Difference Between @Controller and @Service Annotation in Spring

Spring Annotations are a form of metadata that provides data about a program. Annotations are used to provide supplemental information about a program. It does not have a direct effect on the operation of the code they annotate. It does not change the action of the compiled program. 

Spring @Controller Annotation

Spring @Controller annotation is a specialization of @Component annotation. The @Controller annotation indicates that a particular class serves the role of a controller. Spring Controller annotation is typically used in combination with annotated handler methods based on the @RequestMapping annotation. It can be applied to classes only. It’s used to mark a class as a web request handler. It’s mostly used with Spring MVC applications. This annotation acts as a stereotype for the annotated class, indicating its role. The dispatcher scans such annotated classes for mapped methods and detects @RequestMapping annotations.

Implementation: Project 

Step 1: Create a Simple Spring Boot Project

Refer to this article Create and Setup Spring Boot Project in Eclipse IDE and create a simple spring boot project. 

Step 2: Add the spring-web dependency in your pom.xml file. Go to the pom.xml file inside your project and add the following spring-web dependency.

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

Step 3: In your project create one package and name the package "controller". In the controller, the package creates a class and name it as DemoController. This is going to be our final project structure.

// Java Program to Illustrate DemoController File

// Importing package in this code module
package com.example.demo.controller;
// Importing required classes
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

// Annotation
@Controller
// Main class
public class DemoController {

    @RequestMapping("/hello")
    @ResponseBody

    // Method
    public String helloGFG()
    {
        return "Hello GeeksForGeeks";
    }
}

We have used the below annotations in our controller layer. Here in this example, the URI path is /hello.

• @Controller: This is used to specify the controller.
• @RequestMapping: This is used to map to the Spring MVC controller method.
• @ResponseBody: Used to bind the HTTP response body with a domain object in the return type.

Step 4: Now, our controller is ready. Let's run our application inside the DemoApplication.java file. There is no need to change anything inside the DemoApplication.java file.

Example 

// Java Program to Illustrate DemoApplication File

// Importing package in this code module
package com.example.demo;
// Importing required classes
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

// Annotation
@SpringBootApplication

// Main class
public class DemoApplication {

    // Main driver method
    public static void main(String[] args)
    {
        SpringApplication.run(DemoApplication.class, args);
    }
}

Output:

Tip: Try Tomcat URL depicted in below media, which is running on http://localhost:8989/hello

Spring @Service Annotation

In an application, the business logic resides within the service layer so we use the @Service Annotation to indicate that a class belongs to that layer. It is also a specialization of @Component Annotation like the @Repository Annotation. One most important thing about the @Service Annotation is it can be applied only to classes. It is used to mark the class as a service provider. So overall @Service annotation is used with classes that provide some business functionalities. Spring context will autodetect these classes when annotation-based configuration and classpath scanning is used.

Example: Project

Step 1: Create a Simple Spring Boot Project.

tip: Do refer to this article prior to adhering forward on how to create and setup Spring Boot Project in Eclipse IDE and create a simple spring boot project. 

Step 2: Add the spring-context dependency in your pom.xml file. Go to the pom.xml file inside your project and add the following spring-context dependency.

File: pom.xml

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-context</artifactId>
    <version>5.3.13</version>
</dependency>

Step 3: In your project create one package and name the package as "service". In the service, the package creates a class and name it "MyServiceClass". 

File: MyServiceClass

// Java Program to Illustrate MyServiceClass

// Importing package module to code module
package com.example.demo.service;
// Importing required classes
import org.springframework.stereotype.Service;

// Annotation
@Service

// Class
public class MyServiceClass {

    // Method
    // To compute factorial
    public int factorial(int n)
    {
        // Base case
        if (n == 0)
            return 1;

        // Returning factorial of input number
        return n * factorial(n - 1);
    }
}

Code explanation: 

From the above code, we can easily perceive that it’s a simple java class that provides functionalities to calculate the factorial of a number. So we can call it a service provider. We have annotated it with @Service annotation so that spring-context can autodetect it and we can get its instance from the context.

Step 4: Spring Repository Test

So now our Spring Repository is ready, let’s test it out. Go to the DemoApplication.java file and refer to the below code.

File: DemoApplication.java

// Java Program to Illustrate DemoApplication

// Importing package module to code fragment
package com.example.demo;
// Importing required classes
import com.example.demo.service.MyServiceClass;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

// Annotation
@SpringBootApplication

// Main class
public class DemoApplication {

    // Main driver method
    public static void main(String[] args)
    {
        // Creating context of
        // AnnotationConfigApplicationContext class
        AnnotationConfigApplicationContext context
            = new AnnotationConfigApplicationContext();

        context.scan("com.example.demo");

        context.refresh();

        MyServiceClass myServiceClass
            = context.getBean(MyServiceClass.class);

        // Testing the factorial method
        int factorialOf5 = myServiceClass.factorial(5);
        System.out.println("Factorial of 5 is: "
                           + factorialOf5);

        // Closing the spring context
        // using close() method
        context.close();
    }
}

Output:

Lastly, let us do discuss the differences between @Controller annotation and @Service annotation.