1.maven操作过程

首先建一个空的maven项目，将src文件夹删掉，然后建一个我们自己的module文件用来写servlet。在创建的时候点击使用wepapp模板

建完module后，我们在父工程的pom文件需要配置我们需要的jar包

    <dependencies>
        <!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.1</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/javax.servlet.jsp/javax.servlet.jsp-api -->
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>javax.servlet.jsp-api</artifactId>
            <version>2.3.3</version>
        </dependency>

    </dependencies>

jar包配置完成后，开始写servlet
首先在main文件夹下创建Java包和resources包

将两个包设置为源文件夹后建包，写servlet

2.servlet写法

首先servlet继承了一个httpservlet的一个类，这个类继承了GenericServlet类，GenericServlet类又实现了servlet,ServletConfig, Serializable接口。这就是servlet的整体继承关系。
在接口servlet接口中有四个方法：

void init(ServletConfig var1) throws ServletException;
//初始化servlet
    ServletConfig getServletConfig();
//获取servlet配置信息
    void service(ServletRequest var1, ServletResponse var2) throws ServletException, IOException;
//获取请求响应
    String getServletInfo();
//调用销毁方法
    void destroy();

继承HttpServlet类重写doGet()和doPost()方法：

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        ServletInputStream inputStream = req.getInputStream();
//        ServletOutputStream outputStream = resp.getOutputStream();
//        BufferedReader reader = req.getReader();
        PrintWriter writer = resp.getWriter();
        writer.print("Hello,servlet!");
    }

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

在xml文件中注册servlet并且添加servlet映射

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
         http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">
        <!--注册servlet-->
        <servlet>
          <servlet-name>HelloServlet</servlet-name>
          <servlet-class>com.gsy.HelloServlet</servlet-class>
        </servlet>
        <!--设置servlet映射以及响应路径-->
        <servlet-mapping>
          <servlet-name>HelloServlet</servlet-name>
          <url-pattern>/hello</url-pattern>
        </servlet-mapping>

</web-app>

之后将项目部署到tomcat服务器上：

启动tomcat服务器即可完成！