servlet创建

servlet就是一个Java类。类就会有一系列的属性和方法
Java包组成：javax.servlet和javax.servlet.http
在javax.servlet包中定义了所有的Servlet类都必须实现或扩展的的通用接口和类
在javax.servlet.http包中定义了采用HTTP通信协议的HttpServlet类.

1-1.三种创建方式

1.实现servlet接口

import javax.servlet

/**
 * @author:Cherry
 * @createTime:2020-12-31 9:57
 *
 * 要实现接口里面的方法 
 *  - 但实际上有用的只有service方法
 *  基本上不用这个方法创建
 */
public class LoginServlet implements Servlet {
    @Override
    public void init(ServletConfig servletConfig) throws ServletException {
    }
    @Override
    public ServletConfig getServletConfig() {
        return null;
    }
    @Override
    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
    }
    @Override
    public String getServletInfo() {
        return null;
    }
    @Override
    public void destroy() {
j
    }
}

2.继承GenericServlet抽象类

import javax.servlet.GenericServlet;

/**
 * @author:Cherry
 * @createTime:2020-12-31 10:01
 *
 * 这个创建方法也基本不用
 *  - 继承人抽象类只实现一个service方法
 */
public class RegisterServlet extends GenericServlet {
    @Override
    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
    }
}

3.继承HttpServlet抽象类

import javax.servlet.http.HttpServlet;

/**
 * @author:Cherry
 * @createTime:2020-12-30 20:05
 */
public class UserServlet extends HttpServlet {
    private IUserService userService = new UserServiceImpl();
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        List<User> users = userService.showUsersInfo();
        for (User user : users) {
            resp.getWriter().println(user);
        }
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}