智能合约构成
Java 语言的智能合约代码,关键是在于实现以下接口:
/*** Defines methods that all chaincodes must implement.*/public interface Chaincode {/***Called during an instantiate transaction after the container has been*established, allowing the chaincode to initialize its internal data*/public Response init(ChaincodeStub stub);/***Called for every Invoke transaction. The chaincode may change its state*variables.*/public Response invoke(ChaincodeStub stub);}
接口 init 主要是用于智能合约初始化和升级的时候调用这个接口,初始化相关的数据。
接口 invoke 主要是用于实现智能合约里的内部业务逻辑,用户可以根据需要,实现相关的业务。
在实现过程中,用户可以调用 ChaincodeStub 的 API 接口来和链上交互。
智能合约示例
基本示例
本示例以一个基本的智能合约用例为例,只包含智能合约的必须部分,没有实现任何业务逻辑。
/** SimpleAssetDemo implements a simple chaincode to manage an asset*/public class SimpleAssetDemo extends ChaincodeBase {/** Init is called during chaincode instantiation to initialize any data.*/@Overridepublic Response init(ChaincodeStub stub) {}/** Invoke is called per transaction on the chaincode. Each transaction is* either a 'get' or a 'set' on the asset created by Init function. The 'set'* method may create a new asset by specifying a new key-value pair.*/@Overridepublic Response invoke(ChaincodeStub stub) {}public static void main(String[] args) {new SimpleAssetDemo().start(args);}}
官方示例
Hyperledger Fabric 提供了很多官方的智能合约样例,具体请参考 fabric 官方示例。本示例以 Hyperledger Fabric 官方提供的 chaincode_example02 样例为例。该示例的 init 函数用于初始化两个 key/value 键值对,invoke 函数用于根据不同业务逻辑进行细分调用,最终调用以下业务逻辑接口:
invoke :用于 key 之间的 value 转移。
delete:删除一个键值对。
query:查询 key 所对应的值。
init 函数示例
init 函数在智能合约实例化以及升级的时候会被调用。在实现 init 函数的过程中,可使用 Java 语言版本的合约 API 列表 来对参数和账本进行操作。本例通过调用 API getFunction 和 getParameters 获取到用户输入参数。在获取用户输入参数后,通过调用 API putStringState 将数据写到账本中。具体代码如下:
/** init函数用于初始化两个键值对,用户输入的参数为KEY1_NAME, VALUE1,* KEY2_NAME, VALUE2*/@Overridepublic Response init(ChaincodeStub stub) {try {_logger.info("Init java simple chaincode");// 调用API getFunction获取当前的输入函数String func = stub.getFunction();if (!func.equals("init")) {return newErrorResponse("function other than init is not supported");}// 调用API getParameters 获取用户输入参数List<String> args = stub.getParameters();if (args.size() != 4) {newErrorResponse("Incorrect number of arguments. Expecting 4");}// Initialize the chaincodeString account1Key = args.get(0);int account1Value = Integer.parseInt(args.get(1));String account2Key = args.get(2);int account2Value = Integer.parseInt(args.get(3));_logger.info(String.format("account %s, value = %s; account %s, value %s", account1Key, account1Value, account2Key, account2Value));// 调用API putStringState 把数据写入账本stub.putStringState(account1Key, args.get(1));stub.putStringState(account2Key, args.get(3));return newSuccessResponse();} catch (Throwable e) {return newErrorResponse(e);}}
invoke 函数示例
invoke 函数对用户的不同的智能合约业务逻辑进行拆分。本例通过调用 API getFunction 和 getParameters 获取到用户的具体业务类型和参数,根据用户的不同业务类型,分别调用不同的业务函数,如 invoke,delete 和 query 函数。具体代码如下:
// invoke把用户调用的function细分到几个子function, 包含invoke, delete和query@Overridepublic Response invoke(ChaincodeStub stub) {try {_logger.info("Invoke java simple chaincode");// 调用API getFunction和getParameters获取用户输入的业务类型和参数String func = stub.getFunction();List<String> params = stub.getParameters();if (func.equals("invoke")) {return invoke(stub, params);}if (func.equals("delete")) {return delete(stub, params);}if (func.equals("query")) {return query(stub, params);}return newErrorResponse("Invalid invoke function name. Expecting one of: [\\"invoke\\", \\"delete\\", \\"query\\"]");} catch (Throwable e) {return newErrorResponse(e);}}
业务逻辑 invoke 函数示例
业务逻辑 invoke 函数主要用于实现业务逻辑中的资产转移。本例中通过调用 API getStringState 获取到 KEY 对应的资产总值,通过调用用户业务逻辑实现资产转移,通过调用 API putStringState 将用户最终资产写入账本。具体代码如下:
// invoke实现两个键之间的value转移,输入为KEY1_NAME, KEY2_NAME,VALUEprivate Response invoke(ChaincodeStub stub, List<String> args) {if (args.size() != 3) {return newErrorResponse("Incorrect number of arguments. Expecting 3");}String accountFromKey = args.get(0);String accountToKey = args.get(1);// API getStringState获取对应账户的资产String accountFromValueStr = stub.getStringState(accountFromKey);if (accountFromValueStr == null) {return newErrorResponse(String.format("Entity %s not found", accountFromKey));}int accountFromValue = Integer.parseInt(accountFromValueStr);String accountToValueStr = stub.getStringState(accountToKey);if (accountToValueStr == null) {return newErrorResponse(String.format("Entity %s not found", accountToKey));}int accountToValue = Integer.parseInt(accountToValueStr);int amount = Integer.parseInt(args.get(2));// 执行具体业务逻辑,这里对应资产进行转移if (amount > accountFromValue) {return newErrorResponse(String.format("not enough money in account %s", accountFromKey));}accountFromValue -= amount;accountToValue += amount;_logger.info(String.format("new value of A: %s", accountFromValue));_logger.info(String.format("new value of B: %s", accountToValue));// API putStringState将对应资产写入账本stub.putStringState(accountFromKey, Integer.toString(accountFromValue));stub.putStringState(accountToKey, Integer.toString(accountToValue));_logger.info("Transfer complete");return newSuccessResponse("invoke finished successfully", ByteString.copyFrom(accountFromKey + ": " + accountFromValue + " " + accountToKey + ": " + accountToValue, UTF_8).toByteArray());}
delete 函数示例
业务逻辑 delete 函数主要用于实现业务逻辑中的账户删除功能,本示例通过调用 API delState 删除对应账户。具体代码如下:
// delete用于从账本中删除指定的键,输入为KEY_NAME// Deletes an entity from stateprivate Response delete(ChaincodeStub stub, List<String> args) {if (args.size() != 1) {return newErrorResponse("Incorrect number of arguments. Expecting 1");}String key = args.get(0);// API delState删除特定的账户// Delete the key from the state in ledgerstub.delState(key);return newSuccessResponse();}
query 函数示例
业务逻辑 query 函数主要用于实现业务逻辑中账户查询功能,本示例通过调用 API getStringState 查询对应账户的资产。具体代码如下:
// query主要是查询键对应的值,输入为KEY_NAME// query callback representing the query of a chaincodeprivate Response query(ChaincodeStub stub, List<String> args) {if (args.size() != 1) {return newErrorResponse("Incorrect number of arguments. Expecting name of the person to query");}String key = args.get(0);// API getStringState查询特定的账户String val = stub.getStringState(key);if (val == null) {return newErrorResponse(String.format("Error: state for %s is null", key));}_logger.info(String.format("Query Response:\\nName: %s, Amount: %s\\n", key, val));return newSuccessResponse(val, ByteString.copyFrom(val, UTF_8).toByteArray());}