標籤：jsp動態產生驗證碼 動態產生驗證碼 驗證碼
（1）在登入應用中，為防止惡意登入，常常需要伺服器動態產生驗證碼並儲存在session作用範圍中，最後以映像形式返回給用戶端顯示
（2）下邊的代碼實現的功能：寫一個JSP頁，動態產生一個驗證碼，儲存在session作用範圍內，並以映像形式返回給用戶端顯示。
另寫一個JSP頁面，引用此JSP頁面產生的驗證碼；
authen.jsp代碼如下：
<%@ page import="java.awt.*,java.awt.image.*,java.util.*,com.sun.image.codec.jpeg.*" %><%!//根據提供的ab產生隨機的顏色變化範圍Color getColor(int a,int b){ int n=b-a;Random rd=new Random();int cr=a+rd.nextInt(n);int cg=a+rd.nextInt(n);int cb=a+rd.nextInt(n); return new Color(cr,cg,cb); }%><% //下邊三行取消用戶端遊覽器緩衝驗證碼的功能response.setHeader("Pragma","No-cache");response.setHeader("Cache-Control","no-cache");response.setDateHeader("Expires", 0);int width=60, height=20;//在記憶體中產生一個映像BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB); Graphics g = image.getGraphics();Random random = new Random();g.setColor(getColor(200,250));g.fillRect(0, 0, width, height);g.setFont(new Font("Times New Roman",Font.BOLD,18));g.setColor(getColor(160,200));for (int i=0;i<160;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);}String number=String.valueOf(1000+random.nextInt(8999));String name=request.getParameter("name");session.setAttribute(name,number);g.setColor(getColor(20,130));int x=(int)(width*0.2);int y=(int)(height*0.8);g.drawString(number,x,y);g.dispose();JPEGImageEncoder encoder=JPEGCodec.createJPEGEncoder(response.getOutputStream()); encoder.encode(image); out.close(); %>
再建一個test.jsp頁面 調用驗證碼：
<%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*" errorPage="" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=gb2312" /><title>無標題文檔</title></head><body><% //同樣實現取消用戶端緩衝response.setHeader("Pragma","No-cache");response.setHeader("Cache-Control","no-cache");response.setDateHeader("Expires", 0);String name="loginCode";%>驗證碼:<img src="authen.jsp?name=<%=name%>" /> </body></html>
會先將圖片放在緩衝中，當再次請求的時候會現在記憶體中尋找是不是已經有了，有的話就不在請求，這使得在重新整理驗
證碼的時候 失敗，所以要使遊覽器不讀取緩衝的圖片，就需要取消緩衝；
（4）OK！到此結束！
JSP動態產生驗證碼
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