springBoot 2.x过滤器--监听器--拦截器

springboot 2.x过滤器

1.什么是 springboot 2.x过滤器

类似于检票员,检验游客的门票

2.springboot里的过滤器

ApplicationContextHeaderFilter
OrderedCharacterEncodingFilter
OrderedFormContentFilter
OrderedRequestContextFilter

3.过滤器的优先级

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

4.自定义Filter,避免和默认的Filter优先级一样,不然会冲突

注册Filter配置俩种方式
- bean FilterRegistrationBean
- Servlet 3.0 webFilter

5.使用新版servlet 3.0的注解开发自定义Filter

在启动类里添加注解@ServletComponentScan ,进行扫描
新建一个Filter类,implements Filter,并实现对应的接口
@WebFilter 标记一个类为filter,被spring扫描
urlPatterns:拦截规则,支持正则, urlPatterns为过滤的路径,filterName为过滤器的名称
控制chain.doFilter的方法调用,来实现是否放行
不放行,web应用resp.sendRedirect("/index.html")或者返回json字符串

使用范围:权限控制、⽤户登录状态控制

5.1 启动类里添加注解@ServletComponentScan

@SpringBootApplication     //标记此类为springboot 应用
@ServletComponentScan
public class MavenDemoApplication {public static void main(String[] args) {SpringApplication.run(MavenDemoApplication.class, args);}
}

5.2新建一个filter 包,包里创建一个Filter类

5.3类里实现Filter接口,并且类被标注为 @WebFilter, urlPatterns为过滤的路径(过滤/api/v1/pri/ 下所有的路径),filterName为过滤器的名称(登录过滤器)

5.4 在实现接口的类里重写3个方法

public void init(FilterConfig filterConfig) throws ServletException {}

public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {}

public void destroy() {}

上述三个方法均在类加载时使用,初始化–过滤–销毁,过滤的过程发生在第二个过滤的时候
过滤过程中的代码:

@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {System.out.println("过滤开始");HttpServletRequest req = (HttpServletRequest) servletRequest;HttpServletResponse rep = (HttpServletResponse) servletResponse;String token =req.getHeader("token");   //从headers中得到tokenif (StringUtils.isEmpty(token)){           // 如果header里面没有token时,从请求的参数里面拿tokentoken = req.getParameter("token");}if (!StringUtils.isEmpty(token)){            //如果还为空,直接返回json字符串或跳转index页面// 判断token是否合法User user = UserServiceImpl.sessionMap.get(token);  //在登录时在sessionMap里存了token,通过token取出user,若为空则未登录,若不为空则显示正确if(user !=null){filterChain.doFilter(servletRequest,servletResponse);}else{JsonData jsonData = JsonData.buildError("登录失败,token无效",-2);String jsonStr = objectMapper.writeValueAsString(jsonData);         //json转字符renderJson(rep,jsonStr);}}else {JsonData jsonData = JsonData.buildError("登录失败,token无效",-3);String jsonStr = objectMapper.writeValueAsString(jsonData);    renderJson(rep,jsonStr);}}private void renderJson(HttpServletResponse response,String json){response.setCharacterEncoding("UTF-8");response.setContentType("application/json");try(PrintWriter writer=response.getWriter()){writer.print(json);}catch (Exception e){e.printStackTrace();}}

springboot监听器

监听器：

应⽤启动监听器，会话监听器，请求监听器

作用:

ServletContextListener 应⽤启动监听
HttpSessionLisener 会话监听
ServletRequestListener 请求监听

常⽤的监听器

ServletContextListener、HttpSessionListener、ServletRequestListener)

代码:

@WebListener
public class CustomSessionListener implements HttpSessionListener {@Overridepublic void sessionCreated(HttpSessionEvent se) {System.out.println("会话监听已开启");//HttpSessionListener.super.sessionCreated(se);}@Overridepublic void sessionDestroyed(HttpSessionEvent se) {System.out.println("会话监听已销毁");//HttpSessionListener.super.sessionDestroyed(se);}
}

SpringBoot2.X拦截器

1. 拦截器：

和过滤器⽤途基本类似

2.SpringBoot2.X拦截器使用步骤:

2.1 创建一个类(列如:CustomWebConfigurer类)实现WebMvcConfigurer接口 拦截器配置类
2.2 在类上加注解@COnfiguration
2.3 在类里override 重写addInterceptors这个方法,在方法里可添加自定义的多个拦截器
2.4 自定义拦截器
- preHandle：调⽤Controller某个⽅法之前
- postHandle：Controller之后调⽤，视图渲染之前，如果控制器Controller出现了
  异常，则不会执⾏此⽅法
- afterCompletion：不管有没有异常，这个afterCompletion都会被调⽤，⽤于资
  源清理

拦截器的配置类代码:

/*** 拦截器配置类*/
@Configuration
public class CustomWebConfigurer implements WebMvcConfigurer {@Overridepublic void addInterceptors(InterceptorRegistry registry) {registry.addInterceptor(getLoginInterceptor()).addPathPatterns("/api/v1/pri/**");//可添加多个拦截器registry.addInterceptor(new TwoLoginIntercepter()).addPathPatterns("/api/v1/pri/**");WebMvcConfigurer.super.addInterceptors(registry);}@Beanpublic LoginIntercepter getLoginInterceptor(){return new LoginIntercepter();}
}

拦截器实现类代码:

public class LoginIntercepter implements HandlerInterceptor {private static final ObjectMapper objectMapper = new ObjectMapper();@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {System.out.println("LoginIntercepter preHandle...");String token =request.getHeader("token");   //从headers中得到tokenif (StringUtils.isEmpty(token)){token = request.getParameter("token");}if (!StringUtils.isEmpty(token)){// 判断token是否合法User user = UserServiceImpl.sessionMap.get(token);if(user !=null){return true;}else{JsonData jsonData = JsonData.buildError("登录失败,token无效",-2);String jsonStr = objectMapper.writeValueAsString(jsonData);renderJson(response,jsonStr);return false;}}else {JsonData jsonData =JsonData.buildError("未登录",-3);String jsonStr = objectMapper.writeValueAsString(jsonData);renderJson(response,jsonStr);return false;}//return HandlerInterceptor.super.preHandle(request, response, handler);}private void renderJson(HttpServletResponse response,String json){response.setCharacterEncoding("UTF-8");response.setContentType("application/json");try(PrintWriter writer=response.getWriter()){writer.print(json);}catch (Exception e){e.printStackTrace();}}@Overridepublic void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {System.out.println("LoginIntercepter postHandle...");HandlerInterceptor.super.postHandle(request, response, handler, modelAndView);}@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {System.out.println("LoginIntercepter afterCompletion...");HandlerInterceptor.super.afterCompletion(request, response, handler, ex);}
}

拦截器不生效的常见问题:

是否有加@Configuration
拦截路径是否有问题 ** 和 *
拦截器最后路径⼀定要 /** 如果是⽬录的话则是 /*/

和Filter过滤器的区别

Filter和Interceptor⼆者都是AOP编程思想的体现，功能基本都可以实现
拦截器功能更强⼤些，Filter能做的事情它都能做
Filter在只在Servlet前后起作⽤，⽽Interceptor够深⼊到⽅法前后、异常抛出前后等
filter依赖于Servlet容器即web应⽤中，⽽Interceptor不依赖于Servlet容器所以可以运⾏在
多种环境。
在接⼝调⽤的⽣命周期⾥，Interceptor可以被多次调⽤，⽽Filter只能在容器初始化时调⽤⼀
次。
Filter和Interceptor的执⾏顺序过滤前->拦截前->action执⾏->拦截后->过滤后

如何配置不拦截某些路径？

registry.addInterceptor(new
LoginIntercepter()).addPathPatterns("/api/v1/pri/**")

//配置不拦截某些路径，⽐如静态资源
.excludePathPatterns("//*.html","//*.js");