ListDataProvider.java

/*
 * Copyright 2000-2016 Vaadin Ltd.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.vaadin.server.data;

import java.util.Collection;
import java.util.Comparator;
import java.util.Objects;
import java.util.Optional;
import java.util.function.Function;
import java.util.stream.Stream;

import com.vaadin.server.SerializablePredicate;

/**
 * {@link DataProvider} wrapper for {@link Collection}s. This class does not
 * actually handle the {@link Query} parameters.
 *
 * @param <T>
 *            data type
 */
public class ListDataProvider<T>
        extends AbstractDataProvider<T, SerializablePredicate<T>>
        implements AppendableFilterDataProvider<T, SerializablePredicate<T>> {

    private Comparator<T> sortOrder = null;
    private final Collection<T> backend;

    /**
     * Constructs a new ListDataProvider. This method makes a protective copy of
     * the contents of the Collection.
     *
     * @param items
     *            the initial data, not null
     */
    public ListDataProvider(Collection<T> items) {
        Objects.requireNonNull(items, "items cannot be null");
        backend = items;
        sortOrder = null;
    }

    /**
     * Chaining constructor for making modified {@link ListDataProvider}s. This
     * Constructor is used internally for making sorted and filtered variants of
     * a base data provider with actual data.
     *
     * @param items
     *            the backend data from the original list data provider
     * @param sortOrder
     *            a {@link Comparator} providing the needed sorting order
     *
     */
    protected ListDataProvider(Collection<T> items, Comparator<T> sortOrder) {
        this(items);
        this.sortOrder = sortOrder;
    }

    @Override
    public Stream<T> fetch(Query<T, SerializablePredicate<T>> query) {
        Stream<T> stream = backend.stream()
                .filter(t -> query.getFilter().orElse(p -> true).test(t));

        Optional<Comparator<T>> comparing = Stream
                .of(sortOrder, query.getInMemorySorting())
                .filter(c -> c != null)
                .reduce((c1, c2) -> c1.thenComparing(c2));

        if (comparing.isPresent()) {
            stream = stream.sorted(comparing.get());
        }

        return stream.skip(query.getOffset()).limit(query.getLimit());
    }

    /**
     * Creates a new list data provider based on this list data provider with
     * the given sort order.
     * <p>
     * <b>NOTE</b>: this data provider is not modified in any way.
     *
     * @param sortOrder
     *            a {@link Comparator} providing the needed sorting order
     * @return new data provider with modified sorting
     */
    public ListDataProvider<T> sortingBy(Comparator<T> sortOrder) {
        return new ListDataProvider<>(backend, sortOrder);
    }

    /**
     * Creates a new list data provider based on this list data provider with
     * the given sort order.
     * <p>
     * <b>NOTE</b>: this data provider is not modified in any way.
     * <p>
     * This method is a short-hand for
     * {@code sortingBy(Comparator.comparing(sortOrder))}.
     *
     * @param sortOrder
     *            function to sort by
     * @param <U>
     *            the type of the Comparable sort key
     * @return new data provider with modified sorting
     */
    public <U extends Comparable<? super U>> ListDataProvider<T> sortingBy(
            Function<T, U> sortOrder) {
        return sortingBy(Comparator.comparing(sortOrder));
    }

    @Override
    public boolean isInMemory() {
        return true;
    }

    @Override
    public int size(Query<T, SerializablePredicate<T>> query) {
        return (int) backend.stream()
                .filter(t -> query.getFilter().orElse(p -> true).test(t))
                .count();
    }

    @Override
    public SerializablePredicate<T> combineFilters(
            SerializablePredicate<T> filter1,
            SerializablePredicate<T> filter2) {
        return t -> filter1.test(t) && filter2.test(t);
    }
}