copy了一份别人写的生成验证码的servlet，却发现编译时不能通过，提示找不到sun.image.codec.jpeg.JPEGCodec和com.sun.image.codec.jpeg.JPEGImageEncoder。其servlet如下。最后，通过将jre lib目录下的rt.jar拷贝到工程，然后引入，得以通过。
package com.jesse.onlineshop.servlet;import java.awt.Color;import java.awt.Font;import java.awt.Graphics2D;import java.awt.image.BufferedImage;import java.io.IOException;import java.util.Random;import javax.servlet.ServletException;import javax.servlet.ServletOutputStream;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.sun.image.codec.jpeg.JPEGCodec;import com.sun.image.codec.jpeg.JPEGImageEncoder;public class GenerateIdentifyCodeServlet extends HttpServlet { private static final long serialVersionUID = -5083098939508150302L; private static Random random = new Random(); private static final char[] stores = { '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' }; public String getRandonString() { StringBuffer buff = new StringBuffer(); for (int i = 0; i < getLength(); i++) { buff.append(stores[random.nextInt(stores.length)]); } return buff.toString(); } public Color getRandomColor() { return new Color(random.nextInt(255), random.nextInt(255), random.nextInt(255)); } public Color getReverseColor(Color color) { return new Color(255 - color.getRed(), 255 - color.getGreen(), 255 - color.getBlue()); } @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { int width = 100; int height = 30; resp.setContentType("image/jpeg"); String randomString = getRandonString(); req.getSession(true).setAttribute("identifyCode", randomString); Color color = getRandomColor(); Color reverse = getReverseColor(color); BufferedImage bi = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB); Graphics2D g = bi.createGraphics(); g.setFont(new Font(Font.SANS_SERIF, Font.BOLD, 16)); g.setColor(color); g.fillRect(0, 0, width, height); g.setColor(reverse); g.drawString(randomString, 18, 20); for (int i = 0, n = random.nextInt(width); i < n; i++) { g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1); } ServletOutputStream out = resp.getOutputStream(); JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out); encoder.encode(bi); out.flush(); out.close(); } public int getLength() { return Integer.parseInt(getInitParameter("codelength")); }}