protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //1. 获取请求方式 ：GET
        String method = request.getMethod();
        System.out.println(method);
        //2.(*)获取虚拟目录：/day11
        String contextPath = request.getContextPath();
        System.out.println(contextPath);
        //3. 获取Servlet路径: /demo1
        String servletPath = request.getServletPath();
        System.out.println(servletPath);
        //4. 获取get方式请求参数：name=zhangsan
        String queryString = request.getQueryString();
        System.out.println(queryString);
        //5.(*)获取请求URI：/day11/demo1
        String requestURI = request.getRequestURI();
        StringBuffer requestURL = request.getRequestURL();
        System.out.println(requestURI);
        System.out.println(requestURL);
        //6. 获取协议及版本：HTTP/1.1
        String protocol = request.getProtocol();
        System.out.println(protocol);
        //7. 获取客户机的IP地址：
        String remoteAddr = request.getRemoteAddr();
        System.out.println(remoteAddr);
    }

?2.通过Request方法获取用户请求头的键值对

public class ServletDome01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1.获取所有请求头名称
        Enumeration<String> headerNames = req.getHeaderNames();
        //2.遍历
        while(headerNames.hasMoreElements()){
            String name = headerNames.nextElement();
            //根据名称获取请求头的值
            String value = req.getHeader(name);
            System.out.println(name+":"+value);
        }
    }
}

3.?通过Request方法获取用户提交的表单参数

访问事先准备好的html登录页面

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>登录</title>
</head>
<body>
<form action="/demo01">
  账号：
  <input type="text" name="username" ><br>
  密码：
  <input type="password" name="password" ><br>
  <input type="submit" value="登录">
</form>
</body>
</html>

public class ServletDome01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1.设置流的编码
        req.setCharacterEncoding("utf-8");

        //获取请求参数username
        String username = req.getParameter("username");
        String password = req.getParameter("password");

        System.out.println(username);
        System.out.println(password);
    }
}

?成功获取到前端输入的找好密码

4.页内跳转

使用场景：登陆成功或者失败的跳转

req.getRequestDispatcher("/demo03").forward(req,resp);

这个跳转对用户来说是不可见的，就相当于函数内部的跳转一样

public class ServletDome01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1.设置流的编码
        req.setCharacterEncoding("utf-8");

        //获取请求参数username
        String username = req.getParameter("username");
        String password = req.getParameter("password");

        System.out.println(username);
        System.out.println(password);
        
        
//        跳转到Demo03,可以使用setAttribute，把键值对放进request域，可以随时提取
        req.setAttribute("msg","参数");
        req.getRequestDispatcher("/demo03").forward(req,resp);
    }
}