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using web3j for loading a contract which is deployed on the private network following this tutorial https://web3j.readthedocs.io/en/latest/smart_contracts.html#constant-methods

smart contract

pragma solidity ^0.4.10;

contract Counter {
    uint256 counter =0;

    function increase() public {
        counter++;
    }

    function  decrease() public{
        counter--;
    }

    function getCounter() public constant  returns (uint256) {
        return counter;
    }
}

compiled the contract and created its java wrapper code its java wrapper code is

package models.smartcontract;

import java.math.BigInteger;
import java.util.Arrays;
import java.util.Collections;
import org.web3j.abi.TypeReference;
import org.web3j.abi.datatypes.Function;
import org.web3j.abi.datatypes.Type;
import org.web3j.abi.datatypes.generated.Uint256;
import org.web3j.crypto.Credentials;
import org.web3j.protocol.Web3j;
import org.web3j.protocol.core.RemoteCall;
import org.web3j.protocol.core.methods.response.TransactionReceipt;
import org.web3j.tx.Contract;
import org.web3j.tx.TransactionManager;

/**
 * <p>Auto generated code.
 * <p><strong>Do not modify!</strong>
 * <p>Please use the <a href="https://docs.web3j.io/command_line.html">web3j command line tools</a>,
 * or the org.web3j.codegen.SolidityFunctionWrapperGenerator in the 
 * <a href="https://github.com/web3j/web3j/tree/master/codegen">codegen module</a> to update.
 *
 * <p>Generated with web3j version 3.4.0.
 */
public class Counter extends Contract {
    private static final String BINARY = "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";

    public static final String FUNC_GETCOUNTER = "getCounter";

    public static final String FUNC_DECREASE = "decrease";

    public static final String FUNC_INCREASE = "increase";

    protected Counter(String contractAddress, Web3j web3j, Credentials credentials, BigInteger gasPrice, BigInteger gasLimit) {
        super(BINARY, contractAddress, web3j, credentials, gasPrice, gasLimit);
    }

    protected Counter(String contractAddress, Web3j web3j, TransactionManager transactionManager, BigInteger gasPrice, BigInteger gasLimit) {
        super(BINARY, contractAddress, web3j, transactionManager, gasPrice, gasLimit);
    }

    public RemoteCall<BigInteger> getCounter() {
        final Function function = new Function(FUNC_GETCOUNTER, 
                Arrays.<Type>asList(), 
                Arrays.<TypeReference<?>>asList(new TypeReference<Uint256>() {}));
        return executeRemoteCallSingleValueReturn(function, BigInteger.class);
    }

    public RemoteCall<TransactionReceipt> decrease() {
        final Function function = new Function(
                FUNC_DECREASE, 
                Arrays.<Type>asList(), 
                Collections.<TypeReference<?>>emptyList());
        return executeRemoteCallTransaction(function);
    }

    public RemoteCall<TransactionReceipt> increase() {
        final Function function = new Function(
                FUNC_INCREASE, 
                Arrays.<Type>asList(), 
                Collections.<TypeReference<?>>emptyList());
        return executeRemoteCallTransaction(function);
    }

    public static RemoteCall<Counter> deploy(Web3j web3j, Credentials credentials, BigInteger gasPrice, BigInteger gasLimit) {
        return deployRemoteCall(Counter.class, web3j, credentials, gasPrice, gasLimit, BINARY, "");
    }

    public static RemoteCall<Counter> deploy(Web3j web3j, TransactionManager transactionManager, BigInteger gasPrice, BigInteger gasLimit) {
        return deployRemoteCall(Counter.class, web3j, transactionManager, gasPrice, gasLimit, BINARY, "");
    }

    public static Counter load(String contractAddress, Web3j web3j, Credentials credentials, BigInteger gasPrice, BigInteger gasLimit) {
        return new Counter(contractAddress, web3j, credentials, gasPrice, gasLimit);
    }

    public static Counter load(String contractAddress, Web3j web3j, TransactionManager transactionManager, BigInteger gasPrice, BigInteger gasLimit) {
        return new Counter(contractAddress, web3j, transactionManager, gasPrice, gasLimit);
    }
}

java class code is

Web3j web3 = Web3j.build(new org.web3j.protocol.http.HttpService("http://localhost:8080"));
            Web3ClientVersion web3ClientVersion = web3.web3ClientVersion().send();
            String clientVersion = web3ClientVersion.getWeb3ClientVersion();
            System.out.println("clientVersion is -> "+clientVersion);   
            Credentials credentials = WalletUtils.loadCredentials("wss123456", "/home/sara/.ethereum/privatenet/keystore/UTC--2018-07-20T11-40-45.429000000Z--9e0910461ff92d0b77a5aa90769764a8f1a8d6d9.json");
BigInteger gp = BigInteger.valueOf(86440);
            BigInteger gl = BigInteger.valueOf(186440);

Counter contract = Counter.load("0xF9DdE8E8dE5fd4A0a79BA96a9aAf4F7C7c860E13",web3, credentials,gp,gl);  // constructor params



        System.out.println("before increase counter "+contract.getCounter().send());
        TransactionReceipt transactionReceipt = contract1.increase().send();

        System.out.println("after increase counter "+contract.getCounter().send());

contract.getCounter().send() is displaying 0 and i am getting exception on this line

TransactionReceipt transactionReceipt = contract1.increase().send();

here are the exception logs

info] clientVersion is -> Geth/MyNodeName/v1.8.10-stable-eae63c51/linux-amd64/go1.10
[info] before increase counter 0
[error] java.lang.RuntimeException: Error processing transaction request: insufficient funds for gas * price + value
[error]     at org.web3j.tx.TransactionManager.processResponse(TransactionManager.java:67)
[error]     at org.web3j.tx.TransactionManager.executeTransaction(TransactionManager.java:51)
[error]     at org.web3j.tx.ManagedTransaction.send(ManagedTransaction.java:87)
[error]     at org.web3j.tx.Contract.executeTransaction(Contract.java:275)
[error]     at org.web3j.tx.Contract.executeTransaction(Contract.java:259)
[error]     at org.web3j.tx.Contract.executeTransaction(Contract.java:253)
[error]     at org.web3j.tx.Contract.lambda$executeRemoteCallTransaction$3(Contract.java:305)
[error]     at org.web3j.protocol.core.RemoteCall.send(RemoteCall.java:30)
[error]     at models.smartcontract.FirstContractJava.main(FirstContractJava.java:46)

is that the right way to call the methods? also why contract1.increase().send(); methods is throwing an exception is there anything which is missing? please guide

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It seems the account 0x9e0910461ff92d0b77a5aa90769764a8f1a8d6d9 is empty (0 ether). What's the balance of this account in your private blockchain ?

You can check the balance with the following code:

Web3j web3 = Web3j.build(new org.web3j.protocol.http.HttpService("http://localhost:8080"));

EthGetBalance ethGetBalance = web3
  .ethGetBalance("0x9e0910461ff92d0b77a5aa90769764a8f1a8d6d9", DefaultBlockParameterName.LATEST)
  .sendAsync()
  .get();

BigInteger wei = ethGetBalance.getBalance();

When sending a transaction, the sender is charged a little amount of his account for computation (called gas). So you need to fund the account to be able to send a transaction.

  • there is no account in my code "0x9e0910461ff92d0b77a5aa90769764a8f1a8d6d9" – swaheed Jul 21 '18 at 14:39
  • On the line Credentials credentials = WalletUtils.loadCredentials("wss123456", "/home/sara/.ethereum/privatenet/keystore/UTC--2018-07-20T11-40-45.429000000Z--9e0910461ff92d0b77a5aa90769764a8f1a8d6d9.json"); you unlock the account 0x9e0910461ff92d0b77a5aa90769764a8f1a8d6d9 (wallet file: UTC--2018-07-20T11-40-45.429000000Z--9e0910461ff92d0b77a5aa90769764a8f1a8d6d9.json) with the password wss123456 – Greg Jeanmart Jul 21 '18 at 14:41
  • eth.accounts is returning ["0x4f7f384236f79a5e3322e33cc7bb2ccd5143a87c", "0x6723d7db7458e4eef63d6edbe43fa75397fbfab0"] not the one mentioned in the wallet what should i do now ? – swaheed Jul 21 '18 at 14:48
  • You can use one of these genesis accounts, they must be funded I imagine. – Greg Jeanmart Jul 21 '18 at 15:06

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