Prerequisites

1. Java Development Kit (JDK) 11 or higher: Ensure JDK is installed and configured on your system.
2. Integrated Development Environment (IDE): IntelliJ IDEA, Eclipse, or any other IDE.
3. Maven: Ensure Maven is installed and configured on your system.

Step 1: Create a Spring Boot Project

1. Open your IDE and create a new Spring Boot project.
2. Use Spring Initializr or manually create the pom.xml file to include Spring Boot and other required dependencies.

<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>com.example</groupId> <artifactId>spring-boot-blog-example</artifactId> <version>1.0-SNAPSHOT</version> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>3.1.0</version> <relativePath/> </parent> <dependencies> <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>com.h2database</groupId> <artifactId>h2</artifactId> <scope>runtime</scope> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build> </project> 

Explanation

• spring-boot-starter-data-jpa: Includes Spring Data JPA with Hibernate.
• spring-boot-starter-web: Includes Spring MVC for building web applications.
• h2: An in-memory database for testing purposes.

Step 2: Configure the Application Properties

Configure the application.properties file to set up the H2 database.

spring.datasource.url=jdbc:h2:mem:testdb spring.datasource.driverClassName=org.h2.Driver spring.datasource.username=sa spring.datasource.password= spring.jpa.database-platform=org.hibernate.dialect.H2Dialect spring.h2.console.enabled=true spring.jpa.hibernate.ddl-auto=update spring.jpa.show-sql=true spring.jpa.properties.hibernate.format_sql=true 

Step 3: Create the Post Entity Class

Create a package named com.example.entity and a class named Post.

package com.example.entity; import jakarta.persistence.*; import java.util.HashSet; import java.util.Set; @Entity public class Post { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; private String title; private String content; @OneToMany(mappedBy = "post", cascade = CascadeType.ALL, orphanRemoval = true) private Set<Comment> comments = new HashSet<>(); public Post() {} public Post(String title, String content) { this.title = title; this.content = content; } public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getTitle() { return title; } public void setTitle(String title) { this.title = title; } public String getContent() { return content; } public void setContent(String content) { this.content = content; } public Set<Comment> getComments() { return comments; } public void setComments(Set<Comment> comments) { this.comments = comments; } public void addComment(Comment comment) { comments.add(comment); comment.setPost(this); } public void removeComment(Comment comment) { comments.remove(comment); comment.setPost(null); } @Override public String toString() { return "Post{id=" + id + ", title='" + title + '\'' + ", content='" + content + '\'' + '}'; } } 

Explanation

• @Entity: Marks the class as an entity.
• @Id: Marks the field as the primary key.
• @GeneratedValue: Specifies the strategy for generating values for the primary key.
• @OneToMany: Defines a one-to-many relationship with the Comment entity.
• mappedBy: Specifies the field in the Comment entity that owns the relationship.
• cascade: Specifies the cascade operations.
• orphanRemoval: Specifies whether to remove orphaned entities.

Step 4: Create the Comment Entity Class

Create a class named Comment in the same package.

package com.example.entity; import jakarta.persistence.*; @Entity public class Comment { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; private String content; @ManyToOne(fetch = FetchType.LAZY) @JoinColumn(name = "post_id") private Post post; public Comment() {} public Comment(String content) { this.content = content; } public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getContent() { return content; } public void setContent(String content) { this.content = content; } public Post getPost() { return post; } public void setPost(Post post) { this.post = post; } @Override public String toString() { return "Comment{id=" + id + ", content='" + content + '\'' + '}'; } } 

Explanation

• @Entity: Marks the class as an entity.
• @Id: Marks the field as the primary key.
• @GeneratedValue: Specifies the strategy for generating values for the primary key.
• @ManyToOne: Defines a many-to-one relationship with the Post entity.
• @JoinColumn: Specifies the foreign key column.

Step 5: Create Repository Interfaces

Create a package named com.example.repository and interfaces for Post and Comment.

package com.example.repository; import com.example.entity.Post; import org.springframework.data.jpa.repository.JpaRepository; import org.springframework.stereotype.Repository; @Repository public interface PostRepository extends JpaRepository<Post, Long> {} 

package com.example.repository; import com.example.entity.Comment; import org.springframework.data.jpa.repository.JpaRepository; import org.springframework.stereotype.Repository; @Repository public interface CommentRepository extends JpaRepository<Comment, Long> {} 

Step 6: Create Service Classes

Create a package named com.example.service and service classes for Post and Comment.

package com.example.service; import com.example.entity.Post; import com.example.entity.Comment; import com.example.repository.PostRepository; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service; import java.util.List; @Service public class PostService { @Autowired private PostRepository postRepository; public Post save(Post post) { return postRepository.save(post); } public List<Post> findAll() { return postRepository.findAll(); } public Post findById(Long id) { return postRepository.findById(id).orElse(null); } public void deleteById(Long id) { postRepository.deleteById(id); } public Post addComment(Long postId, Comment comment) { Post post = findById(postId); if (post != null) { post.addComment(comment); return save(post); } return null; } public Post removeComment(Long postId, Long commentId) { Post post = findById(postId); if (post != null) { Comment comment = post.getComments().stream().filter(c -> c.getId().equals(commentId)).findFirst().orElse(null); if (comment != null) { post.removeComment(comment); return save(post); } } return null; } } 

package com.example.service; import com.example.entity.Comment; import com.example.repository.CommentRepository; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service; import java.util.List; @Service public class CommentService { @Autowired private CommentRepository commentRepository; public Comment save(Comment comment) { return commentRepository.save(comment); } public List<Comment> findAll() { return commentRepository.findAll(); } public Comment findById(Long id) { return commentRepository.findById(id).orElse(null); } public void deleteById(Long id) { commentRepository.deleteById(id); } } 

Step 7: Create Controller Classes

Create a package named com.example.controller and controller classes for Post and Comment.

package com.example.controller; import com.example.entity.Post; import com.example.entity.Comment; import com.example.service.PostService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.*; import java.util.List; @RestController @RequestMapping("/posts") public class PostController { @Autowired private PostService postService; @PostMapping public Post createPost(@RequestBody Post post) { return postService.save(post); } @GetMapping public List<Post> getAllPosts() { return postService.findAll(); } @GetMapping("/{id}") public Post getPostById(@PathVariable Long id) { return postService.findById(id); } @DeleteMapping("/{id}") public void deletePost(@PathVariable Long id) { postService.deleteById(id); } @PostMapping("/{postId}/comments") public Post addComment(@PathVariable Long postId, @RequestBody Comment comment) { return postService.addComment(postId, comment); } @DeleteMapping("/{postId}/comments/{commentId}") public Post removeComment(@PathVariable Long postId, @PathVariable Long commentId) { return postService.removeComment(postId, commentId); } } 

package com.example.controller; import com.example.entity.Comment; import com.example.service.CommentService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.*; import java.util.List; @RestController @RequestMapping("/comments") public class CommentController { @Autowired private CommentService commentService; @PostMapping public Comment createComment(@RequestBody Comment comment) { return commentService.save(comment); } @GetMapping public List<Comment> getAllComments() { return commentService.findAll(); } @GetMapping("/{id}") public Comment getCommentById(@PathVariable Long id) { return commentService.findById(id); } @DeleteMapping("/{id}") public void deleteComment(@PathVariable Long id) { commentService.deleteById(id); } } 

Step 8: Create Main Application Class

Create a package named com.example and a class named SpringBootBlogExampleApplication.

package com.example; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; @SpringBootApplication public class SpringBootBlogExampleApplication { public static void main(String[] args) { SpringApplication.run(SpringBootBlogExampleApplication.class, args); } } 

Step 9: Run the Application

1. Run the SpringBootBlogExampleApplication class.
2. Use an API client (e.g., Postman) or a web browser to test the endpoints.

Testing the Endpoints

1. Create a Post:

   • URL: POST /posts
   • Body:

     { "title": "First Post", "content": "This is the content of the first post" } 

2. Create Comments:

   • URL: POST /comments
   • Body:

     { "content": "This is the first comment" } 

   • Body:

     { "content": "This is the second comment" } 

3. Add Comments to Post:

   • URL: POST /posts/{postId}/comments
   • Body:

     { "content": "This is the first comment" } 

   • Body:

     { "content": "This is the second comment" } 

4. Get All Posts:

   • URL: GET /posts

5. Get Post by ID:

   • URL: GET /posts/{id}

6. Get All Comments:

   • URL: GET /comments

7. Get Comment by ID:

   • URL: GET /comments/{id}

8. Delete Post by ID:

   • URL: DELETE /posts/{id}

9. Delete Comment by ID:

   • URL: DELETE /comments/{id}

Conclusion

You have successfully created an example using Spring Boot and Hibernate to demonstrate a one-to-many relationship in a blog application context. This tutorial covered setting up a Spring Boot project, configuring Hibernate, creating entity classes with a one-to-many relationship, and performing CRUD operations through RESTful endpoints.