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。