What is bitcoinj?



Some projects using bitcoinj



bitcoinj is a library for working with the Bitcoin protocol. It can maintain a wallet, send/receive transactions without needing a local copy of Bitcoin Core and has many other advanced features. It's implemented in Java but can be used from any JVM compatible language: examples in Python and JavaScript are included.

It comes with full documentation and many large, well known Bitcoin apps and services are built on it.

Features

Highly optimised lightweight simplified payment verification (SPV) mode. In this mode, only a small part of the block chain is downloaded, making bitcoinj suitable for usage on constrained devices like smartphones or cheap virtual private servers.

(SPV) mode. In this mode, only a small part of the block chain is downloaded, making bitcoinj suitable for usage on constrained devices like smartphones or cheap virtual private servers. Experimental full verification mode , which does the same verification work as Bitcoin Core. In this mode, the unspent transaction output set (UTXO set) is calculated and, thanks to a PostgreSQL store, can be indexed into a database allowing for fast lookup of balance by address.

, which does the same verification work as Bitcoin Core. In this mode, the unspent transaction output set (UTXO set) is calculated and, thanks to a PostgreSQL store, can be indexed into a database allowing for fast lookup of balance by address. A wallet class with encryption, fee calculation, multi-signing, deterministic key derivation, pluggable coin selection/coin control, extensions support and event listeners that let you stay up to date with changes in your balance.

with encryption, fee calculation, multi-signing, deterministic key derivation, pluggable coin selection/coin control, extensions support and event listeners that let you stay up to date with changes in your balance. Support for micropayment channels that let you set up a multi-signature contract between client and server, and then negotiate on the channel, allowing fast micropayments that avoid miner fees.

that let you set up a multi-signature contract between client and server, and then negotiate on the channel, allowing fast micropayments that avoid miner fees. Provides both async and thread-per-connection for network IO, allowing you to choose between scalability and blocking-only features like SOCKS proxying.

for network IO, allowing you to choose between scalability and blocking-only features like SOCKS proxying. Easily implement apps that use Bitcoin's contracts features .

. A simple GUI wallet app that you can use as the basis for your own apps. Watch or read a tutorial on how to customise it and build a native installer that does not require Java.

that you can use as the basis for your own apps. Watch or read a tutorial on how to customise it and build a native installer that does not require Java. Command line tools for working with wallet and chain files, the payment protocol, the network and more.

for working with wallet and chain files, the payment protocol, the network and more. Strong Bitcoin standards support.

support. A friendly and helpful community!

Getting started

You can download the library as a JAR, or use Maven/use Gradle, or get the code from github. Then read:

Satoshi's white paper - the bitcoinj documentation assumes basic familiarity with how Bitcoin works, the structure of transactions and the block chain.

Getting started - a step by step tutorial for Java and JavaScript devs on how to use the library.

Important announcements: If you use bitcoinj in an application please sign up for the announcement list so you know when new versions are available and if there are critical bugs found.

Be aware: this library is Apache licensed. By using it, you agree with the terms of that license. In particular pay attention to section 7 and 8, which assert there is NO WARRANTY that this library is safe to use or bug free, and in fact that by using this code you accept that none of the contributors shall be liable for any damages or monetary loss that results from your use of their code, even if due to bugs in that code. In short, according to the license the library is distributed under, there are no situations in which you could sue any of the developers (it's as if you wrote the entire library yourself). If you can't handle that, don't use this library.

Documentation

There are also some more in depth articles covering various topics. For best understanding, read them in order.

Basics

Core APIs in depth

Working with transactions

Working with the wallet, which covers: Setting one up Receiving and sending money Crafting custom transactions and contracts Balances, coin selection and how to customise Wallet maintenance Encryption and passwords Watching/following wallets Multisig/married wallets and pluggable transaction signing Connecting the wallet to an external unspent outputs store e.g. for web wallets

Working with monetary amounts

How to use the network API

bitcoinj TV

Advanced features

You can read the release notes for each release starting from 0.3.

Community