servlet中 doGet和doPost都執(zhí)行doPostpublic void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { BufferedImage bi = new BufferedImage(68,22,BufferedImage.TYPE_INT_RGB);? Graphics g = bi.getGraphics(); Color c = new Color(200,150,255); g.setColor(c); g.fillRect(0, 0, 68,22); char[] code = "ABCDEFGHIGKLMNOPQRSTUVWXYZ0123456789".toCharArray(); Random r= new Random(); int len = code.length,index; StringBuffer sb = new StringBuffer(); for(int i =0; i < 4; i ++){ index = r.nextInt(len); g.setColor(new Color(r.nextInt(88),r.nextInt(188),r.nextInt(255))); g.drawString(code[index] + "", (i*15)+3,18 ); sb.append(code[index]); } request.getSession().setAttribute("picode", sb.toString()); ImageIO.write(bi,"jpg",response.getOutputStream()); }jsp中<form action="ls" method = "get"> ? ?<input type="text" id = "text1" name ="code" /> ? ?<img ?id="img1" alt="驗(yàn)證碼" src="<%=request.getContextPath() %>/is" /> ? ?<a href="javascript:reCode()">看不清楚，換一張</a> ? ?<br/> ? ?驗(yàn)證碼：<%=(String)session.getAttribute("picode") %> ? ?<input type="submit" id="btn1" value="驗(yàn)證"/>? ? </form>這里第一次是在頁(yè)面顯示"驗(yàn)證碼：null"之后每一次顯示的驗(yàn)證碼都是上一次的驗(yàn)證碼比如這次顯示的圖片是：809Y 驗(yàn)證碼：null下一次就是圖片是：8278 驗(yàn)證碼：809Y這是什么原因。不太明白。