JavaWeb开发入门（Servlet）2

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本文介绍如何使用JavaWeb技术创建验证码，并详细讲解了Servlet中处理用户请求的方法，包括接收参数、请求转发与重定向等核心操作。

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JavaWeb开发入门（Servlet）2

制作一个简单的验证码

利用Math函数，和BufferedImage，制作一个简答的变化验证码，
package com.kuang.servlet;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Map;

//验证码
public class ServletDemo04 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req,resp);
    }

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

        //resp.getWriter().println(newRandom());

        //自动刷新网页
        resp.setHeader("refresh","2");
        //验证码是一个图片 ， 我们需要制作一个图片
        BufferedImage image = new BufferedImage(100,30,BufferedImage.TYPE_3BYTE_BGR);

        //图片写入一些东西
        Graphics2D graphics = image.createGraphics();
        graphics.setColor(Color.red);
        String num = String.valueOf(newRandom());
        graphics.drawString(num,10,10);

        //想办法让浏览器知道我们给的是一张图片
        resp.setContentType("image/jpg");

        //让网站去打开图片
        ImageIO.write(image,"jpg",resp.getOutputStream());

    }


    //生成随机数
    public int newRandom(){
        int num = (int)(Math.random()*9+1)*100000;
        return num;
    }

    /*
    @Test
    public void  test(){
        ServletDemo04 servletDemo04 = new ServletDemo04();

        for (int j = 0; j < 100; j++) {
            int i = servletDemo04.newRandom();
            System.out.println(i);
        }
    }
    */



}

Servlet中的Request

JSP获取项目路径，跳转到指定的路径
${pageContext.request.contextPath}/…

request.getContextPath():获得web项目路径
request.getRequestURI():请求获得URI路径
request.getRequestedSessionId():获得sessionId
request.getServletPath():请求servlret的url
request.getLocaclAddr():获得本地地址，防火墙
request.getLocalName();获得本地名字
request.getLocalPort():获得访问的端口号
request.getRemoteUser():获得访问的端口号

Request对象接收前段用户提交的参数

1.写前段注册页面
- 表单的提交方式get/post
- 表单提交的位置action：服务项目的路径/servlet对应的请求url
<%--
  Created by IntelliJ IDEA.
  User: Administrator
  Date: 2019/7/14
  Time: 21:48
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>注册</title>
    <script>
       var status='${sessionScope.pwdFail}';
       if (status=='yes'){
           alert("两次密码输入不一样");
       }
    </script>

</head>
<body>
<h1>注册</h1>
<form action="${pageContext.request.contextPath}/1234" method="post">
<p>
    用户名：<input type="text" name="username"placeholder="请输入用户名" required>

</p>
    <p>
        密码：<input type="password" name="password1">
    </p>
    <p>
        确认密码：<input type="password" name="password2">
    </p>
    爱好：
    <p>
        <input type="checkbox" name="hobby" value="rap">说唱
        <input type="checkbox" name="hobby" value="dance">跳舞
        <input type="checkbox" name="hobby" value="basketball">篮球
        <input type="checkbox" name="hobby" value="music">音乐
    </p>
    性别：
    <p>
        <input type="radio" name="sex" value="girl">女
        <input type="radio" name="sex" value="boy">男
    </p>
    <p>
        <textarea name="textarea" id="" cols="30" rows="10"></textarea>
    </p>
    <p>
        <input type="submit">
        <input type="reset">
    </p>

</form>
</body>
</html>

写处理前端提交信息的Servlet

- 接收前端传递的控件信息
package com.kuang.servlet;


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

//处理前端提交过来的数据
public class RequestDemo02 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req,resp);
    }

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

        //通过HttpServletRequest获取前端用户提交的信息
        //req.getParameterValues(); 获得前端传递的控件信息，通过控件的name；但是可以接受多个参数的控件，比如（多选框....）
        //req.getParameter(); 获得前端传递的控件信息，通过控件的name；

        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");

        String username = req.getParameter("username");
        String password = req.getParameter("password");

        //连接数据库，比较数据库中的信息是否匹配

        if (username.equals("admin")&&password.equals("1234567")){
            System.out.println("登录成功！"); //跳转到成功页面
        }else {
            System.out.println("登录失败！"); //提示重新注册
        }

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


    }
}

配置web.xml

配置对应的XML文件

<?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">
    <servlet>
        <servlet-name>ServletDemo1</servlet-name>
        <servlet-class>com.wang.demo.ServletDemo1</servlet-class>
    </servlet>
    <servlet>
        <servlet-name>ServletDemo2</servlet-name>
        <servlet-class>com.wang.demo.LoginOutServlet</servlet-class>
    </servlet>
    <!--==============================================================-->
    <servlet-mapping>
        <servlet-name>ServletDemo1</servlet-name>
        <url-pattern>/1234</url-pattern>
    </servlet-mapping>
<servlet-mapping>
    <servlet-name>ServletDemo2</servlet-name>
    <url-pattern>/123.do</url-pattern>
</servlet-mapping>
</web-app>

4.提交测试

检查英文提交的情况，服务器是否接收成功
提交中文，看看乱码情况
设置编码统一，解决乱码问题

Request实现请求转发

重定向
- 服务器告诉客户端你应该请求另外一个地址：地址栏汇编
- response.sendRedirect(“url”);
转发
- 服务器把这个请求转向另外一个Servlet去处理，地址栏会变，
- request.getRequestDispacher("/success.jsp").forward(request.response)
  
  package com.kuang.servlet;
  import javax.servlet.RequestDispatcher;
  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 FormServlet1 extends HttpServlet {
  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  doPost(req,resp);
  }
  @Override
  protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  //处理乱码
  req.setCharacterEncoding(“UTF-8”);
  //处理前端的请求
  String username = req.getParameter(“username”);
  String password = req.getParameter(“password”);
  System.out.println(“接收到的用户名：”+username+"\n密码："+password+"\n爱好:");
  String[] hobbies = req.getParameterValues(“hobby”);
```
   for (String hobby : hobbies) {
       System.out.println(hobby);
   }
   /*
   RequestDispatcher requestDispatcher = req.getRequestDispatcher("/success.jsp");
   requestDispatcher.forward(req,resp);
   */

   try {
       Thread.sleep(2000);
   } catch (InterruptedException e) {
       e.printStackTrace();
   }

   req.getRequestDispatcher("/success.jsp").forward(req,resp);
```
  }
  }