Spark Error : A master URL must be set in your configuration_exception in thread "main" org.apache.spark.sparke

Exception in thread "main" org.apache.spark.SparkException: A master URL must be set in your configuration
	at org.apache.spark.SparkContext.<init>(SparkContext.scala:367)
	at org.apache.spark.SparkContext$.getOrCreate(SparkContext.scala:2493)
	at org.apache.spark.sql.SparkSession$Builder$$anonfun$7.apply(SparkSession.scala:933)
	at org.apache.spark.sql.SparkSession$Builder$$anonfun$7.apply(SparkSession.scala:924)
	at scala.Option.getOrElse(Option.scala:121)
	at org.apache.spark.sql.SparkSession$Builder.getOrCreate(SparkSession.scala:924)
	at com.rone.DBUtils.MySQLOperations$.main(MySQLOperations.scala:14)
	at com.rone.DBUtils.MySQLOperations.main(MySQLOperations.scala)
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报这个错误是因为本地跑spark没有设置master为local
错误示例

    val spark = SparkSession.builder().appName("ReadMySQL").getOrCreate()
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当时的情况是因为我把项目打成了jar放到了hdfs上，利用Livy运行在Yarn上（这里不能指定master为local）所以当时就把master注释掉了，只需将其放开就好啦
如下：

    val spark = SparkSession.builder().appName("ReadMySQL").master("local").getOrCreate()
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Best Wishes