[十二]SpringBoot 之 servlet

Web开发使用 Controller 基本上可以完成大部分需求，但是我们还可能会用到 Servlet、Filter、Listener、Interceptor 等等。

当使用spring-Boot时，嵌入式Servlet容器通过扫描注解的方式注册Servlet、Filter和Servlet规范的所有监听器（如HttpSessionListener监听器）。
Spring boot 的主 Servlet 为DispatcherServlet，其默认的url-pattern为“/”。也许我们在应用中还需要定义更多的Servlet，该如何使用SpringBoot来完成呢？

在spring boot中添加自己的Servlet有两种方法，代码注册Servlet和注解自动注册（Filter和Listener也是如此）。
一、代码注册通过ServletRegistrationBean、 FilterRegistrationBean 和ServletListenerRegistrationBean 获得控制。
也可以通过实现 ServletContextInitializer 接口直接注册。

二、在SpringBootApplication 上使用@ServletComponentScan注解后，Servlet、Filter、Listener 可以直接通过 @WebServlet、@WebFilter、@WebListener 注解自动注册，无需其他代码。

1.通过代码注册Servlet示例代码：

package me.shijunjie.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class MyServlet1 extends HttpServlet {
    private static final long serialVersionUID = 1L;



    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        System.out.println(">>>>>>>>>>doGet()<<<<<<<<<<<");

        doPost(req, resp);

    }



    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        System.out.println(">>>>>>>>>>doPost()<<<<<<<<<<<");

        resp.setContentType("text/html"); 

        PrintWriter out = resp.getWriter(); 

        out.println("<html>"); 

        out.println("<head>"); 

        out.println("<title>HelloWorld</title>"); 

        out.println("</head>"); 

        out.println("<body>"); 

        out.println("<h1>这是：MyServlet1</h1>"); 

        out.println("</body>"); 

        out.println("</html>");

    }
}

package me.shijunjie.testspringboot2;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.embedded.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;

import me.shijunjie.servlet.MyServlet1;

@SpringBootApplication
public class App 
{
    
     /**
     * 注册Servlet.不需要添加注解：@ServletComponentScan
     * @return
     */
    @Bean
    public ServletRegistrationBean myServlet1(){

           return new ServletRegistrationBean(new MyServlet1(),"/myServlet/*");
    }
    
    public static void main( String[] args )
    {
        SpringApplication.run(App.class, args);
    }
}

测试

2.使用注解注册Servlet示例代码添加@WebServlet注解

package me.shijunjie.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet(urlPatterns="/myServlet2/*",description="Servlet的说明")
public class MyServlet2 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println(">>>>>>>>>>doGet()<<<<<<<<<<<");
        doPost(req, resp);
    }



    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        System.out.println(">>>>>>>>>>doPost()<<<<<<<<<<<");

        resp.setContentType("text/html"); 

        PrintWriter out = resp.getWriter(); 

        out.println("<html>"); 

        out.println("<head>"); 

        out.println("<title>HelloWorld</title>"); 

        out.println("</head>"); 

        out.println("<body>"); 

        out.println("<h1>这是：MyServlet2</h1>"); 

        out.println("</body>"); 

        out.println("</html>");

    }
}

添加@ServletComponentScan注解

package me.shijunjie.testspringboot2;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.ServletComponentScan;

/**
 * Hello world!
 *
 */
@SpringBootApplication
@ServletComponentScan("me.shijunjie.servlet")
public class App 
{
    
    /* *//**
     * 注册Servlet.不需要添加注解：@ServletComponentScan
     * @return
     *//*
    @Bean
    public ServletRegistrationBean myServlet1(){

           return new ServletRegistrationBean(new MyServlet1(),"/myServlet/*");
    }*/
    
    public static void main( String[] args )
    {
        SpringApplication.run(App.class, args);
    }
}

测试