第二十四章 springboot註入servlet

問：有了springMVC，為什麼還要用servlet？有了servlet3的註解，為什麼還要使用ServletRegistrationBean註入的方式？

使用場景：在有些場景下，比如我們要使用hystrix-dashboard，這時候就需要註入HystrixMetricsStreamServlet（第三方的servlet），該servlet是hystrix的組件。

一、代碼

1、TestServlet（第一個servlet）

 1 package com.xxx.secondboot.servlet;
 2 
 3 import java.io.IOException;
 4 
 5 import javax.servlet.ServletException;
 6 import javax.servlet.http.HttpServlet;
 7 import javax.servlet.http.HttpServletRequest;
 8 import javax.servlet.http.HttpServletResponse;
 9 
10 public class TestServlet extends HttpServlet {
11     
12     private static final long serialVersionUID = -4619665430596950563L;
13 
14     @Override
15     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
16         System.out.println("zhaojigang servlet");
17     }
18 
19     @Override
20     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
21         this.doGet(req, resp);
22     }
23 }

2、Testservlet2（第二個servlet）

 1 package com.xxx.secondboot.servlet;
 2 
 3 import java.io.IOException;
 4 
 5 import javax.servlet.ServletException;
 6 import javax.servlet.http.HttpServlet;
 7 import javax.servlet.http.HttpServletRequest;
 8 import javax.servlet.http.HttpServletResponse;
 9 
10 public class TestServlet2 extends HttpServlet {
11 
12     private static final long serialVersionUID = 3788279972938793265L;
13 
14     @Override
15     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
16         System.out.println("zhaojigang servlet2");
17     }
18 
19     @Override
20     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
21         this.doGet(req, resp);
22     }
23 }

3、ServletConfig（servlet註入配置類）

 1 package com.xxx.secondboot.servlet;
 2 
 3 import org.springframework.boot.context.embedded.ServletRegistrationBean;
 4 import org.springframework.context.annotation.Bean;
 5 import org.springframework.context.annotation.Configuration;
 6 
 7 @Configuration
 8 public class ServletConfig {
 9     
10     @Bean
11     public TestServlet testServlet(){
12         return new TestServlet();
13     }
14     
15     @Bean
16     public ServletRegistrationBean testServletRegistrationBean(TestServlet testServlet){
17         ServletRegistrationBean registration = new ServletRegistrationBean(testServlet);
18         registration.setEnabled(true);
19         registration.addUrlMappings("/servlet/test");
20         return registration;
21     }
22     /********************************************/
23     @Bean
24     public TestServlet2 testServlet2(){
25         return new TestServlet2();
26     }
27     
28     @Bean
29     public ServletRegistrationBean test2ServletRegistrationBean(TestServlet2 testServlet2){
30         ServletRegistrationBean registration = new ServletRegistrationBean(testServlet2);
31         registration.setEnabled(true);
32         registration.addUrlMappings("/servlet/test2");
33         return registration;
34     }
35     
36 }

說明：使用ServletRegistrationBean來註入servlet，對於每一個servlet都有一個ServletRegistrationBean來註入。

註意：如果只是自己要使用servlet，可以直接只用servlet3的註解來聲明servlet就好，但是像HystrixMetricsStreamServlet這樣的第三方servlet，就只能通過上邊這樣的方式來搞了。

二、測試

啟動服務，瀏覽器輸入"http://localhost:8083/servlet/test","http://localhost:8083/servlet/test2"，查看console的輸出。