Spring: REST-Controller cannot be found by SpringBootApplication

Question

I'm building a Spring-REST-API with CRUD-functionality to create, read, update and delete books with a MongoDB-database. My project has the following structure:

BackendBookLibraryApplication.java in main > java > com.lena.backendbooklibrary

BookController.java in main > java > com.lena.backendbooklibrary.controllers

package com.lena.backendbooklibrary;

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

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

package com.lena.backendbooklibrary.controllers;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/api/v1/books")
public class BookController {
    @GetMapping
    public String getAllBooks() {
        return "All books";
    }
}

When I am running my application the path http://localhost:8080/api/v1/books delivers a 404. I cannot find out why the SpringBootApplication can't find my REST-Controller, since they are in the same package (the Controller is in a sub package, but this should be no problem). In my console there aren't any errors.

I tried the following to delimit the problem:

1. Annotated the BackendBookLibraryApplication with @RestController and implemented the GET-Method in there: this works

package com.lena.backendbooklibrary;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
@RestController
@RequestMapping("/api/v1/books")
public class BackendBookLibraryApplication {

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

    @GetMapping
    public String getAllBooks() {
        System.out.println("BackendBookLibraryApplication: getAllBooks()");
        return "All books";
    }

}

2. Moved the BookController from the sub package into the exact same package com.lena.backendbooklibrary like the BackendBookLibraryApplication: this does not work
3. Additionally annotated the BackendBookLibraryApplication with @ComponentScan(basePackageClasses = BookController.class), although I thought this should be summarised in the @SpringBootApplication-Annotation: this does not work

Does anyone have an idea what the problem is? It would be great if any Spring-expert could help me. Thanks in advance!

Answer 1

You probably have used spring boot 3.0.3 version, and are affected by this issue.

The problem which appeared in spring boot 3.0.3 version did not allow your RestController to be exposed for your requested path because of some issue when the directory where your application was placed had empty spaces or special characters. It was a decoding issue with the path where your controller was placed and therefore would not be correctly registered.

If that is the case for the moment you can resolve the issue either by moving to spring boot 3.0.2 version or to spring boot 3.0.4 version.