Now, we will create a simple RESTful API using Spring Boot. Here, we will implement an API to manage ‘Books’ as resources.<\/p>\n
First, we define the ‘Book’ domain model. The properties of the book will include ID, title, author, and publication year.<\/p>\n
\n
package com.example.demo.model;\n\nimport javax.persistence.Entity;\nimport javax.persistence.GeneratedValue;\nimport javax.persistence.GenerationType;\nimport javax.persistence.Id;\n\n@Entity\npublic class Book {\n @Id\n @GeneratedValue(strategy = GenerationType.IDENTITY)\n private Long id;\n \n private String title;\n private String author;\n private int year;\n\n \/\/ Getters and setters omitted\n}\n <\/code><\/pre>\n<\/div>\n5.2 Creating a Repository Interface<\/h3>\n
Create a repository interface to interact with the database using JPA.<\/p>\n
\n
package com.example.demo.repository;\n\nimport com.example.demo.model.Book;\nimport org.springframework.data.jpa.repository.JpaRepository;\n\npublic interface BookRepository extends JpaRepository<Book, Long> {\n}\n\n <\/code><\/pre>\n<\/div>\n5.3 Creating a Service Class<\/h3>\n
Create a service class for business logic processing. This class can add and retrieve book data using the repository.<\/p>\n
\n
package com.example.demo.service;\n\nimport com.example.demo.model.Book;\nimport com.example.demo.repository.BookRepository;\nimport org.springframework.beans.factory.annotation.Autowired;\nimport org.springframework.stereotype.Service;\n\nimport java.util.List;\n\n@Service\npublic class BookService {\n @Autowired\n private BookRepository bookRepository;\n\n public List<Book> getAllBooks() {\n return bookRepository.findAll();\n }\n\n public Book addBook(Book book) {\n return bookRepository.save(book);\n }\n}\n <\/code><\/pre>\n<\/div>\n5.4 Creating a Controller Class<\/h3>\n
Create a REST controller to handle client requests. This controller can define the API endpoints.<\/p>\n
\n
package com.example.demo.controller;\n\nimport com.example.demo.model.Book;\nimport com.example.demo.service.BookService;\nimport org.springframework.beans.factory.annotation.Autowired;\nimport org.springframework.web.bind.annotation.*;\n\nimport java.util.List;\n\n@RestController\n@RequestMapping(\"\/api\/books\")\npublic class BookController {\n @Autowired\n private BookService bookService;\n\n @GetMapping\n public List<Book> getAllBooks() {\n return bookService.getAllBooks();\n }\n\n @PostMapping\n public Book addBook(@RequestBody Book book) {\n return bookService.addBook(book);\n }\n}\n <\/code><\/pre>\n<\/div>\n5.5 Running the Application<\/h3>\n
Now that all settings are complete, start the application by running the DemoApplication<\/strong> class’s main<\/code> method.<\/p>\n<\/section>\n\n6. Testing the API with Postman<\/h2>\n
We will test whether the API we created works correctly using Postman. Follow these steps:<\/p>\n
\n- Run Postman:<\/strong> Open the Postman application and create a new request.<\/li>\n
- Send GET Request:<\/strong> Enter
http:\/\/localhost:8080\/api\/books<\/code> in the URL and send a GET request. The current book list should appear as a response.<\/li>\n- Send POST Request:<\/strong> To add a new book, enter
http:\/\/localhost:8080\/api\/books<\/code> in the URL and set up a POST request. Set the Body to JSON format and enter the book information.<\/li>\n<\/ol>\n<\/section>\n\n7. Connecting to Database<\/h2>\n
In this section, we will learn how to connect Spring Boot with the H2 database. H2 database is an in-memory database suitable for testing and development.<\/p>\n
7.1 Database Configuration<\/h3>\n
Add H2 database settings in the application.properties<\/code> file of the Spring Boot application:<\/p>\n\n
spring.datasource.url=jdbc:h2:mem:testdb\nspring.datasource.driverClassName=org.h2.Driver\nspring.datasource.username=sa\nspring.datasource.password=\nspring.h2.console.enabled=true\nspring.jpa.database-platform=org.hibernate.dialect.H2Dialect\n <\/code><\/pre>\n<\/div>\n7.2 Data Initialization<\/h3>\n
To add initial data when the application runs, you can use a data.sql<\/code> file to set up the initial data.<\/p>\n\n
INSERT INTO book (title, author, year) VALUES ('Effective Java', 'Joshua Bloch', 2020);\nINSERT INTO book (title, author, year) VALUES ('Spring in Action', 'Craig Walls', 2018);\n <\/code><\/pre>\n<\/div>\n<\/section>\n\n8. Exception Handling<\/h2>\n
We will learn how to handle exceptions that may occur in the generated API. Spring allows global exception handling using @ControllerAdvice<\/code>.<\/p>\n\n
package com.example.demo.exception;\n\nimport org.springframework.http.HttpStatus;\nimport org.springframework.http.ResponseEntity;\nimport org.springframework.web.bind.annotation.ControllerAdvice;\nimport org.springframework.web.bind.annotation.ExceptionHandler;\n\n@ControllerAdvice\npublic class GlobalExceptionHandler {\n \n @ExceptionHandler(Exception.class)\n public ResponseEntity<String> handleException(Exception e) {\n return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body(e.getMessage());\n }\n}\n <\/code><\/pre>\n<\/div>\nWith this setup, all exceptions will be handled, and an appropriate response will be returned to the client.<\/p>\n<\/section>\n\n9. Communication with Client<\/h2>\n
In this section, we will learn about the methods of communication between the client and server. Generally, clients interact with servers via REST APIs. The common request methods are as follows:<\/p>\n
\n- GET:<\/strong> Data retrieval<\/li>\n
- POST:<\/strong> Data creation<\/li>\n
- PUT:<\/strong> Data modification<\/li>\n
- DELETE:<\/strong> Data deletion<\/li>\n<\/ul>\n<\/section>\n\n
10. Implementing Client Application<\/h2>\n
Having successfully implemented the API on the server side, let’s create a client application. Here, we will create a simple HTML and JavaScript-based frontend to communicate with the REST API.<\/p>\n