执行mvn exec:java -Dexec:mainClass="com.example.HelloWorld"失败

[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-plugin:3.0.0:java (default-cli) on project test01: The parameters 'mainClass' for goal org.codehaus.mojo:exec-maven-plugin:3

.0.0:java are missing or invalid -> [Help 1]