在 web.xml里面加入 下面的代码：
<servlet> <servlet-name>validatecode</servlet-name> <servlet-class>webapp.servlet.ValidateCodeServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>validatecode</servlet-name> <url-pattern>/images/validatecode.jpeg</url-pattern> </servlet-mapping>
servlet类：
import java.awt.Color; import java.awt.Font; import java.awt.Graphics2D; import java.awt.image.BufferedImage; import java.util.Random; import javax.imageio.ImageIO; import javax.servlet.ServletException; import javax.servlet.ServletOutputStream; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpSession; import webapp.auth.SessionUtil; //项目使用自己编写的session处理类 /** * 验证码生成servlet * @author Administrator * */ public class ValidateCodeServlet extends HttpServlet { /** * */ private static final long serialVersionUID = 1L; int w = 60; int h = 20; int fh = 10; int cy = 0; int x = 1; int cc = 4; char[] cs = { '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', '2', '3', '4', '5', '6', '7', '8', '9' }; protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, java.io.IOException { x = w / (cc + 1); fh = h - 2; cy = h - 4; // image buffer BufferedImage buffImg = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB); Graphics2D g = buffImg.createGraphics(); Random random = new Random(); // fill image with white color g.setColor(Color.WHITE); g.fillRect(0, 0, w, h); // create font Font font = new Font("Fixedsys", Font.PLAIN | Font.BOLD, fh); // set font g.setFont(font); g.setColor(Color.blue); g.drawRect(0, 0, w - 1, h - 1); // draw 200 radom line g.setColor(Color.gray); for (int i = 0; i < 60; i++) { int x1 = random.nextInt(w); int y1 = random.nextInt(h); int x2 = random.nextInt(12); int y2 = random.nextInt(12); g.drawLine(x1, y1, x1 + x2, y1 + y2); } // draw radom code StringBuffer randomCode = new StringBuffer(); int red = 0, green = 0, blue = 0; for (int i = 0; i < cc; i++) { String strRand = String.valueOf(cs[random.nextInt(cs.length - 1)]); red = random.nextInt(120); green = random.nextInt(60); blue = random.nextInt(200); g.setColor(new Color(red, green, blue)); g.drawString(strRand, (i + 1) * x - 6, cy); randomCode.append(strRand); } HttpSession session = req.getSession(); SessionUtil.set(req, SessionUtil.VALIDATE_CODE_KEY, randomCode .toString()); resp.setHeader("Pragma", "no-cache"); resp.setHeader("Cache-Control", "no-cache"); resp.setDateHeader("Expires", 0); resp.setContentType("image/jpeg"); ServletOutputStream sos = resp.getOutputStream(); ImageIO.write(buffImg, "jpeg", sos); sos.close(); } }
javax.imageio.IIOException: Can't create output stream! javax.imageio.ImageIO.write(ImageIO.java:1521) 网上搜此问题，有说法是与JDK有关，并给出解决方案： 把 ImageIO.write(image, "jpeg", response.getOutputStream()); 修改为 JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(response.getOutputStream()); encoder.encode(image); //jsp上要增加com.sun.image.codec.jpeg.JPEGCodec,com.sun.image.codec.jpeg.JPEGImageEncoder这些类的import 经验证，是可以解决问题的。 但是。。。，原因怎会是JDK？我这个环境几分钟前还是正常的，中间没有安装过JDK或者修改环境变量 检查tomcat的日志，终于真相大白： javax.imageio.IIOException: Can't create output stream! at javax.imageio.ImageIO.write(ImageIO.java:1521) 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:1519) ... 34 more Caused by: java.io.IOException: 系统找不到指定的路径。 原来是ImageIO.write(image, "jpeg", response.getOutputStream()); 需要写缓冲文件，但是写文件不成功。 回忆几分钟前的操作，可能是删除了tomcat的temp目录。 手动创建temp目录，问题解决！
