[SPARK-12970][DOCS] Fix the example in SturctType APIs for Scala and Java

[HyukjinKwon]

What changes were proposed in this pull request?

This PR fixes both,

javadoc8 break

[error] .../spark/sql/hive/target/java/org/apache/spark/sql/hive/FindHiveSerdeTable.java:3: error: reference not found
[error]  * Replaces {@link SimpleCatalogRelation} with {@link MetastoreRelation} if its table provider is hive.

and the example in StructType as a self-contained example as below:

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

val struct =
  StructType(
    StructField("a", IntegerType, true) ::
    StructField("b", LongType, false) ::
    StructField("c", BooleanType, false) :: Nil)

// Extract a single StructField.
val singleField = struct("b")
// singleField: StructField = StructField(b,LongType,false)

// If this struct does not have a field called "d", it throws an exception.
struct("d")
// java.lang.IllegalArgumentException: Field "d" does not exist.
//   ...

// Extract multiple StructFields. Field names are provided in a set.
// A StructType object will be returned.
val twoFields = struct(Set("b", "c"))
// twoFields: StructType =
//   StructType(StructField(b,LongType,false), StructField(c,BooleanType,false))

// Any names without matching fields will throw an exception.
// For the case shown below, an exception is thrown due to "d".
struct(Set("b", "c", "d"))
// java.lang.IllegalArgumentException: Field "d" does not exist.
//    ...

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

val innerStruct =
  StructType(
    StructField("f1", IntegerType, true) ::
    StructField("f2", LongType, false) ::
    StructField("f3", BooleanType, false) :: Nil)

val struct = StructType(
  StructField("a", innerStruct, true) :: Nil)
 
// Create a Row with the schema defined by struct
val row = Row(Row(1, 2, true))

Also, now when the column is missing, it throws an exception rather than ignoring.

How was this patch tested?

Manually via sbt unidoc.

• Scaladoc

  

• Javadoc

  

[HyukjinKwon]

cc @srowen and @JoshRosen who are in the JIRA.

[HyukjinKwon]

(I just added some links for StructType and StructField around this examples just for consistency and while I was here. PR description was also updated accordingly)

[SparkQA]

Test build #71990 has finished for PR 16703 at commit 2e9bec8.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #71991 has finished for PR 16703 at commit b9a841d.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #71992 has finished for PR 16703 at commit f6a1059.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[srowen]

Merged to master