[New] Added Paging

Paging is used to page a list, i.e. return a sublist which has a certain
size.

src/main/java/ch/eitchnet/utils/collections/Paging.java

@@ -0,0 +1,111 @@
+/*
+ * Copyright 2015 Robert von Burg <eitch@eitchnet.ch>
+ * 
+ * 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 ch.eitchnet.utils.collections;
+
+import java.util.List;
+
+/**
+ * @author Robert von Burg <eitch@eitchnet.ch>
+ */
+public class Paging<T> {
+
+	private int resultsPerPage;
+	private int indexOfPageToReturn;
+	private int nrOfPages;
+
+	private List<T> input;
+	private List<T> page;
+
+	private Paging(int resultsPerPage, int indexOfPageToReturn) {
+		this.resultsPerPage = resultsPerPage;
+		this.indexOfPageToReturn = indexOfPageToReturn;
+	}
+
+	public int getResultsPerPage() {
+		return this.resultsPerPage;
+	}
+
+	public void setResultsPerPage(int resultsPerPage) {
+		this.resultsPerPage = resultsPerPage;
+	}
+
+	public int getIndexOfPageToReturn() {
+		return this.indexOfPageToReturn;
+	}
+
+	public void setIndexOfPageToReturn(int indexOfPageToReturn) {
+		this.indexOfPageToReturn = indexOfPageToReturn;
+	}
+
+	public int getNrOfPages() {
+		return this.nrOfPages;
+	}
+
+	public void setNrOfPages(int nrOfPages) {
+		this.nrOfPages = nrOfPages;
+	}
+
+	public List<T> getInput() {
+		return this.input;
+	}
+
+	public List<T> getPage() {
+		return this.page;
+	}
+
+	/**
+	 * Creates a sub list of the given list by creating defining start and end from the requested page of the form
+	 * 
+	 * @param list
+	 *            the list to paginate
+	 * @param resultsPerPage
+	 *            The number of items to return in each page
+	 * @param page
+	 *            the page to return - start index is 1
+	 * 
+	 * @return a {@link Paging} instance from which the selected page (list) can be retrieved
+	 */
+	public static <T> Paging<T> asPage(List<T> list, int resultsPerPage, int page) {
+
+		Paging<T> paging = new Paging<T>(resultsPerPage, page);
+
+		if (paging.resultsPerPage < 0 || paging.indexOfPageToReturn < 0) {
+			paging.nrOfPages = -1;
+			paging.input = list;
+			paging.page = list;
+			return paging;
+		}
+
+		int size = list.size();
+
+		// calculate maximum number of pages
+		paging.nrOfPages = size / paging.resultsPerPage;
+		if (size % paging.resultsPerPage != 0)
+			paging.nrOfPages++;
+
+		// and from this validate requested page
+		paging.indexOfPageToReturn = Math.min(paging.indexOfPageToReturn, paging.nrOfPages);
+
+		// now we can calculate the start and end of the page
+		int start = Math.max(0, paging.resultsPerPage * paging.indexOfPageToReturn - paging.resultsPerPage);
+		int end = Math.min(size, paging.resultsPerPage * paging.indexOfPageToReturn);
+
+		// and return the list
+		paging.page = list.subList(start, end);
+
+		return paging;
+	}
+}

src/test/java/ch/eitchnet/utils/collections/PagingTest.java

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+/*
+ * Copyright 2015 Robert von Burg <eitch@eitchnet.ch>
+ * 
+ * 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 ch.eitchnet.utils.collections;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.Arrays;
+import java.util.List;
+
+import org.junit.Test;
+
+/**
+ * @author Robert von Burg <eitch@eitchnet.ch>
+ */
+public class PagingTest {
+
+	@Test
+	public void shouldReturnAll() {
+		List<String> list = Arrays.asList("a", "b", "c", "d", "e", "f");
+		List<String> page = Paging.asPage(list, -1, -1).getPage();
+		assertEquals(list, page);
+	}
+
+	@Test
+	public void shouldReturnFirstPage1() {
+		List<String> list = Arrays.asList("a", "b", "c", "d", "e", "f");
+		List<String> page = Paging.asPage(list, 1, 1).getPage();
+		assertEquals(Arrays.asList("a"), page);
+	}
+
+	@Test
+	public void shouldReturnFirstPage2() {
+		List<String> list = Arrays.asList("a", "b", "c", "d", "e", "f");
+		List<String> page = Paging.asPage(list, 2, 1).getPage();
+		assertEquals(Arrays.asList("a", "b"), page);
+	}
+
+	@Test
+	public void shouldReturnSecondPage1() {
+		List<String> list = Arrays.asList("a", "b", "c", "d", "e", "f");
+		List<String> page = Paging.asPage(list, 1, 2).getPage();
+		assertEquals(Arrays.asList("b"), page);
+	}
+
+	@Test
+	public void shouldReturnSecondPage2() {
+		List<String> list = Arrays.asList("a", "b", "c", "d", "e", "f");
+		List<String> page = Paging.asPage(list, 2, 2).getPage();
+		assertEquals(Arrays.asList("c", "d"), page);
+	}
+
+	@Test
+	public void shouldReturnLastPage1() {
+		List<String> list = Arrays.asList("a", "b", "c", "d", "e", "f");
+		List<String> page = Paging.asPage(list, 1, 6).getPage();
+		assertEquals(Arrays.asList("f"), page);
+	}
+
+	@Test
+	public void shouldReturnLastPage2() {
+		List<String> list = Arrays.asList("a", "b", "c", "d", "e", "f");
+		List<String> page = Paging.asPage(list, 2, 3).getPage();
+		assertEquals(Arrays.asList("e", "f"), page);
+	}
+}