BAEL-6312 Add example code for @JsonMerge Jackson annotation

jackson-modules/jackson-annotations/src/main/java/com/baeldung/jackson/jsonmerge/Keyboard.java

@@ -0,0 +1,37 @@
+package com.baeldung.jackson.jsonmerge;
+
+public class Keyboard {
+
+    private String style;
+    private String layout;
+
+    public Keyboard(){
+        super();
+    }
+
+    public Keyboard(String style, String layout) {
+        this.style = style;
+        this.layout = layout;
+    }
+
+    public String getStyle() {
+        return style;
+    }
+
+    public void setStyle(String style) {
+        this.style = style;
+    }
+
+    public String getLayout() {
+        return layout;
+    }
+
+    public void setLayout(String layout) {
+        this.layout = layout;
+    }
+
+    @Override
+    public String toString() {
+        return "Keyboard{" + "style='" + style + '\'' + ", layout='" + layout + '\'' + '}';
+    }
+}

jackson-modules/jackson-annotations/src/main/java/com/baeldung/jackson/jsonmerge/ObjectWithMap.java

@@ -0,0 +1,38 @@
+package com.baeldung.jackson.jsonmerge;
+
+import java.util.Map;
+
+import com.fasterxml.jackson.annotation.JsonMerge;
+
+public class ObjectWithMap {
+
+    private String name;
+    @JsonMerge
+    private Map<String, String> stringPairs;
+
+    public ObjectWithMap(String name, Map<String, String> stringPairs) {
+        this.name = name;
+        this.stringPairs = stringPairs;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public Map<String, String> getStringPairs() {
+        return stringPairs;
+    }
+
+    public void setStringPairs(Map<String, String> stringPairs) {
+        this.stringPairs = stringPairs;
+    }
+
+    @Override
+    public String toString() {
+        return "ObjectWithMap{" + "name='" + name + '\'' + ", something=" + stringPairs + '}';
+    }
+}

jackson-modules/jackson-annotations/src/main/java/com/baeldung/jackson/jsonmerge/ProgrammerAnnotated.java

@@ -0,0 +1,38 @@
+package com.baeldung.jackson.jsonmerge;
+
+import com.fasterxml.jackson.annotation.JsonMerge;
+
+public class ProgrammerAnnotated {
+
+    private String name;
+    private String favouriteLanguage;
+    @JsonMerge
+    private Keyboard keyboard;
+
+    public ProgrammerAnnotated(String name, String favouriteLanguage, Keyboard keyboard) {
+        this.name = name;
+        this.favouriteLanguage = favouriteLanguage;
+        this.keyboard = keyboard;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getFavouriteLanguage() {
+        return favouriteLanguage;
+    }
+
+    public Keyboard getKeyboard() {
+        return keyboard;
+    }
+
+    @Override
+    public String toString() {
+        return "Programmer{" + "name='" + name + '\'' + ", favouriteLanguage='" + favouriteLanguage + '\'' + ", keyboard=" + keyboard + '}';
+    }
+}

jackson-modules/jackson-annotations/src/main/java/com/baeldung/jackson/jsonmerge/ProgrammerNotAnnotated.java

@@ -0,0 +1,43 @@
+package com.baeldung.jackson.jsonmerge;
+
+public class ProgrammerNotAnnotated {
+
+    private String name;
+    private String favouriteLanguage;
+    private Keyboard keyboard;
+
+    public ProgrammerNotAnnotated(String name, String favouriteLanguage, Keyboard keyboard) {
+        this.name = name;
+        this.favouriteLanguage = favouriteLanguage;
+        this.keyboard = keyboard;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getFavouriteLanguage() {
+        return favouriteLanguage;
+    }
+
+    public void setFavouriteLanguage(String favouriteLanguage) {
+        this.favouriteLanguage = favouriteLanguage;
+    }
+
+    public Keyboard getKeyboard() {
+        return keyboard;
+    }
+
+    public void setKeyboard(Keyboard keyboard) {
+        this.keyboard = keyboard;
+    }
+
+    @Override
+    public String toString() {
+        return "Programmer{" + "name='" + name + '\'' + ", favouriteLanguage='" + favouriteLanguage + '\'' + ", keyboard=" + keyboard + '}';
+    }
+}

jackson-modules/jackson-annotations/src/test/java/com/baeldung/jackson/jsonmerge/JsonMergeUnitTest.java

@@ -0,0 +1,64 @@
+package com.baeldung.jackson.jsonmerge;
+
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.junit.Test;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.ObjectReader;
+
+public class JsonMergeUnitTest {
+
+    @Test
+    public void givenAnObjectAndJson_whenUsingJsonMerge_thenExpectUpdateInPOJO() throws JsonProcessingException {
+        String newData = "{\"name\":\"Steve\",\"keyboard\":{\"style\":\"Mechanical\"}}";
+        ProgrammerAnnotated programmerToUpdate = new ProgrammerAnnotated("John", "Java", new Keyboard("Membrane", "US"));
+
+        ObjectMapper objectMapper = new ObjectMapper();
+        ProgrammerAnnotated update = objectMapper.readerForUpdating(programmerToUpdate)
+          .readValue(newData);
+
+        assert (update.getFavouriteLanguage()).equals("Java");
+        // Only works with annotation
+        assert (update.getKeyboard()
+          .getLayout()).equals("US");
+    }
+
+    @Test
+    public void givenAnObjectAndJson_whenNotUsingJsonMerge_thenExpectNoUpdateInPOJO() throws JsonProcessingException {
+        String newData = "{\"name\":\"Steve\",\"keyboard\":{\"style\":\"Mechanical\"}}";
+        ProgrammerNotAnnotated programmerToUpdate = new ProgrammerNotAnnotated("John", "Java", new Keyboard("Membrane", "US"));
+
+        ObjectMapper objectMapper = new ObjectMapper();
+        ObjectReader objectReader = objectMapper.readerForUpdating(programmerToUpdate);
+        ProgrammerNotAnnotated update = objectReader.readValue(newData);
+
+        assert (update.getFavouriteLanguage()).equals("Java");
+        assertNull(update.getKeyboard()
+          .getLayout());
+    }
+
+    @Test
+    public void givenAnObjectWithAMap_whenUsingJsonMerge_thenExpectAllFieldsInMap() throws JsonProcessingException {
+        String newData = "{\"stringPairs\":{\"field1\":\"value1\",\"field2\":\"value2\"}}";
+        Map<String, String> map = new HashMap<>();
+        map.put("field3", "value3");
+        ObjectWithMap objectToUpdateWith = new ObjectWithMap("James", map);
+
+        ObjectMapper objectMapper = new ObjectMapper();
+        ObjectWithMap update = objectMapper.readerForUpdating(objectToUpdateWith)
+          .readValue(newData);
+
+        assertTrue(update.getStringPairs()
+          .containsKey("field1"));
+        assertTrue(update.getStringPairs()
+          .containsKey("field2"));
+        assertTrue(update.getStringPairs()
+          .containsKey("field3"));
+    }
+}