dimas-b commented on code in PR #1838:
URL: https://github.com/apache/polaris/pull/1838#discussion_r2144161141
##########
polaris-core/src/main/java/org/apache/polaris/core/persistence/pagination/Page.java:
##########
@@ -18,25 +18,96 @@
*/
package org.apache.polaris.core.persistence.pagination;
+import static java.util.Spliterators.iterator;
+
+import jakarta.annotation.Nullable;
+import java.util.ArrayList;
+import java.util.Iterator;
import java.util.List;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
/**
- * An immutable page of items plus their paging cursor. The {@link PageToken}
here can be used to
- * continue the listing operation that generated the `items`.
+ * An immutable page of items plus their paging cursor. The {@link
#encodedResponseToken()} here can
+ * be used to continue the listing operation that generated the `items`.
*/
public class Page<T> {
- public final PageToken pageToken;
- public final List<T> items;
+ private final PageToken request;
+ private final List<T> items;
+ @Nullable private final String encodedDataReference;
- public Page(PageToken pageToken, List<T> items) {
- this.pageToken = pageToken;
+ private Page(PageToken request, @Nullable String encodedDataReference,
List<T> items) {
+ this.request = request;
+ this.encodedDataReference = encodedDataReference;
this.items = items;
}
/**
- * Used to wrap a {@link List<T>} of items into a {@link Page <T>} when
there are no more pages
+ * Builds a complete response page for the full list of relevant items. No
subsequence pages of
+ * related data exist.
*/
public static <T> Page<T> fromItems(List<T> items) {
- return new Page<>(new DonePageToken(), items);
+ return new Page<>(PageToken.readEverything(), null, items);
+ }
+
+ /**
+ * Produces a response page by consuming the number of items from the
provided stream according to
+ * the {@code request} parameter. Source items can be converted to a
different type by providing a
+ * {@code mapper} function. The page token for the response will be produced
from the request data
+ * combined with the pointer to the next page of data provided by the {@code
dataPointer}
+ * function.
+ *
+ * @param request defines pagination parameters that were uses to produce
this page of data.
+ * @param items stream of source data
+ * @param mapper converter from source data types to response data types.
+ * @param dataPointer determines the internal pointer to the next page of
data given the last item
+ * from the previous page. The output of this function will be available
from {@link
+ * PageToken#encodedDataReference()} associated with the request for the
next page.
+ */
+ public static <R, T> Page<R> mapped(
+ PageToken request, Stream<T> items, Function<T, R> mapper, Function<T,
String> dataPointer) {
+ List<R> data;
+ if (request.paginationRequested()) {
+ data = new ArrayList<>(request.pageSize());
+ } else {
+ data = new ArrayList<>();
+ }
+
+ T last = null;
+ Iterator<T> it = iterator(items.spliterator());
+ while (it.hasNext() && (!request.paginationRequested() || data.size() <
request.pageSize())) {
+ last = it.next();
+ data.add(mapper.apply(last));
+ }
+
+ if (request.paginationRequested() && data.size() < request.pageSize()) {
+ // the page was not filled, inform the client that there's no next page
+ last = null;
+ }
+
+ return new Page<>(request, dataPointer.apply(last), data);
+ }
+
+ public List<T> items() {
+ return items;
+ }
+
+ /**
+ * Returns a page token in encoded form suitable for returning to API
clients. The string returned
+ * from this method is expected to be parsed by {@link
PageToken#decode(String, Integer)} when
+ * servicing the request for the next page of related data.
+ */
+ public @Nullable String encodedResponseToken() {
+ return PageTokenUtil.encodePageToken(request, encodedDataReference);
Review Comment:
Calling `PageTokenUtil.encodePageToken(Page)` from a place that has a
reference to a `Page` is less elegant than calling
`Page.encodedResponseToken()`... This is a matter of opinion, of course :)
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