被调用方解决-filter解决方案

1、后台程序先执行还是浏览器先判断？

返回的状态码：200表示执行成功    

说明请求是先执行，浏览器后判断

2、浏览器如何判断？

如果请求跨域，请求头里就会多一个Origin字段，当服务端返回信息的时候，会去判断响应头里是否有对应的字段，如果没有，即出现跨域请求问题，如果有，即允许跨域。

3、后台Filter代码实现

（1）编写CrossFilter过滤器

CrossFilter代码

package com.ajax.server.filter;

import javax.servlet.*;

importjavax.servlet.http.HttpServletResponse;

import java.io.IOException;

public class CrossFilter implements Filter{

   @Override

   public void init(FilterConfig filterConfig) throws ServletException {

    }

   @Override

   public void doFilter(ServletRequest servletRequest, ServletResponseservletResponse, FilterChain filterChain) throws IOException, ServletException{

       HttpServletResponse res = (HttpServletResponse) servletResponse;

        res.addHeader("Access-Control-Allow-Origin","http://localhost:8082");

       res.addHeader("Access-Control-Allow-Methods","GET");

       filterChain.doFilter(servletRequest, servletResponse);

    }

   @Override

   public void destroy() {

    }

}

（2）把过滤器注入到spring container中

AjaxserverApplication代码

package com.ajax.server;

import com.ajax.server.filter.CrossFilter;

importorg.springframework.boot.SpringApplication;

importorg.springframework.boot.autoconfigure.SpringBootApplication;

importorg.springframework.boot.web.servlet.FilterRegistrationBean;

importorg.springframework.context.annotation.Bean;

@SpringBootApplication

public class AjaxserverApplication {

       publicstatic void main(String[] args) {

              SpringApplication.run(AjaxserverApplication.class,args);

       }

       @Bean

       publicFilterRegistrationBean filterRegistrationBean() {

              FilterRegistrationBeanfilterRegistrationBean = new FilterRegistrationBean();

              filterRegistrationBean.addUrlPatterns("/*");

              filterRegistrationBean.setFilter(newCrossFilter());

              returnfilterRegistrationBean;

       }

}

4、测试验证

验证通过，普通请求解决了跨域问题