一：过滤器

1.过滤器介绍

过滤器是处于客户端与服务器资源文件之间的一道过滤网，帮助我们过滤一些不符合要求的请求。通常用作 Session校验，判断用户权限。

2.过滤器生命周期

使用过滤器很简单，只需要实现Filter类，然后重写它的3个方法即可。

• init方法：程序启动调用Filter的init()方法(永远只调用一次)；在容器中创建当前过滤器的时候自动调用这个方法。
• destory方法：程序停止调用Filter的destroy()方法(永远只调用一次)；在容器中销毁当前过滤器的时候自动调用这个方法。
• doFilter方法：doFilter()方法每次的访问请求如果符合拦截条件都会调用(程序第一次运行，会在servlet调用init()方法以后调用；不管第几次，都在调用doGet(),doPost()方法之前)。这个方法有3个参数，分别是ServletRequest、ServletResponse和FilterChain可以从参数中获取HttpServletReguest和HttpServletResponse对象进行相应的处理操作。

  ---

  二：使用注解方式实现过滤器（@WebFilter） 

   1.在springboot 启动类添加该注解@ServletComponentScan

  @SpringBootApplication
  @ServletComponentScan // 过滤器
  public class Springboot02WebTestApplication {
      SpringApplication.run(Springboot02WebTestApplication.class, args);
  }

   2.写个过滤器类，实现Filter接口

  import com.alibaba.fastjson.JSONObject;
  import org.springframework.core.annotation.Order;
  import javax.servlet.*;
  import javax.servlet.annotation.WebFilter;
  import javax.servlet.http.HttpServletRequest;
  import java.io.IOException;
  import java.io.PrintWriter;
  // urlPatterns 过滤路径  filterName 过滤器name
  @WebFilter(urlPatterns = "/user/*", filterName = "tokenFilter1")
  public class TokenFilter1 implements Filter {
      @Override
      public void init(FilterConfig filterConfig) throws ServletException {
  //        Filter.super.init(filterConfig);
          System.out.println("init");
      }
      @Override
      public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
          System.out.println("doFilter");
          HttpServletRequest request = (HttpServletRequest) servletRequest;
          String token = request.getHeader("token");
          System.out.println(token);
          //该方法执行后直接运行至下一个过滤器
          if(token!=null){
              filterChain.doFilter(servletRequest, servletResponse);
          }else{
              servletResponse.setCharacterEncoding("UTF-8");
              servletResponse.setContentType("application/json; charset=utf-8");
              PrintWriter out = servletResponse.getWriter();
              JSONObject res = new JSONObject();
              res.put("msg", "错误");
              res.put("success", "false");
              out.append(res.toString());
          }
      }
      @Override
      public void destroy() {
  //        Filter.super.destroy();
          System.out.println("destroy");
      }
  }
  

  3.访问，我使用的Postman软件进行的测试

          添加请求头token信息，才可以访问成功。

  ---

  三：使用非注解方式实现过滤器（直接注入到spring中）

   1.Filter代码

  import com.alibaba.fastjson.JSONObject;
  import javax.servlet.*;
  import javax.servlet.http.HttpServletRequest;
  import java.io.IOException;
  import java.io.PrintWriter;
  public class TokenFilter2 implements Filter {
      @Override
      public void init(FilterConfig filterConfig) throws ServletException {
          System.out.println("init");
      }
      @Override
      public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
          System.out.println("doFilter");
          HttpServletRequest request = (HttpServletRequest) servletRequest;
          String token = request.getHeader("token");
          System.out.println(token);
          //该方法执行后直接运行至下一个过滤器
          if(token!=null){
              filterChain.doFilter(servletRequest, servletResponse);
          }else{
              servletResponse.setCharacterEncoding("UTF-8");
              servletResponse.setContentType("application/json; charset=utf-8");
              PrintWriter out = servletResponse.getWriter();
              JSONObject res = new JSONObject();
              res.put("msg", "错误");
              res.put("success", "false");
              out.append(res.toString());
          }
      }
      @Override
      public void destroy() {
          System.out.println("destroy");
      }
  }
  

   2.Filter配置文件

  import com.itsufu.filter.TokenFilter2;
  import org.springframework.boot.web.servlet.FilterRegistrationBean;
  import org.springframework.context.annotation.Bean;
  import org.springframework.context.annotation.Configuration;
  @Configuration
  public class FilterConfig {
      // Filter代码类
      @Bean
      public TokenFilter2 tokenFilter2() {
          return new TokenFilter2();
      }
      @Bean
      public FilterRegistrationBean getFilterRegistrationBean(TokenFilter2 tokenFilter2) {
          FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
          filterRegistrationBean.setFilter(tokenFilter2);
          filterRegistrationBean.setOrder(2);
          filterRegistrationBean.addUrlPatterns("/user/*");
          filterRegistrationBean.setName("tokenFilter2");
          return filterRegistrationBean;
      }
  }
  

   3.测试与注解式一样。

  在此，祝各位帅哥美女，步步高升，一帆风顺！！！