The `java.lang.NoClassDefFoundError` for `com/google/common/io/ByteStreams` typically indicates that the necessary Google Guava library is missing from your project or there's a version mismatch.
To resolve this issue in Selenium WebDriver, you can follow these steps:
1. Check Selenium Version:
Ensure that you are using the latest version of Selenium WebDriver. If you are using Maven, check your pom.xml file for the Selenium dependency and update the version to the latest.
Example Maven Dependency:

    <dependencies>
        <dependency>
            <groupId>org.seleniumhq.selenium</groupId>
            <artifactId>selenium-java</artifactId>
            <version>3.141.59</version> <!-- Use the latest version -->
        </dependency>
    </dependencies>

2. Check Google Guava Version:
Selenium might depend on a specific version of Google Guava. Make sure that you have the correct version of Google Guava in your project.
Example Maven Dependency for Google Guava:

    <dependencies>
        <dependency>
            <groupId>com.google.guava</groupId>
            <artifactId>guava</artifactId>
            <version>30.1.3-jre</version> <!-- Use the correct version -->
        </dependency>
    </dependencies>

Note: The version number may change, so check the [Google Guava Maven Repository](https://mvnrepository.com/artifact/com.google.guava/guava) for the latest version.
3. Check for Jar Conflicts:
* Ensure that there are no jar conflicts in your project. Sometimes, multiple versions of the same library might be included, causing conflicts.
4. Clean and Rebuild:
* Clean your project and rebuild it to ensure that the dependencies are correctly resolved.
5. Use a Build Tool:
* If you are not already using a build tool like Maven or Gradle, consider migrating to one. Build tools manage dependencies and versions automatically, reducing the chances of version conflicts.
6. Manual Download and Addition:
If you are not using a build tool, you can manually download the Google Guava JAR from the [Maven Repository](https://mvnrepository.com/artifact/com.google.guava/guava) and add it to your project.

Example for Manual Download:
1. Download the JAR file for the appropriate version.
1. Add the JAR to your project's classpath.

Important Note:
Always use a build tool like Maven or Gradle to manage your dependencies. It simplifies the process of adding, updating, and managing libraries in your project.