Spring Boot中整合Servlet、Filter、Listener的两种方式

一、SpringBoot中整合Servlet

方式一：通过注解扫描完成 Servlet 组件的注册

步骤：
1、编写 servlet，并加上@WebServlet注解

@WebServlet(name="FirstServlet",urlPatterns="/first")
public class FirstServlet extends HttpServlet {
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		System.out.println("FirstServlet............");
	}
}

2、在启动类上添加@ServletComponentScan

@SpringBootApplication
//在springBoot启动时会扫描 @WebServlet，并将该类实例化
@ServletComponentScan 
public class App {
	public static void main(String[] args) {
		SpringApplication.run(App.class, args);
	}
}

方式二：通过方法完成 Servlet 组件的注册

步骤：
1、编写 servlet

public class SecondServlet extends HttpServlet {
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		System.out.println("SecondServlet..........");
	}
}

2、在启动类中注册 Servlet（对应添加一个@Bean）

	//注册 Servlet 
	@Bean
	public ServletRegistrationBean getServletRegistrationBean(){
		ServletRegistrationBean bean = new ServletRegistrationBean(new SecondServlet());
		bean.addUrlMappings("/second");
		return bean;
	}

---

其实就是替代了传统的在web.xml中配置的方式：

 <servlet>
 	<servlet-name>FirstServlet</servlet-name>
 	<servlet-class>com.bw.servlet.FirstServlet</servlet-class>
 </servlet>
 
 <servlet-mapping>
  <servlet-name>FirstServlet</servlet-name>
  <url-pattern>/first</url-pattern>
 </servlet-mapping>

二、SpringBoot中整合Filter

整合Filter与整合Servlet类似，这里只介绍方式二的整合。
步骤：
1、编写 Filter

public class SecondFilter implements Filter {
	@Override
	public void destroy() {
		// TODO Auto-generated method stub
	}
	@Override
	public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2)
			throws IOException, ServletException {
		System.out.println("进入SecondFilter");
		arg2.doFilter(arg0, arg1);
		System.out.println("离开SecondFilter");
	}
	@Override
	public void init(FilterConfig arg0) throws ServletException {
		// TODO Auto-generated method stub
	}
}

2、在启动类中注册 Filter

	@Bean
	public FilterRegistrationBean getFilterRegistrationBean(){
		FilterRegistrationBean bean = new FilterRegistrationBean(new SecondFilter());
		//bean.addUrlPatterns(new String[]{"*.do","*.jsp"});
		bean.addUrlPatterns("/second");
		return bean;
	}

三、SpringBoot中整合Listener

1、编写 Listener

public class SecondListener implements ServletContextListener {

	@Override
	public void contextDestroyed(ServletContextEvent arg0) {
		// TODO Auto-generated method stub
	}

	@Override
	public void contextInitialized(ServletContextEvent arg0) {
		System.out.println("SecondListener..init.....");
	}

}

2、注册 listener

	@Bean
	public ServletListenerRegistrationBean<SecondListener> getServletListenerRegistrationBean(){
		ServletListenerRegistrationBean<SecondListener> bean= new ServletListenerRegistrationBean<SecondListener>(new SecondListener());
		return bean;
	}

总结：其实方式一比方式二简便