How to specify Solidity version in web3j?

Question

I have a simple java maven project whose pom.xml looks like:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>poc</artifactId>
    <version>1.0-SNAPSHOT</version>


    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
        <maven.compiler.source>${java.version}</maven.compiler.source>
        <maven.compiler.target>${java.version}</maven.compiler.target>
        <solidity.version>0.7.4</solidity.version>
    </properties>


    <dependencies>
        <dependency>
            <groupId>org.web3j</groupId>
            <artifactId>core</artifactId>
            <version>4.8.4</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.web3j</groupId>
                <artifactId>web3j-maven-plugin</artifactId>
                <version>4.6.5</version>
                <configuration>
                    <soliditySourceFiles/>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

As you can see I am using web3j library to interact with my blockchain and web3j maven plugin to convert my solidity files to java files.

When I run mvn web3j:generate-sources, it successfully runs and converts the solidity files to java files. But when I run the main method of the project from the IDE, it fails with this error:

From the error message above, I tried removing the constructor from my solidity file and the pragma line, and then my project builds and runs fine as expected. So, I am thinking my java project is picking the wrong solidity version somehow.

Any tips/hints as to what may be going on here or how to fix this?

Answer 1

You can specify solidity version for the web3j-maven-plugin via setting the following property: solidity.version.

In your case, it is already specified as your pom file contains:

   <properties>
         ...
        <solidity.version>0.7.4</solidity.version>
    </properties>

So, the plugin will automatically install the right solc version and compile your contracts using it.

Similarily, for the web3j-gradle-plugin

You can specify the version via adding:

solidity {
      version = "0.7.4"
}

to your build.gradle.