SpringMVC通过CROS协议配置跨域访问

CORS协议：CORS是一个W3C标准，全称是"跨域资源共享"（Cross-origin resource sharing）。它允许浏览器向跨源服务器，发出XMLHttpRequest请求，从而克服了AJAX只能同源使用的限制。只要服务器实现了CORS接口，就可以跨源通信。

CORS常见的header:

• Access-Control-Allow-Origin: http://kbiao.me
  
• Access-Control-Max-Age: 3628800
• Access-Control-Allow-methods: GET, PUT, DELETE, POST
• Access-Control-Allow-Header: content-type
  
• Access-Control-Allow-Credentail: true

"Access-Control-Allow-Origin"表明它允许" http://kbiao.me "发起跨域请求

"Access-Control-Max-Age"表明在3628800秒内，不需要再发送预检验请求，可以缓存该结果（上面的资料上我们知道CROS协议中，一个AJAX请求被分成了第一步的OPTION预检测请求和正式请求）

"Access-Control-Allow-Methods"表明它允许GET、PUT、DELETE的外域请求

"Access-Control-Allow-Headers"表明它允许跨域请求包含content-type头

"Access-Control-Allow-Credentials"表明它允许cookies

定义一个过滤器，命名为SimpleCORSFilter：

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.HttpServletResponse;
import org.springframework.stereotype.Component;

@Component
public class SimpleCORSFilter implements Filter {

    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
        HttpServletResponse response = (HttpServletResponse) res;
        response.setHeader("Access-Control-Allow-Origin", "*");
        response.setHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS, DELETE");
        response.setHeader("Access-Control-Max-Age", "3600");
        response.setHeader("Access-Control-Allow-Headers", "x-requested-with, content-type");
        response.setHeader("Access-Control-Allow-Credentials","true");
        chain.doFilter(req, res);
    }

    public void init(FilterConfig filterConfig) {}

    public void destroy() {}

}

 配置Web.xml使得过滤器生效

<filter>
      <filter-name>cors</filter-name>
      <filter-class>packageName.SimpleCORSFilter</filter-class>
</filter>
<filter-mapping>
      <filter-name>cors</filter-name>
      <url-pattern>/*</url-pattern>
</filter-mapping>

 spring 4.2+ 可以通过注解实现：@CrossOrigin(origins = “ ”)