Spring Boot 注册 Servlet 三大组件

摘要
三大组件包括 Servlet、Filter、Listener
由于SpringBoot默认是以jar包的方式启动嵌入式的Servlet容器来启动SpringBoot的web应用，所以没有web.xml文件。

三大组件的注册

这个注册都是在自定义的配置类里面注册(即有@Configraution的类里)

ServletRegistrationBean

P.s. 这里自定义的Servlet继承HttpServlet

//注册三大组件
@Bean
public ServletRegistrationBean myServlet(){
    ServletRegistrationBean registrationBean = new ServletRegistrationBean(new MyServlet(),"/myServlet");
    return registrationBean;
}

自定义Servlet代码

public class MyServlet extends HttpServlet {
 
   //处理get请求
   @Override
   protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
      doPost(req,resp);
   }
 
   @Override
   protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
      resp.getWriter().write("Hello MyServlet");
   }
}

FilterRegistrationBean

P.s. 自定义的过滤器实现Filter

@Bean
public FilterRegistrationBean myFilter(){
    FilterRegistrationBean registrationBean = new FilterRegistrationBean();
    registrationBean.setFilter(new MyFilter());
    registrationBean.setUrlPatterns(Arrays.asList("/hello","/myServlet"));
    return registrationBean;
}

自定义过滤器代码

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

ServletListenerRegistrationBean

P.s. 自定义监听器 实现ServletContextListener

@Bean
public ServletListenerRegistrationBean myListener(){
    ServletListenerRegistrationBean<MyListener> registrationBean = new ServletListenerRegistrationBean<>(new MyListener());
    return registrationBean;
}

自定义监听器代码

public class MyListener implements ServletContextListener {
   @Override
   public void contextInitialized(ServletContextEvent sce) {
      System.out.println("contextInitialized...web应用启动");
   }
 
   @Override
   public void contextDestroyed(ServletContextEvent sce) {
      System.out.println("contextDestroyed...当前web项目销毁");
   }
}