Filter

Filter

Filter：过滤器：用来过滤网站的数据

Filter：开发步骤

1. 导包

2. 编写过滤器

   1. 导包不要错误

      

   2. 实现Filter接口，重写方法

      @WebFilter("/*")
      public class CharacterEncodingFilter implements Filter {
      //    初始化  web服务器启动已经初始化了
          public void init(FilterConfig filterConfig) throws ServletException {
              System.out.println("初始化文件");
          }
      // chain：链
      /*
      *
      * 1、过滤器中的所有代码，再过滤特定请求的时候会执行
      * 2、必须要让过滤器继续执行下去*/
          public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
              request.setCharacterEncoding("utf-8");
              response.setCharacterEncoding("utf-8");
              response.setContentType("text/html;charset=UTF-8");
      
              System.out.println("CharacterFilter执行前");
              chain.doFilter(request,response); //让请求继续走下去，如果不写，，程序到这里就被拦截了
              System.out.println("CharacterFilter执行后");
          }
      //    销毁  :web服务器关闭的时候过滤器销毁
          public void destroy() {
              System.out.println("文件被销毁了");
          }
      }
      
      

   3. 在xml中配置Filter

      <filter>
          <filter-name>CharterFilter</filter-name>
          <filter-class>com.yt.filter.CharacterEncodingFilter</filter-class>
      </filter>
      <filter-mapping>
      <filter-name>CharterFilter</filter-name>
      <!--        只要是servlet下的任何请求，都会经过这个过滤器-->
      <url-pattern>/servlet/*</url-pattern>
      </filter-mapping>
      

测试过滤器的servlet

public class ShowServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        resp.setCharacterEncoding("utf-8");

        resp.getWriter().write("你好呀！世界");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}