Add FindQueryService for Content

Currently supports finding contents by roomId.

Same MR as !81 (merged). Just this time merged into the correct target branch.

src/main/java/de/thm/arsnova/service/ContentFindQueryService.java

+/*
+ * This file is part of ARSnova Backend.
+ * Copyright (C) 2012-2018 The ARSnova Team and Contributors
+ *
+ * ARSnova Backend is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * ARSnova Backend 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package de.thm.arsnova.service;
+
+import de.thm.arsnova.model.Content;
+import de.thm.arsnova.model.FindQuery;
+import org.springframework.stereotype.Service;
+
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+@Service
+public class ContentFindQueryService implements FindQueryService<Content> {
+	private RoomService roomService;
+	private ContentService contentService;
+
+	public ContentFindQueryService(final RoomService roomService, final ContentService contentService) {
+		this.roomService = roomService;
+		this.contentService = contentService;
+	}
+
+	@Override
+	public Set<String> resolveQuery(final FindQuery<Content> findQuery) {
+		Set<String> contentIds = new HashSet<>();
+		if (findQuery.getProperties().getRoomId() != null) {
+			List<Content> contentList = contentService.getByRoomId(findQuery.getProperties().getRoomId());
+			for (Content c : contentList) {
+				contentIds.add(c.getId());
+			}
+		}
+
+		return contentIds;
+	}
+}