JavaWeb学习-Servlet系列-16-客户端不缓存和刷新功能

客官°小女子只卖身不卖艺 2022-02-01 08:39 120阅读 0赞

接着前面的验证码的中代码，继续本篇的练习和优化代码。前面一篇其实有一点点小问题，鼠标光标定位在浏览器地址栏，键盘上敲回车，其实不会发生验证码的变化，这是因为浏览器有缓存。然后介绍一个刷新功能，在setHead方法中使用属性refresh。

**1.告诉客户端不缓存**

在写HttpServletResponse对象简介这篇的时候，我把setHead()中不缓存相关三个方法都列举出来了，我们这里把前面验证码的代码提取出来成方法。

package com.anthony.servlet;
    
    import java.awt.Color;
    import java.awt.Font;
    import java.awt.Graphics;
    import java.awt.image.BufferedImage;
    import java.io.IOException;
    import java.util.Random;
    
    import javax.imageio.ImageIO;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    
    public class ServletDemo4 extends HttpServlet {
    
    	@Override
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		//告诉客户端不缓存
    		resp.setHeader("pragma","no-cache");
    		resp.setHeader("cache-control","no-cache");
    		resp.setDateHeader("expires",0);
    		test(resp, 110, 25, 4, 9);
    	}
    
    
    	private void test(HttpServletResponse resp, int width, int height, int codeCount, int lineCount) throws IOException {
    		// 在内存中创建一个图像对象
    		BufferedImage img = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
    		
    		//创建一个画笔
    		Graphics g = img.getGraphics();
    		
    		//给图片设置背景颜色和边框
    		g.setColor(Color.PINK);
    		g.fillRect(1, 1, width-2, height-2);
    		
    		//添加边框并设置颜色
    		g.setColor(Color.BLUE);
    		g.drawRect(0, 0, width-1, height-1);
    		
    		//设置字体样式
    		g.setColor(Color.BLUE);
    		g.setFont(new Font("宋体", Font.BOLD | Font.ITALIC, 15)); //设置宋体 加粗和斜体显示，字号15
    		
    		//给图片添加数字
    		Random random = new Random();
    		int position = 20;
    		for (int i = 0; i < codeCount; i++) {
    			g.drawString(random.nextInt(10)+"", position, 18);
    			position += 20;
    		}
    		
    		//添加lineCount条干扰线
    		for (int i = 0; i < lineCount; i++) {
    			g.drawLine(random.nextInt(width), random.nextInt(height), random.nextInt(width), random.nextInt(height));
    		}
    		//讲图片以流的形式输出到网页
    		ImageIO.write(img, "jpg", resp.getOutputStream());
    	}
    	
    	
    	@Override
    	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		doGet(req, resp);
    	}
    	
    }

这个时候重新部署，执行浏览器地址栏回车操作，验证码就会每次回车每次刷新，产生新的验证码。

**刷新功能**

package com.anthony.servlet;
    
    import java.io.IOException;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    
    public class ServletDemo3 extends HttpServlet {
    
    	@Override
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		// 这里模拟 注册成功，3秒之后跳回主页，加入主页是/demo4
    		resp.setContentType("text/html;charset=UTF-8");
    		resp.getWriter().write("注册成功，3秒之后跳到主页。");
    		resp.setHeader("refresh", "3;url=/Servlet01/demo4");
    	}
    	
    	
    	@Override
    	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		doGet(req, resp);
    	}
    	
    }

重新部署之后，效果是这样的。

![20190513231402559.png][]

[20190513231402559.png]: /images/20220201/803a7d668bf84e0b9f2a065839c2f3f5.png