用servlet进行图片验证

<pre name="code" class="java">
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.awt.*;
import java.awt.image.*;
import javax.imageio.ImageIO;

public class CheckCodeServlet extends HttpServlet
{
private static int WIDTH = 60;
private static int HEIGHT = 20;
public void doGet(HttpServletRequest request,HttpServletResponse response)
throws ServletException,IOException
{
HttpSession session = request.getSession();
response.setContentType(&quot;image/jpeg&quot;);
ServletOutputStream sos = response.getOutputStream();

//设置浏览器不要缓存此图片
response.setHeader(&quot;Pragma&quot;,&quot;No-cache&quot;);
response.setHeader(&quot;Cache-Control&quot;,&quot;no-cache&quot;);
response.setDateHeader(&quot;Expires&quot;, 0);

//创建内存图象并获得其图形上下文
BufferedImage image =
new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
Graphics g = image.getGraphics();

//产生随机的认证码
char [] rands = generateCheckCode();

//产生图像
drawBackground(g);
drawRands(g,rands);

//结束图像的绘制过程，完成图像
g.dispose();

//将图像输出到客户端
ByteArrayOutputStream bos = new ByteArrayOutputStream();
ImageIO.write(image, &quot;JPEG&quot;, bos);
byte [] buf = bos.toByteArray();
response.setContentLength(buf.length);
//下面的语句也可写成：bos.writeTo(sos);
sos.write(buf);
bos.close();
sos.close();

//将当前验证码存入到Session中
session.setAttribute(&quot;check_code&quot;,new String(rands));
//直接使用下面的代码将有问题，Session对象必须在提交响应前获得
//request.getSession().setAttribute(&quot;check_code&quot;,new String(rands));
}

private char [] generateCheckCode()
{
//定义验证码的字符表
String chars = &quot;0123456789abcdefghijklmnopqrstuvwxyz&quot;;
char [] rands = new char[4];
for(int i=0; i&lt;4; i++)
{
int rand = (int)(Math.random() * 36);
rands[i] = chars.charAt(rand);
}
return rands;
}

private void drawRands(Graphics g , char [] rands)
{
g.setColor(Color.BLACK);
g.setFont(new Font(null,Font.ITALIC|Font.BOLD,18));
//在不同的高度上输出验证码的每个字符
g.drawString(&quot;&quot; + rands[0],1,17);
g.drawString(&quot;&quot; + rands[1],16,15);
g.drawString(&quot;&quot; + rands[2],31,18);
g.drawString(&quot;&quot; + rands[3],46,16);
System.out.println(rands);
}

private void drawBackground(Graphics g)
{
//画背景
g.setColor(new Color(0xDCDCDC));
g.fillRect(0, 0, WIDTH, HEIGHT);
//随机产生120个干扰点
for(int i=0; i&lt;120; i++)
{
int x = (int)(Math.random() * WIDTH);
int y = (int)(Math.random() * HEIGHT);
int red = (int)(Math.random() * 255);
int green = (int)(Math.random() * 255);
int blue = (int)(Math.random() * 255);
g.setColor(new Color(red,green,blue));
g.drawOval(x,y,1,0);
}
}
}</pre>
<pre name="code" class="java">
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class LogonFormServlet extends HttpServlet
{
public void service(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException
{
response.setContentType(&quot;text/html;charset=GB2312&quot;);
PrintWriter out = response.getWriter();

HttpSession session = request.getSession(false);
if(session == null)
{
out.println(&quot;验证码处理问题!&quot;);
return;
}

String savedCode = (String)session.getAttribute(&quot;check_code&quot;);
if(savedCode == null)
{
out.println(&quot;验证码处理问题!&quot;);
return;
}

String checkCode = request.getParameter(&quot;check_code&quot;);
if(!savedCode.equals(checkCode))
{
/*验证码未通过，不从Session中清除原来的验证码，
以便用户可以后退回登录页面继续使用原来的验证码进行登录*/
out.println(&quot;验证码无效!&quot;);
return;
}
/*验证码检查通过后，从Session中清除原来的验证码，
以防用户后退回登录页面继续使用原来的验证码进行登录*/
session.removeAttribute(&quot;check_code&quot;);
out.println(&quot;验证码通过，服务器正在校验用户名和密码!&quot;);
}
}
</pre>&nbsp;</pre><pre name="code" class="java">&lt;servlet&gt;
&lt;servlet-name&gt;CheckCodeServlet&lt;/servlet-name&gt;
&lt;servlet-class&gt;CheckCodeServlet&lt;/servlet-class&gt;
&lt;/servlet&gt;   
&lt;servlet&gt;
&lt;servlet-name&gt;LogonFormServlet&lt;/servlet-name&gt;
&lt;servlet-class&gt;LogonFormServlet&lt;/servlet-class&gt;
&lt;/servlet&gt; 
&hellip;&hellip;
&lt;servlet-mapping&gt;
&lt;servlet-name&gt;CheckCodeServlet&lt;/servlet-name&gt;
&lt;url-pattern&gt;/servlet/CheckCodeServlet&lt;/url-pattern&gt;
&lt;/servlet-mapping&gt;
&lt;servlet-mapping&gt;
&lt;servlet-name&gt;LogonFormServlet&lt;/servlet-name&gt;
&lt;url-pattern&gt;/servlet/LogonFormServlet&lt;/url-pattern&gt;
&lt;/servlet-mapping&gt;
</pre>&nbsp;