已被CORS策略阻止：请求的资源上没有'Access-Control-Allow-Origin'标头 (使用Access-Control-Allow-Origin解决跨域)

问题：已被CORS策略阻止：请求的资源上没有'Access-Control-Allow-Origin'标头（跨域请求失败）

解决方法：使用过滤器设置Access-Control-Allow-Origin解决跨域请求

第一步： 创建过滤器

package com.ljw.filter;

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 SimpleCORSFilter implements Filter {

	@Override
	public void destroy() {

	}

	@Override
	public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
		HttpServletResponse response = (HttpServletResponse) res;  
		// 指定允许其他域名访问 
		response.setHeader("Access-Control-Allow-Origin", "*"); // 允许所有
		// response.setHeader("Access-Control-Allow-Origin", "http://127.0.0.1, http://locahost"); // 允许白名单IP
		// 响应类型
		response.setHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS, DELETE");  
		// 预检请求的结果缓存60分钟
		response.setHeader("Access-Control-Max-Age", "3600");  
		// 响应头设置 
		response.setHeader("Access-Control-Allow-Headers", "x-requested-with");  
		chain.doFilter(req, res);  
	}

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

	}
}
           

第二步：web.xml 配置过滤器

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