Questions tagged [web3j]
Lightweight Java and Android library for integration with Ethereum clients
314
questions
10
votes
5answers
17k views
why did it returned null after call miner.start()
> miner.start()
> null
before it , I had created a account like this .
user1 = eth.accounts[0]
"0xb62f0bae52d153365661c4e23ab1d594484e9bef"
9
votes
3answers
3k views
Deploy contract on EthereumJS TestRPC
Following https://medium.com/@mvmurthy/full-stack-hello-world-voting-ethereum-dapp-tutorial-part-1-40d2d0d807c2
I've tried to create an instance of a contract using:
VotingContract = web3.eth....
8
votes
2answers
4k views
Web3j listening to events
I'm tinkering with web3j and most of the things that I want to do succeed, however I seem to not be able to listen to events.
I've extended the ballot.sol contract you get with remix by adding an ...
7
votes
2answers
8k views
How to create accounts and also retrieving the ether balance with web3j in a java file?
I do not see anything in creating accounts and retrieving ether balance in web3j's documentation, I wonder if it is possible.
7
votes
1answer
865 views
Deploy contract in web3j quorum problem
I'm trying to deploy a smart contract (7 nodes sample from Quorum) using web3j.
It fails at get() to get the contract wrapper object. If I check the logs, a new transaction will show up, but if I call ...
6
votes
2answers
2k views
Unable to deploy contract to private blockchain using Web3j (Java client) because of TransactionTimeoutException
I am using Web3j for interacting with my private blockchain network created in Azure.
I have created contracts using Remix and Metamask and was able to view that Contract from Java.
However I was ...
6
votes
1answer
3k views
Solidity ecrecover and web3j Sign.signMessage() are not compatible, is it?
Using Web3j to sign and verify a message is fine but when I use the signature generated by Web3j to verify using ecrecover in solidity it doesnot seem to work correctly. The signer address is ...
6
votes
1answer
2k views
how to use Web3j library for android
hi guys i am confuse about the web3j library for android i search about this but i did not get any materiel about this (https://github.com/web3j/web3j). this is lib for using ether node on java and ...
5
votes
1answer
4k views
Convert String to Bytes32 in web3j?
public String solFunction(String str) {
byte[] byteValue = DatatypeConverter.parseHexBinary(str);
Bytes32 strInBytes = new Bytes32(byteValue);
try {
Uint256 value = contract....
5
votes
1answer
609 views
How do I connect Parity and TestRpc
My very much appreciated and valued Conor Svensson -who creates web3j- gave me a very simple task so that we can reproduce the issue https://github.com/web3j/web3j/issues/105#issuecomment-309186331.
"...
5
votes
3answers
2k views
A problem with filters and events (web3j/TestRPC). SOS! ;)
Help me, please, with this little simple task! I cannot solve this problem for several days. SOS! ;)
I'm trying to write a program for filtering events via web3j. I copied to start (for the test) from ...
4
votes
1answer
2k views
send() or sendAsync() while using Web3j to call functions
I built a java web application which connects using Web3j with my smart contract deployed on Ropsten Network.
My web application provides a control panel to allow the user to send transactions to the ...
4
votes
3answers
1k views
How to catch solidity contract revert message using web3j
Is there any way to catch solidity revert message like Remix Javascript VM in web3j
Revert message(Remix)
transact to Erecruitment.issueNewAdmitCard errored: VM error: revert.
revert The ...
4
votes
2answers
1k views
Ethereum remix web3 connection problem
I tried to connect to an ethereum node by using remix. It means that I am using http and not https. However, I receive same error message:
Not possible to connect to the Web3 provider. Make sure the ...
4
votes
1answer
1k views
How do I get the raw private key from a WalletFile object?
How can I get the raw private key from a WalletFile object?
Here is how I am creating the wallet.
String seed = UUID.randomUUID().toString();
ECKeyPair exKey = Keys.createEcKeyPair();
BigInteger ...
4
votes
2answers
284 views
personalUnlockAccount.accountUnlocked() giving NullPointerException even if correct passphrase has been inserted
When I trying to unlock the account with personalUnlockAccount.accountUnlocked() method of PersonalUnlockAccount class of web3j library, it's giving NullPointerException even if I am entering right ...
4
votes
1answer
672 views
Why is web3j java not generating correct return types for my contract
Here is my contract:
pragma solidity ^0.4.17;
contract SignVerify {
function recoverAddr(bytes32 msgHash, uint8 v, bytes32 r, bytes32 s) returns (address) {
return ecrecover(msgHash, v, r,...
4
votes
2answers
5k views
Send Custom ERC20 Tokens from one Address to another
How to send custom ERC20 tokens from one wallet to another, if i want to send EBTC/ECASH custom ERC20 tokens.
I wrote a method that can send the ether from one account to another, how could i do the ...
4
votes
1answer
417 views
how to use web3j over infura to find exact gas price used for a successful transaction
my goal is to compute the cost of gas for a successful tx.
I get a callback when a transaction succeeds and i retrieve gasUsed with
transactionReceipt.getGasUsed(). Now I need to know the exact gas ...
4
votes
1answer
670 views
I am using web3j and geth. How to create default accounts with some ether allocation to it?
I need a default account with huge ether allocation. This I need to set up manually in genesis.json
Hereafter,all accounts need to be created dynamically in java, and they should also be given some ...
4
votes
1answer
437 views
Passing Web3 & Contracts Between Components - React Redux & MetaMask
Curious what's the best way to access and pass a web3 contract instance provided by MetaMask between components when using react-redux.
At this point, I'm tempted to do the following for both web3 ...
3
votes
2answers
3k views
Convert ethereum balance getting in biginteger to ether
public BigInteger getBalance(String address)
{
/*Web3j web3j */
createEthreumConnection();
EthGetBalance ethGetBalance = null;
try {
ethGetBalance = web.ethGetBalance(address, ...
3
votes
1answer
3k views
web3.eth.getBalance returns me the strange values ?
i am trying to get the balance of a wallet, the method is working but the returned result is a json object - { c:(2) [484895,26495000000000],e:19, s: 1}.
In which the value - 484895 corresponds to ...
3
votes
1answer
2k views
How to Query the state of a smart contract using web3j in Android?
I found this documentationQuerying the state of a smart contract.
but i can't get resault,this is my code.
Web3j web3j = Web3jFactory.build(new HttpService(url));
List&...
3
votes
2answers
2k views
Decoding transaction input data with web3j (Java)
My use case is the following:
I would like to have a daemon monitoring how users are interacting with my smart contract.
The way I see it is to look at incoming blocks and try to decode input data ...
3
votes
1answer
2k views
Create ethereum wallet inside android dapp
I am creating a DApp for android and want to be able to create a wallet for each user when they register. I am using web3j, can see how to make wallets in the command line but can't see how to do it ...
3
votes
1answer
1k views
Function of smart contract returns 0 from Web3j
please help me in this problem.
I am successful to compile and deploy my smart contract using web3j on testrpc. But When I call the function that returns uint in this contract from web3j, I always ...
3
votes
2answers
2k views
Compiling Smart Contract in Java
I want to compile a smart contract (solidity code) in Java. Currently I am using the web3j library. When I run the method web3j.ethCompileSolidity(contract) I'm getting the following error: The method ...
3
votes
1answer
864 views
How to use web3j to observe transaction of ERC20 token
Leverage Web3j TransactionObservable together with filter, i can monitor ETH/ETC transactions as following code snippet illustrates.
web3j.transactionObservable().filter(tx -> isWantedTransaction(...
3
votes
2answers
4k views
What is the wallet path for credentials in web3j?
I am using the readme guide https://github.com/web3j/web3j. What I am interested is developing smart contracts from my host with java + web3j to private ethereum network which runs on my virtual ...
3
votes
2answers
284 views
Smart contract listeners
I want to develop a method in a smart contract that act as a listener,
what i mean is when i use eth.sendTransaction(from:, to:@ of smart contract) it will be executed, without calling any smart ...
3
votes
3answers
2k views
How to convert Java String to Bytes32 in Java ? I am using web3j solidity wrapper to interact with Smart contract. I am getting following error:
java.lang.UnsupportedOperationException: Input byte array must be in range 0 < M <= 32 and length must match type
I am trying to do as given below. I wanted to add the people but wrapper ...
3
votes
2answers
1k views
How to use mnemonic to recovery my ethereum wallet
I use web3j to create my ethereum wallet.the Code just like down
import org.web3j.crypto.Bip39Wallet;
import org.web3j.crypto.Credentials;
import org.web3j.crypto.ECKeyPair;
import org.web3j.crypto....
3
votes
1answer
827 views
Recover address from signature using web3j
I have signed a data string using the following code snippet in web3js
var data = "hello world";
web3.personal.sign(web3.fromUtf8(data), web3.eth.accounts[0], function(error, result) {
if (!...
3
votes
2answers
3k views
Web3j - sending erc20 token
I would like to ask how to correctly send ERC20 Token from a wallet to another wallet , followings are my codes :
public static void main(String[] args) throws Exception {
Web3j web3 = Web3j....
3
votes
1answer
460 views
Ethereum - how to get merkle proof
I'm trying to figure out the check of existence and the immutability of the transaction in the Ethereum block, but I do not know how to get mercle branch. With the help of web3j I can get the block ...
2
votes
2answers
6k views
Generate private key and address using web3j
How can i generate private key and address using web3j instead of creating keystore json file
2
votes
3answers
9k views
How to view custom token balance in ether wallet using web3
Hello I am newbie to cryptocurrency. I have created my erc20 custom token. Now, I want to create an API to view the balance(in my token as well as in ethers) using web3 and node js.Can someone please ...
2
votes
2answers
804 views
invalid opcode “0x1c” during smart contract method execution
I have written a smart contract to test event from java project using web3j
I have prepared the web3j wrapper java class using solc compiler version
"0.5.7+commit.6da8b019.Linux.g++"
I am using a ...
2
votes
1answer
942 views
How to change the nonce between transactions in web3j?
I have this line of code where it registers a transaction in blockchain. And I wanted to know how I can make the nonce different between the transactions?
txhash = careercertificate
....
2
votes
1answer
985 views
How could I send transactions continuously by Web3j generated wrapper
I wrote a smart contract and deployed on my private Quorum. I use Web3j to generate java wrapper to call ABIs. For example,
// here is a smart contract function
function getMoney() external payable
...
2
votes
2answers
983 views
How to create a RawTransaction for contract interaction Web3j
I want to sign a transaction that calls a smart contract function and send it to the Rinkeby network.
I found on Web3j documentation the RawTransaction class that supports the methods for the ...
2
votes
1answer
1k views
How can I get the TxReceipt of a transaction with web3j?
How can I get the status of a transaction through the TxHash with web3j.
I tried it like this:
public int getEstado(String trx) {
try {
JSONObject json = readJsonFromUrl("https://api....
2
votes
1answer
672 views
Not able to decode the input data from transaction using web3j
I am creating transactions using web3j and passing some private data in that transaction. The transaction is also getting mined . I have subscribed to the mined blocks, where I am fetching the ...
2
votes
1answer
3k views
How fetch transaction history for account quickly using Web3j?
Intro
We use Web3j java library to work with Ethereum network. I use Rinkeby test network wit Geth client at the moment. I got familiar with blockchains only a week ago, so terms I use can be ...
2
votes
2answers
3k views
Web3j: “Intrinsic gas too low” error when deploying contract in Ethereum from Java
I am a new to Ethereum and Blockchain, I have been trying execution of Contracts using Metamask and Remix using Chrome browser for sometime.
I am trying to deploy the same contract from Java using ...
2
votes
1answer
88 views
Sending private key to server side
I am trying to build new Dapp application for our startup by using web3j , I am facing an issue with signing the transaction from server side , because i need to know the private key for the client (...
2
votes
2answers
730 views
Empty value (0x) returned from contract web3j
I'm trying to deploy a very simple contract on Windows 10, using Web3j 4.2.0. I've created an account using Mist. I've set up one local ethereum node (using geth) on my machine and I'm able to deploy ...
2
votes
1answer
340 views
What does the get Status () method return with a pending state transaction?
If a transaction has a successful state it returns 0x1 but if the transaction has a failed state it returns 0x0. My questions is, what to return when the transaction has a pending status?
public ...
2
votes
2answers
424 views
How do I update data for project using blockchain (Ethereum)?
I am very new to creating blockchain dapps, so some guidance would be appreciated. I am conceptualizing how to approach creating a private blockchain so that users can communicate about the status of ...
