【Spring Boot】四种核心类的依赖关系：实体类、数据处理类、业务处理类、控制器类

//1.配置项目环境，创建Spring Boot项目。
//2.数据库设置，配置数据库。
//3.创建实体类，映射到数据库。
//4.创建数据处理层类，Repository
//5.创建业务处理类，Service类
//6.创建控制器类，Controller类

Article.java

java
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
    public class Article{
    @Id
        @GeneratedValue(strategy = GenerationType.AOTU)
        private Long id;
        private String title;
        private String content;
        private String author;
    
      //省略构造函数、getter和setter方法
      //省略toString方法
      //一个实体类完成了！
} 

ArticleRepository.java（数据访问层类）
    '''java
    import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import java.util.List;
public interface ArticleRepository extends JpaRepository<Article,Long>{
//可以在此自定义查询方法
//根据作者名查询文章
List<Article> findByAuthor(String author);
//根据标题和作者查询文章
List<Article> findByTitleAndAuthor(String title,String author);
//使用JPQL查询语句查询文章
@Query("Select a FROM Article a WHERE a.title LIKE %:keyword% OR a.content LIKE %:keyword%")
List<Article> fintByKeyword(String keyword);
}
    

ArticleService.Java(业务逻辑层)：
    '''java
    import org.springframework.beans.factory. annotation.Autowired;
    import org.springframework.stereotype.Service;
    import java.util.List;
    import java.util.Optional;

@Service
    public class ArticleService{
    private final ArticleRepository articleRepository;
    
    @Autowired
    public ArticleService(ArticleRepository articleRepository){
    this.articleRepository = articleRepository;    
    }
    
    public List<Article>getAllArticles(){
    return articleRepository.findAll();
    }
    
    public Optional<Article>getArticleById(Long id){
        return articleRepository.findByID(id);
    }
    
    public Article createArticle(Article article){
    return articleRepository.save(article);
    }
    
    /**
    public void updateArticle(Long id, Article article) {
        Optional<Article> existingArticle = articleRepository.findById(id);
        if (existingArticle.isPresent()) {
            Article updatedArticle = existingArticle.get();
            updatedArticle.setTitle(article.getTitle());
            updatedArticle.setContent(article.getContent());
            updatedArticle.setAuthor(article.getAuthor());
            articleRepository.save(updatedArticle);
        }
    }
    
    **/
    
    public void deleteArticle(Long id){
        articleRepository.deleteById(id);
    }
    
}

ArticleController.java(控制器类)：
    '''java
    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.List;
import java.util.Optional;

@RestContrller
@RequestMapping("/articles")
public class ArticleController{
    private final ArticleService articleService;
    
    @Autowired
    public ArticleControler(
    ArticleService articleService
    ){
    tihs.articleService = articleService;
    }
    
    @GetMapping
        public ResponseEntity<List<Article>>getAllArticles(){
    List<Article>articles = articleService.getAllArticles;
    return new ResponseEntity<>(articles,HttpStatus.OK)
    }
 //以下为粘贴
        @GetMapping("/{id}")
    public ResponseEntity<Article> getArticleById(@PathVariable Long id) {
        Optional<Article> article = articleService.getArticleById(id);
        return article.map(value -> new ResponseEntity<>(value, HttpStatus.OK))
                      .orElseGet(() -> new ResponseEntity<>(HttpStatus.NOT_FOUND));
    }

    @PostMapping
    public ResponseEntity<Article> createArticle(@RequestBody Article article) {
        Article createdArticle = articleService.createArticle(article);
        return new ResponseEntity<>(createdArticle, HttpStatus.CREATED);
    }

    @PutMapping("/{id}")
    public ResponseEntity<Void> updateArticle(@PathVariable Long id, @RequestBody Article article) {
        articleService.updateArticle(id, article);
        return new ResponseEntity<>(HttpStatus.NO_CONTENT);
    }

    @DeleteMapping("/{id}")
    public ResponseEntity<Void> deleteArticle(@PathVariable Long id) {
        articleService.deleteArticle(id);
        return new ResponseEntity<>(HttpStatus.NO_CONTENT);
    }
}

}