jsp兑现图片验证码的方法

调用方法????
? <img?? src="http://www.31km.cn/getImg">????
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? 原理，在servlet中随机生成一个4位数字1000-9999????
? 然后把这数字写入session????
? 输出一个图片，上面写有这四个数字????
? 在服务器端根据用户输入的数字和????
? session中的值比较。????
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? package?? com.schoolwx.util;????
? import?? java.io.*;????
? import?? java.util.*;????
? import?? com.sun.image.codec.jpeg.*;????
? import?? javax.servlet.*;????
? import?? javax.servlet.http.*;????
? import?? java.awt.*;????
? import?? java.awt.image.*;????
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? /**????
? *?? Title:?? getImg.java????
? *?? Description:?? 实现随机生成一个4位数的验证码，并写入session，????
? *?? Copyright:?? Copyright?? (c)?? 2008????
? *?? Company:???31公里?????
? *?? @author???rye????
? *?? @version?? 1.1????
? */????
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? public?? class?? getImg?? extends?? HttpServlet?? {????
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? private?? Font?? mFont=new?? Font("宋体",?? Font.PLAIN,12);//设置字体????
? //处理post????
? public?? void?? doPost(HttpServletRequest?? request,HttpServletResponse?? response)????
? throws?? ServletException,IOException?? {????
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? doGet(request,response);????
? }????
? public?? void?? doGet(HttpServletRequest?? request,HttpServletResponse?? response)????
? throws?? ServletException,IOException?? {????
? //取得一个1000-9999的随机数????
? String?? s="";????
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? int?? intCount=0;????
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? intCount=(new?? Random()).nextInt(9999);//????
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? if(intCount<1000)intCount+=1000;????
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? s=intCount+"";????
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? //对session付值。????
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? HttpSession?? session=request.getSession?? (true);????
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? session.setAttribute("getImg",s);????
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? response.setContentType("image/gif");????
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? ServletOutputStream?? out=response.getOutputStream();????
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? BufferedImage?? image=new?? BufferedImage(35,14,BufferedImage.TYPE_INT_RGB);????
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? Graphics?? gra=image.getGraphics();????
? //设置背景色????
? gra.setColor(Color.yellow);????
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? gra.fillRect(1,1,33,12);????
? //设置字体色????
? gra.setColor(Color.black);????
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? gra.setFont(mFont);????
? //输出数字????
? char?? c;????
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? for(int?? i=0;i<4;i++)?? {????
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? c=s.charAt(i);????
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? gra.drawString(c+"",i*7+4,11);?? //7为宽度，11为上下高度位置????
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? }????
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? JPEGImageEncoder?? encoder=JPEGCodec.createJPEGEncoder(out);????
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? encoder.encode(image);????
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? out.close();????
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? }????
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? }