OrderControllerV1.java

//...

@GetMapping("/capture")
public String captureOrder(){
    return "";
}

@PostMapping
public String placeOrder(@RequestParam Double amountId, HttpServletRequest request){
    final URI returnUrl = buildReturnUrl(request);
    return "";
}

private URI buildReturnUrl(HttpServletRequest request) {
    try {
        URI requestUri = URI.create(request.getRequestURL().toString());
        return new URI(requestUri.getScheme(), 
                requestUri.getUserInfo(), 
                requestUri.getHost(), 
                requestUri.getPort(), 
                "/orders/capture", 
                null, null);
    } catch (URISyntaxException e) {
        throw new RuntimeException(e);
    }
}

//...