Spring Boot - Web 应用开发 - Servlet, Filter, Listener

素颜马尾好姑娘i 2022-05-29 04:45 206阅读 0赞

Web 开发使用 Controller 基本上可以完成大部分需求，但是我们还可能会用到 Servlet, Filter, Listener 等

# 1. 在 Spring Boot 中的三种实现方式 #

### (1) 方法一：通过注册`ServletRegistrationBean`、`FilterRegistrationBean`和`ServletListenerRegistrationBean`获得控制 ###

public class CustomerServlet extends HttpServlet { 
    
        private static final long serialVersionUID = 1L;
    
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            System.out.println("Servlet get method");
            doPost(req, resp);
        }
    
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            System.out.println("Servlet post method");
            resp.getWriter().write("hello world");
        }
    }

public class CustomFilter implements Filter { 
    
        @Override
        public void init(FilterConfig filterConfig) throws ServletException {
            System.out.println("init filter");
        }
    
        @Override
        public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
                throws IOException, ServletException {
            System.out.println("do filter");
            chain.doFilter(request, response);
        }
    
        @Override
        public void destroy() {
            System.out.println("destroy filter");
        }
    
    }

public class CustomListener implements ServletContextListener { 
    
        @Override
        public void contextInitialized(ServletContextEvent sce) {
            System.out.println("contextInitialized");
        }
    
        @Override
        public void contextDestroyed(ServletContextEvent sce) {
            System.out.println("contextDestroyed");
        }
    
    }

@Bean
    public ServletRegistrationBean servletRegistrationBean() {
        return new ServletRegistrationBean(new CustomerServlet(), "/oktfolio");
    }
    
    @Bean
    public FilterRegistrationBean filterRegistrationBean() {
        return new FilterRegistrationBean(new CustomFilter()/*, servletRegistrationBean()*/);
    }
    
    @Bean
    public ServletListenerRegistrationBean<CustomListener> servletListenerRegistrationBean() {
        return new ServletListenerRegistrationBean<CustomListener>(new CustomListener());
    }

### (2) 方法二：通过实现`ServletContextInitializer`接口直接注册 ###

@Override
        public void onStartup(ServletContext servletContext) throws ServletException {
            servletContext.addServlet("customServlet", new CustomerServlet()).addMapping("/oktfolio");
            servletContext.addFilter("customFilter", new CustomFilter()).addMappingForServletNames(EnumSet.of
                    (DispatcherType.REQUEST), true, "customServlet");
            servletContext.addListener(new CustomListener());
        }

### (3) 方法三：在`SpringBootApplication`上使用`@ServletComponentScan`注解后，直接通过```WebServlet``@WebFilter``@WebListener```注解自动注册 ###