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May 8, 2020: I have abandoned this project and will not update it. If someone else wants to take it over please contact me.

-- Mike

Web3J-Scala Library

GitHub version

web3j-scala is an idiomatic Scala wrapper around Web3J for Ethereum. Web3J is a lightweight, reactive, somewhat type safe Java and Android library for integrating with nodes on Ethereum blockchains.

Web3J features RxJava extensions, and web3j-scala wraps that syntax in Scala goodness. For example, the web3j-scala observable methods provide simple and efficient application code. Scala's value classes are used to provide much stronger type safety than Web3J, without incurring a runtime penalty.

Use As a Library

Add this to your SBT project's build.sbt:

resolvers ++= Seq(
  "micronautics/scala on bintray" at "",
  "ethereum" at ""

libraryDependencies += "com.micronautics" %% "web3j-scala" % "4.5.17" withSources()

This library is cross-built for Scala 2.12 and 2.13. Tested with Oracle JDK 8 and OpenJDK 8 & 11.

Questions and Problems

This library merely wraps Web3J, so if you have questions about how to use this library, please read their docs, and participate in their Gitter channel.

If you find a bug in this library you can post an issue here.

Run the Demo Program

The demo program performs the following:

  • Follows the outline of the Web3J Getting Started documentation, adapted for Web3J-Scala, including synchronous and asynchronous versions of the available methods.
  • Compiles an example Solidity program that defines a smart contract.
  • Creates a JVM wrapper from an example smart contract.

To run the demo:

  1. Start up an Ethereum client if you don’t already have one running, such as geth. The bin/runGeth script invokes geth with the following options, which are convenient for development but not secure enough for production:
    • The Ethereum data directory is set to ~/.ethereum, or a subdirectory that depends on the network chosen; the directory will be created if required.
    • HTTP-RPC server at localhost:8545 is enabled, and all APIs are allowed.
    • Ethereum's experimental Whisper message facility is enabled.
    • Inter-process communication will be via a virtual file called geth.ipc, located at ~/.ethereum or a subdirectory.
    • WS-RPC server at localhost:8546 is enabled, and all APIs are allowed.
    • Info verbosity is specified.
    • A log file for the geth output will be written, or overwritten, in logs/geth.log; the log/ directory will be created if it does not already exist.
    $ mkdir logs/
    $ geth \
       #--datadir .ethereum/devnet --dev \      # boots quickly but has no deployed contracts from others
       --datadir .ethereum/rinkeby --rinkeby \  # takes about 15 minutes to boot, but has contracts
       --ipcpath geth.ipc \
       --metrics \
       --rpc \
       --rpcapi eth,net,web3,clique,debug,eth,miner,personal,rpc,ssh,txpool \
       --shh \
       --ws \
       --wsapi eth,net,web3,clique,debug,eth,miner,personal,rpc,ssh,txpool \
       --verbosity 2
    You will see the message No etherbase set and no accounts found as default. Etherbase is the index into personal.listAccounts which determines the account to send Ether too. You can specify this value with the option --etherbase 0.
  2. The shell that you just used will continuously scroll output so long as geth continues to run, so type the following into another shell:
    $ bin/demo
    The demo has two major components:
    1. Creates a JVM wrapper for the sample smart contract.
    2. The second portion of the demo consists of the following:
  3. The bin/web3j script runs the Web3J command-line console. The script builds a fat jar the first time it is run, so the command runs quickly on subsequent invocations.
  4. More scripts are provided in the bin/ directory, including:
    • bin/attachHttp - Attach to a running geth instance via HTTP and open a JavaScript console
    • bin/attachIpc - Attach to a running geth instance via IPC and open a JavaScript console. This script might need to be edited if a network other than devnet is used.
    • bin/getApis - Reports the available APIs exposed by this geth instance.
    • bin/isGethListening - Verifies that geth is listening on HTTP port 8545


API Documentation


  1. Update the version string in build.sbt and in this before attempting to publish to Bintray.
  2. Commit changes with a descriptive comment:
    $ git add -a && git commit -m "Comment here"
  3. Publish a new version of this library, including committing changes and updating the Scaladoc with this command:
    $ sbt publishAndTag

Updating Scaladoc

  1. Use the Scaladoc project; first do a preflight check of the Scaladoc output:

     sbt "; project web3j-scala; doc; project demo; doc"
  2. Now Update the Git Version String and Make a New Tag.

  3. Now edit the multi-scaladoc settings

    export SCALADOC_SUB_PROJECT_NAMES="web3j-scala,demo"
  4. Run multi-scaladoc:


Updating Scaladoc and Committing Changes Without Publishing a New Version

This task rebuilds the docs, commits the git repository, and publishes the updated Scaladoc without publishing a new version:

$ sbt commitAndDoc


This project is sponsored by Micronautics Research Corporation, the company that delivers online Scala training via You can learn Scala by taking the Introduction to Scala, and Intermediate Scala courses.

Please contact us to discuss your organization’s training needs.


This software is published under the Apache 2.0 License.


Lightweight and idiomatic Scala wrapper around Web3J for Ethereum.



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