SpringBoot CRUD Operations with H2 In Memory Database

1. Create a Springboot project using https://start.spring.io/

Choose Spring Web,H2 Database, Spring Data JPA and Lombok dependencies

2 Add below configurations in the application.properties.

In the properties file provide below configurations to enable H2 database

server.port=9090

spring.datasource.url=jdbc:h2:mem:testdb
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=

spring.jpa.show-sql=true
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.H2Dialect
spring.jpa.hibernate.ddl-auto= update
spring.h2.console.enabled=true
# default path: h2-console
spring.h2.console.path=/h2-ui

3. Create Model classes as shown below

package com.example.SpringBootCRUDH2.model;

import jakarta.persistence.*;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;

@Entity
@Table(name = "Books")
@Data
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class Book {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    private String title;
    private String author;
}

4. Create JPA Repository as follows

package com.example.SpringBootCRUDH2.repo;

import com.example.SpringBootCRUDH2.model.Book;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;


@Repository
public interface BookRepo extends JpaRepository<Book, Long> {
}

5. Create Controller class as follows

package com.example.SpringBootCRUDH2.controller;

import com.example.SpringBootCRUDH2.model.Book;
import com.example.SpringBootCRUDH2.repo.BookRepo;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;

import java.util.ArrayList;
import java.util.List;
import java.util.Optional;

@RestController
public class BookController {


    @Autowired
    private BookRepo bookRepo;

    @GetMapping("/books")
    public ResponseEntity<List<Book>> getAllBooks() {
        try {
            List<Book> bookList = new ArrayList<>();
            bookRepo.findAll().forEach(bookList::add);

            if (bookList.isEmpty()) {
                return new ResponseEntity<>(bookList, HttpStatus.NO_CONTENT);
            }

            return new ResponseEntity<>(bookList,HttpStatus.OK);
        } catch (Exception e) {
            return new ResponseEntity<>(HttpStatus.INTERNAL_SERVER_ERROR);
        }

    }

    @GetMapping("/books/{id}")
    public ResponseEntity<Book> getBookById(@PathVariable Long id) {

        Optional<Book> bookData = bookRepo.findById(id);
        if (bookData.isPresent()) {
            return new ResponseEntity<>(bookData.get(), HttpStatus.OK);
        }
        return new ResponseEntity<>(HttpStatus.NOT_FOUND);
    }

    @PostMapping("/book")
    public ResponseEntity<Book> addBook(@RequestBody Book book) {
        Book bookObj = bookRepo.save(book);


        return new ResponseEntity<>(bookObj, HttpStatus.OK);
    }

    @PutMapping("/books/{id}")
    public ResponseEntity<Book> updateBookById(@PathVariable Long id, @RequestBody Book newBookData) {
        Optional<Book> oldBookData = bookRepo.findById(id);
        if (oldBookData.isPresent()) {
            Book updatedBookData = oldBookData.get();
            updatedBookData.setAuthor(newBookData.getAuthor());
            updatedBookData.setTitle(newBookData.getTitle());
            bookRepo.save(updatedBookData);

            Book bookObj = bookRepo.save(updatedBookData);
            return new ResponseEntity<>(bookObj, HttpStatus.OK);
        }
        return new ResponseEntity<>(HttpStatus.NOT_FOUND);
    }

    @DeleteMapping("/books/{id}")
    public ResponseEntity<Book> deleteBookById(@PathVariable Long id) {
        bookRepo.deleteById(id);
        return new ResponseEntity<>(HttpStatus.OK);

    }
}

6. Run the application by hitting the Run icon in the main method

7. Open the H2 console (http://localhost:9090/h2-ui/login.jsp)

8. Provide below connection details and test the connection

jdbc:h2:mem:testdb

9. Connection is success as per below status

10. Open and connect to H2 Database using http://localhost:9090/h2-ui/login.jsp

11) First Check the Book table for the content in H2 by querying the Books table

12) Run the postman to add the content to Book table

http://localhost:9090/book

with payload

{

“title” : “Book1”,

“author”: “Author1”

}

13) After creating a Book table row, now check H2 by running select query

Now the data is present after the POST API

14) After creating a Book, now run below command to retrieve all the books

uri :http://localhost:9090/books

15) After getting all books, try to get specific book by specifying the Id

uri:http://localhost:9090/books/2

16) Now update the Book by using PUT Mapping as shown below

uri:http://localhost:9090/books/2

{

“title” : “Book21”,

“author”: “Author21”

}

17) Delete the book using Delete Mapping

uri: http://localhost:9090/books/2

18) By this we able to perform CRUD ( Create Read Update Delete ) options using REST API methods on H2 In Memory Database.