As a part of End to End REST Assured Tutorial, in this post, We will learn about how unknown properties during deserialization creates a problem and how can we avoid them using @JsonIgnorePropertoies.
@JsonIgnoreProperties Annotation Of Jackson API – Exclude Field Of Pojo From Serialization Or Deserialization Or Both
Since we are using Jackson API of Java for this example, make sure you have the latest dependency of Jackson Databind in your project classpath. I have used below Jackson dependency for this post:-
com.fasterxml.jackson.core jackson-databind 2.11.1
Before we go for an actual topic let’s understand the meaning of words “known” and “unknown” properties. If a property is included in a POJO class or if a property exists in POJO class then it is a known property for that POJO class. A property that is not known to a POJO class is unknown. Let’s see the behavior when a known property is missing during deserialization.
Suppose we have a POJO as below:-
package JacksonTutorials;
public class Employee {
// private variables or data members of pojo class
private String firstName;
private String lastName;
private String gender;
private int age;
private double salary;
private boolean married;
// Getter and setter methods
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getGender() {
return gender;
}
public void setGender(String gender) {
this.gender = gender;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public double getSalary() {
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
public boolean getMarried() {
return married;
}
public void setMarried(boolean married) {
this.married = married;
}
}
We will not include all known properties in JSON during deserialization as shown below:-
package JacksonTutorials;
import org.testng.annotations.Test;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
public class DeserializationWithMissingKnownProperties {
@Test
public void deserializationWithMissingKnownProperties() throws JsonMappingException, JsonProcessingException
{
String employeeString = "{\r\n" +
" \"firstName\" : \"Amod\",\r\n" +
" \"lastName\" : \"Mahajan\",\r\n" +
" \"gender\" : \"Male\"\r\n" +
"}";
ObjectMapper objectMapper = new ObjectMapper();
//objectMapper.con
Employee employee = objectMapper.readValue(employeeString, Employee.class);
System.out.println("Deserialization...");
System.out.println("First name :- "+employee.getFirstName());
System.out.println("Last name :- "+employee.getLastName());
System.out.println("Age :- "+employee.getAge());
System.out.println("Gender :- "+employee.getGender());
System.out.println("Salary :- "+employee.getSalary());
System.out.println("Married :- "+employee.getMarried());
}
}
Deserialization... First name :- Amod Last name :- Mahajan Age :- 0 Gender :- Male Salary :- 0.0 Married :- false
In JSON string three known properties are missing i.e. age, salary, and married. After deserialization, these fields have a default value. There is no error thrown for those missing values for known properties.
In the previous example, we had missing known properties in our JSON. Now we will have some additional unknown properties in JSON and observe behavior during deserialization.
package JacksonTutorials;
import org.testng.annotations.Test;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
public class DeserializationWithAdditionalUnknownProperties {
@Test
public void deserializationWithAdditionalUnknownProperties() throws JsonMappingException, JsonProcessingException
{
String employeeString = "{\r\n" +
" \"firstName\" : \"Amod\",\r\n" +
" \"lastName\" : \"Mahajan\",\r\n" +
" \"gender\" : \"Male\",\r\n" +
" \"age\" : 29,\r\n" +
" \"salary\" : 12323.56,\r\n" +
" \"married\" : false,\r\n" +
" \"fullName\" : \"Amod Mahajan Gupta\",\r\n" +
" \"eligibleForVote\" : false\r\n" +
"}";
ObjectMapper objectMapper = new ObjectMapper();
//objectMapper.con
Employee employee = objectMapper.readValue(employeeString, Employee.class);
System.out.println("Deserialization...");
System.out.println("First name :- "+employee.getFirstName());
System.out.println("Last name :- "+employee.getLastName());
System.out.println("Age :- "+employee.getAge());
System.out.println("Gender :- "+employee.getGender());
System.out.println("Salary :- "+employee.getSalary());
System.out.println("Married :- "+employee.getMarried());
}
}
There are some additional unknown fields that are present in JSON string i.e. fullName and eligibleForVote. When we try to deserialize above JSON string we get the output as below:-
[RemoteTestNG] detected TestNG version 7.0.1
FAILED: deserializationWithMissingKnownProperties
com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "fullName" (class JacksonTutorials.Employee), not marked as ignorable (6 known properties: "lastName", "married", "salary", "firstName", "age", "gender"])
at [Source: (String)"{
"firstName" : "Amod",
"lastName" : "Mahajan",
"gender" : "Male",
"age" : 29,
"salary" : 12323.56,
"married" : false,
"fullName" : "Amod Mahajan Gupta",
"eligibleForVote" : false
}"; line: 8, column: 17] (through reference chain: JacksonTutorials.Employee["fullName"])
As you can see deserialization failed at the encounter of first unknown property “fullName”. It also gives a list of all known properties.
We want that if there are any unknown fields in JSON then the deserialization process should ignore them. This we can achieve using a property called “ignoreUnknown” of @JsonIgnoreProperties annotation. It accepts a boolean value and the default value is false. To ignore unknown property we need to set it true at the class level.
package JacksonTutorials;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
@JsonIgnoreProperties(ignoreUnknown = true)
public class Employee {
// private variables or data members of pojo class
private String firstName;
private String lastName;
private String gender;
private int age;
private double salary;
private boolean married;
// Getter and setter methods
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getGender() {
return gender;
}
public void setGender(String gender) {
this.gender = gender;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public double getSalary() {
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
public boolean getMarried() {
return married;
}
public void setMarried(boolean married) {
this.married = married;
}
}
There is no change in the above deserialization code.
Deserialization... First name :- Amod Last name :- Mahajan Age :- 29 Gender :- Male Salary :- 12323.56 Married :- false
You can download/clone the above sample project from here.
If you have any doubt, feel free to comment below.If you like my posts, please like, comment, share and subscribe.#ThanksForReading
#HappyLearning