Make Canonical ViewFns Public

Mark all of the ViewFns as both deprecated and experimental. These fns
will all be removed once Runners have multimap support, and are not
suitable for users to use explicitly.

sdks/java/core/src/main/java/org/apache/beam/sdk/util/PCollectionViews.java

@@ -32,6 +32,8 @@
 import java.util.Objects;
 import javax.annotation.Nullable;
 import org.apache.beam.sdk.Pipeline;
+import org.apache.beam.sdk.annotations.Experimental;
+import org.apache.beam.sdk.annotations.Experimental.Kind;
 import org.apache.beam.sdk.coders.Coder;
 import org.apache.beam.sdk.coders.IterableCoder;
 import org.apache.beam.sdk.transforms.ViewFn;
@@ -228,8 +230,13 @@ public MultimapPCollectionView(
  * <p>For internal use only.
  *
  * <p>Instantiate via {@link PCollectionViews#singletonView}.
+ *
+ * @deprecated Beam views are migrating off of {@code Iterable<WindowedValue<T>>} as a primitive
+ * view type.
  */
- private static class SingletonViewFn<T> extends ViewFn<Iterable<WindowedValue<T>>, T> {
+ @Deprecated
+ @Experimental(Kind.CORE_RUNNERS_ONLY)
+ public static class SingletonViewFn<T> extends ViewFn<Iterable<WindowedValue<T>>, T> {
  @Nullable private byte[] encodedDefaultValue;
  @Nullable private transient T defaultValue;
  @Nullable private Coder<T> valueCoder;
@@ -292,8 +299,13 @@ public T apply(Iterable<WindowedValue<T>> contents) {
  * <p>For internal use only.
  *
  * <p>Instantiate via {@link PCollectionViews#iterableView}.
+ *
+ * @deprecated Beam views are migrating off of {@code Iterable<WindowedValue<T>>} as a primitive
+ * view type.
  */
- private static class IterableViewFn<T>
+ @Deprecated
+ @Experimental(Kind.CORE_RUNNERS_ONLY)
+ public static class IterableViewFn<T>
  extends ViewFn<Iterable<WindowedValue<T>>, Iterable<T>> {
 
  @Override
@@ -315,8 +327,13 @@ public T apply(WindowedValue<T> input) {
  * <p>For internal use only.
  *
  * <p>Instantiate via {@link PCollectionViews#listView}.
+ *
+ * @deprecated Beam views are migrating off of {@code Iterable<WindowedValue<T>>} as a primitive
+ * view type.
  */
- private static class ListViewFn<T> extends ViewFn<Iterable<WindowedValue<T>>, List<T>> {
+ @Deprecated
+ @Experimental(Kind.CORE_RUNNERS_ONLY)
+ public static class ListViewFn<T> extends ViewFn<Iterable<WindowedValue<T>>, List<T>> {
  @Override
  public List<T> apply(Iterable<WindowedValue<T>> contents) {
  return ImmutableList.copyOf(
@@ -333,8 +350,13 @@ public T apply(WindowedValue<T> input) {
  /**
  * Implementation of conversion {@code Iterable<WindowedValue<KV<K, V>>>}
  * to {@code Map<K, Iterable<V>>}.
+ *
+ * @deprecated Beam views are migrating off of {@code Iterable<WindowedValue<T>>} as a primitive
+ * view type.
  */
- private static class MultimapViewFn<K, V>
+ @Deprecated
+ @Experimental(Kind.CORE_RUNNERS_ONLY)
+ public static class MultimapViewFn<K, V>
  extends ViewFn<Iterable<WindowedValue<KV<K, V>>>, Map<K, Iterable<V>>> {
 
  @Override
@@ -352,11 +374,15 @@ public Map<K, Iterable<V>> apply(Iterable<WindowedValue<KV<K, V>>> elements) {
  }
 
  /**
- * Implementation of conversion {@code Iterable<WindowedValue<KV<K, V>>} with one value per key
- * to {@code Map<K, V>}.
+ * Implementation of conversion {@code Iterable<WindowedValue<KV<K, V>>} with one value per key to
+ * {@code Map<K, V>}.
+ *
+ * @deprecated Beam views are migrating off of {@code Iterable<WindowedValue<T>>} as a primitive
+ * view type.
  */
- private static class MapViewFn<K, V>
- extends ViewFn<Iterable<WindowedValue<KV<K, V>>>, Map<K, V>> {
+ @Deprecated
+ @Experimental(Kind.CORE_RUNNERS_ONLY)
+ public static class MapViewFn<K, V> extends ViewFn<Iterable<WindowedValue<KV<K, V>>>, Map<K, V>> {
  /**
  * Input iterable must actually be {@code Iterable<WindowedValue<KV<K, V>>>}.
  */