SpringBoot(8) SpringBoot过滤器Filter

1、SpringBoot启动默认加载的Filter
　　characterEncodingFilter

　　hiddenHttpMethodFilter

　　httpPutFormContentFilter

　　requestContextFilter

2、Filter优先级（Ordered.HIGHEST_PRECEDENCE  Ordered.LOWEST_PRECEDENCE）

低位值意味着更高的优先级 Higher values are interpreted as lower priority

自定义Filter，避免和默认的Filter优先级一样，不然会冲突

3、自定义Filter
1）使用Servlet3.0的注解进行配置

2）启动类里面增加 @ServletComponentScan，进行扫描

3）新建一个Filter类，implements Filter，并实现对应的接口

4) @WebFilter 标记一个类为filter，被spring进行扫描，urlPatterns：拦截规则，支持正则

5）控制chain.doFilter的方法的调用，来实现是否通过放行 不放行，web应用resp.sendRedirect("/index.html");

场景：权限控制、用户登录(非前端后端分离场景)等

 @WebFilter(urlPatterns = "/api/*", filterName = "loginFilter")
 public class LoginFilter  implements Filter{

      /**
       * 容器加载的时候调用
       */
       @Override
       public void init(FilterConfig filterConfig) throws ServletException {
           System.out.println("init loginFilter");
       }

       /**
        * 请求被拦截的时候进行调用
        */
       @Override
       public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
           System.out.println("doFilter loginFilter");

           HttpServletRequest req = (HttpServletRequest) servletRequest;
           HttpServletResponse resp = (HttpServletResponse) servletResponse;
           String username = req.getParameter("username");

           if ("admin".equals(username)) {
               filterChain.doFilter(servletRequest,servletResponse);
           } else {
               resp.sendRedirect("/index.html");
               return;
           }

       }

       /**
        * 容器被销毁的时候被调用
        */
       @Override
       public void destroy() {
           System.out.println("destroy loginFilter");
       }

 }

启动日志里，已经启动默认加载的Filter和自定义的Filter

官网地址：https://docs.spring.io/spring-boot/docs/2.1.0.BUILD-SNAPSHOT/reference/htmlsingle/#boot-features-embedded-container-servlets-filters-listeners