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Example of Complete Code

/pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<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/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>4.0.0-M1</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <groupId>com.in28minutes.springboot.rest.example</groupId>
    <artifactId>spring-boot-2-rest-service-basic</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>spring-boot-2-rest-service</name>
    <description>Spring Boot 2 and REST - Example Project</description>

    <properties>
        <java.version>21</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
    </build>
    
</project>

---

/src/main/java/com/in28minutes/springboot/rest/example/SpringBoot2RestServiceApplication.java

package com.in28minutes.springboot.rest.example;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SpringBoot2RestServiceApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringBoot2RestServiceApplication.class, args);
    }
}

---

/src/main/java/com/in28minutes/springboot/rest/example/student/Student.java

package com.in28minutes.springboot.rest.example.student;

import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.Id;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@NoArgsConstructor
@Entity
public class Student {
    @Id
    @GeneratedValue
    private Long id;

    private String name;

    private String passportNumber;

}

---

/src/main/java/com/in28minutes/springboot/rest/example/student/StudentNotFoundException.java

package com.in28minutes.springboot.rest.example.student;

public class StudentNotFoundException extends RuntimeException {

    public StudentNotFoundException(String exception) {
        super(exception);
    }

}

---

/src/main/java/com/in28minutes/springboot/rest/example/student/StudentRepository.java

package com.in28minutes.springboot.rest.example.student;

import org.jspecify.annotations.NonNull;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface StudentRepository extends JpaRepository<@NonNull Student, @NonNull Long> {

}

---

/src/main/java/com/in28minutes/springboot/rest/example/student/StudentResource.java

package com.in28minutes.springboot.rest.example.student;

import org.jspecify.annotations.NonNull;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.servlet.support.ServletUriComponentsBuilder;

import java.net.URI;
import java.util.List;
import java.util.Optional;

@RestController
public class StudentResource {

    private final StudentRepository studentRepository;

    public StudentResource(StudentRepository studentRepository) {
        this.studentRepository = studentRepository;
    }

    @GetMapping("/students")
    public List<Student> retrieveAllStudents() {
        return studentRepository.findAll();
    }

    @GetMapping("/students/{id}")
    public Student retrieveStudent(@PathVariable long id) {
        Optional<Student> student = studentRepository.findById(id);

        if (student.isEmpty())
            throw new StudentNotFoundException("id-" + id);

        return student.get();
    }

    @DeleteMapping("/students/{id}")
    public void deleteStudent(@PathVariable long id) {
        studentRepository.deleteById(id);
    }

    @PostMapping("/students")
    public ResponseEntity<@NonNull Student> createStudent(@RequestBody Student student) {
        var savedStudent = studentRepository.save(student);

        URI location = ServletUriComponentsBuilder.fromCurrentRequest()
                .path("/{id}")
                .buildAndExpand(savedStudent.getId())
                .toUri();

        return ResponseEntity.created(location)
                .build();

    }

    @PutMapping("/students/{id}")
    public ResponseEntity<@NonNull Student> updateStudent(@RequestBody Student student,
                                                          @PathVariable long id) {

        Optional<Student> studentDetails = studentRepository.findById(id);

        if (studentDetails.isEmpty())
            return ResponseEntity.notFound().build();

        student.setId(id);
        studentRepository.save(student);
        return ResponseEntity.noContent()
                .build();
    }
}

---

/src/main/resources/application.properties

# Enabling H2 Console
spring.h2.console.enabled=true
#Turn Statistics on
spring.jpa.properties.hibernate.generate_statistics=true
logging.level.org.hibernate.stat=debug
# Show all queries
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.format_sql=true
logging.level.org.hibernate.type=trace
spring.datasource.url=jdbc:h2:mem:testdb
spring.data.jpa.repositories.bootstrap-mode=default

---

/src/main/resources/data.sql

insert into student
values(10001,'Ranga', 'E1234567');

insert into student
values(10002,'Ravi', 'A1234568');

---

/src/main/resources/schema.sql

create table student
(
   id integer not null,
   name varchar(255) not null,
   passport_number varchar(255) not null,
   primary key(id)
);

---

/src/test/java/com/in28minutes/springboot/rest/example/SpringBoot2RestServiceApplicationTests.java

package com.in28minutes.springboot.rest.example;

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit.jupiter.SpringExtension;

@ExtendWith(SpringExtension.class)
@SpringBootTest
public class SpringBoot2RestServiceApplicationTests {

    @Test
    public void contextLoads() {
    }

}

---