Spring Boot启动报错：无法找到service.ProductService类型的Bean

我正在开发一个支持GET、PUT、POST、DELETE请求的Spring Boot应用，启动时遇到报错，多次修改仍无法解决，期望能在浏览器访问http://localhost:8080/products看到页面。

报错信息 #

Error starting ApplicationContext. To display the condition evaluation report re-run your application with 'debug' enabled.
2024-01-13T01:58:33.595-05:00 ERROR 10400 --- [           main] o.s.b.d.LoggingFailureAnalysisReporter   : 

***************************
APPLICATION FAILED TO START
***************************

Description:

Parameter 0 of constructor in com.example.sqch8ex5.ProductController required a bean of type 'service.ProductService' that could not be found.


Action:

Consider defining a bean of type 'service.ProductService' in your configuration.

项目结构说明 #

项目包含以下包结构：

• com.example.sqch8ex5：存放启动类和控制器
• service：存放服务类
• model：存放实体类

相关代码文件 #

SqCh8Ex5Application.java #

package com.example.sqch8ex5;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SqCh8Ex5Application {
    public static void main(String[] args) {
        SpringApplication.run(SqCh8Ex5Application.class, args);
    }
}

ProductController.java #

package com.example.sqch8ex5;

import model.Product;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestParam;
import service.ProductService;

@Controller
public class ProductController {
    private final ProductService productService;

    @Autowired
    public ProductController(ProductService productService){
        this.productService = productService;
    }

    @GetMapping("/products")
    public String viewProducts(Model model){
        var products = productService.findAll();
        model.addAttribute("products", products);
        return "products.html";
    }

    @PostMapping("/products")
    public String addProduct(@RequestParam String name,
                             @RequestParam double price,
                             Model model){
        Product p = new Product();
        p.setName(name);
        p.setPrice(price);
        productService.addProduct(p);

        var products = productService.findAll();
        model.addAttribute("products",products);
        return "products.html";
    }
}

products.html #

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Home Page</title>
</head>
<body>
  <h1>Products</h1>
  <h2>View products</h2>
  <table>
    <tr>
      <th>PRODUCT NAME</th>
      <th>PRODUCT PRICE</th>
    </tr>
    <tr th:each="p:${products}">
      <td th:text="${p.name}"></td>
      <td th:text="${p.price}"></td>
    </tr>
  </table>

  <h2>Add a product</h2>
<form action="/products" method="post">
  Name:<input type="text" name="name"><br />
  Price:<input type="number" step="any" name ="price"><br />
  <buttom type="submit">Add product</buttom>
</form>
</body>
</html>

ProductService.java #

package service;

import model.Product;
import org.springframework.stereotype.Service;

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

@Service
public class ProductService {
    private List<Product> products = new ArrayList<>();

    public ProductService() {
    }

    public void addProduct(Product p){
        products.add(p);
    }

    public List<Product> findAll(){
        return products;
    }
}

解决方案 #

核心原因 #

Spring Boot的@SpringBootApplication注解默认只扫描启动类所在包（com.example.sqch8ex5）及其子包下的组件。而你的ProductService在独立的service包中，不在默认扫描范围内，因此Spring无法识别这个@Service注解的类，无法创建对应的Bean注入到控制器中。

解决方法（二选一即可） #

方法1：调整包结构（推荐）

把ProductService移动到启动类所在包的子包中：

1. 修改ProductService的包声明为：

   package com.example.sqch8ex5.service;
   

2. 同时修改ProductController中的导入语句：

   import com.example.sqch8ex5.service.ProductService;
   

这样Spring会自动扫描到这个服务类，创建Bean。

方法2：扩展组件扫描范围

在启动类的@SpringBootApplication注解中指定要扫描的所有包：

@SpringBootApplication(scanBasePackages = {"com.example.sqch8ex5", "service", "model"})

这样Spring会扫描指定的三个包下的所有带有@Service、@Controller等注解的类。

额外修复点 #

products.html中的提交按钮标签拼写错误：<buttom>应该改为<button>，否则按钮可能无法正常触发提交操作：

<button type="submit">Add product</button>

内容的提问来源于stack exchange，提问作者Dheeraj A Kumar