javaweb02_HttpServletResponse和HttpServletRequest

不念不忘少年蓝@ 2022-12-08 05:26 106阅读 0赞

**javaweb02\_HttpServletResponse和HttpServletRequest**

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**HttpServletResponse**

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**文件下载示例：**

@Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 
    	//文件全路径
    	String realPath = "D:\\eclipseworkspace\\javawebdemo\\src\\main\\resources\\头像.jpg";
    	//通过字符串截取获得文件名
    	String fileName = realPath.substring(realPath.lastIndexOf("\\")+1);
    	//Content-Disposition: attachment 表示消息体应该被下载到本地，filename的值指定下载后的文件名（中文需要经URLEncoder类进行编码）
    	resp.setHeader("Content-Disposition","attachment;filename="+URLEncoder.encode(fileName,"UTF-8"));
    	//获取下载文件的输入流
    	FileInputStream in =  new FileInputStream(realPath);
    	//创建缓冲区
    	int len = 0;
    	byte[] buffer = new byte[1024];
    	//获取输出流对象
    	ServletOutputStream out = resp.getOutputStream();
    	//使用输出流将缓冲区数据输出到客户端
    	while ((len=in.read(buffer))>0){ 
    		out.write(buffer,0,len);
    	}
    	out.close();
    	in.close();
    }

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**生成验证码示例：**

@Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 
    	//让浏览器3秒刷新一次
    	resp.setHeader("refresh", "3");
    	//在内存中创建一个图片
    	BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);
    	//得到画笔
    	Graphics2D graphics = (Graphics2D) image.getGraphics();
    	//设置图片背景色
    	graphics.setColor(Color.white);
    	graphics.fillRect(0, 0, 80, 20);
    	//给图片写数据
    	graphics.setColor(Color.BLUE);
    	graphics.setFont(new Font(null, Font.BOLD, 20));	
    	graphics.drawString(makeNum(), 0, 20);
    	//告诉浏览器这个请求用图片打开
    	resp.setContentType("image/jpeg");
    	//不让浏览器缓存
    	resp.setDateHeader("expires",-1);
    	resp.setHeader("Cache-Control", "no-cache");
    	resp.setHeader("Pragma", "no-cache");
    	//将图片写给浏览器
    	ImageIO.write(image,"jpg",resp.getOutputStream());
    }
    
    /** * 生成7位随机数并转换为字符串 */
    private String makeNum() { 
    	Random random = new Random();
    	String num = random.nextInt(9999999)+"";
    	StringBuffer sb = new StringBuffer();
    	for(int i=0;i<7-num.length();i++) { 
    		sb.append("0");
    	}
    	return num = sb.toString()+num;
    }

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**HttpServletResponse实现请求重定向（重点）：**

@Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 
    	System.out.println("进入AServlet");
    	resp.sendRedirect("/javawebdemo/b");
    }

![在这里插入图片描述][20200918163821851.png_pic_left]  
请求url：http://localhost:8080/javawebdemo/a  
结果页面重定向至：http://localhost:8080/javawebdemo/b  
地址栏url发生了改变！

**重定向还可以写成以下形式：**

@Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 
    	System.out.println("进入AServlet");
    	resp.setHeader("Location", "/javawebdemo/b");
    	resp.setStatus(302);
    }

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**重定向与请求转发的区别：**

请求转发的url不会改变  
重定向的url会发生改变

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**重定向的应用：登录逻辑**

**添加依赖：**

<dependency>
    	<groupId>javax.servlet.jsp</groupId>
    	<artifactId>javax.servlet.jsp-api</artifactId>
    	<version>2.3.3</version>
    </dependency>

**登录页面：**

<html>
    <body>
    <h2>Login</h2>
    <%-- ${pageContext.request.contextPath} 代表当前的项目路径 --%>
    <form action="${pageContext.request.contextPath}/login" method="post">
    	用户名：<input type="text" name="username"/>
    	密码：<input type="password" name="password"/>
    	<input type="submit"/>
    </form>
    </body>
    </html>

**LoginServlet：**

@Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 
    	System.out.println("Post进入LoginServlet");
    	//解决请求中文乱码
    	req.setCharacterEncoding("utf-8");
    	String username = req.getParameter("username");
    	String password = req.getParameter("password");
    	
    	System.out.println(username);
    	System.out.println(password);
    	
    	resp.sendRedirect(req.getContextPath()+"/success.jsp");
    }

**success.jsp：**

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
        pageEncoding="ISO-8859-1"%>
    <!DOCTYPE html>
    <html>
    <head>
    <meta charset="ISO-8859-1">
    <title>Insert title here</title>
    </head>
    <body>
    	<h1>Success</h1>
    </body>
    </html>

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**HttpServletRequest**

**获取前端传递的参数：**

String username = req.getParameter("username");
    String password = req.getParameter("password");
    //这个一般用于获取多选框的值
    String[] hobbys = req.getParameterValues("hobbys");

**请求转发的两种方式：**

this.getServletContext().getRequestDispatcher("/success.jsp").forward(req, resp);
    req.getRequestDispatcher("/success.jsp").forward(req, resp);

**注意：**  
请求转发的映射地址为项目根路径：http://localhost:8080/javawebdemo  
重定向的映射地址为：http://localhost:8080

[20200918163821851.png_pic_left]: /images/20221123/b6f8c55c08c34f0d826964b1c4b93a47.png