第二十四章 springboot注入servlet

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;

 @Configuration
 public 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。