6、SpringBoot之Web原生组件注入（Servlet、Filter、Listener） javaspringboot

1、使用Servlet API

注入Servlet：

@ServletComponentScan(basePackages = "com.atguigu.admin") ：指定原生Servlet组件都放在那里
@WebServlet(urlPatterns = "/my")：效果：直接响应，没有经过Spring的拦截器？

/* 步骤：使用@WebServlet注解并设置匹配的路径 + @ServletComponentScan扫描Servlet组件继承HttpServlet类并重写方法 */ @WebServlet(urlPatterns = "/my") public class MyServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { resp.getWriter().write("666"); } }

@ServletComponentScan(basePackages = "com.atguigu.admin")//扫描Servlet组件 @SpringBootApplication public class Boot05WebAdminApplication {public static void main(String[] args) { SpringApplication.run(Boot05WebAdminApplication.class, args); }}

注入Filter：@WebFilter(urlPatterns={"/css/*","/images/*"})

/* 步骤：使用@WebFilter注解并设置拦截路径实现Filter接口并重写方法 */ @Slf4j @WebFilter(urlPatterns = {"/css/*","/images/*"}) public class MyFilter implements Filter {@Override public void init(FilterConfig filterConfig) throws ServletException { log.info("MyFilter初始化完成。。。。。。。。。"); }@Override public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException { log.info("MyFilter执行过滤。。。。。。。。。"); filterChain.doFilter(servletRequest,servletResponse); }@Override public void destroy() { log.info("MyFilter销毁。。。。。。。。。"); } }

注入Listener：@WebListener

/* 步骤：使用@WebListener注解实现ServletContextListener接口并实现方法 */ @Slf4j @WebListener public class MyListener implements ServletContextListener { //项目一运行就执行这个方法 @Override public void contextInitialized(ServletContextEvent sce) { log.info("MyListener监听到项目初始化完成"); }//项目真正被停掉后才执行方法(点idea里的红色小正方形按钮没有效) @Override public void contextDestroyed(ServletContextEvent sce) { log.info("MyListener监听到项目被终止了"); } }

推荐可以这种方式：
2、使用RegistrationBean ServletRegistrationBean, FilterRegistrationBean, ServletListenerRegistrationBean
先把@WebServlet，@WebFilter，@WebListener这三个注解注释掉

@Slf4j //@WebServlet(urlPatterns = "/my") public class MyServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { log.info("servlet执行"); resp.getWriter().write("666"); } }

@Slf4j //@WebFilter(urlPatterns = {"/css/*","/images/*"}) public class MyFilter implements Filter {@Override public void init(FilterConfig filterConfig) throws ServletException { log.info("MyFilter初始化完成。。。。。。。。。"); }@Override public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException { log.info("MyFilter执行过滤。。。。。。。。。"); filterChain.doFilter(servletRequest,servletResponse); }@Override public void destroy() { log.info("MyFilter销毁。。。。。。。。。"); } }

@Slf4j //@WebListener public class MyListener implements ServletContextListener { @Override public void contextInitialized(ServletContextEvent sce) { log.info("MyListener监听到项目初始化完成"); }@Override public void contextDestroyed(ServletContextEvent sce) { log.info("MyListener监听到项目被终止了"); } }

//将这个类标注为配置类，并保证每个@Bean方法被调用多少次返回的组件都是单实例的 @Configuration(proxyBeanMethods = true) public class MyRegistConfig { @Bean public ServletRegistrationBean myservlet(){ MyServlet myServlet = new MyServlet(); return new ServletRegistrationBean(myServlet,"/my","/my2"); }@Bean public FilterRegistrationBean myFilter(){ MyFilter myFilter = new MyFilter(); //第一种写法 //Servlet拦截的是什么路径，我Filter就拦截什么路径 //return new FilterRegistrationBean(myFilter,myservlet()); /* * 第二种写法 * 可以自己设置拦截什么路径 * */ FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean(myFilter); filterRegistrationBean.setUrlPatterns(Arrays.asList("/my","/css/*")); return filterRegistrationBean; }@Bean public ServletListenerRegistrationBean myListener(){ MyListener myListener = new MyListener(); return new ServletListenerRegistrationBean(myListener); }

执行顺序：执行Listener的contextInitialized容器初始化方法->执行Filter的init初始化方法 ->执行Filter的doFilter方法->执行Servlet的doGet或doPost方法 ->执行Filter的destroy方法->执行Listener的contextDestroyed销毁方法

扩展：DispatchServlet 如何注册进来

容器中自动配置了 DispatcherServlet，属性绑定到 WebMvcProperties 类；对应的配置文件配置项（prefix前缀）是 spring.mvc。
通过 ServletRegistrationBean 把 DispatcherServlet 配置进来。
默认映射的是 / 路径。所以项目下的所有请求都来到DispatchServlet 处理

以前使用Tomcat做原生的Servlet开发的时候：
多个Servlet都能处理到同一层路径时，使用精确优选原则：