利用IDEA开发Spark-SQL：
1.创建子模块Spark-SQL，并添加依赖
<dependency>
<groupId>org.apache.spark</groupId>
<artifactId>spark-sql_2.12</artifactId>
<version>3.0.0</version>
</dependency>
2.创建Spark-SQL的测试代码：
case class User(id:Int,name:String,age:Int)
object SparkSQLDemo {
def main(args: Array[String]): Unit = {
//创建上下文环境配置对象
val sparkConf = new SparkConf().setMaster("local[*]").setAppName("SQLDemo")
//创建SparkSession对象
val spark :SparkSession = SparkSession.builder().config(sparkConf).getOrCreate()
import spark.implicits._
//读取json文件
val df : DataFrame = spark.read.json("Spark-SQL/input/user.json")
df.show()
//SQL风格语法
df.createOrReplaceTempView("user")
spark.sql("select * from user").show
spark.sql("select avg(age) from user").show
//DSL风格语法
df.select("username","age").show()
//RDD=>DataFrame=>DataSet
//RDD
val rdd1 :RDD[(Int,String,Int)] = spark.sparkContext.makeRDD(
List((1,"zhangsan",30),(2,"lisi",40))
)
//DataFrame
val df1 :DataFrame = rdd1.toDF("id","name","age")
df1.show()
//DataSet
val ds1 :Dataset[User] = df1.as[User]
ds1.show()
//DataSet=>DataFrame=>RDD
val df2 =ds1.toDF()
df2.show()
val rdd2 :RDD[Row] = df2.rdd
rdd2.foreach(a=>println(a.getString(1)))
rdd1.map{
case (id,name,age)=>User(id,name,age)
}.toDS().show()
val rdd3 = ds1.rdd
rdd3.foreach(a=>println(a.age))
rdd3.foreach(a=>println(a.id))
rdd3.foreach(a=>println(a.name))
spark.stop()
}
}
自定义函数：
val sparkConf = new SparkConf().setMaster("local[*]").setAppName("SQLDemo")
//创建SparkSession对象
val spark :SparkSession = SparkSession.builder().config(sparkConf).getOrCreate()
import spark.implicits._
//读取json文件
val df : DataFrame = spark.read.json("Spark-SQL/input/user.json")
spark.udf.register("addName",(x:String)=>"Name:"+x)
df.createOrReplaceTempView("people")
spark.sql("select addName(username),age from people").show()
spark.stop()
UDAF（自定义聚合函数）
强类型的 Dataset 和弱类型的 DataFrame 都提供了相关的聚合函数， 如 count()，
countDistinct()，avg()，max()，min()。除此之外，用户可以设定自己的自定义聚合函数。Spark3.0之前我们使用的是UserDefinedAggregateFunction作为自定义聚合函数，从 Spark3.0 版本后可以统一采用强类型聚合函数 Aggregator
实验需求：计算平均工资
实现方式一：RDD
val sparkconf: SparkConf = new SparkConf().setAppName("app").setMaster("local[*]")
val sc: SparkContext = new SparkContext(conf)
val resRDD: (Int, Int) = sc.makeRDD(List(("zhangsan", 20), ("lisi", 30), ("wangwu",40))).map {
case (name, salary) => {
(salary, 1)
}
}.reduce {
(t1, t2) => {
(t1._1 + t2._1, t1._2 + t2._2)
}
}
println(resRDD._1/resRDD._2)
// 关闭连接
sc.stop()
实现方式二：弱类型UDAF
class MyAverageUDAF extends UserDefinedAggregateFunction{
def inputSchema: StructType =
StructType(Array(StructField("salary",IntegerType)))
// 聚合函数缓冲区中值的数据类型(salary,count)
def bufferSchema: StructType = {
StructType(Array(StructField("sum",LongType),StructField("count",LongType)))
}
// 函数返回值的数据类型
def dataType: DataType = DoubleType
// 稳定性：对于相同的输入是否一直返回相同的输出。
def deterministic: Boolean = true
// 函数缓冲区初始化
def initialize(buffer: MutableAggregationBuffer): Unit = {
// 存薪资的总和
buffer(0) = 0L
// 存薪资的个数
buffer(1) = 0L
}
// 更新缓冲区中的数据
def update(buffer: MutableAggregationBuffer,input: Row): Unit = {
if (!input.isNullAt(0)) {
buffer(0) = buffer.getLong(0) + input.getInt(0)
buffer(1) = buffer.getLong(1) + 1
}
}
// 合并缓冲区
def merge(buffer1: MutableAggregationBuffer,buffer2: Row): Unit = {
buffer1(0) = buffer1.getLong(0) + buffer2.getLong(0)
buffer1(1) = buffer1.getLong(1) + buffer2.getLong(1)
}
// 计算最终结果
def evaluate(buffer: Row): Double = buffer.getLong(0).toDouble /
buffer.getLong(1)
}
val sparkconf: SparkConf = new SparkConf().setAppName("app").setMaster("local[*]")
val spark:SparkSession = SparkSession.builder().config(conf).getOrCreate()
import spark.implicits._
val res :RDD[(String,Int)]= spark.sparkContext.makeRDD(List(("zhangsan", 20), ("lisi", 30), ("wangwu",40)))
val df :DataFrame = res.toDF("name","salary")
df.createOrReplaceTempView("user")
var myAverage = new MyAverageUDAF
//在 spark 中注册聚合函数
spark.udf.register("avgSalary",myAverage)
spark.sql("select avgSalary(salary) from user").show()
// 关闭连接
spark.stop()
实现方式三：强类型UDAF
case class Buff(var sum:Long,var cnt:Long)
class MyAverageUDAF extends Aggregator[Long,Buff,Double]{
override def zero: Buff = Buff(0,0)
override def reduce(b: Buff, a: Long): Buff = {
b.sum += a
b.cnt += 1
b
}
override def merge(b1: Buff, b2: Buff): Buff = {
b1.sum += b2.sum
b1.cnt += b2.cnt
b1
}
override def finish(reduction: Buff): Double = {
reduction.sum.toDouble/reduction.cnt
}
override def bufferEncoder: Encoder[Buff] = Encoders.product
override def outputEncoder: Encoder[Double] = Encoders.scalaDouble
}
val sparkconf: SparkConf = new SparkConf().setAppName("app").setMaster("local[*]")
val spark:SparkSession = SparkSession.builder().config(conf).getOrCreate()
import spark.implicits._
val res :RDD[(String,Int)]= spark.sparkContext.makeRDD(List(("zhangsan", 20), ("lisi", 30), ("wangwu",40)))
val df :DataFrame = res.toDF("name","salary")
df.createOrReplaceTempView("user")
var myAverage = new MyAverageUDAF
//在 spark 中注册聚合函数
spark.udf.register("avgSalary",functions.udaf(myAverage))
spark.sql("select avgSalary(salary) from user").show()
// 关闭连接
spark.stop()