DirectRunner./bin/spark-submit --master=spark://vm:7077 main.go --runner=SparkRunner --job_endpoint=localhost:8099 --artifact_endpoint=localhost:8098 --environment_type=LOOPBACK --output=/tmp/output
job_endpoint
./gradlew :runners:spark:job-server:runShadow -PsparkMasterUrl=spark://localhost:7077
WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable Exception in thread "main" org.apache.spark.SparkException: Failed to get main class in JAR with error 'null'.  Please specify one with --class.

似乎我需要指定类参数，但是我不明白这个错误是什么意思？我能得到帮助吗？