BAEL-7264 How to Pretty-print a Map in Java (#15909)

core-java-modules/core-java-collections-maps-7/pom.xml

@@ -32,17 +32,22 @@
         <dependency>
             <groupId>com.google.guava</groupId>
             <artifactId>guava</artifactId>
-            <version>32.1.2-jre</version>
+            <version>${guava.version}</version>
         </dependency>
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-core</artifactId>
-            <version>1.37</version>
+            <version>${jmh.version}</version>
         </dependency>
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-generator-annprocess</artifactId>
-            <version>1.37</version>
+            <version>${jmh.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-collections4</artifactId>
+            <version>${commons-collections.version}</version>
         </dependency>
     </dependencies>
 
@@ -63,6 +68,9 @@
     <properties>
         <gson.version>2.10.1</gson.version>
         <csv.version>1.5</csv.version>
+        <guava.version>32.1.2-jre</guava.version>
+        <jmh.version>1.37</jmh.version>
+        <commons-collections.version>4.4</commons-collections.version>
     </properties>
 
 </project>

core-java-modules/core-java-collections-maps-7/src/test/java/com/baeldung/map/prettyprintmap/PrettyPrintMapUnitTest.java

@@ -0,0 +1,202 @@
+package com.baeldung.map.prettyprintmap;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.google.common.base.Joiner;
+import com.google.gson.GsonBuilder;
+import org.apache.commons.collections4.MapUtils;
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.PrintStream;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+class PrettyPrintMapUnitTest {
+
+    private static final Map<String, Object> MAP;
+
+    static {
+        // using LinkedHashMap to keep insertion order, helpful in assertions
+        MAP = new LinkedHashMap<>();
+        MAP.put("one", 1);
+        MAP.put("two", 2);
+
+        Map<String, Integer> innerMap = new LinkedHashMap<>();
+        innerMap.put("ten", 10);
+        innerMap.put("eleven", 11);
+
+        MAP.put("inner", innerMap);
+    }
+
+    @Test
+    void givenMap_whenToString_thenOneLine() {
+        String result = MAP.toString();
+
+        String expected = "{one=1, two=2, inner={ten=10, eleven=11}}";
+        Assertions.assertThat(result).isEqualTo(expected);
+    }
+
+    @Test
+    void givenMap_whenSimpleForEachLoop_thenPrettyPrintWithoutNested() {
+        StringBuilder result = new StringBuilder();
+
+        for (Map.Entry<?, ?> entry : MAP.entrySet()) {
+            result.append(String.format("%-15s : %s%n", entry.getKey(), entry.getValue()));
+        }
+
+        String expected =
+            "one             : 1\n" +
+            "two             : 2\n" +
+            "inner           : {ten=10, eleven=11}\n";
+        Assertions.assertThat(result.toString()).isEqualToIgnoringNewLines(expected);
+    }
+
+    @Test
+    void givenMap_whenRecursionForEachLoop_thenPrettyPrint() {
+        String result = printMap(0, MAP);
+
+        String expected =
+            "one             : 1\n" +
+            "two             : 2\n" +
+            "inner           :\n" +
+            "    ten             : 10\n" +
+            "    eleven          : 11\n";
+        Assertions.assertThat(result).isEqualToIgnoringNewLines(expected);
+    }
+
+    @Test
+    void givenMap_whenStream_thenPrettyPrintWithoutNested() {
+        StringBuilder result = new StringBuilder();
+
+        MAP.forEach((k, v) -> result.append(String.format("%-15s : %s%n", k, v)));
+
+        String expected =
+            "one             : 1\n" +
+            "two             : 2\n" +
+            "inner           : {ten=10, eleven=11}\n";
+        Assertions.assertThat(result.toString()).isEqualToIgnoringNewLines(expected);
+    }
+
+    @Test
+    void givenMap_whenExtendedStream_thenPrettyPrintWithoutNested() {
+        String result = MAP.entrySet().stream()
+            .map(entry -> String.format("%-15s : %s", entry.getKey(), entry.getValue()))
+            .collect(Collectors.joining("\n"));
+
+        String expected =
+            "one             : 1\n" +
+            "two             : 2\n" +
+            "inner           : {ten=10, eleven=11}\n";
+        Assertions.assertThat(result).isEqualToIgnoringNewLines(expected);
+    }
+    @Test
+    void givenMap_whenJackson_thenPrettyPrint() throws JsonProcessingException {
+        String result = new ObjectMapper().writerWithDefaultPrettyPrinter().writeValueAsString(MAP);
+
+        String expected =
+            "{\n" +
+            "  \"one\" : 1,\n" +
+            "  \"two\" : 2,\n" +
+            "  \"inner\" : {\n" +
+            "    \"ten\" : 10,\n" +
+            "    \"eleven\" : 11\n" +
+            "  }\n" +
+            "}";
+        Assertions.assertThat(result).isEqualToIgnoringNewLines(expected);
+    }
+
+    @Test
+    void givenMap_whenGson_thenPrettyPrint() {
+        String result = new GsonBuilder().setPrettyPrinting().create().toJson(MAP);
+
+        String expected =
+            "{\n" +
+            "  \"one\": 1,\n" +
+            "  \"two\": 2,\n" +
+            "  \"inner\": {\n" +
+            "    \"ten\": 10,\n" +
+            "    \"eleven\": 11\n" +
+            "  }\n" +
+            "}";
+        Assertions.assertThat(result).isEqualToIgnoringNewLines(expected);
+    }
+
+    @Test
+    void givenMap_whenApacheCommonsCollectionsDebugPrint_thenPrettyPrintWithClassNames() throws IOException {
+        try (ByteArrayOutputStream baos = new ByteArrayOutputStream();
+             PrintStream ps = new PrintStream(baos)) {
+
+            MapUtils.debugPrint(ps, "map", MAP);
+            String result = baos.toString();
+
+            String expected =
+                "map = \n" +
+                "{\n" +
+                "    one = 1 java.lang.Integer\n" +
+                "    two = 2 java.lang.Integer\n" +
+                "    inner = \n" +
+                "    {\n" +
+                "        ten = 10 java.lang.Integer\n" +
+                "        eleven = 11 java.lang.Integer\n" +
+                "    } java.util.LinkedHashMap\n" +
+                "} java.util.LinkedHashMap\n";
+            Assertions.assertThat(result).isEqualToIgnoringNewLines(expected);
+        }
+    }
+
+    @Test
+    void givenMap_whenApacheCommonsCollectionsVerbosePrint_thenPrettyPrint() throws IOException {
+        try (ByteArrayOutputStream baos = new ByteArrayOutputStream();
+             PrintStream ps = new PrintStream(baos)) {
+
+            MapUtils.verbosePrint(ps, "map", MAP);
+            String result = baos.toString();
+
+            String expected =
+                "map = \n" +
+                "{\n" +
+                "    one = 1\n" +
+                "    two = 2\n" +
+                "    inner = \n" +
+                "    {\n" +
+                "        ten = 10\n" +
+                "        eleven = 11\n" +
+                "    }\n" +
+                "}\n";
+            Assertions.assertThat(result).isEqualToIgnoringNewLines(expected);
+        }
+    }
+
+    @Test
+    void givenMap_whenGuavaJoiner_thenPrettyPrintWithoutNested() {
+        String result = Joiner.on(",\n").withKeyValueSeparator("=").join(MAP);
+
+        String expected =
+            "one=1,\n" +
+            "two=2,\n" +
+            "inner={ten=10, eleven=11}";
+        Assertions.assertThat(result).isEqualToIgnoringNewLines(expected);
+    }
+
+    private static String printMap(int leftPadding, Map<?, ?> map) {
+        StringBuilder ret = new StringBuilder();
+
+        for (Map.Entry<?, ?> entry : map.entrySet()) {
+            if (entry.getValue() instanceof Map) {
+                ret.append(String.format("%-15s :%n", entry.getKey()));
+                ret.append(printMap(leftPadding + 4, (Map<?, ?>) entry.getValue()));
+            }
+            else {
+                ret.append(String.format("%" + (leftPadding > 0 ? leftPadding : "") + "s" // adding padding
+                        + "%-15s : %s%n",
+                    "", entry.getKey(), entry.getValue()));
+            }
+        }
+        return ret.toString();
+    }
+
+}