Access to XMLHttpRequest at 'http://localhost:8080/room/v1/reservation/' from origin 'http://localhost:4200' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. code example

Example 1: origin 'http://localhost:4200' has been blocked by CORS policy

'Content-Type': 'application/json',
      'Access-Control-Allow-Origin': '*',
      'Access-Control-Allow-Headers': 'Content-Type',
      'Access-Control-Allow-Methods': 'GET,POST,OPTIONS,DELETE,PUT',
      'Authorization': 'Bearer key',

Example 2: what is cors

“CORS” stands for Cross-Origin Resource Sharing. 
It allows you to make requests from one website to another website 
in the browser, which is normally prohibited by another browser policy 
called the Same-Origin Policy (SOP).

Example 3: from origin 'http://localhost:4200' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

@CrossOrigin(origins = "http://localhost:4200")
@GetMapping("/yourPath")

Example 4: what is CORS

Use CORS to allow cross-origin access. 
CORS is a part of HTTP that lets servers specify any other hosts 
from which a browser should permit loading of content.

How to block cross-origin access
To prevent cross-origin writes, 
	check an unguessable token in the request — known as a Cross-Site Request Forgery (CSRF) token. 
    prevent cross-origin reads of pages that require this token.
To prevent cross-origin reads of a resource, 
	ensure that it is not embeddable.
    prevent embedding because embedding a resource always leaks some information about it.
To prevent cross-origin embeds, 
	ensure that your resource cannot be interpreted
    Browsers may not respect the Content-Type header. 
For example, if you point a <script> tag at an HTML document, the browser will try to parse the HTML as JavaScript. When your resource is not an entry point to your site, you can also use a CSRF token to prevent embedding.