Spring Boot Basic Hands-on Exercises

Exercise 1: Build a RESTful Service with Multiple Endpoints

Objective: Create a RESTful service with multiple endpoints that handle different HTTP methods.

1. Create a UserController Class:

   • Define endpoints for creating, retrieving, updating, and deleting a user.

   • Use HTTP methods: GET, POST, PUT, DELETE.

package com.example.demo;

import org.springframework.web.bind.annotation.*;

import java.util.HashMap;
import java.util.Map;

@RestController
@RequestMapping("/users")
public class UserController {

    private Map<Integer, String> userDatabase = new HashMap<>();

    @PostMapping
    public String createUser(@RequestParam String name) {
        int id = userDatabase.size() + 1;
        userDatabase.put(id, name);
        return "User created with ID: " + id;
    }

    @GetMapping("/{id}")
    public String getUser(@PathVariable int id) {
        return userDatabase.getOrDefault(id, "User not found");
    }

    @PutMapping("/{id}")
    public String updateUser(@PathVariable int id, @RequestParam String name) {
        if (userDatabase.containsKey(id)) {
            userDatabase.put(id, name);
            return "User updated: " + name;
        } else {
            return "User not found";
        }
    }

    @DeleteMapping("/{id}")
    public String deleteUser(@PathVariable int id) {
        if (userDatabase.containsKey(id)) {
            userDatabase.remove(id);
            return "User deleted";
        } else {
            return "User not found";
        }
    }
}

2. Test Each Endpoint:

   • Use a tool like Postman or curl to test each endpoint.

   • POST /users?name=John to create a user.

   • GET /users/1 to retrieve a user.

   • PUT /users/1?name=Jane to update a user.

   • DELETE /users/1 to delete a user.

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Exercise 2: Configure Application Properties

Objective: Customize your Spring Boot application by modifying the application.properties file.

1. Change the Server Port:

   • Open src/main/resources/application.properties.

   • Set the application to run on port 8081.

properties

    server.port=8081

2. Add a Custom Property:

   • Define a custom application property to store a welcome message.

properties

    app.welcome-message=Welcome to my Spring Boot application!

3. Access Custom Property in Your Application:

   • Use @Value annotation to inject the property value into a controller.

java

    package com.example.demo;

    import org.springframework.beans.factory.annotation.Value;
    import org.springframework.web.bind.annotation.GetMapping;
    import org.springframework.web.bind.annotation.RestController;

    @RestController
    public class WelcomeController {

        @Value("${app.welcome-message}")
        private String welcomeMessage;

        @GetMapping("/welcome")
        public String welcome() {
            return welcomeMessage;
        }
    }

4. Test the Custom Endpoint:

   • Run your application and access http://localhost:8081/welcome to see the custom message.

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Exercise 3: Integrate Spring Data JPA

Objective: Set up a simple persistence layer using Spring Data JPA and an in-memory H2 database.

1. Add Dependencies:

   • Update your pom.xml to include Spring Data JPA and H2 Database dependencies.

xml

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
    <dependency>
        <groupId>com.h2database</groupId>
        <artifactId>h2</artifactId>
        <scope>runtime</scope>
    </dependency>

2. Configure H2 Database:

   • Add H2 configuration to application.properties.

properties

    spring.datasource.url=jdbc:h2:mem:testdb
    spring.datasource.driver-class-name=org.h2.Driver
    spring.datasource.username=sa
    spring.datasource.password=
    spring.h2.console.enabled=true

3. Create an Entity and Repository:

   • Define a User entity and a UserRepository.

java

    package com.example.demo;

    import javax.persistence.Entity;
    import javax.persistence.GeneratedValue;
    import javax.persistence.GenerationType;
    import javax.persistence.Id;

    @Entity
    public class User {
        @Id
        @GeneratedValue(strategy = GenerationType.AUTO)
        private Long id;
        private String name;

        // Getters and setters
    }

java

    package com.example.demo;

    import org.springframework.data.repository.CrudRepository;

    public interface UserRepository extends CrudRepository<User, Long> {
    }

4. Update UserController to Use Repository:

   • Modify the controller to persist users using UserRepository.

java

    package com.example.demo;

    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.web.bind.annotation.*;

    @RestController
    @RequestMapping("/users")
    public class UserController {

        @Autowired
        private UserRepository userRepository;

        @PostMapping
        public User createUser(@RequestParam String name) {
            User user = new User();
            user.setName(name);
            return userRepository.save(user);
        }

        @GetMapping("/{id}")
        public User getUser(@PathVariable Long id) {
            return userRepository.findById(id).orElse(null);
        }

        // Update and Delete methods using userRepository...
    }

5. Test Persistence:

   • Use Postman to create and retrieve users, and verify data persistence in the H2 console at http://localhost:8081/h2-console.

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These exercises should give you a solid foundation in creating and managing Spring Boot applications.