Spring Boot with redirecting with single page angular2

If you're tired of trying to solve this problem by following so many conflicting solutions - look here!!

After hours upon hours trying to follow all the scattered advice from dozens of stack overflow and blog posts, I've finally found the minimum PURE spring boot + angular 6 application to always redirect to index.html after a refresh on a non-root page WHILE maintaining all your REST API endpoint paths. No @EnableWebMvc, no @ControllerAdvice, no changes to application.properties, no custom ResourceHandlerRegistry modifications, just simplicity:

Very important pre-requisite

You *must* include the output of ng build into Spring's resources/static folder. You can accomplish this via the maven-resources-plugin. Learn here: Copying multiple resource directories to independent target directories with maven

Code

@Controller
@SpringBootApplication
public class MyApp implements ErrorController {

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

    private static final String PATH = "/error";

    @RequestMapping(value = PATH)
    public String error() {
        return "forward:/index.html";
    }

    @Override
    public String getErrorPath() {
        return PATH;
    }
}

Reasoning

• Including the output of ng-build into resources/static at build time allows spring view redirects ("forward:/index.html") to succeed. It seems spring cannot redirect to anything outside of the resources folder so if you're trying to access pages at the root of the site, it won't work.
• With default functionality (i.e. no additions of @EnableWebMvc or changes to application.properties) navigating to / automatically serves the index.html (iff it was included in the resources/static folder) so no need to make changes there.
• With default functionality (as stated above), any error encountered in a spring boot app routes to /error and implementing ErrorController overrides that behavior to - you guessed it - route to index.html which allows Angular to take over the routing.

Remarks

• Don't settle for the HashLocationStrategy to get over this problem as it is not recommended by Angular: https://angular.io/guide/router#which-strategy-is-best

For every local REST request not starting with /api overwrite and redirect to default webapp/index.html. I plan to serve anything /api to the spring controllers.

Update 15/05/2017

Let me re-phrase your query for other readers. (Correct me, if misunderstood)

Background
Using Spring Boot and Serving static resources from classpath

Requirement
All 404 non api requests should be redirected to index.html.

NON API - means Requests in which URL doesn't start with /api.
API - 404 should throw 404 as usual.

Sample Response
/api/something - will throw 404
/index.html - will server index.html
/something - will redirect to index.html

My Solution

Let the Spring MVC throw exceptions, if any handler is not available for the given resource.

Add following to application.properties

spring.mvc.throw-exception-if-no-handler-found=true
spring.resources.add-mappings=false

Add a ControllerAdvice as follows

@ControllerAdvice
public class RedirectOnResourceNotFoundException {

    @ExceptionHandler(value = NoHandlerFoundException.class)
    public Object handleStaticResourceNotFound(final NoHandlerFoundException ex, HttpServletRequest req, RedirectAttributes redirectAttributes) {
        if (req.getRequestURI().startsWith("/api"))
            return this.getApiResourceNotFoundBody(ex, req);
        else {
            redirectAttributes.addFlashAttribute("errorMessage", "My Custom error message");
            return "redirect:/index.html";
        }
    }

    private ResponseEntity<String> getApiResourceNotFoundBody(NoHandlerFoundException ex, HttpServletRequest req) {
        return new ResponseEntity<>("Not Found !!", HttpStatus.NOT_FOUND);
    }
}

You can customize the error message as you like.

Is there a way to prefix all controllers with api so that I do not have to write api every time.

For this, you can create a BaseController and set the RequestMapping path to /api

Example

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

@RequestMapping("/api")
public abstract class BaseController {}

And extend this BaseController and make sure you do not annotate child class with @RequestMapping

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

@RestController
public class FirstTestController extends BaseController {
    @RequestMapping(path = "/something")
    public String sayHello() {
        return "Hello World !!";
    }

}

Previous Answer

You can create a Filter which redirects to /index.html if request path doesn't startsWith /api.

// CODE REMOVED. Check Edit History If you want.

Try this instead

@SpringBootApplication
@Controller
class YourSpringBootApp { 

    // Match everything without a suffix (so not a static resource)
    @RequestMapping(value = "/**/{path:[^.]*}")       
    public String redirect() {
        // Forward to home page so that route is preserved.(i.e forward:/intex.html)
        return "forward:/";
    }
}