如何用几种类型的对象数组为Spark schema构建正确的StructType？

import org.apache.spark.sql.types._

val schema = new StructType()

val field1 = StructField("name", StringType, nullable = true)
val field2 = StructField("age", IntegerType, nullable = true)
val field3 = StructField("salary", DoubleType, nullable = true)

schema.add(field1)
schema.add(field2)
schema.add(field3)

val schema = new StructType()
  .add("name", StringType, nullable = true)
  .add("age", IntegerType, nullable = true)
  .add("salary", DoubleType, nullable = true)

val data = Seq(
  Row("John", 30, 5000.0),
  Row("Alice", 25, 6000.0),
  Row("Bob", 35, 4000.0)
)

val df = spark.createDataFrame(spark.sparkContext.parallelize(data), schema)