问：有了springMVC，为什么还要用servlet？有了servlet3的注解，为什么还要使用ServletRegistrationBean注入的方式？

使用场景：在有些场景下，比如我们要使用hystrix-dashboard，这时候就需要注入HystrixMetricsStreamServlet（第三方的servlet），该servlet是hystrix的组件。

一、代码

1、TestServlet（第一个servlet）

package com.xxx.secondboot.servlet;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class TestServlet extends HttpServlet { private static final long serialVersionUID = -4619665430596950563L; @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { System.out.println("zhaojigang servlet"); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { this.doGet(req, resp); }}

2、Testservlet2（第二个servlet）

package com.xxx.secondboot.servlet;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class TestServlet2 extends HttpServlet { private static final long serialVersionUID = 3788279972938793265L; @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { System.out.println("zhaojigang servlet2"); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { this.doGet(req, resp); }}

3、ServletConfig（servlet注入配置类）

package com.xxx.secondboot.servlet;import org.springframework.boot.context.embedded.ServletRegistrationBean;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;@Configurationpublic class ServletConfig { @Bean public TestServlet testServlet(){ return new TestServlet(); } @Bean public ServletRegistrationBean testServletRegistrationBean(TestServlet testServlet){ ServletRegistrationBean registration = new ServletRegistrationBean(testServlet); registration.setEnabled(true); registration.addUrlMappings("/servlet/test"); return registration; } /********************************************/ @Bean public TestServlet2 testServlet2(){ return new TestServlet2(); } @Bean public ServletRegistrationBean test2ServletRegistrationBean(TestServlet2 testServlet2){ ServletRegistrationBean registration = new ServletRegistrationBean(testServlet2); registration.setEnabled(true); registration.addUrlMappings("/servlet/test2"); return registration; } }

说明：使用ServletRegistrationBean来注入servlet，对于每一个servlet都有一个ServletRegistrationBean来注入。

注意：如果只是自己要使用servlet，可以直接只用servlet3的注解来声明servlet就好，但是像HystrixMetricsStreamServlet这样的第三方servlet，就只能通过上边这样的方式来搞了。

二、测试

启动服务，浏览器输入"http://localhost:8083/servlet/test","http://localhost:8083/servlet/test2"，查看console的输出。

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。