Boot

Spring Boot HATEOAS in REST API Example

Photo of Yatin YatinJune 26th, 2019Last Updated: June 26th, 2019
2 147 9 minutes read

Welcome readers, in this tutorial, we will implement the HATEOAS principle to REST resources in a spring boot application.

1. Introduction

  • Spring Boot is a module that provides rapid application development feature to the spring framework including auto-configuration, standalone-code, and production-ready code
  • It creates applications that are packaged as jar and are directly started using embedded servlet container (such as Tomcat, Jetty or Undertow). Thus, no need to deploy the war files
  • It simplifies the maven configuration by providing the starter template and helps to resolve the dependency conflicts. It automatically identifies the required dependencies and imports them in the application
  • It helps in removing the boilerplate code, extra annotations, and xml configurations
  • It provides a powerful batch processing and manages the rest endpoints
  • It provides an efficient jpa-starter library to effectively connect the application with the relational databases
  • It offers a Microservice architecture and cloud configuration that manages all the application related configuration properties in a centralized manner.

1.1 What is HATEOAS?

HATEOAS is known as Hypermedia As The Engine Of Application State. It is used to present the REST API information to the client allowing better API understanding and documentation. With each request returned from the server it tells the user what interactions he/she can do next as well as where he/she can navigate to. It is the final level of REST API and implements the standard verbs of POST, GET, PUT, PATCH, and DELETE.

Now, open the eclipse ide and let’s see how to implement this tutorial in spring boot.

2. Spring Boot HATEOAS in REST API Example

Here is a systematic guide for implementing this tutorial.

2.1 Tools Used

We are using Eclipse Kepler SR2, JDK 8 and Maven.

2.2 Project Structure

In case you are confused about where you should create the corresponding files or folder, let us review the project structure of the spring boot application.

Spring Boot HATEOAS - Application Structure
Fig. 1: Application Structure

2.3 Project Creation

This section will demonstrate how to create a Java-based Maven project with Eclipse. In Eclipse IDE, go to File -> New -> Maven Project.

Spring Boot HATEOAS - Maven Project
Fig. 2: Create a Maven Project

In the New Maven Project window, it will ask you to select a project location. By default, ‘Use default workspace location’ will be selected. Just click on the next button to proceed.

Spring Boot HATEOAS - Project Details
Fig. 3: Project Details

Select the Maven Web App archetype from the list of options and click next.

Spring Boot HATEOAS - Archetype Selection
Fig. 4: Archetype Selection

It will ask you to ‘Enter the group and the artifact id for the project’. We will input the details as shown in Fig. 5. The version number will be by default: 0.0.1-SNAPSHOT.

Spring Boot HATEOAS - Archetype Parameters
Fig. 5: Archetype Parameters

Click on Finish and the creation of the maven project will be completed. If you observe, it has downloaded the maven dependencies and a pom.xml file will be created for the project. Let’s start building the application!

3. Application Creation

Below are the steps involved in developing the application.

3.1 Maven Dependencies

Here, we specify the dependencies for Spring Hateoas and Faker. Maven will automatically resolve the other dependencies. The updated file will have the following code.

pom.xml

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<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>jcg.tutorial</groupId>
    <artifactId>Springboothateoastutorial</artifactId>
    <packaging>war</packaging>
    <version>0.0.1-SNAPSHOT</version>
 
    <name>Springboot Hateoas Tutorial</name>
    <url>http://maven.apache.org</url>
 
    <!-- Spring boot parent dependency jar -->
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.6.RELEASE</version>
    </parent>
 
    <dependencies>
        <!-- Spring boot web mvc jar. Automatically adds tomcat and jackson-databind
            jars. -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <!-- Spring boot library to support hateoas principle in rest api resources. -->
        <!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-hateoas -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-hateoas</artifactId>
        </dependency>
        <!-- Library that generates the dummy data for a new project. -->
        <dependency>
            <groupId>com.github.javafaker</groupId>
            <artifactId>javafaker</artifactId>
            <version>0.18</version>
        </dependency>
    </dependencies>
 
    <build>
        <finalName>Springboothateoastutorial</finalName>
    </build>
</project>

3.2 Configuration File

Create a new properties file at the Springboothateoastutorial/src/main/resources/ location and add the following code to it.

application.properties

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#Application startup port.
server.port: 9090
 
#To remove the null fields from the link attribute in the rest api response.
spring.jackson.default-property-inclusion=NON_NULL

3.3 Implementation Class

Add the following code the main class to bootstrap the application from the main method. Always remember, the entry point of the spring boot application is the class containing @SpringBootApplication annotation and the static main method.

Hateoasapplication.java

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package com.springboot.hateoas;
 
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
 
/**
 * @author yatinbatra
 *
 */
@SpringBootApplication  // This annotation boostraps and auto-configure the application.
public class Hateoasapplication {
 
    public static void main(String[] args) {
        SpringApplication.run(Hateoasapplication.class, args);
    }
}

3.4 Model Class

This POJO class defines the employee schema which we’ll use to implement this tutorial. Add the following code the model class.

Employee.java

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package com.springboot.hateoas.model;
 
import org.springframework.stereotype.Component;
 
// Model class.
@Component
public class Employee {
 
    private int id;
    private String name;
    private String mobile;
    private String address;
 
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getMobile() {
        return mobile;
    }
    public void setMobile(String mobile) {
        this.mobile = mobile;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
 
    @Override
    public String toString() {
        return "Employee [id=" + id + ", name=" + name + ", mobile=" + mobile + ", address=" + address + "]";
    }
}

3.5 Dao Class

The data-access-object class will prepare the mock data for the employee object. Add the following code to the Dao class.

Employeedaoimpl.java

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package com.springboot.hateoas.dao;
 
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;
 
import org.springframework.stereotype.Repository;
 
import com.github.javafaker.Faker;
import com.springboot.hateoas.model.Employee;
 
@Repository
public class Employeedaoimpl implements Employeedao {
 
    // Employee list.
    static List<Employee> employees;
 
    static {
        employees = new ArrayList<Employee>();
        // To generate the dummy identity for the employees.
        Faker faker = new Faker();
        // Creating dummy employees.
        for(int i=1; i<=10; i++) {
            Employee emp = new Employee();
            emp.setId(i);
            emp.setName(faker.name().fullName());
            emp.setMobile(faker.phoneNumber().cellPhone());
            emp.setAddress(faker.address().fullAddress());
            // Adding the employee records to the list.
            employees.add(emp);
        }
    }
 
    // Returning mocked employee details on the basis of employee id.
    @Override
    public Optional<Employee> getEmployeeByIdFromDb(int eid) {
        return employees.stream().filter((employee) -> employee.getId() == eid).findFirst();
    }
 
    // Returning mocked employee list.
    @Override
    public List<Employee> getAllEmployeesFromDb() {
        return employees;
    }
}

3.6 Service Class

The Service class calls the implementation methods of the DAO layer class. Add the following code to the service class.

Employeeservimpl.java

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package com.springboot.hateoas.service;
 
import java.util.List;
import java.util.Optional;
 
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
 
import com.springboot.hateoas.dao.Employeedao;
import com.springboot.hateoas.model.Employee;
 
@Service
public class Employeeservimpl implements Employeeserv {
 
    @Autowired
    Employeedao edao;
 
    // Service method to fetch employee details from the repository.
    @Override
    public Optional<Employee> getEmployeeByIdFromService(int eid) {
        return edao.getEmployeeByIdFromDb(eid);
    }
 
    // Service method to fetch the employee list.
    @Override
    public List<Employee> getAllEmployeesFromService() {
        return edao.getAllEmployeesFromDb();
    }
}

3.7 Controller Class

This Controller class consists of the request mapping methods that interacts with the Service and Dao layer to fetch the employee data. Add the following code to the controller class.

Employeecontroller.java

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package com.springboot.hateoas.controller;
 
import static org.springframework.hateoas.mvc.ControllerLinkBuilder.linkTo;
import static org.springframework.hateoas.mvc.ControllerLinkBuilder.methodOn;
 
import java.util.ArrayList;
import java.util.List;
 
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.hateoas.Resource;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
 
import com.springboot.hateoas.model.Employee;
import com.springboot.hateoas.service.Employeeserv;
import com.springboot.hateoas.util.Helper;
 
@RestController
@RequestMapping(value= "/employee")
public class Employeecontroller {
 
    @Autowired
    Employeeserv eserv;
 
    private final Logger logger = LoggerFactory.getLogger(this.getClass());
 
    // Fetch employee details on the basis of employee id.
    @GetMapping(value= "/get/{id}")
    public Resource<Employee> getEmployeeById(@PathVariable(name= "id") int eid) {
        logger.info("employee byId() invoked= " + eid);
 
        // Fetching employee details from the mocked service.
        Employee emp= eserv.getEmployeeByIdFromService(eid).get();
        logger.info("employee byId() found= " + emp.toString());
 
        // Creating links as per the hateoas principle.
        Resource<Employee> empres= new Resource<Employee>(emp);
        empres.add(linkTo(methodOn(Employeecontroller.class).getEmployeeById(eid)).withRel("_self"));
        return empres;
    }
 
    // Fetch all employees.
    @GetMapping(value= "/getall")
    public List<Resource<Employee>> getAllEmployees() {
        logger.info("employees all() invoked");
 
        // Fetching employees from the mocked service.
        List<Employee> employees = eserv.getAllEmployeesFromService();
        List<Resource<Employee>> empreslist= new ArrayList<Resource<Employee>>();
 
        // Creating links as per the hateoas principle.
        for (Employee employee : employees) {
            empreslist.add(Helper.getEmployeeResource(employee));
        }
 
        logger.info("employees all() found: " + empreslist.size());
        return empreslist;
    }
}

3.8 Helper Class

Add the following code the helper class for creating the HATEOAS link for the controller method.

Helper.java

package com.springboot.hateoas.util;

import static org.springframework.hateoas.mvc.ControllerLinkBuilder.linkTo;
import static org.springframework.hateoas.mvc.ControllerLinkBuilder.methodOn;

import org.springframework.hateoas.Resource;

import com.springboot.hateoas.controller.Employeecontroller;
import com.springboot.hateoas.model.Employee;

public class Helper {

	// Utility method to prepare the self link.
	public static Resource<Employee> getEmployeeResource(Employee employee) {
		Resource<Employee> resource = new Resource<Employee>(employee);
		resource.add(linkTo(methodOn(Employeecontroller.class).getEmployeeById(employee.getId())).withRel("_self"));
		return resource;
	}
}

4. Run the Applications

As we are ready with all the changes, let us compile the project and run the application as a java project.

  • Right click on the Hateoasapplication.java class, Run As -> Java Application. The application will be started on the 9090 port

Developers can debug the example and see what happens after every step. Enjoy!

5. Project Demo

We will test this sample application using a GUI based client. Launch the Postman tool and hit the different URL’s to fetch the data from the database and display the results in the JSON format.

5.1 Get all Employees

The HTTP Get method fetches the resources. Hit the following URL in the Postman tool to display the list of employees and the links in the JSON format.

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localhost:9090/employee/getall

Output

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[
    {
        "id": 1,
        "name": "Anjelica Hudson",
        "mobile": "864-889-3507",
        "address": "Apt. 318 035 Brown Mall, Lake Amaltown, KY 96909",
        "links": [
            {
                "rel": "_self",
                "href": "http://localhost:9090/employee/get/1"
            }
        ]
    },
    {
        "id": 2,
        "name": "Criselda Towne",
        "mobile": "(303) 343-0486",
        "address": "00621 Hintz Freeway, West Nida, AK 42886-0284",
        "links": [
            {
                "rel": "_self",
                "href": "http://localhost:9090/employee/get/2"
            }
        ]
    },
    {
        "id": 3,
        "name": "Chung Johns",
        "mobile": "209.424.0014",
        "address": "65888 Mia Grove, Lake Demetrius, NH 39781-6111",
        "links": [
            {
                "rel": "_self",
                "href": "http://localhost:9090/employee/get/3"
            }
        ]
    },
    {
        "id": 4,
        "name": "Lupe Bartell",
        "mobile": "788-049-6951",
        "address": "1950 Runolfsson Street, South Isaborough, MD 01756-5925",
        "links": [
            {
                "rel": "_self",
                "href": "http://localhost:9090/employee/get/4"
            }
        ]
    },
    {
        "id": 5,
        "name": "Randal Hirthe II",
        "mobile": "1-384-142-3230",
        "address": "6676 Manual Curve, Myongburgh, GA 54069",
        "links": [
            {
                "rel": "_self",
                "href": "http://localhost:9090/employee/get/5"
            }
        ]
    },
    {
        "id": 6,
        "name": "Daryl D'Amore",
        "mobile": "825.047.4049",
        "address": "2031 Patricia Views, South Erasmomouth, AZ 06034-3243",
        "links": [
            {
                "rel": "_self",
                "href": "http://localhost:9090/employee/get/6"
            }
        ]
    },
    {
        "id": 7,
        "name": "Joelle Kerluke",
        "mobile": "834.393.3339",
        "address": "22436 Vikki Green, Lake Marilee, TX 30069",
        "links": [
            {
                "rel": "_self",
                "href": "http://localhost:9090/employee/get/7"
            }
        ]
    },
    {
        "id": 8,
        "name": "Terese Hahn",
        "mobile": "1-846-627-3143",
        "address": "Apt. 993 73270 Marlin Coves, Wehnerberg, KS 00485-8780",
        "links": [
            {
                "rel": "_self",
                "href": "http://localhost:9090/employee/get/8"
            }
        ]
    },
    {
        "id": 9,
        "name": "Bryce Ebert DVM",
        "mobile": "(894) 479-0826",
        "address": "Apt. 798 3224 Bianca Cliffs, New Shalanda, SD 70088",
        "links": [
            {
                "rel": "_self",
                "href": "http://localhost:9090/employee/get/9"
            }
        ]
    },
    {
        "id": 10,
        "name": "Cherryl Heidenreich MD",
        "mobile": "652-528-5738",
        "address": "98135 Zulauf Land, East Charismouth, AK 24104-1016",
        "links": [
            {
                "rel": "_self",
                "href": "http://localhost:9090/employee/get/10"
            }
        ]
    }
]

5.2 Get Employee by Id

The HTTP Get method fetches the resources. Hit the following URL in the Postman tool to display the details of an employee and the link in the JSON format.

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localhost:9090/employee/get/1

Output

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{
    "id": 1,
    "name": "Anjelica Hudson",
    "mobile": "864-889-3507",
    "address": "Apt. 318 035 Brown Mall, Lake Amaltown, KY 96909",
    "_links": {
        "_self": {
            "href": "http://localhost:9090/employee/get/1"
        }
    }
}

That is all for this tutorial and I hope the article served you whatever you were looking for. Happy Learning and do not forget to share!

6. Conclusion

In this section, developers learned how to implement HATEOAS to the REST API in a spring boot application. Developers can download the sample application as an Eclipse project in the Downloads section.

7. Download the Eclipse Project

This was an example of implementing HATEOAS in the REST API.

Download
You can download the full source code of this example here: Spring Boot HATEOAS in REST API Example
Tags
Photo of Yatin YatinJune 26th, 2019Last Updated: June 26th, 2019
2 147 9 minutes read
Photo of Yatin

Yatin

An experience full-stack engineer well versed with Core Java, Spring/Springboot, MVC, Security, AOP, Frontend (Angular & React), and cloud technologies (such as AWS, GCP, Jenkins, Docker, K8).
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chason zhang
chason zhang
5 years ago

what is the difference between hateoas and swagger

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Yatin
Author
Yatin
5 years ago
Reply to  chason zhang

Swagger: Swagger aides in development across the entire API lifecycle, from design and documentation, to test and deployment. [Refer to swagger.io]

HATEOAS: Hypermedia as the Engine of Application State

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