网页验证码小知识
在一本教材中看到如何生成并调用显示验证码。
代码如下,文件命名为:image.jsp
<%@ page contentType="image/jpeg" import="java.awt.*, java.awt.image.*,java.util.*,javax.imageio.*" pageEncoding="GB2312" %> <%! Color getRandColor(int fc,int bc){// 给定范围获得随机颜色 Random random = new Random(); if(fc>255) fc=255; if(bc>255) bc=255; int r=fc+random.nextInt(bc-fc); int g=fc+random.nextInt(bc-fc); int b=fc+random.nextInt(bc-fc); return new Color(r,g,b); } %> <% //设置页面不缓存 response.setHeader("Pragma","No-cache"); response.setHeader("Cache-Control","no-cache"); response.setDateHeader("Expires", 0); //在内存中创建图象 int width=60, height=20; BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB); //获取图形上下文 Graphics g = image.getGraphics(); //生成随机类 Random random = new Random(); //设定背景色 g.setColor(getRandColor(200,250)); g.fillRect(0, 0, width, height); //设定字体 g.setFont(new Font("Times New Roman",Font.PLAIN,18)); //随机产生155 条干扰线,使图象中的认证码不易被其它程序探测到 g.setColor(getRandColor(160,200)); for (int i=0;i<155;i++) { int x = random.nextInt(width); int y = random.nextInt(height); int xl = random.nextInt(12); int yl = random.nextInt(12); g.drawLine(x,y,x+xl,y+yl); } //取随机产生的认证码(4位数字) String sRand=""; for (int i=0;i<4;i++){ String rand=String.valueOf(random.nextInt(10)); sRand+=rand; //将认证码显示到图象中 g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110) )); //调用函数出来的颜色相同,可能是因为种子太接近,所以只能直接生成 g.drawString(rand,13*i+6,16); } //将认证码存入SESSION session.setAttribute("rand",sRand); //图象生效 g.dispose(); //输出图象到页面 ImageIO.write(image, "JPEG", response.getOutputStream()); out.clear(); out = pageContext.pushBody(); %>
调用并显示是在另一个文件中,如login.jsp
<input type="text" name="rand" size="20" maxlength="20"> <IMG SRC="<%=request.getContextPath()%>/jsp/image.jsp" />
完成