JavaWeb笔记008 Filter的使用

Filter用的比较多，比较典型的一个场景就是解决跨域问题（什么是跨域问题这里先不解释）
下面是示例
在web.xml中加入配置即可

<!--这个是声明Filter-->
<filter>
   <filter-name>corsFilter</filter-name>
   <filter-class>com.xxxx.CorsFilter</filter-class>
 </filter>
 <!--指定Filter的拦截规则-->
 <filter-mapping>
   <filter-name>corsFilter</filter-name>
   <url-pattern>/*</url-pattern> <!--表示拦截所有-->
 </filter-mapping>

/**
 * 跨域，先允许所有
 */
public class CorsFilter implements Filter {

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

	}

	@Override
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
			throws IOException, ServletException {
		HttpServletResponse httpServletResponse = (HttpServletResponse) response;
		HttpServletRequest httpServletRequest = (HttpServletRequest) request;
		// 这里你可以做你想做的事情，所有的请求都会先经过这里，比如你可以在这里做个是否已经登录的判断，如果没有，可以重定向到登录页面
		httpServletResponse.setHeader("Access-Control-Allow-Origin", "*");
		httpServletResponse.setHeader("Access-Control-Allow-Methods", "POST,GET,OPTIONS,DELETE");
		httpServletResponse.setHeader("Access-Control-Max-Age", "3600");
		httpServletResponse.setHeader("Access-Control-Allow-Headers", "x-requested-with,Authorization");

		if ("OPTIONS".equals(httpServletRequest.getMethod())) {
			httpServletResponse.setStatus(HttpStatus.NO_CONTENT.value());
		}
		// 最后放行，否则不会走到你的servlet里面
		chain.doFilter(httpServletRequest, httpServletResponse);
	}
}