How to send ethereum transactions with java
When you no longer need a Web3j instance you need to call the shutdown method to close resources used by it. To connect simply use the relevant IpcService implementation instead of HttpService when you create your service:. For more information refer to Solidity smart contract wrappers. To receive all pending transactions as they are submitted to the network i. There are a number of other transaction and block replay Observables described in Filters and Events.
For further information refer to Filters and Events and the Web3jRx interface. A web3j fat jar is distributed with each release providing command line tools.
The command line tools allow you to use some of the functionality of web3j from the command line:. Please refer to the documentation for further information. Enter search terms or a module, class or function name. To connect simply use the relevant IpcService implementation instead of HttpService when you create your service: To generate the wrapper code, compile your smart contract: To receive all new blocks as they are added to the blockchain: In particular, with Ethereum.
I needed to send a transaction with Java, so I looked at EthereumJ. You have three options:. Transactions can have additional data stored inside them, e. Transactions then get verified by peers currently using a Proof-of-work based consensus and get stored on the blockchain, which means every connected peer gets the newly created blocks each block consisting of multiple transactions.
Why you may want to send transactions? For example in my case I wanted to store the head of a hash chain on the blockchain so that it cannot be tampered with. In my particular case I was more interested in storing a particular piece of data as part of the transaction, rather than the transaction itself, so I had two nodes that sent very small transactions to each other randomly choosing sender and recipient.
The initial code can be found here , and is based heavily on the EthereumJ samples. The most important piece of the code can be seen further below in this post, only slightly modified. You should have a user. The more important part is the external user1 and user2 conf files which in the general scenario can just be one conf file. The light node would do the difference should be simply switching sync. All you need is your private key and a library EthereumJ in this case to prepare your transaction.
So you can forget everything you read in the previous paragraphs. What you need is just the RLP encoded transaction after you have signed it. In this example, I use the Etherscan.
It also has a manual entry form to test your transactions the link is for the Ropsten test network. After that you sign the raw representation of the transaction with your private key the raw representation is RLP Recursive Length Prefix. But now you are relying on a central party Etherscan instead of becoming part of the network. That probably applies to most of programming, though.
Anyway, I hope the above examples can get people started more easily. I appreciate you taking the time and effort to put this short article together.