract.create(ABIJson, '0x{address in hex}');
List<Type> result = contract.call("get", "test");
System.out.println((String)result.get(0).getValue());
} catch (IOException | TransactionException | ClassNotFoundException | NoSuchMethodException | InvocationTargetException | InstantiationException | IllegalAccessException e) {
//handle exception..
}
}

When the above code is executed, the value is shown as an output below.


testValue

To find more information, see caver-java API

IPFS ​

IPFS (InterPlanetary File System) is a distributed file system for storing and accessing files, websites, application, and data.

You can upload and download a file through IPFS with Caver.

Connecting with IPFS ​

The IPFS class in the caver.ipfs package is defined as a class member variable in Caver, so you can interact with IPFS through Caver.

In order to use an IPFS instance through the Caver instance, you must call method setIPFSNode() first to connect to an IPFS node.

The function setIPFSNode() requires following parameters:

  • IPFS HTTP API Host URL
  • IPFS HTTP API Host port number
  • Whether the host use SSL or not.

String host = "The URL of an IPFS node";
int port = 5001; // API host port number
boolean isSSL = true; // API host support ssl
Caver caver = new Caver();
caver.ipfs.setIPFSNode(host, port, isSSL);

Uploading a file through IPFS​

To upload a file through IPFS, please use add() like below.

This function returns CID(Content Identifier) of the uploaded file.


String filePath = "/path/to/file";
String cid = caver.ipfs.add(filePath);
System.out.println(cid);

The execution result of the above code is shown below.


QmYzW1fXbapdxkZXMQeCYoDCjVc18H8tLfMfrxXRySmQiq

Likewise, you can upload a byte array.


String text = "sample data";
byte[] data = text.getBytes();
String cid = caver.ipfs.add(data);
System.out.println(cid);

The execution result of the above code is shown below.


QmYzW1fXbapdxkZXMQeCYoDCjVc18H8tLfMfrxXRySmQiq

Downloading a file from IPFS​

To download a file from IPFS, please use get() like below.

This function requires CID of the file to be downloaded.


String cid = "QmYzW1fXbapdxkZXMQeCYoDCjVc18H8tLfMfrxXRySmQiq";
byte[] content = caver.ipfs.get(cid);

Conversion between CID and multihash ​

You can convert a CID to a Multihash using toHex().

A CID is a Base58 encoded value of a multihash. toHex() decodes the CID and returns the corresponding multihash.


String cid = "QmYtUc4iTCbbfVSDNKvtQqrfyezPPnFvE33wFmutw9PBBk";
String multihash = caver.ipfs.toHex(cid);
System.out.println(multihash);

The execution result of the above code is shown below.


0x12209cbc07c3f991725836a3aa2a581ca2029198aa420b9d99bc0e131d9f3e2cbe47

To convert a multihash to CID, please use fromHex().


String multihash = "0x12209cbc07c3f991725836a3aa2a581ca2029198aa420b9d99bc0e131d9f3e2cbe47";
String cid = caver.ipfs.fromHex(multihash);
System.out.println(cid);

The execution result of the above code is shown below.


QmYtUc4iTCbbfVSDNKvtQqrfyezPPnFvE33wFmutw9PBBk

Detect KCT interface​

KCT (Kaia Compatible Token) contracts such as KIP-7, KIP-17, and KIP-37 define and provide various interfaces, and KIP-13 allows you to see whether a contract complies with KCT specifications and which interface it implements, by sending a query to the contract.

KIP-13 was implemented in Caver v1.5.7. It could detect interface through detectInterface() for any of the KCT contract classes (KIP7, KIP17, and KIP37).

Detecting KIP-7 Interfaces ​

To detect KIP-7 interfaces, you can use detectInterface() in the KIP7 class. It returns the mapping between KIP-7 interface identifier and a boolean that the interface is supported or not.

detectInterface() supports both static and instance methods, so you can select and use the method that suits your needs.

The interface detected through detectInterface() for KIP7 is shown in the table below.

InterfaceKIP-13 Identifier
IKIP70x65787371
IKIP7Metadata0xa219a025
IKIP7Mintable0xeab83e20
IKIP7Burnable0x3b5a0bf8
IKIP7Pausable0x4d5507ff

Caver caver = new Caver(Caver.DEFAULT_URL);
ObjectMapper mapper = new ObjectMapper();
String contractAddress = "0x{address}";
//using static method.
Map<String, Boolean> resultStatic = caver.kct.kip7.detectInterface(caver, contractAddress);
String resultJson = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(resultStatic);
System.out.println(resultJson);
//using instance method.
KIP7 kip7 = caver.kct.kip7.create(contractAddress);
Map<String, Boolean> resultInstance = kip7.detectInterface();
String resultJson = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(resultInstance);
System.out.println(resultJson);

The execution result of the above code is shown below.


{
"IKIP7Metatdata" : true,
"IKIP7Burnable" : true,
"IKIP7" : true,
"IKIP7Pausable" : true,
"IKIP7Mintable" : true
}

Detecting KIP-17 Interfaces ​

To detect the interface implemented in a KIP-17 token contract, you can use detectInterface() in the KIP17 class. It returns the mapping between KIP-17 interface identifier and interface support.

detectInterface() supports both static and instance methods, so you can select and use the method that suits your needs.

The interface detect through detectInterface() for KIP17 is shown in the table below.

InterfaceKIP-13 Identifier
IKIP170x80ac58cd
IKIP17Metadata0x5b5e139f
IKIP17Enumerable0x780e9d63
IKIP17Mintable0xeab83e20
IKIP17MetadataMintable0xfac27f46
IKIP17Burnable0x42966c68
IKIP17Pausable0x4d5507ff

Caver caver = new Caver(Caver.DEFAULT_URL);
ObjectMapper mapper = new ObjectMapper();
String contractAddress = "0x{address}";
//using static method.
Map<String, Boolean> resultStatic = caver.kct.kip17.detectInterface(caver, contractAddress);
String resultJson = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(resultStatic);
System.out.println(resultJson);
//using instance method.
KIP17 kip17 = caver.kct.kip17.create(contractAddress);
Map<String, Boolean> resultInstance = kip17.detectInterface();
String resultJson = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(resultInstance);
System.out.println(resultJson);

The execution result of the above code is shown below.


{
"IKIP17Enumerable" : true,
"IKIP17Metadata" : true,
"IKIP17Burnable" : true,
"IKIP17Mintable" : true,
"IKIP17" : true,
"IKIP17MetadataMintable" : true,
"IKIP17Pausable" : true
}

Detecting KIP-37 interfaces ​

To detect the interface implemented in a KIP-37 token contract, you can use detectInterface() in the KIP37 class. It returns the mapping between KIP-37 interface identifier and interface support.

detectInterface() supports both static and instance methods, so you can select and use the appropriate method.

The interface detection through detectInterface() for KIP37 is shown in the table below.

InterfaceKIP-13 Identifier
IKIP370x6433ca1f
IKIP37Metadata0x0e89341c
IKIP37Mintable0xdfd9d9ec
IKIP37Burnable0x9e094e9e
IKIP37Pausable0x0e8ffdb7

Caver caver = new Caver(Caver.DEFAULT_URL);
ObjectMapper mapper = new ObjectMapper();
String contractAddress = "0x{address}";
//using static method.
Map<String, Boolean> resultStatic = caver.kct.kip37.detectInterface(contractAddress);
String resultJson = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(resultStatic);
System.out.println(resultJson);
//using instance method.
KIP37 kip37 = caver.kct.kip37.create(contractAddress);
Map<String, Boolean> resultInstance = kip37.detectInterface();
String resultJson = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(resultInstance);
System.out.println(resultJson);

The execution result of the above code is shown below.


{
"IKIP37Metatdata" : true,
"IKIP37Burnable" : true,
"IKIP37" : true,
"IKIP37Pausable" : true,
"IKIP37Mintable" : true
}