idea找不到或无法加载主类

浪费了我好长时间查找错误源头，百度终无果，最终解决办法：

1.Mark Directory as 给予scala一个Source root（变成蓝色的）
2.修改pom.xml配置文件

    4.0.0

    com.etc
    spark-sql
    1.0-SNAPSHOT

    
        2.10.6
        UTF-8
    

    
        
        
          org.scala-lang
          scala-library
          ${scala.version}
      

      
          junit
          junit
          3.8.1
          test
      

      
          org.apache.spark
          spark-core_2.10
          1.5.1
      
      
          org.apache.spark
          spark-sql_2.10
          1.5.1
      
      
          org.apache.spark
          spark-hive_2.10
          1.5.1
      
      
          org.apache.spark
          spark-streaming_2.10
          1.5.1
      
      
          org.apache.hadoop
          hadoop-client
          2.4.1
      
      
          org.apache.spark
          spark-streaming-kafka_2.10
          1.5.1
      
      
          org.apache.spark
          spark-streaming-flume_2.10
          1.5.1
      
      
          mysql
          mysql-connector-java
          8.0.11
      
      
          org.apache.hive
          hive-jdbc
          0.13.0
      
      
          org.apache.httpcomponents
          httpclient
          4.4.1
      
      
          org.apache.httpcomponents
          httpcore
          4.4.1
      
    

    
      src/main/java
      src/main/

      
        
        maven-assembly-plugin
        
            
                jar-with-dependencies
            
            
                
                    
                
            
        
        
            
                make-assembly
                package
                
                    single
                
            
        
    

    
        org.codehaus.mojo
        exec-maven-plugin
        1.2.1
        
            
                
                    exec
                
            
        
        
            java
            true
            false
            compile
            cn.spark.study.App
        
    

    
        org.apache.maven.plugins
        maven-compiler-plugin
        
            1.6
            1.6
        
    


    
        
          net.alchim31.maven
          scala-maven-plugin
          3.2.2
          
              
                  
                      compile
                      testCompile
                  
                  
                                                      
                          -dependencyfile
                          ${project.build.directory}/.scala_dependencies
                      
                  
                
            
        


        
        
            org.apache.maven.plugins
            maven-shade-plugin
            2.4.3
            
         
              package
              
                  shade
              
              
                  
                      
                          *:*
                          
                              META-INF/*.SF
                              META-INF/*.DSA
                              META-INF/*.RSA
                          
                      
                  
                  
                      
                          reference.conf
                      
                      
                          cn.itcast.rpc.Master 
                      
                  
              
           /execution>