❮❮ PREV NEXT ❯❯

Spring Boot - Read data from Database with Spring Data JPA

In the previous tutorial we have seen, how we can insert data to the H2 database. In this tutorial we will see, how we can read data from the database.

Below are the preliminary steps, we will follow :

Write the 'pom.xml',

<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>
	<groupId>org.example</groupId>
	<artifactId>springbootproject</artifactId>
	<version>1.0-SNAPSHOT</version>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.4.1</version>
	</parent>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
		<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>
	</dependencies>
</project>

Create the 'Student' class and annotate it with @Entity and @Id annotation, so that Spring Boot can understand that the contents of 'Student' class needs to be saved to the database.
```
@Entity
public class Student {
	@Id
	int roll;
	String name;
	int age;
	int className;
}
```

Create the controller class in Spring Boot. And along with 'insertStudent()' method, create a method called 'readStudent(...)' that reads the student details calling 'StudentService'.

@RestController
public class HelloWorldController {
	@Autowired
	StudentService studentService;
	@RequestMapping(method = RequestMethod.POST, value = "/students")
	public void insertStudent(@RequestBody Student student) {
		studentService.insertStudentDetails(student);
	}
	@RequestMapping(method = RequestMethod.GET, value = "/students")
	public List readStudent() {
		return studentService.readStudentDetails();
	}
}

Spring Boot - Read data from Database with Spring Data JPA

Next, in the 'StudentService' class, create the method 'readStudentDetails()' that reads the student details from H2 database.

@Service
public class StudentService {
	@Autowired
	StudentRepository studentRepository;
	public void insertStudentDetails(Student student) {
		studentRepository.save(student);
	}
	public List readStudentDetails() {
		List studentList = (List) studentRepository.findAll();
		return studentList;
	}
}

Now, in the readStudentDetails() method,

public List readStudentDetails() {
	List studentList = (List) studentRepository.findAll();
	return studentList;
}

We have used the findAll() method provided by Spring Data JPA to get all the details of the Student table from the H2 Database.

List studentList = (List) studentRepository.findAll();

And to get the findAll() method, we have taken the help of StudentRepository Interface that performs the CRUD operations.

StudentRepository

public interface StudentRepository extends CrudRepository<Student, Integer> {
}

Now, that we are done with the coding (In Spring Boot). Let us start Spring Boot application.

Then open Postman and try adding the details of John,

{"name": "John", "roll": 1, "age": 8, "className": 5}

To the endpoint

localhost:8080/students

Using the method as POST

And once the details of John is added. Let us try to retrieve the details of John from the H2 database.

Read the details from H2 Database

To retrieve the details of John from the H2 database, let us change the method to GET and hit the same endpoint (i.e. localhost:8080/students).

And we are able to retrieve the details of John from the database.