Spring boot hello world example – Spring boot REST example

Spring boot is sub-project developed by developers of spring framework – to create stand-alone, production-grade application with minimum configuration possible. Spring boot applications are typically bundled as fat/uber jar files and can be deployed in any platform as a simple jar file. This is why spring boot applications are a good candidate for building microservices in java.

Let’s learn it by starting with a spring boot hello world example in eclipse step by step.

Table of Contents

1. Create spring boot hello world project template
2. Import spring boot project to eclipse
3. Spring boot auto configuration
4. Spring boot annotations
5. How to verify auto-configured beans by spring boot
6. Spring boot REST API example
7. Demo

1. Create spring boot hello world project template

To create a template for spring boot application, I will suggest to use http://start.spring.io/. Here, you can select all dependencies which you have currently in mind, and generate the project.

Spring Boot Options
Spring Boot Options

I have selected dependencies like Jersey, Spring Web, Spring HATEOAS, Spring JPA and Spring Security etc. You can add more dependencies after you have downloaded and imported the project or in future when requirements arise.

Generate Project button will generate a .zip file. Download and extract the file into your workspace.

2. Import spring boot project to eclipse

Next step is to import the generated project into your IDE. I have used eclipse for this purpose.

1) Import the spring boot project as existing maven project.

Import Existing Maven Project into Eclipse
Import Existing Maven Project into Eclipse

2) Select the pom.xml file to import it.

Select pom.xml file to import maven project
Select pom.xml file to import maven project

3) Project will be imported and the dependencies you added while generating zip file, will be automatically downloaded and added into classpath.

Imported Spring Boot Project Structure
Imported Spring Boot Project Structure

You have now successfully imported spring boot application. Now let’s see what it has already configured for you.

3. Spring boot auto configuration

With spring boot, good thing is when you add a dependency (e.g. Spring security), it make fair assumptions and automatically configure some defaults for you. So you can start immediately.

Spring Boot uses convention over configuration by scanning the dependent libraries available in the class path. For each spring-boot-starter-* dependency in the POM file, Spring Boot executes a default AutoConfiguration class. AutoConfiguration classes use the *AutoConfiguration lexical pattern, where * represents the library. For example, the autoconfiguration of spring security is done through SecurityAutoConfiguration.

At the same time, if you don’t want to use auto configuration for any project, it makes it very simple. Just use exclude = SecurityAutoConfiguration.class like below.

@SpringBootApplication (exclude = SecurityAutoConfiguration.class)
public class SpringBootDemoApplication {
   public static void main(String[] args) 
   {
      SpringApplication.run(SpringBootDemoApplication.class, args);
   }
}

It is also possible to override default configuration values using the application.properties file in src/main/resources folder.

4. Spring boot annotations

Now look at @SpringBootApplication annotation what it actually does.

4.1. @SpringBootApplication annotation

SpringBootApplication is defined as below:

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class))
public @interface SpringBootApplication 
{
   //more code
}

It adds 3 important annotations for application configuration purpose.

  1. @SpringBootConfiguration
    @Configuration
    public @interface SpringBootConfiguration 
    {
       //more code
    }
    

    This annotation adds @Configuration annotation to class which mark the class a source of bean definitions for the application context.

  2. @EnableAutoConfiguration

    This tells spring boot to auto configure important bean definitions based on added dependencies in pom.xml by start adding beans based on classpath settings, other beans, and various property settings.

  3. @ComponentScan

    This annotation tells spring boot to scan base package, find other beans/components and configure them as well.

5. How to verify auto-configured beans by spring boot

If you ever want to know what all beans have been automatically configured into your spring boot hello world application, then use this code and run it.

import java.util.Arrays;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.security.SecurityAutoConfiguration;
import org.springframework.context.ApplicationContext;

@SpringBootApplication (exclude = SecurityAutoConfiguration.class)
public class SpringBootDemoApplication {

   public static void main(String[] args) 
   {
      ApplicationContext ctx = SpringApplication.run(SpringBootDemoApplication.class, args);

        String[] beanNames = ctx.getBeanDefinitionNames();
        
        Arrays.sort(beanNames);
        
        for (String beanName : beanNames) 
        {
            System.out.println(beanName);
        }
   }
}

With my pom.xml file, it generates following beans names along with plenty of other springframework.boot.autoconfigure dependencies.

simpleControllerHandlerAdapter
sortResolver
spring.datasource-org.springframework.boot.autoconfigure.jdbc.DataSourceProperties
spring.hateoas-org.springframework.boot.autoconfigure.hateoas.HateoasProperties
spring.http.encoding-org.springframework.boot.autoconfigure.web.HttpEncodingProperties
spring.http.multipart-org.springframework.boot.autoconfigure.web.MultipartProperties
spring.info-org.springframework.boot.autoconfigure.info.ProjectInfoProperties
spring.jackson-org.springframework.boot.autoconfigure.jackson.JacksonProperties
spring.jpa-org.springframework.boot.autoconfigure.orm.jpa.JpaProperties
spring.jta-org.springframework.boot.autoconfigure.transaction.jta.JtaProperties
spring.mvc-org.springframework.boot.autoconfigure.web.WebMvcProperties
spring.resources-org.springframework.boot.autoconfigure.web.ResourceProperties
springBootDemoApplication
standardJacksonObjectMapperBuilderCustomizer
stringHttpMessageConverter
tomcatEmbeddedServletContainerFactory
tomcatPoolDataSourceMetadataProvider
transactionAttributeSource
transactionInterceptor
transactionManager
transactionTemplate
viewControllerHandlerMapping
viewResolver
websocketContainerCustomizer

6. Spring boot REST API example

Now it’s time to build any functionality into hello world application. You can add functionality as per your need, I am adding a REST API.

6.1. Create REST Controller

Create a package com.howtodoinjava.demo.controller and create rest controller inside it.

import java.util.ArrayList;
import java.util.List;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import com.howtodoinjava.demo.model.Employee;

@RestController
public class EmployeeController 
{
   @RequestMapping("/")
    public List<Employee> getEmployees() 
    {
      List<Employee> employeesList = new ArrayList<Employee>();
      employeesList.add(new Employee(1,"lokesh","gupta","howtodoinjava@gmail.com"));
      return employeesList;
    }
}

6.2. Create Model

Create model class Employee.

public class Employee {

   public Employee() {
      
   }
   public Employee(Integer id, String firstName, String lastName, String email) {
      super();
      this.id = id;
      this.firstName = firstName;
      this.lastName = lastName;
      this.email = email;
   }
   
   private Integer id;
   private String firstName;
   private String lastName;
   private String email;
   
   //getters and setters

   @Override
   public String toString() {
      return "Employee [id=" + id + ", firstName=" + firstName
            + ", lastName=" + lastName + ", email=" + email + "]";
   }
}

7. Spring boot hello world example demo

Now start the application by running main() method in SpringBootDemoApplication. It will start the embedded tomcat server on port 8080.

As we have configured the demo REST API URL to root URL, you can access it on http;//localhost:8080/ itself.

Verify Spring Boot REST API
Verify Spring Boot REST API

You will get the below response in testing tool or browser.

[{"id":1,"firstName":"lokesh","lastName":"gupta","email":"howtodoinjava@gmail.com"}]

That’s all for this spring boot rest hello world example with simple rest api example.

Drop me your questions related to how to create spring boot project in eclipse using maven.

Happy Learning !!

Resources:

Spring Boot Project
http://start.spring.io/
@SpringBootApplication Annotation

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27 thoughts on “Spring boot hello world example – Spring boot REST example”

  1. This example provides novices with steps to follow at ease. However, these two things may need to mention to get desired result:
    1) In initial creating template phase, picking Spring Web only as dependency would suffice;
    2) In Employee class, one needs to add getters and setters for all private attributes defined there (all such methods were put in the associated file from downloadable)
    Thanks

  2. i use below line of code to avoid the run time exception, its working fine
    @SpringBootApplication(exclude={DataSourceAutoConfiguration.class, SecurityAutoConfiguration.class})

    But am getting below response

    {
      "timestamp": "2020-01-17T13:06:12.158+0000",
      "status": 404,
      "error": "Not Found",
      "message": "No message available",
      "path": "/"
    }
  3. Hi Lokesh,
    I hope you are well. I am a very beginner.
    I am using STS 4 doing this exercise.
    I have experienced two problems when doing this exercise:
    1. at this step from your work: 5. How to verify auto-configured beans by spring boot.
    I use your code and there are two error message shows:
    a: The import org.springframework.boot.autoconfigure.security.SecurityAutoConfiguration cannot be resolved (this is from one of the import )
    b: org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration (this is from exclude = SecurityAutoConfiguration.class)
    So I didn’t run this code. Would you know what have I done wrong?

    2. I have followed your work till 7. Spring boot hello world example demo. and I run the springbootdemo on STS Boot Dashboard and right click it and click open web browser. It took me to the http://localhost:8080/login. Then request me to sign in with name and password. I used the name from console which is default and copied the generated security password that also from console but still can’t sign in. Is this normal? Thus for now I didn’t get the result as what you get above.

    Would you please help. I would be much appreciated.

    • Hi Lokesh,

      I guess it is to do with the Security dependencies that’s why I need to sign in. I don’t know what is the correct sign in detail as I used the name and password created from console and It won’t work. So I have tried to delete the Security dependencies and run the application again. It took me to http://localhost:8080/ this time without sign in page, but shows The webpage cannot be found.

      Any advise would be help. Thanks.

  4. After removing “spring-boot-starter-security” dependency from pom.xml also. It is asking for username and password.

  5. Do I need to update application.properties? I am using Spring boot 2 and on startup get the exception:

    ConfigServletWebServerApplicationContext : Exception encountered during context initialization – cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name ‘org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaConfiguration’: Unsatisfied dependency expressed through constructor parameter 0; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name ‘dataSource’ defined in class path resource [org/springframework/boot/autoconfigure/jdbc/DataSourceConfiguration$Hikari.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.zaxxer.hikari.HikariDataSource]: Factory method ‘dataSource’ threw exception; nested exception is org.springframework.boot.autoconfigure.jdbc.DataSourceProperties$DataSourceBeanCreationException: Failed to determine a suitable driver class

    Could you please guide?

  6. Hello,

    Your site is amazing and post was just what a need.

    Always that a do a Post request my postman got a 403 status. Its only works when security is enable.

    How could i work with security in this example?

    Thank for your help,
    Adolpho

  7. How do it for multiple objects in json and also i tried to consume for existing multiple object from json but i am getting array exception.

    please post the demo on consuming rest api for multiple objects

  8. i am getting login page requesting username and password ? What is the username & password to login to application.

      • yes its working once i commented the spring-boot-starter-security dependency and maven clean and install
        thanks

        • Hi Hareesh,

          I have deleted the security dependency from pom.xml and run again, it tells The webpage cannot be found. How did you get yours working? Thanks.

    • Hi,
      I faced the same issue and took me some time to resolve this. I am using Spring boot 2.3.0 version.
      Commenting pring-boot-starter-security in pom.xml didn’t help me, neither “security.basic.enabled=false”
      Anyways, what i did was created a new Configuration class “WebSecurityConfig.java” , like so and allowed all requests.

      Also maybe for some of you, this cud help “Spring Boot 2.0 disable default security”- Stack Overflow

      @Configuration
      @EnableWebSecurity
      public class WebSecurityConfig extends WebSecurityConfigurerAdapter{
      @Override
      protected void configure(HttpSecurity http) throws Exception{
      http.authorizeRequests().antMatchers(“/”).permitAll();
      }
      }

  9. Hi Lokesh ,
    Which book or web link is good for becoming expert in spring boot. I having good knowledge of it.
    Thanks and Regards,
    Vikram
    9028163305

  10. Hi Lokesh,

    I am new to Spring boot thanks for your efforts putting this tutorial.

    Can we create parent child modules with spring boot?
    e.g. My student project have web-module that creates war file and it uses,
    created jar from service/data module and business module
    or
    We create/add them separately and update pom file?

    Thanks

  11. Hi Lokesh,

    I have requirement in our project that, We need to integrate our spring application with Kibana(ELK) to get total response and request time for API request Method (GET,PUT). Currently we are using Splunk. Can you please let me know if have any idea in this ?, By the way our project is Spring boot.

    • Hello Likesh,
      thank you for the nice and helpfull tutorial!

      On sending one request I got this error: “No converter found for return value of type”
      To solve this, I needed to add public getters for all fields of the class Employee.
      I hope this helps anyone…

      BR

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