A Java Framework for Smart Contracts

This article defines a framework for programming, in Java, smart contracts over blockchain. The framework consists of a restricted runtime and of an instrumentation procedure for classes that need to be persisted to blockchain, for payable contract methods and for gas metering. This instrumentation abstracts away any difference between storage and memory data location, which is at the origin of tricky semantical issues and bugs in Solidity. Moreover, this framework allows one to leverage, in a transparent way, existing expertise and tools from the Java world, in order to build smart contracts in a simple and comfortable way. The resulting contracts are strongly-typed and work over a shared storage, that allows simple intercontract communication. This makes it easy to install libraries or microservices in blockchain.