SpringBoot报错：No bean named 'myController' available，HelloWorld程序求助

Hey there, let's break down why you're hitting this error and how to fix it step by step!

1. The Root Cause: Spring Can't Find Your Controller Class #

Spring Boot automatically scans for components (like @Controller, @Service, etc.) starting from the package where your main application class (DemoApplication) lives, plus all its sub-packages.

Looking at your code:

• DemoApplication sits in the di.prac package
• MyController is in the standalone controllers package

Since controllers isn't a sub-package of di.prac, Spring has no idea this class exists—so it never creates a bean for it, hence the error.

Fixes for Package Scanning #

You have two straightforward options here:

• Option 1: Move the controller to a valid sub-package
  Relocate MyController.java to di.prac.controllers (just create the controllers sub-package under di.prac). This way, Spring's default scan will pick it up automatically without extra configuration.

• Option 2: Explicitly tell Spring which packages to scan
  Update your DemoApplication to use the scanBasePackages attribute in @SpringBootApplication, specifying both your main app package and the controllers package:

  package di.prac;
  import org.springframework.boot.SpringApplication;
  import org.springframework.boot.autoconfigure.SpringBootApplication;
  
  @SpringBootApplication(scanBasePackages = {"di.prac", "controllers"})
  public class DemoApplication {
      public static void main(String[] args) {
          SpringApplication.run(DemoApplication.class, args);
      }
  }
  

2. Add Request Mapping to Your Controller Method #

Even once Spring finds your controller, your hello() method won't work as expected without a request mapping annotation. Right now, Spring doesn't know which HTTP requests this method should handle.

Update your MyController to add a @GetMapping (or @RequestMapping) annotation:

package controllers;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;

@Controller
public class MyController {
    @GetMapping("/hello") // Maps GET requests to /hello to this method
    public String hello() {
        System.out.println("Hello World");
        return "foo";
    }
}

Quick Note: @Controller vs @RestController #

If you want to return plain text (like "Hello World") directly as the HTTP response instead of looking for a view template named "foo", swap @Controller with @RestController:

package controllers;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class MyController {
    @GetMapping("/hello")
    public String hello() {
        System.out.println("Hello World");
        return "Hello World"; // Sends this string as the response body
    }
}

Final Checks #

After making these changes, restart your Spring Boot app. You should now be able to access the /hello endpoint (via browser or tools like Postman) and see "Hello World" in your console (and in the response if you used @RestController).

内容的提问来源于stack exchange，提问作者Ankit Halder