Resolving java.lang.IllegalAccessError in Lombok with OpenJDK 16

What causes the java.lang.IllegalAccessError when using Lombok with OpenJDK 16?

import lombok.Data;

@Data
public class Ingredient {

    private final String id;
    private final String name;
    private final Type type;

    public enum Type {
        WRAP, PROTEIN, VEGGIES, CHEESE, SAUCE
    }

}

The java.lang.IllegalAccessError regarding Lombok and OpenJDK indicates an issue with access permissions between Lombok and Java's internal APIs, especially when using a newer Java version such as OpenJDK 16.

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.8.1</version>
            <configuration>
                <source>16</source>
                <target>16</target>
                <compilerArgs>
                    <arg>--add-opens</arg>
                    <arg>jdk.compiler/com.sun.tools.javac.processing=ALL-UNNAMED</arg>
                </compilerArgs>
            </configuration>
        </plugin>
    </plugins>
</build>

Causes

• Lombok's reliance on internal Java APIs that were not exported by OpenJDK.
• Java 16's stricter module system prevents Lombok from accessing certain internal classes.
• Incompatibility between the Lombok version and the OpenJDK version.

Solutions

• Ensure that you are using the latest stable version of Lombok compatible with your JDK.
• Add necessary JVM arguments to allow access to internal APIs: `--add-opens jdk.compiler/com.sun.tools.javac.processing=ALL-UNNAMED`
• Upgrade or downgrade your JDK version if the specific combination of Lombok and your current JDK is known to have issues.

Mistake: Not using the latest version of Lombok.

Solution: Regularly check for updates in the Lombok repository and upgrade if necessary.

Mistake: Failing to add JVM arguments to access internal APIs.

Solution: Modify your project’s build configuration to include the necessary `--add-opens` argument.