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file to map article (eugenp#11838)
* file to map article * add aggregateByKeys method
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‎core-java-modules/core-java-io-4/src/main/java/com/baeldung/filetomap/FileToHashMap.java‎

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package com.baeldung.filetomap;
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import java.io.BufferedReader;
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import java.io.FileReader;
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import java.io.IOException;
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import java.nio.file.Files;
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import java.nio.file.Paths;
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import java.util.HashMap;
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import java.util.List;
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import java.util.Map;
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import java.util.stream.Collectors;
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import java.util.stream.Stream;
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public class FileToHashMap {
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enum DupKeyOption {
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OVERWRITE, DISCARD
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}
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public static Map<String, String> byBufferedReader(String filePath, DupKeyOption dupKeyOption) {
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HashMap<String, String> map = new HashMap<>();
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String line;
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try (BufferedReader reader = new BufferedReader(new FileReader(filePath))) {
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while ((line = reader.readLine()) != null) {
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String[] keyValuePair = line.split(":", 2);
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if (keyValuePair.length > 1) {
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String key = keyValuePair[0];
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String value = keyValuePair[1];
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if (DupKeyOption.OVERWRITE == dupKeyOption) {
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map.put(key, value);
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} else if (DupKeyOption.DISCARD == dupKeyOption) {
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map.putIfAbsent(key, value);
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}
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} else {
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System.out.println("No Key:Value found in line, ignoring: " + line);
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}
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}
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} catch (IOException e) {
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e.printStackTrace();
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}
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return map;
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}
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public static Map<String, String> byStream(String filePath, DupKeyOption dupKeyOption) {
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Map<String, String> map = new HashMap<>();
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try (Stream<String> lines = Files.lines(Paths.get(filePath))) {
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lines.filter(line -> line.contains(":"))
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.forEach(line -> {
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String[] keyValuePair = line.split(":", 2);
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String key = keyValuePair[0];
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String value = keyValuePair[1];
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if (DupKeyOption.OVERWRITE == dupKeyOption) {
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map.put(key, value);
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} else if (DupKeyOption.DISCARD == dupKeyOption) {
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map.putIfAbsent(key, value);
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}
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});
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} catch (IOException e) {
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e.printStackTrace();
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}
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return map;
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}
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public static Map<String, List<String>> aggregateByKeys(String filePath) {
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Map<String, List<String>> map = new HashMap<>();
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try (Stream<String> lines = Files.lines(Paths.get(filePath))) {
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lines.filter(line -> line.contains(":"))
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.forEach(line -> {
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String[] keyValuePair = line.split(":", 2);
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String key = keyValuePair[0];
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String value = keyValuePair[1];
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if (map.containsKey(key)) {
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map.get(key).add(value);
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} else {
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map.put(key, Stream.of(value).collect(Collectors.toList()));
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}
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});
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} catch (IOException e) {
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e.printStackTrace();
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}
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return map;
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}
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}

‎core-java-modules/core-java-io-4/src/test/java/com/baeldung/filetomap/FileToHashMapUnitTest.java‎

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package com.baeldung.filetomap;
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import org.junit.Before;
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import org.junit.Test;
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import java.net.URISyntaxException;
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import java.nio.file.Paths;
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import java.util.Arrays;
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import java.util.List;
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import java.util.Map;
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import java.util.stream.Collectors;
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import java.util.stream.Stream;
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import static org.assertj.core.api.Assertions.assertThat;
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public class FileToHashMapUnitTest {
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private String filePath;
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private static final Map<String, String> EXPECTED_MAP_DISCARD = Stream.of(new String[][]{
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{"title", "The Lord of the Rings: The Return of the King"},
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{"director", "Peter Jackson"},
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{"actor", "Sean Astin"}
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}).collect(Collectors.toMap(data -> data[0], data -> data[1]));
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private static final Map<String, String> EXPECTED_MAP_OVERWRITE = Stream.of(new String[][]{
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{"title", "The Lord of the Rings: The Return of the King"},
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{"director", "Peter Jackson"},
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{"actor", "Ian McKellen"}
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}).collect(Collectors.toMap(data -> data[0], data -> data[1]));
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private static final Map<String, List<String>> EXPECTED_MAP_AGGREGATE = Stream.of(new String[][]{
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{"title", "The Lord of the Rings: The Return of the King"},
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{"director", "Peter Jackson"},
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{"actor", "Sean Astin", "Ian McKellen"}
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}).collect(Collectors.toMap(arr -> arr[0], arr -> Arrays.asList(Arrays.copyOfRange(arr, 1, arr.length))));
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@Before
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public void setPath() throws URISyntaxException {
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if (filePath == null) {
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filePath = Paths.get(ClassLoader.getSystemResource("filetomap/theLordOfRings.txt").toURI()).toString();
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}
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}
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@Test
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public void givenInputFile_whenInvokeByBufferedReaderPriorToJava8_shouldGetExpectedMap() {
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Map<String, String> mapOverwrite = FileToHashMap.byBufferedReader(filePath, FileToHashMap.DupKeyOption.OVERWRITE);
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Map<String, String> mapDiscard = FileToHashMap.byBufferedReader(filePath, FileToHashMap.DupKeyOption.DISCARD);
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assertThat(mapOverwrite).isEqualTo(EXPECTED_MAP_OVERWRITE);
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assertThat(mapDiscard).isEqualTo(EXPECTED_MAP_DISCARD);
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}
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@Test
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public void givenInputFile_whenInvokeByStream_shouldGetExpectedMap() {
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Map<String, String> mapOverwrite = FileToHashMap.byStream(filePath, FileToHashMap.DupKeyOption.OVERWRITE);
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Map<String, String> mapDiscard = FileToHashMap.byStream(filePath, FileToHashMap.DupKeyOption.DISCARD);
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assertThat(mapOverwrite).isEqualTo(EXPECTED_MAP_OVERWRITE);
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assertThat(mapDiscard).isEqualTo(EXPECTED_MAP_DISCARD);
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}
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@Test
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public void givenInputFile_whenInvokeAggregateByKeys_shouldGetExpectedMap() {
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Map<String, List<String>> mapAgg = FileToHashMap.aggregateByKeys(filePath);
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assertThat(mapAgg).isEqualTo(EXPECTED_MAP_AGGREGATE);
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}
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}

‎core-java-modules/core-java-io-4/src/test/resources/filetomap/theLordOfRings.txt‎

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title:The Lord of the Rings: The Return of the King
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director:Peter Jackson
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actor:Sean Astin
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actor:Ian McKellen
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Gandalf and Aragorn lead the World of Men against Sauron's
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army to draw his gaze from Frodo and Sam as they approach Mount Doom with the One Ring.

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