From 614d91076694c4454f97d845757ab325faab53df Mon Sep 17 00:00:00 2001 From: "Kai.Yuan" Date: Mon, 18 Mar 2024 20:02:15 +0100 Subject: [PATCH 1/2] [map-stream-to-map] merge a stream of maps to a single map --- .../MapStreamToMapUnitTest.java | 153 ++++++++++++++++++ 1 file changed, 153 insertions(+) create mode 100644 core-java-modules/core-java-streams-maps/src/test/java/com/baeldung/streams/mapstreamtomap/MapStreamToMapUnitTest.java diff --git a/core-java-modules/core-java-streams-maps/src/test/java/com/baeldung/streams/mapstreamtomap/MapStreamToMapUnitTest.java b/core-java-modules/core-java-streams-maps/src/test/java/com/baeldung/streams/mapstreamtomap/MapStreamToMapUnitTest.java new file mode 100644 index 0000000000..cbefd58396 --- /dev/null +++ b/core-java-modules/core-java-streams-maps/src/test/java/com/baeldung/streams/mapstreamtomap/MapStreamToMapUnitTest.java @@ -0,0 +1,153 @@ +package com.baeldung.streams.mapstreamtomap; + +import static java.lang.Math.max; +import static org.junit.jupiter.api.Assertions.assertEquals; +import static org.junit.jupiter.api.Assertions.assertThrows; + +import java.util.Collections; +import java.util.HashMap; +import java.util.List; +import java.util.Map; +import java.util.stream.Collectors; +import java.util.stream.Stream; + +import org.junit.jupiter.api.Test; + +import com.google.common.collect.Lists; + +public class MapStreamToMapUnitTest { + + Map playerMap1 = new HashMap() {{ + put("Kai", 92); + put("Liam", 100); + }}; + Map playerMap2 = new HashMap() {{ + put("Eric", 42); + put("Kevin", 77); + }}; + Map playerMap3 = new HashMap() {{ + put("Saajan", 35); + }}; + Map playerMap4 = new HashMap() {{ + put("Kai", 76); + }}; + Map playerMap5 = new HashMap() {{ + put("Kai", null); + put("Jerry", null); + }}; + + static Stream> getMapStream(Map... playerMaps) { + List> theList = Lists.newArrayList(playerMaps); + Collections.shuffle(theList); + return theList.stream(); + } + + @Test + void givenMapsStream_whenUsingFlatMapAndToMap_thenMultipleMapsMergedIntoOneMap() { + + Map expectedMap = new HashMap() {{ + put("Saajan", 35); + put("Liam", 100); + put("Kai", 92); + put("Eric", 42); + put("Kevin", 77); + }}; + + Map mergedMap = getMapStream(playerMap1, playerMap2, playerMap3).flatMap(map -> map.entrySet() + .stream()) + .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue)); + + assertEquals(expectedMap, mergedMap); + } + + @Test + void givenMapsWithDuplicateKeys_whenUsingFlatMapAndToMap_thenMultipleMapsMergedIntoOneMap() { + + Map expectedMap = new HashMap() {{ + put("Saajan", 35); + put("Liam", 100); + put("Kai", 92); // max of 76 and 92 + put("Eric", 42); + put("Kevin", 77); + }}; + + assertThrows(IllegalStateException.class, () -> getMapStream(playerMap1, playerMap2, playerMap3, playerMap4).flatMap(map -> map.entrySet() + .stream()) + .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue)), "Duplicate key Kai (attempted merging values 92 and 76)"); + + Map mergedMap = getMapStream(playerMap1, playerMap2, playerMap3, playerMap4).flatMap(map -> map.entrySet() + .stream()) + .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, Integer::max)); + + assertEquals(expectedMap, mergedMap); + } + + private Integer maxInteger(Integer int1, Integer int2) { + if (int1 == null) { + return int2; + } + if (int2 == null) { + return int1; + } + return max(int1, int2); + } + + @Test + void givenMapsWithDuplicateKeysAndNullValues_whenUsingFlatMapWithForEach_thenMultipleMapsMergedIntoOneMap() { + + Map expectedMap = new HashMap() {{ + put("Saajan", 35); + put("Liam", 100); + put("Kai", 92); // max of 92, 76, and null + put("Eric", 42); + put("Kevin", 77); + put("Jerry", null); + }}; + + assertThrows(NullPointerException.class, () -> getMapStream(playerMap1, playerMap2, playerMap3, playerMap4, playerMap5).flatMap(map -> map.entrySet() + .stream()) + .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, Integer::max))); + + Map mergedMap = new HashMap<>(); + getMapStream(playerMap1, playerMap2, playerMap3, playerMap4, playerMap5).flatMap(map -> map.entrySet() + .stream()) + .forEach(entry -> { + String k = entry.getKey(); + Integer v = entry.getValue(); + if (mergedMap.containsKey(k)) { + mergedMap.put(k, maxInteger(mergedMap.get(k), v)); + } else { + mergedMap.put(k, v); + } + }); + assertEquals(expectedMap, mergedMap); + + } + + @Test + void givenMapsWithDuplicateKeysAndNullValues_whenUsingReduce_thenMultipleMapsMergedIntoOneMap() { + + Map expectedMap = new HashMap() {{ + put("Saajan", 35); + put("Liam", 100); + put("Kai", 92); // max of 92, 76, and null + put("Eric", 42); + put("Kevin", 77); + put("Jerry", null); + }}; + Stream> mapStream = getMapStream(playerMap1, playerMap2, playerMap3, playerMap4, playerMap5); + Map mergedMap = mapStream.reduce(new HashMap<>(), (resultMap, theMap) -> { + theMap.forEach((k, v) -> { + if (resultMap.containsKey(k)) { + resultMap.put(k, maxInteger(resultMap.get(k), v)); + } else { + resultMap.put(k, v); + } + }); + return resultMap; + }); + + assertEquals(expectedMap, mergedMap); + + } +} \ No newline at end of file From 9456b4b953c7e95c22b85ae66a934d123d8eecfc Mon Sep 17 00:00:00 2001 From: "Kai.Yuan" Date: Tue, 19 Mar 2024 09:32:58 +0100 Subject: [PATCH 2/2] [map-stream-to-map] updates.. 1 --- .../MapStreamToMapUnitTest.java | 46 ++++++++----------- 1 file changed, 18 insertions(+), 28 deletions(-) diff --git a/core-java-modules/core-java-streams-maps/src/test/java/com/baeldung/streams/mapstreamtomap/MapStreamToMapUnitTest.java b/core-java-modules/core-java-streams-maps/src/test/java/com/baeldung/streams/mapstreamtomap/MapStreamToMapUnitTest.java index cbefd58396..b23dd07fc8 100644 --- a/core-java-modules/core-java-streams-maps/src/test/java/com/baeldung/streams/mapstreamtomap/MapStreamToMapUnitTest.java +++ b/core-java-modules/core-java-streams-maps/src/test/java/com/baeldung/streams/mapstreamtomap/MapStreamToMapUnitTest.java @@ -1,20 +1,20 @@ package com.baeldung.streams.mapstreamtomap; import static java.lang.Math.max; +import static java.util.stream.Collectors.flatMapping; +import static java.util.stream.Collectors.groupingBy; +import static java.util.stream.Collectors.mapping; +import static java.util.stream.Collectors.reducing; import static org.junit.jupiter.api.Assertions.assertEquals; import static org.junit.jupiter.api.Assertions.assertThrows; -import java.util.Collections; import java.util.HashMap; -import java.util.List; import java.util.Map; import java.util.stream.Collectors; import java.util.stream.Stream; import org.junit.jupiter.api.Test; -import com.google.common.collect.Lists; - public class MapStreamToMapUnitTest { Map playerMap1 = new HashMap() {{ @@ -36,12 +36,6 @@ public class MapStreamToMapUnitTest { put("Jerry", null); }}; - static Stream> getMapStream(Map... playerMaps) { - List> theList = Lists.newArrayList(playerMaps); - Collections.shuffle(theList); - return theList.stream(); - } - @Test void givenMapsStream_whenUsingFlatMapAndToMap_thenMultipleMapsMergedIntoOneMap() { @@ -53,7 +47,8 @@ public class MapStreamToMapUnitTest { put("Kevin", 77); }}; - Map mergedMap = getMapStream(playerMap1, playerMap2, playerMap3).flatMap(map -> map.entrySet() + Map mergedMap = Stream.of(playerMap1, playerMap2, playerMap3) + .flatMap(map -> map.entrySet() .stream()) .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue)); @@ -71,11 +66,13 @@ public class MapStreamToMapUnitTest { put("Kevin", 77); }}; - assertThrows(IllegalStateException.class, () -> getMapStream(playerMap1, playerMap2, playerMap3, playerMap4).flatMap(map -> map.entrySet() + assertThrows(IllegalStateException.class, () -> Stream.of(playerMap1, playerMap2, playerMap3, playerMap4) + .flatMap(map -> map.entrySet() .stream()) .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue)), "Duplicate key Kai (attempted merging values 92 and 76)"); - Map mergedMap = getMapStream(playerMap1, playerMap2, playerMap3, playerMap4).flatMap(map -> map.entrySet() + Map mergedMap = Stream.of(playerMap1, playerMap2, playerMap3, playerMap4) + .flatMap(map -> map.entrySet() .stream()) .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, Integer::max)); @@ -104,12 +101,14 @@ public class MapStreamToMapUnitTest { put("Jerry", null); }}; - assertThrows(NullPointerException.class, () -> getMapStream(playerMap1, playerMap2, playerMap3, playerMap4, playerMap5).flatMap(map -> map.entrySet() + assertThrows(NullPointerException.class, () -> Stream.of(playerMap1, playerMap2, playerMap3, playerMap4, playerMap5) + .flatMap(map -> map.entrySet() .stream()) .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, Integer::max))); Map mergedMap = new HashMap<>(); - getMapStream(playerMap1, playerMap2, playerMap3, playerMap4, playerMap5).flatMap(map -> map.entrySet() + Stream.of(playerMap1, playerMap2, playerMap3, playerMap4, playerMap5) + .flatMap(map -> map.entrySet() .stream()) .forEach(entry -> { String k = entry.getKey(); @@ -135,19 +134,10 @@ public class MapStreamToMapUnitTest { put("Kevin", 77); put("Jerry", null); }}; - Stream> mapStream = getMapStream(playerMap1, playerMap2, playerMap3, playerMap4, playerMap5); - Map mergedMap = mapStream.reduce(new HashMap<>(), (resultMap, theMap) -> { - theMap.forEach((k, v) -> { - if (resultMap.containsKey(k)) { - resultMap.put(k, maxInteger(resultMap.get(k), v)); - } else { - resultMap.put(k, v); - } - }); - return resultMap; - }); - + Map mergedMap = Stream.of(playerMap1, playerMap2, playerMap3, playerMap4, playerMap5) + .flatMap(x -> x.entrySet() + .stream()) + .collect(groupingBy(Map.Entry::getKey, mapping(Map.Entry::getValue, reducing(null, this::maxInteger)))); assertEquals(expectedMap, mergedMap); - } } \ No newline at end of file