JavaWeb筆記008 Filter的使用

Filter用的比較多，比較典型的一個場景就是解決跨域問題（什麼是跨域問題這裏先不解釋）
下面是示例
在web.xml中加入配置即可

<!--這個是聲明Filter-->
<filter>
   <filter-name>corsFilter</filter-name>
   <filter-class>com.xxxx.CorsFilter</filter-class>
 </filter>
 <!--指定Filter的攔截規則-->
 <filter-mapping>
   <filter-name>corsFilter</filter-name>
   <url-pattern>/*</url-pattern> <!--表示攔截所有-->
 </filter-mapping>

/**
 * 跨域，先允許所有
 */
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;
		// 這裏你可以做你想做的事情，所有的請求都會先經過這裏，比如你可以在這裏做個是否已經登錄的判斷，如果沒有，可以重定向到登錄頁面
		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());
		}
		// 最後放行，否則不會走到你的servlet裏面
		chain.doFilter(httpServletRequest, httpServletResponse);
	}
}