[SPARK-10289] [SQL] Fixes JSONRelation refreshing on read path

[liancheng]

PR #8035 added a refresh() call in JSONRelation.buildScan(). However, when reading a partition table, buildScan() is invoked for each individual partition. This PR works around this issue by special casing JSONRelation in DataSourceStrategy. We should revisit this issue and deliver a more appropriate fix later.

[liancheng]

This method was marked as final at the very beginning, and wasn't designed to be overridden by subclasses. The final decorator was removed in #8035 to work around the refreshing issue.

[liancheng]

cc @yhuai

[SparkQA]

Test build #41624 has finished for PR 8460 at commit ac00522.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • class GaussianMixtureModel @Since("1.3.0") (
  • class KMeansModel @Since("1.1.0") (@Since("1.0.0") val clusterCenters: Array[Vector])
  • class PowerIterationClusteringModel @Since("1.3.0") (
  • class StreamingKMeansModel @Since("1.2.0") (
  • class StreamingKMeans @Since("1.2.0") (
  • class ChiSqSelectorModel @Since("1.3.0") (
  • class ChiSqSelector @Since("1.3.0") (
  • class ElementwiseProduct @Since("1.4.0") (
  • class IDF @Since("1.2.0") (@Since("1.2.0") val minDocFreq: Int)
  • class Normalizer @Since("1.1.0") (p: Double) extends VectorTransformer
  • class PCA @Since("1.4.0") (@Since("1.4.0") val k: Int)
  • class StandardScaler @Since("1.1.0") (withMean: Boolean, withStd: Boolean) extends Logging
  • class StandardScalerModel @Since("1.3.0") (
  • class PoissonGenerator @Since("1.1.0") (
  • class ExponentialGenerator @Since("1.3.0") (
  • class GammaGenerator @Since("1.3.0") (
  • class LogNormalGenerator @Since("1.3.0") (
  • abstract class GeneralizedLinearModel @Since("1.0.0") (
  • class IsotonicRegressionModel @Since("1.3.0") (
  • case class LabeledPoint @Since("1.0.0") (
  • class LassoModel @Since("1.1.0") (
  • class LinearRegressionModel @Since("1.1.0") (
  • class RidgeRegressionModel @Since("1.1.0") (
  • class MultivariateGaussian @Since("1.3.0") (
  • case class BoostingStrategy @Since("1.4.0") (
  • class Strategy @Since("1.3.0") (
  • class DecisionTreeModel @Since("1.0.0") (
  • class Node @Since("1.2.0") (
  • class Predict @Since("1.2.0") (
  • class RandomForestModel @Since("1.2.0") (
  • class GradientBoostedTreesModel @Since("1.2.0") (

[liancheng]

#8469 supersedes this one, closing it.