Filter

过滤器：用来过滤网站数据

• 乱码问题
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实现对乱码的过滤

@WebServlet("/show")
public class ShowServlet extends HttpServlet{
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        resp.setCharacterEncoding("UTF-8");
//        resp.setContentType("text/html;charset=UTF-8");
        resp.getWriter().write("你好，下午");
    }
}

@WebFilter("/show/*")
//@WebFilter("/show")效果一样
public class filter implements Filter {
    @Override
    //初始化 web服务器启动时进行初始化
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("filter初始化...");
    }
        /*
        chain：链
        过滤中的所有代码，在过滤特定请求时都会执行
        必须要让过滤器继续通行
         */
    @Override
    //doFilter()处理拦截，再通过filterChain.doFilter()来放行
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        servletRequest.setCharacterEncoding("UTF-8");
        servletResponse.setCharacterEncoding("UTF-8");
        servletResponse.setContentType("text/html;charset=UTF-8");
        System.out.println("doFilter执行前...");
        filterChain.doFilter(servletRequest, servletResponse);//让我们的请求继续，如果不写程序到这里结束
        System.out.println("doFilter执行后...");
    }

    @Override
    //销毁  web服务器关闭时进行销毁
    public void destroy() {
        System.out.println("filter销毁...");
    }
}