1 首先有可能是各种jar包错误，删除掉maven里面的jar包就好，
2 其他：
Error:(21, 8) Symbol 'term org.apache.spark.annotation' is missing from the classpath.
This symbol is required by ' <none>'.
Make sure that term annotation is in your classpath and check for conflicting dependencies with `-Ylog-classpath`.
A full rebuild may help if 'package.class' was compiled against an incompatible version of org.apache.spark.
import org.apache.spark.sql.SparkSession
File-> Project -Structure-> Modules -> spark exampes 2.11 -> 点击dependancies -> 点击右边绿色+按钮 -> addd jar or directories -> 进入spark/common/tags/targets 选择对应的jar包
参考：https://stackoverflow.com/questions/42327777/spark-sql-errors
Error:(111, 5) Symbol 'term org.apache.hadoop' is missing from the classpath.
This symbol is required by 'type org.apache.spark.rdd.RDD._$12'.
Make sure that term hadoop is in your classpath and check for conflicting dependencies with `-Ylog-classpath`.
A full rebuild may help if 'RDD.class' was compiled against an incompatible version of org.apache.
fileRDD.saveAsTextFile(dfsFilename)
错误：
Intellij compile failures: “is already defined as” 这是因为我又重复的把scala marked as source dierectory了
https://stackoverflow.com/questions/16885489/intellij-compile-failures-is-already-defined-as/16888290，第二个答案