Jackson ObjectMapper Tutorial –

Jackson ObjectMapper is the fastest and most feature-rich way to map objects in Java. With this tutorial, we will be covering how to import a JSON file into an object model with Jackson.

The “jackson objectmapper readvalue” is a tutorial that will teach you how to use the Jackson ObjectMapper. The tutorial will teach you how to parse JSON data from a file or from an HTTP request.

In this article, you’ll learn how to serialize and deserialize Java objects using Jackson ObjectMapper and a Spring Boot application.

Overview

The JSON format is one of the most widely used data transport and exchange formats on the internet today. JSON is supported as an input and output structure by almost all RESTful web services. Furthermore, it is commonly utilized to store records by numerous NoSQL databases such as MongoDB.

In this article, we’ll go over the basics of Jackson ObjectMapper and how to serialize JSON requests and replies in a Spring Boot application using different Jackson setups.

Preparation:

I’ll be utilizing the following tools in this example:

  • JDK 1.8
  • Idea for Intellij IDE
  • Maven
  • Version 2.5.5 of the Springboot application
  • Lombok

The following is the post’s structure:

This blog’s growth plan will be as follows:

  1. Setup of the Project
  2. Jackson ObjectMapper is a new tool from Jackson.

Step 1: Get the project started. 

We’ll start by building a basic Spring Boot application. To construct an initial project template, go to the Spring Initializr website.

We’ll create the following sub-packages under our main package ‘com.appsdeveloperblog.ObjectMapperTutorial’ after loading the project into the IDE:

  • Config: The configuration class config.java is located in this folder.
  • Controller: The file ‘EmployeeController.java’ in this folder includes the class ‘EmployeeController.java’.
  • Employee DTO structure with filename ‘Employee.java’ is included in this folder.

The ultimate structure of the project will be as follows:

 

We’ll go through the components of config and controller classes in depth in the next sections.

Dependencies in Maven

In our pom.xml, we’ll just add spring-boot-starter-web and Lombok dependencies. Because Spring Boot currently manages dependencies for multiple Jackson modules, this isn’t a problem. As an example,

  • jackson-core
  • jackson-databind
  • jackson-annotations

As a result, we don’t need to include it directly in pom.xml.

4.0.0org.springframework.bootspring-boot-starter-parent2.5.0com.appsdeveloperblog.ObjectMapperTutorialSpring-boot-custom-JSON0.0.1-SNAPSHOT Tutorial for Jackson ObjectMapper Jackson ObjectMapper Tutorial111111org.springframework.bootspring-boot-starter-weborg.projectlomboklombok1.18.20org.springframework.bootspring-boot-maven-pluginorg.projectlomboklombok1.18.20org.springframework.bootspring-boot-maven-plugin

Employee POJO should be created.

Now we’ll create a basic POJO class that we’ll use in our app. The “Employee” object is used here, containing basic member attributes such as ID, FirstName, and so on.

The code for ‘Employee.java’ may be found here.

import lombok.AllArgsConstructor; import lombok.Getter; import lombok.Setter; import java.io.Serializable; import java.util.ArrayList; import java.util.List; @AllArgsConstructor @NoArgsConstructor @Getter @Setter; @AllArgsConstructor @NoArgsConstructor @Getter @Setter; @AllArgsConstructor @NoArgsConstructor public class Employee; private int id; private String firstName; private String jobTitle; private String gender; public static java.util.List; public static java.util.List; public static java.util.List; public static java.util.List; public static java.util.List; public static java.util. getEmployee() employees.add(new Employee(1, “damian”, “Developer”, “Male”)); employees.add(new Employee(2, “noel”, “Developer”, “Male”); employees.add(new Employee(3, “amena”, “CEO”, “Female”)); employees.add(new Employee(4, “eugenia”, “Developer”, “Male”)); employees.add(new Employee(5, “mckee

Make a controller

The controller for GET and POST services is next. The following is the whole source code for “EmployeeController.java”:

import com.appsdeveloperblog.ObjectMapperTutorial.model.Employee; import org.springframework.web.bind.annotation.*; import java.util.List; package com.appsdeveloperblog.ObjectMapperTutorial.controller; import com.appsdeveloperblog.ObjectMapperTutorial.model.Employee; import org.springframework.web.bind.annotation.* RestController is a public class created by @RestController. @RequestMapping(“/getEmployees”) public List EmployeeController Employee.getEmployee(); getEmployees() return Employee.getEmployee(); @ResponseBody public Employee @PostMapping(“/createEmployees”) createProduct(@RequestBody Employee employee, @RequestBody Employee employee, @RequestBody Employee employee, @Request employee.setID(employee.getID() + 100); employee.setJobTitle(“software ” + employee.getJobTitle()); return employee; /* sample logic to illustrate employee object enhancement*/ employee.setID(employee.getID() + 100); employee.setJobTitle(“software ” + employee.getJobTitle()); return employee;

Application Execution

Now we can start the Spring Boot application by creating the main class:

@SpringBootApplication public class SpringBootCustomJsonApplication public static void main(String[] args) SpringApplication.run(SpringBootCustomJsonApplication.class, args); @SpringBootApplication public class SpringBootCustomJsonApplication public static void main(String[] args) SpringApplication.run(SpringBoot

Finally, we’ll start our program by typing the following command or using the IDE’s ‘Run’ button. The application began on Tomcat port 8080, as you can see.

To test GET, just type in the following URL:

http://localhost:8080/getEmployees

As a result, we will get the following response:

1634998448_288_Jackson-ObjectMapper-Tutorial

Similarly, if we use Postman to make a POST request to the below URL, we should obtain the following answer.

http://localhost:8080/createEmployees

The following is an example of a request and answer.

1634998449_355_Jackson-ObjectMapper-Tutorial

 

Now we’ll look at how we can use the Jackson object mapper in our project to transform a DTO object to a JSON object and vice versa.

Step 2: Jackson ObjectMapper is introduced.

Even though we did not construct an instance of ObjectMapper in the previous example, we saw a rudimentary version of its capability. Let’s have a look at how things went down in order:

During an HTTP GET request, the following happens:

  1. We used the browser to make a GET request to “/getEmployees.”
  2. Employee DTO objects were returned by the controller.
  3. Internally, a Spring ObjectMapper instance was built, and the employee objects were transformed to JSON.

Because spring transformed the list of employee objects to JSON, this process is known as serialization.

During a POST request via HTTP:

  1. We use Postman to make a POST request to “/createEmployees” with a JSON request payload.
  2. Spring automatically turned the requested JSON into an Employee DTO object in the Controller.
  3. Employee DTO was changed and returned to the controller according to logic.
  4. Spring transformed the received “Employee” object DTO to JSON once again and delivered it to the client as a JSON response.

Deserialization is the process of turning a JSON payload to a Java object.

ObjectMapper may be customized.

We’ll learn how to adjust the default ObjectMapper behavior so that we may change the Serialization/Deserialization depending on our needs in this part.

1st example:

To begin, we’ll create a bean named “Config.java” in our config subdirectory.

import com.fasterxml.jackson.annotation.JsonInclude; import com.fasterxml.jackson.databind.ObjectMapper; import com.fasterxml.jackson.databind.PropertyNamingStrategy; import org.springframework.context.annotation; import com.fasterxml.jackson.databind.PropertyNamingStrategy; import @Configuration class; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Primary; import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder; @Configuration class; @Configuration class; @Configuration class; @Configuration class; @Configuration class; @Configuration class; @Configuration class; @Configuration class; @Configuration class; @ @Bean @Primary public ObjectMapper customJson() return new Jackson2ObjectMapperBuilder(). WebConfig @Bean @Primary public ObjectMapper customJson() return new Jackson2ObjectMapperBuilder(). true; indentOutput(); indentOutput(); indentOutput(); indentOutput() .propertyNamingStrategy(PropertyNamingStrategy.UPPER CAMEL CASE).build(); serializationInclusion(JsonInclude.Include.NON NULL).propertyNamingStrategy(PropertyNamingStrategy.UPPER CAMEL CASE).build();

Now, if we rerun our app and type GET /getEmployees, we’ll receive the following result.

1634998450_362_Jackson-ObjectMapper-Tutorial

 

We’ve set ObjectMapper to indent the output answer, as you may have observed. We’ve also asked ObjectMapper to change all names to higher case. As a result, following POJO conversion, all keys are now in camelcase format, and the output is also indented.

Explanation 2:

We sometimes have a use-case when the API sends more field JSON than the internal java object structure expects. We may utilize the ObjectMapper functionality in this situation to have tougher checks during serialization and raise exceptions in such circumstances.

To do this, we may make the following changes to our config class:

import com.appsdeveloperblog.ObjectMapperTutorial.config; import com.fasterxml.jackson.annotation.JsonInclude; import com.fasterxml.jackson.databind.DeserializationFeature; import com.fasterxml.jackson.databind.ObjectMapper; import com.fasterxml.jackson.databind.PropertyNamingStrategy; import

The object mapper property “DeserializationFeature.FAIL ON UNKNOWN PROPERTIES” has now been added. As a result, ObjectMapper will give an error if any JSON keys are sent that are not in the Employee object, as seen below.

1634998451_389_Jackson-ObjectMapper-Tutorial

 

The console error is as follows:

17:17:45.343 2021-10-21 WARNING: WARNING: WARNING: WARNING: WARNING .w.s.m.s.DefaultHandlerException [nio-8080-exec-4] [org.springframework.http.converter.HttpMessageNotReadable] [org.springframework.http.converter.HttpMessageNotReadable] [org.springframework.http.converter.HttpMessageNotReadable Exception: JSON parse error: Unrecognized field “Name” (class com.appsdeveloperblog.ObjectMapperTutorial.model.Employee), not designated as ignorable; nested exception is com.fasterxml.jackson.databind.exc; nested exception is com.fasterxml.jackson.databind.exc; nested exception is com.fasterxml. UnrecognizedProperty Exception: Unknown field “Name” (class com.appsdeveloperblog.ObjectMapperTutorial.model.Employee), not designated as ignorable (4 known properties: “gender”, “firstName”, “jobTitle”, “id”) at [Source: (PushbackInputStream); line: 2, column: 14] at [Source: (PushbackInputStream); line: 2, column: 14] (com.appsdeveloperblog.ObjectMapperTutorial.model.Employee[“Name”])]

There are numerous similar attributes on ObjectMapper that may be defined; the official Javadoc for Jackson-databind features can be found here.

Directly interacting with ObjectMapper

We usually don’t need to explicitly build the ObjectMapper object using Spring Boot since the framework does it for us. We should try to avoid manually constructing ObjectMapper objects as much as possible. However, if we need to manually build an ObjectMapper object to serialize and deserialize our own data, we may do so by following the steps below.

This example demonstrates how to convert a Java object to a JSON String using the JACKSON API. For our conversion, we may make advantage of the Jackson API’s ObjectMapper class.

  • Serialization: To convert a Java object to JSON, use writeValueAsString().

mapper = new ObjectMapper(); ObjectMapper mapper = new ObjectMapper(); ObjectMapper mapper = new ObjectMap try System.out = mapper.writeValueAsString(cat); String json = mapper.writeValueAsString(cat); /System.out. println(“ResultingJSONstring = ” + json); println(json); println(json); println(json); println( take note of (JsonProcessingException e) e.printStackTrace(); e.printStackTrace(); e.printStackTrace(); e.printStackT

  • Deserialization: To convert JSON to a Java object, use readValue().

emp = new Employee(); emp.setID(200); emp.setfirstName(“David”); emp.setjobTitle(“Associate”); emp.gender(“Male”); emp.gender(“Male”); emp.gender(“Male”); emp.gender(“Male”); emp.gender(“Male”); emp.gender(“Male”); emp.gender( try mapper = new ObjectMapper(); ObjectMapper mapper = new ObjectMapper(); ObjectMapper mapper = new ObjectMapper System.out.println(“ResultingJSONstring = ” + json); /System.out.println(json); json = mapper.writeValueAsString(Employee); json = mapper.writeValueAsString(Employee); json = mapper.writeValueAsString(Employee); json = mapper.writeValue e.printStackTrace(); catch (JsonProcessingException e)

Conclusion

We learnt about ObjectMapper and its features in this lesson. To make the process easier, we looked into creating our own own serializer and deserializer. I hope you found this tutorial useful.

The “jackson object to json” is a tutorial that will teach you how to use the Jackson ObjectMapper. The tutorial includes an example of using the ObjectMapper with Spring Boot.

Frequently Asked Questions

What is ObjectMapper class in Jackson?

A: ObjectMapper is a class that registers to be notified when an object has been created or destroyed.

Is Jackson an ObjectMapper Threadsafe?

A: Jackson is not an ObjectMapper Threadsafe, but it can be used in a thread-safe manner.

What does ObjectMapper readValue do?

A: This command will read a value from a file and assign that value to the specified property of an object.

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