跨域问题

报错信息为：post request is No ‘Access-Control-Allow-Origin’ header is present on the requested resource.

原因：例如我们需要在A网址获取B网的资源，由于A，B不在同一个域名之中导致出现了跨域访问资源的情况。在浏览器的协议中，默认这样的访问是不安全的。跨域访问被认为违反了同源策略，它规定只能访问跟他html同源的资源
跨域限制是浏览器行为，不是服务器行为。 浏览器认为地址栏输入时安全的,所以不限制认为是跨域。

如何解决跨域问题：在后台添加过滤器，在需要跨域的请求体头部添加Header属性

首先新建过滤器的类

package com.jfly.apps.restful.springmvc;

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;

public class CORSInterceptor implements Filter {

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

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain)
            throws IOException, ServletException {
        HttpServletResponse response = (HttpServletResponse) servletResponse;
        String origin = (String) servletRequest.getRemoteHost() + ":" + servletRequest.getRemotePort();
        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,Authorization,Content-Type");
        response.setHeader("Access-Control-Allow-Credentials", "true");
        filterChain.doFilter(servletRequest, servletResponse);

    }

    @Override
    public void destroy() {
    }
}

其次在web.xml中配置过滤器，完成

<filter>
    <filter-name>CORSInterceptor</filter-name>
    <filter-class>com.jfly.apps.restful.springmvc.CORSInterceptor</filter-class>
</filter>
<filter-mapping>
    <filter-name>CORSInterceptor</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>