Add a Pageable object that can be transferred

src/main/java/nl/tudelft/librador/dto/helper/LCPageable.java

+/*
+ * Librador - A utilities library for Labrador
+ * Copyright (C) 2020-  Delft University of Technology
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package nl.tudelft.librador.dto.helper;
+
+import java.util.Arrays;
+import java.util.stream.Collectors;
+
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+import org.springframework.data.domain.PageRequest;
+import org.springframework.data.domain.Pageable;
+import org.springframework.data.domain.Sort;
+
+@Data
+@Builder
+@NoArgsConstructor
+@AllArgsConstructor
+public class LCPageable {
+	private int page;
+	private int size;
+	private String sort;
+
+	public LCPageable(Pageable pageable) {
+		this.page = pageable.getPageNumber();
+		this.size = pageable.getPageSize();
+		this.sort = sortToString(pageable.getSort());
+	}
+
+	/**
+	 * Converts this LCPageable object into a Spring Pageable to be used for Spring Data queries.
+	 *
+	 * @return The Pageable object representing the fully serialized version of this data.
+	 */
+	public Pageable toPageable() {
+		return PageRequest.of(page, size, sortFromString(sort));
+	}
+
+	/**
+	 * Turns a Sort object into a String that fully represents the Sort object. This method can be used for
+	 * serializing a Sort object, usually part of a Pageable over an HTTP request.
+	 *
+	 * @param  sort The Sort object to serialize into a String.
+	 * @return      The serialized Sort object as a String.
+	 */
+	public static String sortToString(Sort sort) {
+		return sort.stream()
+				.map(o -> o.getProperty() + " " + o.getDirection())
+				.collect(Collectors.joining(","));
+	}
+
+	/**
+	 * Reads a String into the Order object that the String represents. This method can be used for
+	 * deserializing an Order object sent over an HTTP request as part of a Sort object.
+	 *
+	 * @param  order The String that represents the Order sent.
+	 * @return       The resulting Order object.
+	 */
+	public static Sort.Order orderFromString(String order) {
+		String[] split = order.split(" ");
+		if (split.length < 2) {
+			return Sort.Order.by(split[0]);
+		} else {
+			return new Sort.Order(Sort.Direction.fromString(split[1]), split[0]);
+		}
+	}
+
+	/**
+	 * Reads a String into the Sort object that the String represents. This method can be used for
+	 * deserializing a Sort object sent over an HTTP request.
+	 *
+	 * @param  sort The String to convert back into the Sort object.
+	 * @return      The resulting Sort object as represented by the given String.
+	 */
+	public static Sort sortFromString(String sort) {
+		if (sort.isEmpty()) {
+			return Sort.unsorted();
+		}
+
+		return Sort.by(Arrays.stream(sort.split(","))
+				.map(LCPageable::orderFromString)
+				.collect(Collectors.toList()));
+	}
+}