hyperledger fabric使用java开发智能合约，也较为简单，我们今天就来聊一聊如何使用java开发智能合约，如需完整的学习fabric，可以参考视频教程

首先需要在pom里面引入fabric的智能合约的jar包，如下图所示，需要注意的点如下，引入maven-shade-plugin包，设置mainclass，且finalname必须为chaincode。

<dependencies>
        <dependency>
            <groupId>org.hyperledger.fabric-chaincode-java</groupId>
            <artifactId>fabric-chaincode-shim</artifactId>
            <version>1.4.0</version>
        </dependency>
</dependencies>

<build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.1</version>
                <configuration>
                    <source>${java.version}</source>
                    <target>${java.version}</target>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>3.1.0</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <finalName>chaincode</finalName>
                            <transformers>
                                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <mainClass>com.fabric.chaincode.MyChaincode</mainClass>
                                </transformer>
                            </transformers>
                            <filters>
                                <filter>
                                    <!-- filter out signature files from signed dependencies, else repackaging fails with security ex -->
                                    <artifact>*:*</artifact>
                                    <excludes>
                                        <exclude>META-INF/*.SF</exclude>
                                        <exclude>META-INF/*.DSA</exclude>
                                        <exclude>META-INF/*.RSA</exclude>
                                    </excludes>
                                </filter>
                            </filters>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build> ```
java-fabric的示例代码如下：

public class MyChaincode extends ChaincodeBase {

private static Log _logger = LogFactory.getLog(MyChaincode.class);

@Override
public Response init(ChaincodeStub stub) {
    return newSuccessResponse();
}

@Override
public Response invoke(ChaincodeStub stub) {
    try {
        _logger.info("Invoke java simple chaincode");
        String func = stub.getFunction();
        List<String> params = stub.getParameters();
        if (func.equals("invoke")) {
            return invoke(stub, params);
        }
       else 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);
    }
}

private Response invoke(ChaincodeStub stub, List<String> args) {
    if (args.size() != 2) {
        return newErrorResponse("Incorrect number of arguments. Expecting 3");
    }
    String key = args.get(0);
    String json = args.get(1);
    if(StringUtil.isNullOrEmpty(key) || StringUtil.isNullOrEmpty(json)){
        return newErrorResponse("arguments error");
    }else{
        stub.putStringState(key,json);
        return newSuccessResponse("put success!");
    }
}


// query callback representing the query of a chaincode
private 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);
    //byte[] stateBytes
    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());
}

public static void main(String[] args) {
    System.out.println("OpenSSL avaliable: " + OpenSsl.isAvailable());
    new MyChaincode().start(args);
}

}

智能合约的安装和实例化,需要注意的是 -l java指定java语言为智能合约，智能合约的路径需要补全，go开发的话无需补全。

peer chaincode install -n jcode -v 1.0 -p /opt/gopath/src/github.com/chaincode/javachaincode/ -l java

peer chaincode instantiate -o orderer.example.com:7050 --tls --cafile /opt/gopath/src/github.com/hyperledger/fabric/peer/crypto/ordererOrganizations/example.com/orderers/orderer.example.com/msp/tlscacerts/tlsca.example.com-cert.pem -C mychannel -n jcode -v 1.0 -c '{"Args":["init"]}' -P "AND ('Org1MSP.peer')"

        
        
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