SDK - Java

Chain Connector for Java

Git repository:

The Java language SDK for accessing and operating on blockchain platforms is based on openJDK 18.


The project is managed based on Apache Maven.


$mvn compile

Build JAR

$mvn package

Run testing

$mvn test


Connect the chain

Initial the connector using the private key data allocated by the chain platform, then connect to the gateway module.

AccessKey accessKey = gson.fromJson(fileContent, AccessKey.class);
ChainConnector connector = ChainConnector.NewConnectorFromAccess(accessKey);
connector.connect(gatewayHost, gatewayPort);

Build and manage digital assets

Define a data schema for digital assets, and then you can add, update, delete, and query documents (digital assets) under the schema. All changes are automatically persistently stored using blockchain and could be queried using getSchemaLog and getDocumentLog.

//create new schema
String schemaName = "sample";
List<DocumentProperty> properties = new ArrayList<>();
properties.add(new DocumentProperty("name", PropertyType.String));
properties.add(new DocumentProperty("age", PropertyType.Integer));
properties.add(new DocumentProperty("available", PropertyType.Boolean));
conn.createSchema(schemaName, properties);
DocumentSchema schema = conn.getSchema(schemaName);

//add a document
String content = "{\"name\": \"hello\", \"age\": 20, \"available\": true}";
String docID = conn.addDocument(schemaName, "", content);

//check a document
if (conn.hasDocument(schemaName, docID)){
	//update a existed document
    String updatedContent = "{\"name\": \"alice\", \"age\": 18, \"available\": false}";
    conn.updateDocument(schemaName, docID, updatedContent);

//get change trace of a document
LogRecords logs = conn.getDocumentLogs(schemaName, docID);

//query documents
QueryCondition condition = new QueryBuilder()
DocumentRecords records = conn.queryDocuments(schemaName, condition);

//remove document
conn.removeDocument(schemaName, docID);

Deploy and invoke the Smart Contract

It is necessary to assign a name and execute steps to deploy a Smart Contract. Then initiate execution using the contract name and call parameters. The system can enable the trace option for a contract, which allows the user to review the contract’s execution plan and steps.

String contractName = "contract_create";
List<ContractStep> steps = new ArrayList<>();
steps.add(new ContractStep("create_doc", new String[]{"$s", "@1", "@2"}));
steps.add(new ContractStep("set_property", new String[]{"$s", "catalog", "@3"}));
steps.add(new ContractStep("set_property", new String[]{"$s", "balance", "@4"}));
steps.add(new ContractStep("set_property", new String[]{"$s", "number", "@5"}));
steps.add(new ContractStep("set_property", new String[]{"$s", "available", "@6"}));
steps.add(new ContractStep("set_property", new String[]{"$s", "weight", "@7"}));
steps.add(new ContractStep("update_doc", new String[]{"@1", "$s"}));
steps.add(new ContractStep("submit"));

ContractDefine contractDefine = new ContractDefine(steps);
//check existed contract
if (conn.hasContract(contractName)) {
    //withdraw existed contract
    System.out.printf("previous contract %s removed\n", contractName);

//deploy contact
conn.deployContract(contractName, contractDefine);

//enable trace option
ContractInfo info = conn.getContractInfo(contractName);
if (!info.isEnabled()) {

final String docID = "contract-doc";
String[] parameters = {
    String.valueOf((int) (Math.random() * 1000)),
    Math.random() > 0.5 ? "true" : "false",
    String.format("%.2f", Math.random() * 200)

//call contract with parameters
conn.callContract(createContractName, new ArrayList<>(Arrays.asList(parameters)));

Audit the block chain and transaction

Through the SDK, you can obtain and check all the details of chains, blocks, and transactions, which can be used to audit data security and monitor the background operation.

//check chain status
ChainStatus status = conn.getStatus();

//query blocks from height 1 to 10
BlockRecords blockRecords = conn.queryBlocks(1, 10);
for (String blockID : blockRecords.getBlocks()) {
    //get block data
    BlockData blockData = conn.getBlock(blockID);
    //query transactions in a block
    TransactionRecords transactionRecords = conn.queryTransactions(blockID, 0, 20);
    for (String transID : transactionRecords.getTransactions()) {
        //get transaction data
        TransactionData transactionData = conn.getTransaction(blockID, transID);