https://medium.com/@ronaizacard/wow-i-wrot-my-fist-java-production-code-and-this-make-me-happy-a-lot-261a70a2e507

CorsFilter.java

package yor.package.addres.goes.here;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class CorsFilter implements Filter {

	@Override
	public void destroy() {}

	@Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain chain) throws IOException, ServletException {
	    HttpServletRequest request = (HttpServletRequest) servletRequest;
	    HttpServletResponse resp = (HttpServletResponse) servletResponse;
	    
	    System.out.println("Request:" + request.getMethod());
	
	    
	    resp.addHeader("Access-Control-Allow-Origin","*");
	    resp.addHeader("Access-Control-Allow-Methods","GET,POST,PUT,DELETE,OPTIONS");
	    resp.addHeader("Access-Control-Allow-Headers","Origin, X-Requested-With, Content-Type, Accept");
	
	    // Just ACCEPT and REPLY OK if OPTIONS
      // TODO removing this if
	    if ( request.getMethod().equals("OPTIONS") ) {
	        resp.setStatus(HttpServletResponse.SC_OK);
	        return;
	    }
	    
	    chain.doFilter(request, servletResponse);
	}

	@Override
	public void init(FilterConfig arg0) throws ServletException {}

}