Getting started with blockchain for Java developers ~ Bilgin Ibryam (@bibryam)

Follow me on twitter for other posts in this space. This post was originally published on Opensource.com under CC BY-SA 4.0. If you prefer, read the same post on Hacker Noon.

Top technology prognosticators have listed blockchain among the top 10 emerging technologies with the potential to revolutionize our world in the next decade, which makes it well worth investing your time now to learn. If you are a developer with a Java background who wants to get up to speed on blockchain technology, this article will give you the basic information you need to get started.
Blockchain is a huge space and at first it can be overwhelming to navigate. Blockchain is different from other software technologies as it has a parallel non-technical universe with a focus on speculations, scams, price volatility, trading, ICOs, cryptocurrencies, Bitcoin maximalism, game theory, human greed, etc. Here we will ignore that side of blockchain completely and look at the technical aspects only.

The theoretical minimum for blockchain

Regardless of the programing language, implementation details, there is a theoretical minimum about blockchain that you should be familiar with. Without this understanding, it is impossible to grasp the foundations, and build on. Based on my experience, the very minimum two technologies that must be understood are Bitcoin and Ethereum. It happens that both projects introduced something new in this space, both currently have the highest market cap, and highest developer community, etc. Most other blockchain projects, whether they are public or private, permissionless or permissioned, are forks of Bitcoin or Ethereum, or build and improve their shortcomings in some ways by making certain trade-offs. Understanding these two projects is like taking networking, database theory, messaging, data structures and two programing language classes in the university. Understanding how these two blockchain technologies will open your mind for the blockchain universe.

Tech books to start with blockchain

The two books I recommend for this purpose happen to be from the same author - Andreas M. Antonopoulos:

Mastering Bitcoin is the most in depth, technical but still understandable and easy to read book I could find about Bitcoin. The tens of other books I checked on this topic were either mostly philosophical and non-technical.
On the Ethereum side, there are many more technical books, but I liked the level of detail in Mastering Ethereum most.
Building Ethereum Dapps is another book I found very thorough and covering the Ethereum development very well.

Most popular Java based blockchain projects

If you are coming from a technical background, it makes sense to build on that knowledge and see what blockchain brings to the table. In the end, blockchain is a fully new technology, but a new combination of existing technologies with human behavior fueled by network effects.

It is worth stating that the popular technologies such as Java, .Net, relational databases are not common in the blockchain space. This space is primarily dominated by C, Go, Rust on the server side, and JavaScript on the client side. But if you know Java, there are a few projects and components written in Java that can be used as a leveraged entry point to the blockchain space.

Assuming you read the above two books, and want to get your hands dirty, here are a few open source blockchain projects written in Java:

Popular Java-based blockchain projects

Corda - this is probably the most natural starting point for a Java developer. Corda is JVM based project that builds on top of popular widely used Java projects such as Apache Artemis, Hibernate, Apache Shiro, Jackson, and relational databases. It is inspired by Bitcoin, but has elements of business processes, messaging, and other familiar concepts. Check out my first impressions from it as a Java developer here.
Pantheon - is a full implementation of an Ethereum node in Java. It is specifically created to attract developers from the Java ecosystem into the blockchain world. Here is an intro and a getting started video by its creators.
BitcoinJ - is the most popular Java implementation of the Bitcoin protocol. If you prefer to start with Bitcoin directly, this is the Java project to explore.
Web3J - while Corda, Pantheon are examples of a full blockchain node implemented in Java, Web3J is client library written in Java. It is very well documented and active project that makes talking to Ethereum compatible nodes straight forward. I created a Apache Camel connector for it and wrote about it here.
Hyperledger Fabric Java SDK - one of the most popular enterprise blockchain projects is Hyperledger Fabric and it has a full-featured Java SDK to play with.

FundRequest - I also want to point you to full end user applications written in Java. While the above projects are examples of clients or nodes, FundRequest is an open source funding platform implemented on top of Ethereum network and fully written in Java. It gives a good idea how to implement a complete blockchains project interacting with the Ethereum network.
Eventum - this is a Java project that can help you monitor the Ethereum network and store Events on Kafka. It addresses a few of the common challenges when integrating with blockchain networks which are decentralized.

If you are still not sure where to start, I suggest you read Mastering Bitcoin, that will give you the solid foundation. If you like touching technology before reading, go to Github and play with one of the projects listed above. The rest will follow. The future is open and decentralized.