怎样将中内存中画好的图像，输出在jsp页面指定的位置。比如说，<td></td>内

做了一个BufferedImage，嵌入随机验证码。用于，网站登录时，防止别人用程序暴力猜码进入系统。可是输出时，只能在jsp页面最左上角显示。而且，其它jsp元素内容也没有了。怎么弄？

解决方案 »

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import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.Random;import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;public class Image extends HttpServlet { /**
*
*/
private static final long serialVersionUID = 5688443850114813473L; private static Color getRandColor(int fc, int bc) {
Random random = new Random();
if (fc > 255)
fc = 255;
if (bc > 255)
bc = 255;
int r = fc + random.nextInt(bc - fc);
int g = fc + random.nextInt(bc - fc);
int b = fc + random.nextInt(bc - fc);
return new Color(r, g, b);
} private static String charsLong = "23456789abcdefghjklmnpqrstuvwxyzABCDEFGHIJKLMNPQRSTUVWXYZ"; private static String chars = charsLong; public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { int charsLength = chars.length(); response.setHeader("ragma", "No-cache");
response.setHeader("Cache-Control", "no-cache");
response.setDateHeader("Expires", 0); int width = 70, height = 20;
BufferedImage image = new BufferedImage(width, height,
BufferedImage.TYPE_INT_RGB);
Graphics g = image.getGraphics(); Random random = new Random();
g.setColor(getRandColor(200, 250));//a
g.fillRect(0, 0, width, height);
g.setFont(new Font("Times New Roman", Font.ITALIC, height));
g.setColor(getRandColor(160, 200));//b for (int i = 0; i < 35; 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);
}
StringBuilder sRand = new StringBuilder();
String[] fontNames = { "Times New Roman", "Arial", "Book antiqua", "" };
for (int i = 0; i < 4; i++) {
g.setFont(new Font(fontNames[random.nextInt(3)], Font.ITALIC,
height));  //a
char rand = chars.charAt(random.nextInt(charsLength));
sRand.append(rand);
g.setColor(new Color(20 + random.nextInt(110), 20 + random
.nextInt(110), 20 + random.nextInt(110)));  //b
g.drawString(String.valueOf(rand), 16 * i + random.nextInt(6) + 3,
height - random.nextInt(4)); }
  g.setColor(getRandColor(160, 200));
for (int i = 0; i < 30; i++) {
int x = random.nextInt(width);
int y = random.nextInt(height);
int xl = random.nextInt(width);
int yl = random.nextInt(width);
g.drawLine(x, y, x + xl, y + yl);
}
request.getSession().setAttribute("Login_Image_Code", sRand.toString()); g.dispose();
try {
Thread.sleep(100);
} catch (Exception ex) {
}
OutputStream os = response.getOutputStream();
ImageIO.write(image, "JPEG", os);
//RequestDispatcher re = request.getRequestDispatcher("MyJsp.jsp");
//re.forward(request, response);
os.flush();
os.close(); }
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { response.setContentType("text/html");
PrintWriter out = response.getWriter();
out
.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
out.println("<HTML>");
out.println("  <HEAD><TITLE>A Servlet</TITLE></HEAD>");
out.println("  <BODY>");
out.print("    This is ");
out.print(this.getClass());
out.println(", using the POST method");
out.println("  </BODY>");
out.println("</HTML>");
out.flush();
out.close();
}}
程序是www.java2000.net上的!
用servlet输出图像，然后在页面上用img标签调用，src地址就是servlet的地址
可以这样输出<td>
  <img src="/servlet/image.do" /> 
</td>