错误日志

开发环境:JDK1.4,Myeclipse6.6,WEB Logic8.1
出错记录:在WEB Logic后台报错如下：
Servlet failed with IOException
javax.imageio.IIOException: Can't create output stream ![color=red][/color]
        at javax.imageio.ImageIO.write(ImageIO.java:1505)
        at com.sclh.common.ValidateCodeServlet.service(ValidateCodeServlet.java:
111)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
        at weblogic.servlet.internal.ServletStubImpl$ServletInvocationAction.run
(ServletStubImpl.java:996)
        at weblogic.servlet.internal.ServletStubImpl.invokeServlet(ServletStubIm
pl.java:419)
        at weblogic.servlet.internal.ServletStubImpl.invokeServlet(ServletStubIm
pl.java:315)
        at weblogic.servlet.internal.WebAppServletContext$ServletInvocationActio
n.run(WebAppServletContext.java:6452)
        at weblogic.security.acl.internal.AuthenticatedSubject.doAs(Authenticate
dSubject.java:321)
        at weblogic.security.service.SecurityManager.runAs(SecurityManager.java:
118)
        at weblogic.servlet.internal.WebAppServletContext.invokeServlet(WebAppSe
rvletContext.java:3661)
        at weblogic.servlet.internal.ServletRequestImpl.execute(ServletRequestIm
pl.java:2630)
        at weblogic.kernel.ExecuteThread.execute(ExecuteThread.java:219)
        at weblogic.kernel.ExecuteThread.run(ExecuteThread.java:178)
Caused by: javax.imageio.IIOException: Can't create cache file!
        at javax.imageio.ImageIO.createImageOutputStream(ImageIO.java:395)
        at javax.imageio.ImageIO.write(ImageIO.java:1503)
        ... 12 more
Caused by: java.io.IOException: 系统找不到指定的路径。
        at java.io.WinNTFileSystem.createFileExclusively(Native Method)
        at java.io.File.checkAndCreate(File.java:1314)
        at java.io.File.createTempFile(File.java:1402)
        at javax.imageio.stream.FileCacheImageOutputStream.<init>(FileCacheImage
OutputStream.java:66)
        at com.sun.imageio.spi.OutputStreamImageOutputStreamSpi.createOutputStre
amInstance(OutputStreamImageOutputStreamSpi.java:50)
        at javax.imageio.ImageIO.createImageOutputStream(ImageIO.java:391)
        ... 13 more

在网上查了一下：有二个答案
1:Tomcat下创建一个临时目录temp,可惜我用的是Web Logic,只有用第二个方法了.
2 把代码最后一句改为:
//将图像输出到Servlet输出流中。
  

/*ServletOutputStream sos = response.getOutputStream();
   ImageIO.write(buffImg, "jpeg", sos);   
   sos.close();*/   
   JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(response.getOutputStream());
   encoder.encode(buffImg);

代码如下:

public class ValidateCode extends HttpServlet { 
 public void service(HttpServletRequest request, HttpServletResponse response)
               throws ServletException, java.io.IOException {   
    HttpSession session = (HttpSession) request.getSession();
    String action = request.getParameter("action");
    if("getSession".equals(action)){
     String validateCodeSession = (String) session.getAttribute("validateCode");
   PrintWriter out = response.getWriter();
   response.setContentType("text/html");
   response.setHeader("Cache-Control", "no-cache");
   out.print(validateCodeSession);
   out.close();
    }else{
     if(session.getAttribute("validateCode") != null){
      session.removeAttribute("validateCode");
     }
            //验证码图片的宽度。
   int width = 120;
   //验证码图片的高度。
   int height = 30;
   //验证码字符个数
   int codeCount = 4;
   int x_v = 0;
   //字体高度
   int fontHeight;
   int codeY;
   char[] codeSequence = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
     'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
     'U', 'V', 'W', 'X', 'Y', 'Z', '0', '1', '2', '3', '4', '5',
     '6', '7', '8', '9' };
   //初始化图片大小
   x_v = width / (codeCount + 1);
   fontHeight = height - 2;
   codeY = height - 4;
   //定义图像buffer
   BufferedImage buffImg = new BufferedImage(width, height,
     BufferedImage.TYPE_INT_RGB);
   Graphics2D g = buffImg.createGraphics();
   //创建一个随机数生成器类
   Random random = new Random();
   //将图像填充为白色
   g.setColor(Color.WHITE);
   g.fillRect(0, 0, width, height);
   //创建字体，字体的大小应该根据图片的高度来定。
   Font font = new Font("Arial", Font.BOLD, fontHeight);
   //设置字体。
   g.setFont(font);
   //画边框。
   g.setColor(Color.WHITE);
   g.drawRect(0, 0, width - 1, height - 1);
   //随机产生160条干扰线，使图象中的认证码不易被其它程序探测到。
   g.setColor(Color.yellow);
   for (int i = 0; i < 30; 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);
   }
   //randomCode用于保存随机产生的验证码，以便用户登录后进行验证。
   StringBuffer randomCode = new StringBuffer();
   int red = 0, green = 0, blue = 0;
   //随机产生codeCount数字的验证码。
   for (int i = 0; i < codeCount; i++) {
    //得到随机产生的验证码数字。
    String strRand = String
      .valueOf(codeSequence[random.nextInt(36)]);
    //产生随机的颜色分量来构造颜色值，这样输出的每位数字的颜色值都将不同。
    red = random.nextInt(255);
    green = random.nextInt(255);
    blue = random.nextInt(255);
    //用随机产生的颜色将验证码绘制到图像中。
    g.setColor(new Color(red, green, blue));
    g.drawString(strRand, (i + 1) * x_v, codeY);
    //将产生的四个随机数组合在一起。
    randomCode.append(strRand);
   }
   // 将四位数字的验证码保存到Session中。
   session.setAttribute("validateCode", randomCode.toString());
   // 禁止图像缓存。
   response.setHeader("Pragma", "no-cache");
   response.setHeader("Cache-Control", "no-cache");
   response.setDateHeader("Expires", 0);
   response.setContentType("image/jpeg");
   //将图像输出到Servlet输出流中。
   /*ServletOutputStream sos = response.getOutputStream();
   ImageIO.write(buffImg, "jpeg", sos);   
   sos.close();*/
   
   JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(response.getOutputStream());
   encoder.encode(buffImg);

          }
     }
}

Web.xml内容如下：
   

 <servlet>
     <servlet-name>ValidateCode </servlet-name>   
     <servlet-class>com.ValidateCode </servlet-class>
    </servlet>

     <servlet-mapping>
     <servlet-name>ValidateCode </servlet-name>
     <url-pattern>/ValidateCode</url-pattern>
    </servlet-mapping>

JSP内容如下：

<img src="/ValidateCode " id="ImgId" width="120" height="30" />