Featured White Papers

• Measuring Risk to Improve Java Software Quality
• Do You Really Get Classloaders?
• Pragmatic Continuous Delivery with Jenkins, Nexus, and LiveRebel
• Your Next Java Web App: Less XML, No Long Restarts, Fewer Hassles
• Coding with JRebel, Java Forever Changed
• 2012 Developer Productivity Report: Java Tools, Tech, Devs, and Data

Sponsored Links

• Graph databases are 1000x faster than relational.

  Learn More!

• Career opportunities at Harman- Careers That'll Rock Your Socks Off.

  Learn More!

• Developer-friendly Java PDF libraries by Qoppa Software

  Live Demos

• Stop blaming your app! Diagnose Java performance issues.

  Free tool >

• UrbanCode: Go From Continuous Integration to
  Continuous Delivery

  Learn More!

Sponsored Links

Optimize with a SATA RAID Storage Solution
Range of capacities as low as $1250 per TB. Ideal if you currently rely on servers/disks/JBODs

Bitcoin for beginners, Part 3: The BitCoinJ API

Build a Java-based Bitcoin transaction client

By Dirk Merkel, JavaWorld.com, 01/10/12

For Java developers, BitCoinJ is an entry point to developing applications that interact with the Bitcoin network. In this final article in a three-part series, Dirk Merkel helps you set up BitCoinJ in an Eclipse development environment, then walks through several short exercises that will familiarize you with this lightweight implementation of the Bitcoin transaction protocol.

Previous installments in this three-part series have introduced the conceptual and technological framework of Bitcoin, a virtual currency and peer-to-peer network. This article, a tutorial introduction to the BitCoinJ API, assumes that you are familiar with Bitcoin addresses, transactions, blocks, and the block chain.

BitCoinJ is an open source Java implementation of the Bitcoin protocol. As such, it's a handy tool to have if you want to write Java applications that interact with the Bitcoin network. In order to explore the BitCoinJ API, we'll construct various sample applications that illustrate the programming steps necessary to construct more complex Bitcoin applications in Java. After using Maven to built and set up a project in the Eclipse IDE, we'll practice creating a Bitcoin address, storing it in a wallet, and saving the wallet to disk. We'll then establish a connection to the Bitcoin test network and retrieve its genesis block. Finally, we'll tie together our sample code so far by sending some Bitcoins to an address on the test network.

Get started with BitCoinJ

BitCoinJ is hosted by Google Code in a Subversion repository, and can be anonymously checked out. Once you check out the trunk of the BitCoinJ project you'll be able to easily keep it updated. You will not, however, be able to commit any changes.

You can use the Subversion client built into your favorite IDE or simply check out the project from the command-line, as I did:

Figure 1. Check out BitCoinJ from the command-line (click to enlarge)

Once you have the code, you'll compile it with Maven, BitCoinJ's build system. Maven takes a lifecycle approach to building projects and is highly extensible with many core and third-party plugins. What Maven does exceedingly well is manage dependencies. If you look at the Maven pom.xml file in BitCoinJ's root directory, you'll see that it uses only a handful of dependencies; these include JUnit and EasyMock for unit testing, SLF4J for logging, and the Bouncy Castle Crypto APIs for cryptographic operations such as hashing and signing.

From the command-line, run mvn clean package and Maven will retrieve these and other dependencies, compile the project, run the unit test suite, and package the compiled code into a snapshot JAR file. As shown in Figure 2, Maven first executes the clean lifecycle to get rid of any artifacts from previous builds. It then executes the phases of the default lifecycle up to and including the package phase.