JavaEE-Servlet的使用

显示 HttpServletRequest 的常用属性

能够返回一个页面, 显示以下内容:

• URL
• 方法
• 版本号
• query string
• context path
• 所有的 header

• 
  import javax.servlet.ServletException;
  import javax.servlet.annotation.WebServlet;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  import java.io.IOException;
  import java.util.Enumeration;
  
  @WebServlet("/ShowRequest")
  public class ShowRequest extends HttpServlet {
      @Override
      protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          StringBuilder result = new StringBuilder();
          result.append(req.getProtocol());
          result.append("
  ");
          result.append(req.getMethod());
          result.append("
  ");
          result.append(req.getRequestURI());
          result.append("
  ");
          result.append(req.getQueryString());
          result.append("
  ");
          result.append(req.getContextPath());
          result.append("
  ");
  
          result.append("==================
  ");
  
          Enumeration<String> headerNames = req.getHeaderNames();
          while (headerNames.hasMoreElements()) {
              String headerName = headerNames.nextElement();
              String headerValue = req.getHeader(headerName);
              result.append(headerNames + ":" + headerValue + "
  ");
          }
          resp.setContentType("text/html;charset=utf8");
          resp.getWriter().write(result.toString());
      }
  }
  

  

  获取GET请求中的query string 的内容

  import javax.servlet.ServletException;
  import javax.servlet.annotation.WebServlet;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  import java.io.IOException;
  
  @WebServlet("/message")
  public class GetStirng extends HttpServlet {
      @Override
      protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          String aa = req.getParameter("aa");
          String bb = req.getParameter("bb");
          resp.getWriter().write("aa=" + aa + ",bb=" + bb);
      }
  }
  

  

  获取 POST 请求中 body 的内容

  分别实现这两种 body 格式的处理:

  1. aa=10&bb=20

  import javax.servlet.ServletException;
  import javax.servlet.annotation.WebServlet;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  import java.io.IOException;
  
  @WebServlet("/message")
  public class GetStirng extends HttpServlet {
      @Override
      protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          String aa = req.getParameter("aa");
          String bb = req.getParameter("bb");
          resp.getWriter().write("aa=" + aa + ",bb=" + bb);
      }
  }
  
  

  

  2. { “aa”: 10, “bb”:20}

  import javax.servlet.ServletException;
  import javax.servlet.annotation.WebServlet;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  import java.io.IOException;
  
  @WebServlet("/message")
  public class GetStirng extends HttpServlet {
      @Override
      protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          String aa = req.getParameter("aa");
          String bb = req.getParameter("bb");
          resp.getWriter().write("aa=" + aa + ",bb=" + bb);
      }
  
      @Override
      protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          // 前端通过body，以form表单格式，把aa和bb传到服务器
          String aa = req.getParameter("aa");
          String bb = req.getParameter("bb");
          resp.getWriter().write("aa=" + aa + ",bb=" + bb);
      }
  }
  
  

  

  实现自动刷新

  1. 实现 Servlet, 设置 header, 实现每隔 1s 自动刷新页面的效果. 页面上要显示当前时间戳

  import javax.servlet.ServletException;
  import javax.servlet.annotation.WebServlet;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  import java.io.IOException;
  
  @WebServlet("/servletResponse")
  public class ServletResponse extends HttpServlet {
      @Override
      protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          resp.setContentType("text/html;charset=utf8");
          resp.setStatus(200);
          resp.setHeader("Refresh", "3");
          resp.getWriter().write("timeStamp:" + System.currentTimeMillis());
      }
  }
  
  

  

  2. 网上搜索 SimpleDateFormat 类的用法, 让页面上能够显示格式化的事前. 例如 2022-01-19 12:00:00

  import javax.servlet.ServletException;
  import javax.servlet.annotation.WebServlet;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  import java.io.IOException;
  import java.text.DateFormat;
  import java.util.Date;
  
  @WebServlet("/servletResponse")
  public class ServletResponse extends HttpServlet {
      @Override
      protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          resp.setContentType("text/html;charset=utf8");
          resp.setStatus(200);
          resp.setHeader("Refresh", "3");
          resp.getWriter().write("timeStamp:" + System.currentTimeMillis());
  
          DateFormat df1 = null;
          DateFormat df2 = null;
          df1 = DateFormat.getDateInstance();
          df2 = DateFormat.getDateTimeInstance();
  //        System.out.println("DATE:" + df1.format(new Date()));
  //        System.out.println("DATETIME:" + df2.format(new Date()));
  
          resp.getWriter().write("
  ");
          resp.getWriter().write("DATE:" + df1.format(new Date()));
          resp.getWriter().write("
  ");
          resp.getWriter().write("DATE:" + df2.format(new Date()));
      }
  }
  
  

  

  构造重定向页面

  实现访问 /redirect 路径后, 自动重定向到 搜狗主页 的代码.

  package com.example.test_20230602;
  
  import javax.servlet.annotation.WebServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  import java.io.IOException;
  
  @WebServlet("/redirectServlet")
  public class RedirectServlet extends HelloServlet{
      @Override
      public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
          resp.setStatus(302);
          resp.setHeader("Location","https://sogou.com");
      }
  }