Spark中RDD转换成DataFrame的两种方式（分别用Java和Scala实现）

一：准备数据源

    在项目下新建一个student.txt文件，里面的内容为：

1,zhangsan,20  
2,lisi,21  
3,wanger,19  
4,fangliu,18

 二：实现

     Java版：

    1.首先新建一个student的Bean对象，实现序列化和toString()方法，具体代码如下：

import java.io.Serializable;  
  
@SuppressWarnings("serial")  
public class Student implements Serializable {  
  
    String sid;  
    String sname;  
    int sage;  
    public String getSid() {  
        return sid;  
    }  
    public void setSid(String sid) {  
        this.sid = sid;  
    }  
    public String getSname() {  
        return sname;  
    }  
    public void setSname(String sname) {  
        this.sname = sname;  
    }  
    public int getSage() {  
        return sage;  
    }  
    public void setSage(int sage) {  
        this.sage = sage;  
    }  
    @Override  
    public String toString() {  
        return "Student [sid=" + sid + ", sname=" + sname + ", sage=" + sage + "]";  
    }    
}  

2.转换，具体代码如下

import java.util.ArrayList;  
  
import org.apache.spark.SparkConf;  
import org.apache.spark.api.java.JavaRDD;  
import org.apache.spark.sql.Dataset;  
import org.apache.spark.sql.Row;  
import org.apache.spark.sql.RowFactory;  
import org.apache.spark.sql.SaveMode;  
import org.apache.spark.sql.SparkSession;  
import org.apache.spark.sql.types.DataTypes;  
import org.apache.spark.sql.types.StructField;  
import org.apache.spark.sql.types.StructType;  
  
public class TxtToParquetDemo {  
  
    public static void main(String[] args) {  
          
        SparkConf conf = new SparkConf().setAppName("TxtToParquet").setMaster("local");  
        SparkSession spark = SparkSession.builder().config(conf).getOrCreate();  
  
        reflectTransform(spark);//Java反射  
        dynamicTransform(spark);//动态转换  
    }  
      
    /** 
     * 通过Java反射转换 
     * @param spark 
     */  
    private static void reflectTransform(SparkSession spark)  
    {  
        JavaRDD<String> source = spark.read().textFile("stuInfo.txt").javaRDD();  
          
        JavaRDD<Student> rowRDD = source.map(line -> {  
            String parts[] = line.split(",");  
  
            Student stu = new Student();  
            stu.setSid(parts[0]);  
            stu.setSname(parts[1]);  
            stu.setSage(Integer.valueOf(parts[2]));  
            return stu;  
        });  
          
        Dataset<Row> df = spark.createDataFrame(rowRDD, Student.class);  
        df.select("sid", "sname", "sage").  
        coalesce(1).write().mode(SaveMode.Append).parquet("parquet.res");  
    }  
    /** 
     * 动态转换 
     * @param spark 
     */  
    private static void dynamicTransform(SparkSession spark)  
    {  
        JavaRDD<String> source = spark.read().textFile("stuInfo.txt").javaRDD();  
          
        JavaRDD<Row> rowRDD = source.map( line -> {  
            String[] parts = line.split(",");  
            String sid = parts[0];  
            String sname = parts[1];  
            int sage = Integer.parseInt(parts[2]);  
              
            return RowFactory.create(  
                    sid,  
                    sname,  
                    sage  
                    );  
        });  
          
        ArrayList<StructField> fields = new ArrayList<StructField>();  
        StructField field = null;  
        field = DataTypes.createStructField("sid", DataTypes.StringType, true);  
        fields.add(field);  
        field = DataTypes.createStructField("sname", DataTypes.StringType, true);  
        fields.add(field);  
        field = DataTypes.createStructField("sage", DataTypes.IntegerType, true);  
        fields.add(field);  
          
        StructType schema = DataTypes.createStructType(fields);  
          
        Dataset<Row> df = spark.createDataFrame(rowRDD, schema);  
        df.coalesce(1).write().mode(SaveMode.Append).parquet("parquet.res1");                    
    }      
}  

 scala版本：

import org.apache.spark.sql.SparkSession  
import org.apache.spark.sql.types.StringType  
import org.apache.spark.sql.types.StructField  
import org.apache.spark.sql.types.StructType  
import org.apache.spark.sql.Row  
import org.apache.spark.sql.types.IntegerType  
  
object RDD2Dataset {  
    
  case class Student(id:Int,name:String,age:Int)  
  def main(args:Array[String])  
  {  
      
    val spark=SparkSession.builder().master("local").appName("RDD2Dataset").getOrCreate()  
    import spark.implicits._  
    reflectCreate(spark)  
    dynamicCreate(spark)  
  }  
    
 /**  
     * 通过Java反射转换  
     * @param spark  
     */  
  private def reflectCreate(spark:SparkSession):Unit={  
    import spark.implicits._  
    val stuRDD=spark.sparkContext.textFile("student2.txt")  
    //toDF()为隐式转换  
    val stuDf=stuRDD.map(_.split(",")).map(parts⇒Student(parts(0).trim.toInt,parts(1),parts(2).trim.toInt)).toDF()  
    //stuDf.select("id","name","age").write.text("result") //对写入文件指定列名  
    stuDf.printSchema()  
    stuDf.createOrReplaceTempView("student")  
    val nameDf=spark.sql("select name from student where age<20")  
    //nameDf.write.text("result") //将查询结果写入一个文件  
    nameDf.show()  
  }  
    
  /**  
     * 动态转换  
     * @param spark  
     */  
  private def dynamicCreate(spark:SparkSession):Unit={  
    val stuRDD=spark.sparkContext.textFile("student.txt")  
    import spark.implicits._  
    val schemaString="id,name,age"  
    val fields=schemaString.split(",").map(fieldName => StructField(fieldName, StringType, nullable = true))  
    val schema=StructType(fields)  
    val rowRDD=stuRDD.map(_.split(",")).map(parts⇒Row(parts(0),parts(1),parts(2)))  
    val stuDf=spark.createDataFrame(rowRDD, schema)  
        stuDf.printSchema()  
    val tmpView=stuDf.createOrReplaceTempView("student")  
    val nameDf=spark.sql("select name from student where age<20")  
    //nameDf.write.text("result") //将查询结果写入一个文件  
    nameDf.show()  
  }  
}  

  注：1.上面代码全都已经测试通过，测试的环境为spark2.1.0，jdk1.8。

         2.此代码不适用于spark2.0以前的版本。