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Spring Boot 4 Microservices & REST APIs · 课时

使用 REST 执行 CRUD 操作

通过 REST 端点为实体实现创建、读取、更新和删除操作。

第 5 / 6 课12 个步骤

使用 REST 执行 CRUD 操作 是 CoddyKit 上的免费 Spring Boot 4 Microservices & REST APIs 课时。 这是第 5 节课，共 6 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 Spring Boot 4 Microservices & REST APIs 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Spring Boot 4 Microservices & REST APIs 课程共包含 6 节课。

本课时的部分内容尚未翻译，以英文显示。

CRUD Operations: The Basics

Welcome to implementing CRUD operations with Spring Boot! CRUD stands for Create, Read, Update, and Delete.

These are the four fundamental operations for persistent storage, allowing you to manage data in your application.

In REST APIs, each CRUD operation typically maps to a specific HTTP method.

Mapping CRUD to HTTP Methods

Understanding how CRUD maps to HTTP methods is key for RESTful design:

  • Create (C): Handled by POST requests.
  • Read (R): Handled by GET requests.
  • Update (U): Handled by PUT requests.
  • Delete (D): Handled by DELETE requests.

We'll use a simple Product entity and its ProductRepository from previous lessons.

Implementing Create (POST)

To create a new resource, we use the POST HTTP method. In Spring Boot, this is handled by the @PostMapping annotation.

The new product data is sent in the request body, which Spring automatically maps to our Product object using @RequestBody.

Create Product Example

Here's how you'd create an endpoint to add a new product. Run it, then try adding a product via a tool like Postman (e.g., POST to /api/products with JSON body {"name": "Laptop", "price": 1200.0}).

package com.coddykit.crud;

import jakarta.persistence.*;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import org.springframework.web.bind.annotation.*;
import org.springframework.beans.factory.annotation.Autowired;

@Entity
public class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private double price;
    public Product() {}
    public Product(String name, double price) {
        this.name = name;
        this.price = price;
    }
    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public double getPrice() { return price; }
    public void setPrice(double price) { this.price = price; }
}

@Repository
interface ProductRepository extends JpaRepository<Product, Long> {}

@RestController
@RequestMapping("/api/products")
class ProductController {
    @Autowired
    private ProductRepository productRepository;

    @PostMapping
    public Product createProduct(@RequestBody Product product) {
        return productRepository.save(product);
    }
}

@SpringBootApplication
class CrudApplication {
    public static void main(String[] args) {
        SpringApplication.run(CrudApplication.class, args);
    }
}

Implementing Read (GET)

Reading resources is done with the GET HTTP method. We'll create two types of read operations:

  • Get all products: Maps to @GetMapping.
  • Get a single product by ID: Maps to @GetMapping("/{id}") using a @PathVariable.

When fetching by ID, we use Optional to handle cases where the product might not exist.

Read Products Example

This code adds methods to fetch all products and a single product by its ID. Notice the use of ResponseEntity to return a 404 if a product isn't found.

package com.coddykit.crud;

import jakarta.persistence.*;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import org.springframework.web.bind.annotation.*;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.ResponseEntity;
import java.util.List;
import java.util.Optional;

@Entity
public class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private double price;
    public Product() {}
    public Product(String name, double price) {
        this.name = name;
        this.price = price;
    }
    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public double getPrice() { return price; }
    public void setPrice(double price) { this.price = price; }
}

@Repository
interface ProductRepository extends JpaRepository<Product, Long> {}

@RestController
@RequestMapping("/api/products")
class ProductController {
    @Autowired
    private ProductRepository productRepository;

    @GetMapping
    public List<Product> getAllProducts() {
        return productRepository.findAll();
    }

    @GetMapping("/{id}")
    public ResponseEntity<Product> getProductById(@PathVariable Long id) {
        Optional<Product> product = productRepository.findById(id);
        return product.map(ResponseEntity::ok)
                      .orElseGet(() -> ResponseEntity.notFound().build());
    }
}

@SpringBootApplication
class CrudApplication {
    public static void main(String[] args) {
        SpringApplication.run(CrudApplication.class, args);
    }
}

Implementing Update (PUT)

To update an existing resource, we use the PUT HTTP method, annotated with @PutMapping.

The endpoint typically includes the resource's ID in the path (/{id}) to identify which item to update, and the updated data is sent in the @RequestBody.

Update Product Example

This method updates an existing product. It first checks if the product exists using the ID from the path. If found, it updates the fields from the request body and saves it.

package com.coddykit.crud;

import jakarta.persistence.*;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import org.springframework.web.bind.annotation.*;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.ResponseEntity;
import java.util.Optional;

@Entity
public class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private double price;
    public Product() {}
    public Product(String name, double price) {
        this.name = name;
        this.price = price;
    }
    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public double getPrice() { return price; }
    public void setPrice(double price) { this.price = price; }
}

@Repository
interface ProductRepository extends JpaRepository<Product, Long> {}

@RestController
@RequestMapping("/api/products")
class ProductController {
    @Autowired
    private ProductRepository productRepository;

    @PutMapping("/{id}")
    public ResponseEntity<Product> updateProduct(
        @PathVariable Long id, @RequestBody Product productDetails) {
        Optional<Product> product = productRepository.findById(id);
        if (product.isPresent()) {
            Product existingProduct = product.get();
            existingProduct.setName(productDetails.getName());
            existingProduct.setPrice(productDetails.getPrice());
            return ResponseEntity.ok(productRepository.save(existingProduct));
        } else {
            return ResponseEntity.notFound().build();
        }
    }
}

@SpringBootApplication
class CrudApplication {
    public static void main(String[] args) {
        SpringApplication.run(CrudApplication.class, args);
    }
}

Implementing Delete (DELETE)

To remove a resource, we use the DELETE HTTP method, annotated with @DeleteMapping.

Similar to update, the ID of the resource to delete is passed as a @PathVariable. After deletion, it's common to return a 204 No Content status.

Delete Product Example

This method deletes a product by ID. It finds the product and, if present, deletes it. Returning ResponseEntity.noContent().build() is a good practice for successful deletions.

package com.coddykit.crud;

import jakarta.persistence.*;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import org.springframework.web.bind.annotation.*;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.ResponseEntity;
import java.util.Optional;

@Entity
public class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private double price;
    public Product() {}
    public Product(String name, double price) {
        this.name = name;
        this.price = price;
    }
    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public double getPrice() { return price; }
    public void setPrice(double price) { this.price = price; }
}

@Repository
interface ProductRepository extends JpaRepository<Product, Long> {}

@RestController
@RequestMapping("/api/products")
class ProductController {
    @Autowired
    private ProductRepository productRepository;

    @DeleteMapping("/{id}")
    public ResponseEntity<Void> deleteProduct(@PathVariable Long id) {
        Optional<Product> product = productRepository.findById(id);
        if (product.isPresent()) {
            productRepository.delete(product.get());
            return ResponseEntity.noContent().build();
        } else {
            return ResponseEntity.notFound().build();
        }
    }
}

@SpringBootApplication
class CrudApplication {
    public static void main(String[] args) {
        SpringApplication.run(CrudApplication.class, args);
    }
}

Quick Check: HTTP Methods

Which HTTP method is typically used to update an existing resource in a REST API, and which one is for creating a new resource?

在交互式课程中回答

Recap: CRUD with REST

You've successfully learned how to implement all four CRUD operations using Spring Boot REST controllers!

  • Create: Use @PostMapping.
  • Read: Use @GetMapping (for all or by ID).
  • Update: Use @PutMapping.
  • Delete: Use @DeleteMapping.

These are the building blocks for almost any data-driven API. Next, we'll explore validation and error handling!

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常见问题解答

「使用 REST 执行 CRUD 操作」课时是免费的吗？

是的 — 「使用 REST 执行 CRUD 操作」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Spring Boot 4 Microservices & REST APIs 课程的其余内容，请升级到 CoddyKit PRO。 Spring Boot 4 Microservices & REST APIs 课程共包含 6 节课。

「使用 REST 执行 CRUD 操作」这节课中我会学到什么？

通过 REST 端点为实体实现创建、读取、更新和删除操作。 你通过在浏览器中直接运行的动手代码来练习 Spring Boot 4 Microservices & REST APIs，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 Spring Boot 4 Microservices & REST APIs 需要有经验吗？

无需任何先前经验。CoddyKit 上的 Spring Boot 4 Microservices & REST APIs 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 5 节课，共 6 节。

「使用 REST 执行 CRUD 操作」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

我能在这节 Spring Boot 4 Microservices & REST APIs 课中编写并运行代码吗？

能。每节 Spring Boot 4 Microservices & REST APIs 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

此课程中的所有课时

  1. 集成 H2 数据库与 JPA
  2. Spring Data JPA 简介
  3. 创建实体与存储库
  4. 定义实体与存储库
  5. 使用 REST 执行 CRUD 操作
  6. 执行增删改查操作
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