Compiling Smart Contract in Java

Question

I want to compile a smart contract (solidity code) in Java. Currently I am using the web3j library. When I run the method web3j.ethCompileSolidity(contract) I'm getting the following error: The method eth_compileSolidity does not exist/is not available

I created the following code to compile a smart contract at runtime:

EthCompileSolidity ethCompileSolidity = web3j.ethCompileSolidity(contract).send();
Map<String, EthCompileSolidity.Code> compiledSolidity = ethCompileSolidity.getCompiledSolidity();

The method web3j.ethGetCompilers() doesn't work either. It's returning the following error: The method eth_compileSolidity does not exist/is not available

On Github I read something about deprecated eth_compile methods.

Is there still a way to compile smart contracts in Java using this library?

Answer 1

You are right is's because of deprecated eth_compile

There is no easy way to solve it. You can:

• downgrade geth version on your dev machine
• create a custom version of geth with a diff and keep it in your branch

Answer 2

I got it by running solc executable from my java code (I'm running windows os). I downloaded solc.exe from https://github.com/ethereum/solidity/releases, put it in my classpath and used the following code:

List<String> commandParts = Lists.newArrayList("path.to.solc.exe", "--bin", "path.to.sol.file");
//loading solc.exe file
InputStream fileURL = MyClass.class.getResourceAsStream(pathToFile)
solcFile = File.createTempFile("solc", "exe");
FileUtils.copyInputStreamToFile(fileURL, solcFile); // FileUtils of org.apache.commons.io
ProcessBuilder processBuilder = new ProcessBuilder(commandParts)
        .directory(executable.getParentFile());
processBuilder.environment().put("LD_LIBRARY_PATH",
        executable.getParentFile().getCanonicalPath());

Process process = processBuilder.start();

Remember to close your stream (fileURL), compilation output is taken from process.getInputStream(), if compilation fails errors are taken from process.getErrorStream()