Add shorthands for creating lazy DataProviders (#8511)

server/src/main/java/com/vaadin/ui/ComboBox.java

@@ -16,6 +16,7 @@
 
 package com.vaadin.ui;
 
+import java.io.Serializable;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.HashMap;
@@ -28,6 +29,7 @@ import org.jsoup.nodes.Element;
 
 import com.vaadin.data.HasFilterableDataProvider;
 import com.vaadin.data.HasValue;
+import com.vaadin.data.provider.CallbackDataProvider;
 import com.vaadin.data.provider.DataCommunicator;
 import com.vaadin.data.provider.DataKeyMapper;
 import com.vaadin.data.provider.DataProvider;
@@ -44,6 +46,7 @@ import com.vaadin.server.ResourceReference;
 import com.vaadin.server.SerializableBiPredicate;
 import com.vaadin.server.SerializableConsumer;
 import com.vaadin.server.SerializableFunction;
+import com.vaadin.server.SerializableToIntFunction;
 import com.vaadin.shared.Registration;
 import com.vaadin.shared.data.DataCommunicatorConstants;
 import com.vaadin.shared.ui.combobox.ComboBoxConstants;
@@ -69,6 +72,35 @@ public class ComboBox<T> extends AbstractSingleSelect<T>
         implements HasValue<T>, FieldEvents.BlurNotifier,
         FieldEvents.FocusNotifier, HasFilterableDataProvider<T, String> {
 
+    /**
+     * A callback method for fetching items. The callback is provided with a
+     * non-null string filter, offset index and limit.
+     *
+     * @param <T>
+     *            item (bean) type in ComboBox
+     */
+    @FunctionalInterface
+    public interface FetchItemsCallback<T> extends Serializable {
+
+        /**
+         * Returns a stream of items that match the given filter, limiting the
+         * results with given offset and limit.
+         * <p>
+         * This method is called after the size of the data set is asked from a
+         * related size callback. The offset and limit are promised to be within
+         * the size of the data set.
+         *
+         * @param filter
+         *            a non-null filter string
+         * @param offset
+         *            the first index to fetch
+         * @param limit
+         *            the fetched item count
+         * @return stream of items
+         */
+        public Stream<T> fetchItems(String filter, int offset, int limit);
+    }
+
     /**
      * Handler that adds a new item based on user input when the new items
      * allowed mode is active.
@@ -730,6 +762,29 @@ public class ComboBox<T> extends AbstractSingleSelect<T>
                 .accept(convertOrNull.apply(filter));
     }
 
+    /**
+     * Sets a CallbackDataProvider using the given fetch items callback and a
+     * size callback.
+     * <p>
+     * This method is a shorthand for making a {@link CallbackDataProvider} that
+     * handles a partial {@link Query} object.
+     *
+     * @param fetchItems
+     *            a callback for fetching items
+     * @param sizeCallback
+     *            a callback for getting the count of items
+     *
+     * @see CallbackDataProvider
+     * @see #setDataProvider(DataProvider)
+     */
+    public void setDataProvider(FetchItemsCallback<T> fetchItems,
+            SerializableToIntFunction<String> sizeCallback) {
+        setDataProvider(new CallbackDataProvider<>(
+                q -> fetchItems.fetchItems(q.getFilter().orElse(""),
+                        q.getOffset(), q.getLimit()),
+                q -> sizeCallback.applyAsInt(q.getFilter().orElse(""))));
+    }
+
     @Override
     protected void setSelectedFromClient(String key) {
         super.setSelectedFromClient(key);

server/src/main/java/com/vaadin/ui/Grid.java

@@ -15,6 +15,7 @@
  */
 package com.vaadin.ui;
 
+import java.io.Serializable;
 import java.lang.reflect.Method;
 import java.lang.reflect.Type;
 import java.util.ArrayList;
@@ -49,6 +50,7 @@ import com.vaadin.data.HasValue;
 import com.vaadin.data.PropertyDefinition;
 import com.vaadin.data.PropertySet;
 import com.vaadin.data.ValueProvider;
+import com.vaadin.data.provider.CallbackDataProvider;
 import com.vaadin.data.provider.DataCommunicator;
 import com.vaadin.data.provider.DataProvider;
 import com.vaadin.data.provider.GridSortOrder;
@@ -68,6 +70,7 @@ import com.vaadin.server.Extension;
 import com.vaadin.server.JsonCodec;
 import com.vaadin.server.SerializableComparator;
 import com.vaadin.server.SerializableFunction;
+import com.vaadin.server.SerializableSupplier;
 import com.vaadin.server.Setter;
 import com.vaadin.shared.MouseEventDetails;
 import com.vaadin.shared.Registration;
@@ -134,6 +137,36 @@ import elemental.json.JsonValue;
 public class Grid<T> extends AbstractListing<T> implements HasComponents,
         HasDataProvider<T>, SortNotifier<GridSortOrder<T>> {
 
+    /**
+     * A callback method for fetching items. The callback is provided with a
+     * list of sort orders, offset index and limit.
+     *
+     * @param <T>
+     *            the grid bean type
+     */
+    @FunctionalInterface
+    public interface FetchItemsCallback<T> extends Serializable {
+
+        /**
+         * Returns a stream of items ordered by given sort orders, limiting the
+         * results with given offset and limit.
+         * <p>
+         * This method is called after the size of the data set is asked from a
+         * related size callback. The offset and limit are promised to be within
+         * the size of the data set.
+         *
+         * @param sortOrder
+         *            a list of sort orders
+         * @param offset
+         *            the first index to fetch
+         * @param limit
+         *            the fetched item count
+         * @return stream of items
+         */
+        public Stream<T> fetchItems(List<QuerySortOrder> sortOrder, int offset,
+                int limit);
+    }
+
     @Deprecated
     private static final Method COLUMN_REORDER_METHOD = ReflectTools.findMethod(
             ColumnReorderListener.class, "columnReorder",
@@ -3419,6 +3452,30 @@ public class Grid<T> extends AbstractListing<T> implements HasComponents,
         internalSetDataProvider(dataProvider);
     }
 
+    /**
+     * Sets a CallbackDataProvider using the given fetch items callback and a
+     * size callback.
+     * <p>
+     * This method is a shorthand for making a {@link CallbackDataProvider} that
+     * handles a partial {@link Query} object.
+     *
+     * @param fetchItems
+     *            a callback for fetching items
+     * @param sizeCallback
+     *            a callback for getting the count of items
+     *
+     * @see CallbackDataProvider
+     * @see #setDataProvider(DataProvider)
+     */
+    public void setDataProvider(FetchItemsCallback<T> fetchItems,
+            SerializableSupplier<Integer> sizeCallback) {
+        internalSetDataProvider(
+                new CallbackDataProvider<>(
+                        q -> fetchItems.fetchItems(q.getSortOrders(),
+                                q.getOffset(), q.getLimit()),
+                        q -> sizeCallback.get()));
+    }
+
     @Override
     protected void doReadDesign(Element design, DesignContext context) {
         Attributes attrs = design.attributes();