From 9bbd08c6a8297334ed8f2092b7a30d505202c5dc Mon Sep 17 00:00:00 2001
From: sam-gardner <53271849+sam-gardner@users.noreply.github.com>
Date: Mon, 19 Jun 2023 16:15:16 +0100
Subject: [PATCH] BAEL-5830 Add code for setting default values for null fields
 with Jackson (#14265)

---
 .../defaultvalues/JsonSetterDefaultValue.java | 30 +++++++++++++++
 .../NonAnnotatedDefaultValue.java             | 20 ++++++++++
 .../defaultvalues/NullsSkipDefaultValue.java  | 27 ++++++++++++++
 .../defaultvalues/DefaultValuesUnitTest.java  | 37 +++++++++++++++++++
 4 files changed, 114 insertions(+)
 create mode 100644 jackson-modules/jackson-core/src/main/java/com/baeldung/jackson/defaultvalues/JsonSetterDefaultValue.java
 create mode 100644 jackson-modules/jackson-core/src/main/java/com/baeldung/jackson/defaultvalues/NonAnnotatedDefaultValue.java
 create mode 100644 jackson-modules/jackson-core/src/main/java/com/baeldung/jackson/defaultvalues/NullsSkipDefaultValue.java
 create mode 100644 jackson-modules/jackson-core/src/test/java/com/baeldung/jackson/defaultvalues/DefaultValuesUnitTest.java

diff --git a/jackson-modules/jackson-core/src/main/java/com/baeldung/jackson/defaultvalues/JsonSetterDefaultValue.java b/jackson-modules/jackson-core/src/main/java/com/baeldung/jackson/defaultvalues/JsonSetterDefaultValue.java
new file mode 100644
index 0000000000..5d8c758e86
--- /dev/null
+++ b/jackson-modules/jackson-core/src/main/java/com/baeldung/jackson/defaultvalues/JsonSetterDefaultValue.java
@@ -0,0 +1,30 @@
+package com.baeldung.jackson.defaultvalues;
+
+import com.fasterxml.jackson.annotation.JsonSetter;
+
+public class JsonSetterDefaultValue {
+
+    private String required;
+    private String optional = "valueIfMissingEntirely";
+
+    @JsonSetter("optional")
+    public void setOptional(String optional){
+        if(optional == null){
+            this.optional = "valueIfNull";
+        }
+    }
+
+    public String getRequired() {
+        return required;
+    }
+
+    public String getOptional() {
+        return optional;
+    }
+
+    @Override
+    public String toString() {
+        return "NonAnnotatedDefaultValue{" + "required='" + required + '\'' + ", optional='" + optional + '\'' + '}';
+    }
+
+}
diff --git a/jackson-modules/jackson-core/src/main/java/com/baeldung/jackson/defaultvalues/NonAnnotatedDefaultValue.java b/jackson-modules/jackson-core/src/main/java/com/baeldung/jackson/defaultvalues/NonAnnotatedDefaultValue.java
new file mode 100644
index 0000000000..54747642ef
--- /dev/null
+++ b/jackson-modules/jackson-core/src/main/java/com/baeldung/jackson/defaultvalues/NonAnnotatedDefaultValue.java
@@ -0,0 +1,20 @@
+package com.baeldung.jackson.defaultvalues;
+
+public class NonAnnotatedDefaultValue {
+
+    private String required;
+    private String optional = "defaultValue";
+
+    public String getRequired() {
+        return required;
+    }
+
+    public String getOptional() {
+        return optional;
+    }
+
+    @Override
+    public String toString() {
+        return "NonAnnotatedDefaultValue{" + "required='" + required + '\'' + ", optional='" + optional + '\'' + '}';
+    }
+}
diff --git a/jackson-modules/jackson-core/src/main/java/com/baeldung/jackson/defaultvalues/NullsSkipDefaultValue.java b/jackson-modules/jackson-core/src/main/java/com/baeldung/jackson/defaultvalues/NullsSkipDefaultValue.java
new file mode 100644
index 0000000000..8dc585ea30
--- /dev/null
+++ b/jackson-modules/jackson-core/src/main/java/com/baeldung/jackson/defaultvalues/NullsSkipDefaultValue.java
@@ -0,0 +1,27 @@
+package com.baeldung.jackson.defaultvalues;
+
+import com.fasterxml.jackson.annotation.JsonSetter;
+import com.fasterxml.jackson.annotation.Nulls;
+
+public class NullsSkipDefaultValue {
+
+    private String required;
+    @JsonSetter(nulls = Nulls.SKIP)
+    private String optional = "defaultValue";
+
+    public void setOptional(String optional){}
+
+    public String getRequired() {
+        return required;
+    }
+
+    public String getOptional() {
+        return optional;
+    }
+
+    @Override
+    public String toString() {
+        return "NonAnnotatedDefaultValue{" + "required='" + required + '\'' + ", optional='" + optional + '\'' + '}';
+    }
+
+}
diff --git a/jackson-modules/jackson-core/src/test/java/com/baeldung/jackson/defaultvalues/DefaultValuesUnitTest.java b/jackson-modules/jackson-core/src/test/java/com/baeldung/jackson/defaultvalues/DefaultValuesUnitTest.java
new file mode 100644
index 0000000000..813cfaae16
--- /dev/null
+++ b/jackson-modules/jackson-core/src/test/java/com/baeldung/jackson/defaultvalues/DefaultValuesUnitTest.java
@@ -0,0 +1,37 @@
+package com.baeldung.jackson.defaultvalues;
+
+import org.junit.Test;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+public class DefaultValuesUnitTest {
+
+    @Test
+    public void givenAClassWithADefaultValue_whenReadingJsonWithoutOptionalValue_thenExpectDefaultValueInResult() throws JsonProcessingException {
+        String noOptionalField = "{\"required\": \"value\"}";
+        ObjectMapper objectMapper = new ObjectMapper();
+        NonAnnotatedDefaultValue createdObject = objectMapper.readValue(noOptionalField, NonAnnotatedDefaultValue.class);
+        assert(createdObject.getRequired()).equals("value");
+        assert(createdObject.getOptional()).equals("defaultValue");
+    }
+
+    @Test
+    public void givenAClassWithAJsonSetter_whenReadingJsonWithNullOptionalValue_thenExpectDefaultValueInResult() throws JsonProcessingException {
+        String nullOptionalField = "{\"required\": \"value\", \"optional\": null}";
+        ObjectMapper objectMapper = new ObjectMapper();
+        JsonSetterDefaultValue createdObject = objectMapper.readValue(nullOptionalField, JsonSetterDefaultValue.class);
+        assert(createdObject.getRequired()).equals("value");
+        assert(createdObject.getOptional()).equals("valueIfNull");
+    }
+
+    @Test
+    public void givenAClassWithAJsonSetterNullsSkip_whenReadingJsonWithNullOptionalValue_thenExpectDefaultValueInResult() throws JsonProcessingException {
+        String nullOptionalField = "{\"required\": \"value\", \"optional\": null}";
+        ObjectMapper objectMapper = new ObjectMapper();
+        NullsSkipDefaultValue createdObject = objectMapper.readValue(nullOptionalField, NullsSkipDefaultValue.class);
+        assert(createdObject.getRequired()).equals("value");
+        assert(createdObject.getOptional()).equals("defaultValue");
+    }
+
+}