jsp验证码，解决无法更新验证码问题

首先给你个验证码模板，文件名为Num.jsp

<% @ page pageEncoding = " gbk " contentType = " image/jpeg " import = " javax.imageio.*,java.util.*,java.awt.image.*,java.awt.* " %>

window.self.location.reload( true );

<%!

// 在此处 获取并生成随机颜色

Color getRandColor(Random random, int ff, int cc) {

if (ff > 255 )

ff = 255 ;

if (cc > 255 )

cc = 255 ;

int r = ff + random.nextInt(cc - ff);

int g = ff + random.nextInt(cc - ff);

int b = ff + random.nextInt(cc - ff);

return new Color(r, g, b);

} %>

<%

response.setHeader( " Pragma " , " No-cache " );

response.setHeader( " Cache-Control " , " no-cache " );

response.setDateHeader( " Expires " , 0 );

int width = 60 ; // 定义验证码图片的长度

int height = 20 ; // 定义验证码图片的宽度

BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);

Graphics g = image.getGraphics();

Random random = new Random();

g.setColor(getRandColor(random, 200 , 250 ));

g.fillRect( 0 , 0 , width, height);

g.setFont( new Font( " Times New Roman " ,Font.PLAIN, 18 ));

// 定义字体形式

g.setColor(getRandColor(random, 160 , 200 ));

for ( int i = 0 ;i < 155 ;i ++ )

{

int i_x = random.nextInt(width);

int i_y = random.nextInt(height);

int i_xl = random.nextInt( 12 );

int i_yl = random.nextInt( 12 );

g.drawLine(i_x,i_y,i_x + i_xl,i_y + i_yl);

}

// 用线条画背景

String s_Rand = "" ;

for ( int i = 0 ;i < 4 ;i ++ )

{

String rand = String.valueOf(random.nextInt( 10 ));

s_Rand += rand;

g.setColor( new Color( 20 + random.nextInt( 110 ), 20 + random.nextInt( 110 ), 20 + random.nextInt( 110 )));

g.drawString(rand, 13 * i + 6 , 16 );

}

// 产生4位随机码

session.setAttribute( " rand " ,s_Rand);

// 将验证码存入Session中

g.dispose();

ImageIO.write(image, " JPEG " , response.getOutputStream());

// 输出验证图片

out .clear();

out = pageContext.pushBody();

%>

重要的是如何调用这个验证码，而且单击验证码让它自动换一张，看下面代码，文件名为test.jsp

<% @ page language = " java " import = " java.util.* " pageEncoding = " gbk " %>

<%

String path = request.getContextPath();

String basePath = request.getScheme() + " :// " + request.getServerName() + " : " + request.getServerPort() + path + " / " ;

%>

<! DOCTYPE HTML PUBLIC " -//W3C//DTD HTML 4.01 Transitional//EN " >

< html >

< head >

< base href = " <%=basePath%> " >

< title > My JSP ' index.jsp ' starting page </ title >

< meta http - equiv = " pragma " content = " no-cache " >

< meta http - equiv = " cache-control " content = " no-cache " >

< meta http - equiv = " expires " content = " 0 " >

< meta http - equiv = " keywords " content = " keyword1,keyword2,keyword3 " >

< meta http - equiv = " description " content = " This is my page " >

< script type = " text/javascript " >

function change()

{

var img = document.getElementById( " code " );

img.src = " Num.jsp?date= " + new Date(); // 此处很重要，不加后面的就不会变

}

</ script >

</ head >

< body >

< center >

< form id = " dForm " method = post action = "" >

用户名: < input name = " username " >< br >

密 & nbsp;码: < input type = " password " name = " password " >< br >

校验码: < input id = " check " size = " 10 " >

< img id = " code " border = 0 src = " Num.jsp " onclick = " change() " />< br >

< input type = " reset " value = " 重置 " >

< input type = " submit " value = " 提交 " >

</ form >

</ center >

</ body >

</ html >

转载于:https://www.cnblogs.com/lhxfzu/archive/2011/04/28/2032254.html