others-how to solve 'Resource not found 404 NOT_FOUND' when running spring boot program ?

Problem

When we run a spring boot progam , and visit a url as follows:

curl http://localhost:8080/admin

sometimes , we get this error:

2021-03-02 12:32:30,208 DEBUG org.springframework.web.servlet.DispatcherServlet : GET "/home_admin", parameters={}
2021-03-02 12:32:30,216 DEBUG org.springframework.web.servlet.handler.SimpleUrlHandlerMapping : Mapped to ResourceHttpRequestHandler [class path resource [META-INF/resources/], class path resource [resources/], class path resource [static/], class path resource [public/], ServletContext resource [/]]
2021-03-02 12:32:30,221 DEBUG org.springframework.web.servlet.resource.ResourceHttpRequestHandler : Resource not found
2021-03-02 12:32:30,222 DEBUG org.springframework.web.servlet.DispatcherServlet : Completed 404 NOT_FOUND

Why do this error happen? The program is correct, I promise!!!

Environment

• spring boot 1.x and 2.x

The code

The TheController.java mapping code of the spring boot program is:

    @GetMapping("/admin")
    public String adminHome(Authentication authentication, Model model) {
        model.addAttribute("username",authentication==null?"":authentication.getName());
        model.addAttribute("products",productService.findAll());
        return "home_admin";
    }

The structure of the project

.
└── src/
    └── main/
        ├── java/
        │   └── com.bswen.app9/
        │       └── TheController.java
        └── resources/
            └── templates
                └── home_admin.html

Reason

After the adminHome method, the controller returns a “home_admin” view, which can not be resloved by spring boot.

Solution

We should change the mapping to make it the same name as the view name:

    @GetMapping("/home_admin")
    public String adminHome(Authentication authentication, Model model) {
        model.addAttribute("username",authentication==null?"":authentication.getName());
        model.addAttribute("products",productService.findAll());
        return "home_admin";
    }

The key point is :

@GetMapping("/home_admin")

It should has the same name as the view name:

 return "home_admin";

Run the app again, No error messages ,It works!