=================6、SpringBoot拦截器实战和 Servlet3.0自定义Filter、Listener ============

1、深入SpringBoot2.x过滤器Filter和使用Servlet3.0配置自定义Filter实战(核心知识)
简介:讲解SpringBoot里面Filter讲解和使用Servlet3.0配置自定义Filter实战

filter简单理解：人--->检票员（filter）---> 景点

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

注册Filter的bean FilterRegistrationBean
同模块里面有相关默认Filter
web->servlet->filter

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

6）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

1、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

packagenet.xdclass.demo.Filter;importjava.io.IOException;importjavax.servlet.Filter;importjavax.servlet.FilterChain;importjavax.servlet.FilterConfig;importjavax.servlet.ServletException;importjavax.servlet.ServletRequest;importjavax.servlet.ServletResponse;importjavax.servlet.annotation.WebFilter;importjavax.servlet.http.HttpServletRequest;importjavax.servlet.http.HttpServletResponse;@WebFilter(urlPatterns= "/api/*", filterName = "loginFilter")public class LoginFilter  implementsFilter{/*** 容器加载的时候调用*/@Overridepublic void init(FilterConfig filterConfig) throwsServletException {System.out.println("init loginFilter");}/*** 请求被拦截的时候进行调用*/@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throwsIOException, ServletException {System.out.println("doFilter loginFilter");HttpServletRequest req=(HttpServletRequest) servletRequest;HttpServletResponse resp=(HttpServletResponse) servletResponse;String username= req.getParameter("username");if ("xdclass".equals(username)) {filterChain.doFilter(servletRequest,servletResponse);}else{resp.sendRedirect("/index.html");return;}}/*** 容器被销毁的时候被调用*/@Overridepublic voiddestroy() {System.out.println("destroy loginFilter");}}

2、Servlet3.0的注解自定义原生Servlet实战
讲解：使用 Servlet3.0的注解自定义原生Servlet和Listener
1、自定义原生Servlet

@WebServlet(name = "userServlet",urlPatterns = "/test/customs")
public class UserServlet extends HttpServlet{

@Override
public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.getWriter().print("custom sevlet");
resp.getWriter().flush();
resp.getWriter().close();
}

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

3、Servlet3.0的注解自定义原生Listener监听器实战
简介：监听器介绍和Servlet3.0的注解自定义原生Listener监听器实战

1、自定义Listener(常用的监听器 servletContextListener、httpSessionListener、servletRequestListener)
@WebListener
public class RequestListener implements ServletRequestListener {

@Override
public void requestDestroyed(ServletRequestEvent sre) {
// TODO Auto-generated method stub
System.out.println("======requestDestroyed========");
}

@Override
public void requestInitialized(ServletRequestEvent sre) {
System.out.println("======requestInitialized========");

}

4、SpringBoot2.X自定义拦截器实战及新旧配置对比(核心知识)
简介: 讲解拦截器使用，Spingboot2.x新版本配置拦截拦截器和旧版本SpringBoot配置拦截器区别讲解
类似filter，但是不等同。
1、@Configuration
继承WebMvcConfigurationAdapter(SpringBoot2.X之前旧版本)

packagenet.xdclass.demo.intecpter;importorg.springframework.context.annotation.Configuration;importorg.springframework.web.servlet.config.annotation.InterceptorRegistry;importorg.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;//@Configuration
public class CustomOldWebMvcConfigurer extendsWebMvcConfigurerAdapter {@Overridepublic voidaddInterceptors(InterceptorRegistry registry) {registry.addInterceptor(new LoginIntercepter()).addPathPatterns("/api/");super.addInterceptors(registry);}}

SpringBoot2.X 新版本配置拦截器 implements WebMvcConfigurer

packagenet.xdclass.demo.intecpter;importorg.springframework.context.annotation.Configuration;importorg.springframework.web.servlet.config.annotation.InterceptorRegistry;importorg.springframework.web.servlet.config.annotation.WebMvcConfigurer;@Configurationpublic class CustomWebMvcConfigurer implementsWebMvcConfigurer  {@Overridepublic voidaddInterceptors(InterceptorRegistry registry) {registry.addInterceptor(new LoginIntercepter()).addPathPatterns("/api2/*/**");registry.addInterceptor(new TwoIntercepter()).addPathPatterns("/api2/*/**");//.excludePathPatterns("/api2/xxx/**");//拦截全部 /*/*/**
WebMvcConfigurer.super.addInterceptors(registry);}}

2、自定义拦截器 HandlerInterceptor （分2步骤：1.新建intercept实现接口 2配置类实现接口，注解注册，添加新建的拦截器到url映射）
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

packagecom.atguigu.springboot.interceptor;importjavax.servlet.http.HttpServletRequest;importjavax.servlet.http.HttpServletResponse;importorg.springframework.web.servlet.HandlerInterceptor;importorg.springframework.web.servlet.ModelAndView;public class LoginIntercepter implementsHandlerInterceptor{/*** 进入controller方法之前*/@Overridepublic booleanpreHandle(HttpServletRequest request,HttpServletResponse response, Object handler)throwsException {System.out.println("LoginIntercepter------->preHandle");//String token = request.getParameter("access_token");//
//response.getWriter().print("fail");return HandlerInterceptor.super.preHandle(request, response, handler);}/*** 调用完controller之后，视图渲染之前*/@Overridepublic voidpostHandle(HttpServletRequest request,HttpServletResponse response, Object handler,ModelAndView modelAndView)throwsException {System.out.println("LoginIntercepter------->postHandle");HandlerInterceptor.super.postHandle(request, response, handler, modelAndView);}/*** 整个完成之后，通常用于资源清理*/@Overridepublic voidafterCompletion(HttpServletRequest request,HttpServletResponse response, Object handler, Exception ex)throwsException {System.out.println("LoginIntercepter------->afterCompletion");HandlerInterceptor.super.afterCompletion(request, response, handler, ex);}}

3、按照注册顺序进行拦截，先注册，先被拦截

拦截器不生效常见问题：
1）是否有加@Configuration
2）拦截路径是否有问题 ** 和 *
3）拦截器最后路径一定要 “/**”， 如果是目录的话则是 /*/

Filter
是基于函数回调 doFilter()，而Interceptor则是基于AOP思想
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

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