Jackson Annotations for JSON

Jackson Annotations for JSON

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Jackson is a suite of data-processing tools for Java comprising of three components:

  • Streaming (jackson-core) defines low-level streaming API and includes JSON-specific implementations.
  • Annotations (jackson-annotations) contains standard Jackson annotations.
  • Databind (jackson-databind) implements data-binding (and object serialization) support on streaming package. This package depends both on streaming and annotations packages

In this post, I will explain the Java objects to JSON data-binding using Jackson annotations. I will take up each of the Jackson annotations and explain with code snippets how to use them. Each annotation usage is accompanied with proper test cases.

Jackson Serialization and Deserialization Annotations

The Jackson library provides annotations that you can use in POJO’s to control both serialization and deserialization between POJOs and JSON. Below are annotations used in both serialization and deserialization operations:

  • @JsonIgnore
  • @JsonIgnoreProperties
  • @JsonIgnoreType
  • @JsonAutoDetect

@JsonIgnore

The @JsonIgnore annotation marks a field in a POJO to be ignored by Jackson during serialization and deserialization. Jackson ignores the field in both JSON serialization and deserialization. An example of Java class that uses the @JsonIgnore annotation is this.

IgnoreDemoBean.java

   //package guru.springframework.blog.jsonannotation.domain.serializationanddeserialization;


import com.fasterxml.jackson.annotation.JsonIgnore;

public class IgnoreDemoBean {
    @JsonIgnore
    public long personId = 0;
    public String  name = "James Clark";

    @Override
    public String toString() {
        return "IgnoreDemoBean{" +
                "personId=" + personId +
                ", name='" + name + '\'' +
                '}';
    }
}

The test class to the @JsonIgnore annotation is this.

IgnoreDemoBeanTest.java

   //package guru.springframework.blog.jsonannotation.domain.serializationanddeserialization;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import java.io.IOException;
import static org.hamcrest.Matchers.containsString;
import static org.hamcrest.Matchers.is;
import static org.hamcrest.Matchers.not;
import static org.hamcrest.core.IsEqual.equalTo;
import static org.junit.Assert.*;

public class IgnoreDemoBeanTest {
    private ObjectMapper objectMapper ;
    @Before
    public void setUp() throws Exception{
        objectMapper = new ObjectMapper();
    }
    @After
    public void tearDown() throws Exception{
        objectMapper = null;
    }
    @Test
    public void testSerializingWithJsonIgnore()
            throws JsonProcessingException {
        String jsonString = objectMapper.writeValueAsString(new IgnoreDemoBean());
        System.out.println(jsonString);
        assertThat(jsonString, containsString("James Clark"));
        assertThat(jsonString, not(containsString("productId")));
    }

    @Test
    public void testDeSerializingWithJsonIgnore() throws IOException {
        String jsonString = "{\"personId\": 231, \"name\": \"Mary Parker\"}";
        ObjectMapper mapper = new ObjectMapper();
        IgnoreDemoBean bean = objectMapper.readValue(jsonString, IgnoreDemoBean.class);
        System.out.println(bean);
        assertThat(bean.name, is(equalTo("Mary Parker")));
        assertThat(bean.personId, is(not(equalTo(231L))));
    }

}

The output on running the test in IntelliJ is this.
@JsonIgnore Annotation Test Output

As you can see, the @JsonIgnore annotation ignored the field personId during serialization and deserialization.

@JsonIgnoreProperties

The @JsonIgnoreProperties annotation is used at the class level to ignore fields during serialization and deserialization. The properties that are declared in this annotation will not be mapped to the JSON content.

Let us consider an example of Java class that uses the @JsonIgnoreProperties annotation.

IgnorePropertiesDemoBean.java

   //package guru.springframework.blog.jsonannotation.domain.serializationanddeserialization;

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;

@JsonIgnoreProperties({"userId", "gender"})
public class IgnorePropertiesDemoBean {
    public long  userId = 0;
    public String  name = "James Clark";
    public String  gender  = null;

    @Override
    public String toString() {
        return "IgnorePropertiesDemoBean{" +
                "userId=" + userId +
                ", name='" + name + '\'' +
                ", gender='" + gender + '\'' +
                '}';
    }
}

The test code to the @JsonIgnoreProperties annotation is this.

IgnorePropertiesDemoBeanTest

   //package guru.springframework.blog.jsonannotation.domain.serializationanddeserialization;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import java.io.IOException;

import static org.hamcrest.Matchers.containsString;
import static org.hamcrest.Matchers.is;
import static org.hamcrest.Matchers.not;
import static org.hamcrest.core.IsEqual.equalTo;
import static org.junit.Assert.*;

public class IgnorePropertiesDemoBeanTest {
    private ObjectMapper objectMapper ;
    @Before
    public void setUp() throws Exception{
        objectMapper = new ObjectMapper();
    }
    @After
    public void tearDown() throws Exception{
        objectMapper = null;
    }

    @Test
    public void testSerializingWithJsonIgnoreProperties()
            throws JsonProcessingException {
        String jsonString = objectMapper.writeValueAsString(new IgnorePropertiesDemoBean());
        System.out.println(jsonString);
        assertThat(jsonString, containsString("James Clark"));
        assertThat(jsonString, not(containsString("userId")));
    }

    @Test
    public void testDeSerializingWithJsonIgnoreProperties() throws IOException {
        String jsonString = "{\"userId\": 231, \"name\": \"Mary Parker\", \"gender\": \"male\"}";
        ObjectMapper mapper = new ObjectMapper();
        IgnorePropertiesDemoBean bean = objectMapper.readValue(jsonString, IgnorePropertiesDemoBean.class);
        System.out.println(bean);
        assertThat(bean.name, is(equalTo("Mary Parker")));
        assertThat(bean.userId, is(not(equalTo(231L))));
    }

}

The output of running the test in IntelliJ is this.


As you can see, the @JsonIgnoreProperties annotation ignored the field userId and gender both during serialization and deserialization.

@JsonIgnoreType

The @JsonIgnoreType annotation is used to mark a class to be ignored during serialization and deserialization. It marks all the properties of the class to be ignored while generating and reading JSON. An example of Java class that uses the @JsonIgnoreType annotation is this.

IgnoreTypeDemoBean.java

   //package guru.springframework.blog.jsonannotation.domain.serializationanddeserialization;

import com.fasterxml.jackson.annotation.JsonIgnoreType;

public class IgnoreTypeDemoBean {
    @JsonIgnoreType
    public static class Address {
        public String doorNumber = null;
        public String streetName = null;
        public String pinCode = null;
        public String city = null;

        @Override
        public String toString() {
            return "Address{" +
                    "doorNumber='" + doorNumber + '\'' +
                    ", streetName='" + streetName + '\'' +
                    ", pinCode='" + pinCode + '\'' +
                    ", city='" + city + '\'' +
                    '}';
        }
    }
    public long personId = 0;
    public String  name = "James Clark";
    public Address address = new Address();

    @Override
    public String toString() {
        return "IgnoreTypeDemoBean{" +
                "personId=" + personId +
                ", name='" + name + '\'' +
                ", address=" + address +
                '}';
    }
}

The test code to the @JsonIgnoreProperties annotation is this.

IgnoreTypeDemoBeanTest.java

The output of running the test in IntelliJ is this.

@JsonAutoDetect

The @JsonAutoDetect annotation is used at the class level to tell Jackson to override the visibility of the properties of a class during serialization and deserialization. You can set the visibility with the following elements:

  • creatorVisibility
  • fieldVisibility
  • getterVisibility
  • setterVisibility
  • isGetterVisibility

The JsonAutoDetect class defines public static constants that are similar to Java class visibility levels. They are:

  • ANY
  • DEFAULT
  • NON_PRIVATE
  • NONE
  • PROTECTED_AND_PRIVATE
  • PUBLIC_ONLY

Let us consider an example of Java class that uses the @JsonAutoDetect annotation.

AutoDetectDemoBean.java

   //package guru.springframework.blog.jsonannotation.domain.serializationanddeserialization;

import com.fasterxml.jackson.annotation.JsonAutoDetect;

@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY)
public class AutoDetectDemoBean {
    private long personId = 123L;
    private String  name = "James Clark";

    public long getPersonId() {
        return personId;
    }

    public void setPersonId(long personId) {
        this.personId = personId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "IgnoreDemoBean{" +
                "personId=" + personId +
                ", name='" + name + '\'' +
                '}';
    }
}

The test code to the @JsonAutoDetect annotation is this.

@Test
public void testSerializingWithJsonAutoDetect()
   throws JsonProcessingException {
 String jsonString = objectMapper.writeValueAsString(new AutoDetectDemoBean());
 System.out.println(jsonString);
 assertThat(jsonString, containsString("123"));
 assertThat(jsonString, containsString("James Clark"));
}

The output of running the test in IntelliJ is this.

Jackson Serialization Annotations

Jackson provides several annotations that you can use in POJO’s to serialize Java objects to JSON. These annotations are:

  • @JsonValue
  • @JsonInclude
  • @JsonGetter
  • @JsonAnyGetter
  • @JsonPropertyOrder
  • @JsonRawValue
  • @JsonSerialize
  • @JsonRootName

@JsonValue

The @JsonValue annotation is used at the method level. This annotation tells Jackson to use this method to generate the JSON string from the Java object.

Typically, if you want to print a serialized object, you override the toString() method. But, by using the @JsonValue annotation, you can define the way in which the Java object is to be serialized.

Note: Jackson omits any quotation marks inside the String that is returned by the custom serializer.

Let us consider an example Java class that uses the @JsonValue annotation.

ValueDemoBean.java

   //package guru.springframework.blog.jsonannotation.domain.serialization;

import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonValue;

public class ValueDemoBean {
    @JsonProperty
    private long personId = 123L;
    @JsonProperty
    private String  name = "James Clark";

    @JsonValue
    public String toJson(){
        return this.name+","+this.personId+","+this.toString();
    }

    @Override
    public String toString() {
        return "ValueDemoBean{" +
                "personId=" + personId +
                ", name='" + name + '\'' +
                '}';
    }
}

In order to explain the difference between the serialized object with and without the @JsonValue annotation, the code includes the toString() method. You can also run the code without overriding the toString() method.

The code to test the @JsonValue annotation is this.

ValueDemoBeanTest

   //package guru.springframework.blog.jsonannotation.domain.serialization;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import java.io.IOException;
import static org.hamcrest.Matchers.containsString;
import static org.hamcrest.Matchers.is;
import static org.hamcrest.Matchers.not;
import static org.hamcrest.core.IsEqual.equalTo;
import static org.junit.Assert.*;

public class ValueDemoBeanTest {
    private ObjectMapper objectMapper;
    @Before
    public void setUp() throws Exception{
        objectMapper = new ObjectMapper();
    }
    @After
    public void tearDown() throws Exception{
        objectMapper = null;
    }
    @Test
    public void testSerializingWithJsonValue() throws JsonProcessingException{
        String jsonString = objectMapper.writeValueAsString(new ValueDemoBean());
        System.out.println(jsonString);
        assertThat(jsonString, containsString("James Clark"));
        assertThat(jsonString, containsString("James Clark,123"));
    }
}

The output of running the test in IntelliJ is this.

As shown in the preceding figure, the Java object is serialized by Jackson by calling the defined method toJson(). The quotation marks are added by Jackson.

@JsonInclude

The @JsonInclude annotation is used to exclude properties or fields of a class under certain conditions. This is defined using the JsonInclude.Include enum. This enum contains constants, that determine whether or not to exclude the property. The constants are:

  • ALWAYS
  • NON_DEFAULT
  • NON_EMPTY
  • NON_NULL

Let us consider an example Java class that uses the @JsonInclude annotation.

IncludeDemoBean.java

   //package guru.springframework.blog.jsonannotation.domain.serialization;

import com.fasterxml.jackson.annotation.JsonInclude;

@JsonInclude(JsonInclude.Include.NON_EMPTY)
public class IncludeDemoBean {
    public long personId = 123L;
    public String  name = null;

    @Override
    public String toString() {
        return "IncludeDemoBean{" +
                "personId=" + personId +
                ", name='" + name + '\'' +
                '}';
    }
}

The test code to the @JsonInclude annotation is this.

@Test
public void testSerializingWithJsonInclude() throws JsonProcessingException{
  String jsonString = objectMapper.writeValueAsString(new IncludeDemoBean());
  System.out.println(jsonString);
  assertThat(jsonString, containsString("123"));
  assertThat(jsonString, not(containsString("name")));
}

The output of running the test in IntelliJ is this.
@JsonInclude Test Output

As shown in the preceding figure, the JSON string does not contain the property name as it is initialized to null.

@JsonGetter

The @JsonGetter annotation is used to customize the generated JSON keys. This is accomplished with the value argument of @JsonGetter. The value passed is the name that should be used as the JSON key.

Let us consider an example Java class that uses the @JsonGetter annotation.

GetterDemoBean.java

   //package guru.springframework.blog.jsonannotation.domain.serialization;

import com.fasterxml.jackson.annotation.JsonGetter;

public class GetterDemoBean {
    public long personId = 123L;
    public String  personName = "James Clark";

    @JsonGetter(value = "person-id")
    public long getPersonId() {
        return personId;
    }
    @JsonGetter(value = "person-name")
    public String getPersonName() {
        return personName;
    }
}

The code to test the @JsonGetter annotation is this.

@Test
public void testSerializingWithJsonGetter() throws JsonProcessingException {
  String jsonString = objectMapper.writeValueAsString(new GetterDemoBean());
  System.out.println(jsonString);
  assertThat(jsonString, containsString("person-id"));
  assertThat(jsonString, containsString("person-name"));
}

The output of running the test in IntelliJ is this.

As you can see in the example, the Java object is serialized with the property names that you defined using the @JsonGetter annotation. Without the annotations, the serialized JSON would contain the property names: personId and personName.

@JsonAnyGetter

The @JsonAnyGetter annotation can be used when you don’t want to declare a property or a method for every possible key in JSON. This annotation is used on the getter methods, which enables you to use a Map to hold all your properties that you want to serialize.

Let us consider an example Java class that uses the @JsonAnyGetter annotation.

AnyGetterDemoBean.java

   //package guru.springframework.blog.jsonannotation.domain.serialization;

import com.fasterxml.jackson.annotation.JsonAnyGetter;

import java.util.HashMap;
import java.util.Map;

public class AnyGetterDemoBean {
    public long personId = 123L;
    public String  personName = "James Clark";
    private Map properties = new HashMap();

    @JsonAnyGetter
    public Map getProperties() {
        return properties;
    }
}

The code to test the @JsonAnyGetter annotation is this.

@Test
public void testSerializingWithJsonAnyGetter() throws JsonProcessingException {
  AnyGetterDemoBean bean = new AnyGetterDemoBean();
  Map<String, String > stringMap = bean.getProperties();
  stringMap.put("emailId","[email protected]");
  stringMap.put("gender","male");
  String jsonString = objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(bean);
  System.out.println(jsonString);
  assertThat(jsonString, containsString("emailId"));
  assertThat(jsonString, containsString("gender"));
}

The output of running the test in IntelliJ is this.

@JsonAnyGetter Test Output
As you can see, all the properties are serialized as the properties of AnyGetterDemoBean object.

@JsonPropertyOrder

The @JsonPropertyOrder annotation tells Jackson to serialize the Java object to JSON, in the order specified as the arguments of the annotation. This annotation also allows partial ordering. The properties are first serialized in the order, in which they are found. Followed by any other properties not included in the annotation.

Let us consider an example of Java class that uses the @JsonPropertyOrder annotation.

PropertyOrderDemoBean.java

   //package guru.springframework.blog.jsonannotation.domain.serialization;

import com.fasterxml.jackson.annotation.JsonPropertyOrder;

@JsonPropertyOrder({"name", "personId"})
public class PropertyOrderDemoBean {
    public long personId = 123L;
    public String  name = "James Clark";
}

The test code to the @JsonPropertyOrder annotation is this.

@Test
public void testSerializingWithJsonPropertyOrder() throws JsonProcessingException {
  String jsonString = objectMapper.writeValueAsString(new PropertyOrderDemoBean());
  System.out.println(jsonString);
  assertThat(jsonString, containsString("123"));
  assertThat(jsonString, containsString("James Clark"));
}

The output of running the test in IntelliJ is this.
@JsonPropertyOrder Test Output

As you can see the result, the name property is first serialized before the personId. Without the @JsonPropertyOrder annotation, the object would have been serialized in the order found in the class.

@JsonRawValue

The @JsonRawValue annotation is used on methods and fields. It tells Jackson to serialize the field or property as declared. For example, if you have a String field in your Java class, the JSON value that Jackson generates is enclosed within quotes (” “). But when you annotate the field with @JsonRawValue, Jackson omits the quotes.

Let us consider an example Java class that explains the use of @JsonRawValue.

RawValueDemoBean.java

   //package guru.springframework.blog.jsonannotation.domain.serialization;

import com.fasterxml.jackson.annotation.JsonRawValue;

public class RawValueDemoBean {
    public long personId = 0;
    public String  name = "James Clark";
    @JsonRawValue
    public String address = "{\"doorNumber\": 1234, \"street\": \"phase-1\", " +
            "\"city\": \"New York\"}";
}

Here, the address field is a JSON string. This JSON string will be serialized as a part of the final JSON string of the RawValueDemoBean object.

The test code to test the @JsonRawValue annotation is this.

@Test
public void testSerializingWithJsonRawValue() throws JsonProcessingException {
  String jsonString = objectMapper.writeValueAsString(new RawValueDemoBean());
  System.out.println(jsonString);
  assertThat(jsonString, containsString("James Clark"));
  assertThat(jsonString, containsString("{\"doorNumber\": 1234, " +
          "\"street\": \"phase-1\", \"city\": \"New York\"}"));
}

The output of running the test in IntelliJ is this.

As you can see, the final JSON string of the Java object is generated as defined in the POJO class omitting the quotes.

@JsonSerialize

The @JsonSerialize annotation is used tell Jackson to use the declared custom serializer during the serialization of the field, which is marked with this annotation. Let us consider a POJO that uses the @JsonSerialize annotation.

SerializeDemoBean.java

   //package guru.springframework.blog.jsonannotation.domain.serialization;

import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import guru.springframework.blog.jsonannotation.domain.custom.CustomDateSerializer;

import java.util.Date;

public class SerializeDemoBean {
    public long personId = 123L;
    public String  name = "James Clark";
    @JsonSerialize(using = CustomDateSerializer.class)
    public Date activeDate;

    public void setActiveDate(Date activeDate) {
        this.activeDate = activeDate;
    }
}

Next, let us define a custom serializer that will serialize the activeDate field with a specific format.

CustomDateSerializer.java

   //package guru.springframework.blog.jsonannotation.domain.custom;

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.ser.std.StdSerializer;

import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class CustomDateSerializer extends StdSerializer{
    private static SimpleDateFormat simpleDateFormat =
            new SimpleDateFormat("dd-MM-yyyy hh:mm:ss");
    public CustomDateSerializer(){
        this(null);
    }
    public CustomDateSerializer(Class t) {
        super(t);
    }

    @Override
    public void serialize(Date date, JsonGenerator jsonGenerator,
                          SerializerProvider serializerProvider) throws IOException {
        jsonGenerator.writeString(simpleDateFormat.format(date));
    }
}

The code to test the @JsonSerialize annotation is this.

@Test
public void testSerializingWithJsonSerialize() throws JsonProcessingException,ParseException {
  SimpleDateFormat simpleDateFormat = new SimpleDateFormat("dd-MM-yyyy hh:mm:ss");
  String date = "29-09-2017 10:00:00";
  Date newDate = simpleDateFormat.parse(date);
  SerializeDemoBean bean = new SerializeDemoBean();
  bean.setActiveDate(newDate);
  String jsonString = objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(bean);
  System.out.println(jsonString);
  assertThat(jsonString, containsString("James Clark"));
  assertThat(jsonString, containsString("123"));
  assertThat(jsonString, containsString("29-09-2017 10:00:00"));
}

The output of running the test in IntelliJ is this.

@JsonRootName

The @JsonRootName annotation can be used to tell Jackson to wrap the object to be serialized with a top-level element. You can pass the name as a parameter to the @JsonRootName annotation. Let us consider that you want to wrap your serialized Java object with the key user.

Here is an example of Java class that uses the @JsonRootName annotation.

RootNameDemoBean.java

   //package guru.springframework.blog.jsonannotation.domain.serialization;

import com.fasterxml.jackson.annotation.JsonRootName;

@JsonRootName(value = "user")
public class RootNameDemoBean {
    public long personId = 0;
    public String  name = "James Clark";
}

The code to test the @JsonRootName annotation is this.

@Test
public void testSerializingWithJsonRootName() throws JsonProcessingException {
  String jsonString = objectMapper.enable(SerializationFeature.WRAP_ROOT_VALUE)
   .writeValueAsString(new RootNameDemoBean());
  System.out.println(jsonString);
  assertThat(jsonString, containsString("James Clark"));
  assertThat(jsonString, containsString("user"));
}

The output of running the test in IntelliJ is this.
@JsonRootName Test Output

As you can see, the fields personId and name are wrapped within the user, where the latter is the key, and the former is the value of the property of the generated JSON.

Deserialization Annotations

Let us explore the JSON annotations that can be used to control deserialization of JSON into POJOs. The Jackson deserialization annotations are:

  • @JsonSetter
  • @JsonAnySetter
  • @JsonCreator
  • @JacksonInject
  • @JsonDeserialize

@JsonSetter

The @JsonSetter annotation tells Jackson to deserialize the JSON into Java object using the name given in the setter method. Use this annotation when your JSON property names are different to the fields of the Java object class, and you want to map them.

A Java class that uses the @JsonSetter annotation is this.

SetterDemoBean.java

   //package guru.springframework.blog.jsonannotation.domain.deserialization;

import com.fasterxml.jackson.annotation.JsonSetter;

public class SetterDemoBean {
    public long personId = 0;
    public String  name = "James Clark";
    @JsonSetter("id")
    public void setPersonId(long personId) {
        this.personId = personId;
    }
    @Override
    public String toString() {
        return "SetterDemoBean{" +
                "personId=" + personId +
                ", name='" + name + '\'' +
                '}';
    }
}

The @JsonSetter annotation takes the name of the JSON key that must be mapped to the setter method.

The test code to test the @JsonSetter annotation is this.

@Test
public void testDeSerializingWithJsonSetter() throws IOException {
  String jsonString = "{\"id\": 231, \"name\": \"Mary Parker\"}";
  ObjectMapper mapper = new ObjectMapper();
  SetterDemoBean bean = objectMapper.readValue(jsonString, SetterDemoBean.class);
  System.out.println(bean);
  assertThat(bean.name, is(equalTo("Mary Parker")));
  assertThat(bean.personId, is(equalTo(231L)));
}

The output of running the test in IntelliJ is this.

@JsonSetter Test Output

As you can see, the JSON to be serialized has a property id. But no field in the POJO matches this property. Now how will Jackson read this JSON? Here is where the @JsonSetter annotation can be used to map the property id to the field personId. This annotation instructs Jackson to use a setter method for a given JSON property.

@JsonAnySetter

The @JsonAnySetter annotation is used on setter methods of a Map field. Sometimes, you may find some JSON values that cannot be mapped to the fields in the Java object class. In such a case, the @JsonAnySetter captures the data and stores them in a Map.

A Java class that uses the @JsonAnySetter annotation is this.

AnySetterDemoBean.java

   //package guru.springframework.blog.jsonannotation.domain.deserialization;

import com.fasterxml.jackson.annotation.JsonAnySetter;

import java.util.HashMap;
import java.util.Map;

public class AnySetterDemoBean {
    public long personId = 123L;
    public String  personName = "James Clark";
    private Map properties = new HashMap();

    @JsonAnySetter
    public void setProperties(String key, String value){
        properties.put(key, value);
    }

    @Override
    public String toString() {
        return "AnySetterDemoBean{" +
                "personId=" + personId +
                ", personName='" + personName + '\'' +
                ", properties=" + properties +
                '}';
    }
}

The test code to test the @JsonAnySetter annotation is this.

@Test
public void testDeSerializingWithJsonSetter() throws IOException {
  String jsonString = "{\"personId\": 231, \"personName\": \"Mary Parker\", \"emailId\": \"[email protected]\", \"gender\": \"female\"}";
  ObjectMapper mapper = new ObjectMapper();
  AnySetterDemoBean bean = objectMapper.readValue(jsonString, AnySetterDemoBean.class);
  System.out.println(bean);
  assertThat(bean.personName, is(equalTo("Mary Parker")));
  assertThat(bean.personId, is(equalTo(231L)));
  assertEquals("female", bean.getProperties().get("gender"));
}

The output of running the test in IntelliJ is this.
@JsonAnySetter Test Output

@JsonCreator

The @JsonCreator annotation tells Jackson that the JSON properties can be mapped to the fields of a constructor of the POJO. This is helpful when the JSON properties do not match with the names of the Java object field names. The @JsonCreator annotation can be used where @JsonSetter cannot be used. For example, immutable objects which need their initial values to be injected through constructors.

An example of Java class that uses the @JsonCreator annotation is this.

CreatorDemoBean.java

   //package guru.springframework.blog.jsonannotation.domain.deserialization;

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;

public class CreatorDemoBean {
    public long personId = 0;
    public String  name = "James Clark";

    @JsonCreator
    public CreatorDemoBean(@JsonProperty("id") long personId, @JsonProperty("name") String name) {
        this.personId = personId;
        this.name = name;
    }

    @Override
    public String toString() {
        return "CreatorDemoBean{" +
                "personId=" + personId +
                ", name='" + name + '\'' +
                '}';
    }
}

The test code to test the @JsonCreator annotation is this.

@Test
public void testDeSerializingWithJsonCreator() throws IOException {
  String jsonString = "{\"id\": 231, \"name\": \"Mary Parker\"}";
  ObjectMapper mapper = new ObjectMapper();
  CreatorDemoBean bean = objectMapper.readValue(jsonString, CreatorDemoBean.class);
  System.out.println(bean);
  assertThat(bean.name, is(equalTo("Mary Parker")));
  assertThat(bean.personId, is(equalTo(231L)));
}

The output of running the test in IntelliJ is this.

@JacksonInject

The @JacksonInject annotation is used to tell Jackson that particular values of the deserialized object will be injected and not read from the JSON string.

An example of Java class where the personId field is injected by Jackson is this.

JacksonInjectDemoBean.java

   //package guru.springframework.blog.jsonannotation.domain.deserialization;

import com.fasterxml.jackson.annotation.JacksonInject;

public class JacksonInjectDemoBean {
    @JacksonInject
    public long personId = 0;
    public String  name = "James Clark";

    @Override
    public String toString() {
        return "Jack