javaweb中的验证码实现

验证码现在在网络中发挥的作用非常大。本文主要介绍如何使用Servlet中制作一个验证码。

代码实例：

<span style="font-size:18px;">package com.zhong.servlet;import java.awt.Color;import java.awt.Font;import java.awt.Graphics2D;import java.awt.image.BufferedImage;import java.io.IOException;import java.io.PrintWriter;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 ImageServlet extends HttpServlet {//字典，验证码中的字符从这里取出。private static final char[] CHARS={'2','3','4','5','6','7','8','9','A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T'};//一个随机数生成器private static Random random=new Random();/** * 获得一个随机字符串 * @return */public static String getRandomString(){StringBuilder sb=new StringBuilder();for(int i=0;i<6;i++){sb.append(CHARS[random.nextInt(CHARS.length)]);}return sb.toString();}/** * 获得一个随机的颜色值 * @return */public static Color getRandomColor(){return new Color(random.nextInt(255),random.nextInt(255),random.nextInt(255));}public static Color getReverseColor(Color c){return new Color(255-c.getRed(),255-c.getGreen(),255-c.getBlue());}public ImageServlet() {super();}public void destroy() {super.destroy(); }public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("image/jpeg");String randomString=getRandomString();request.getSession(true).setAttribute("randomString", randomString);int width=100;int height=30;Color color=getRandomColor();Color reverseColor=getReverseColor(color);BufferedImage bi=new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);//创建图像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(reverseColor);g.drawString(randomString, 18, 20);for(int i=0,n=random.nextInt(100);i<n;i++){g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1);}ServletOutputStream sout=response.getOutputStream();JPEGImageEncoder endocer=JPEGCodec.createJPEGEncoder(sout);endocer.encode(bi);sout.flush();}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("image/jpeg");String randomString=getRandomString();request.getSession(true).setAttribute("randomString", randomString);int width=100;int height=30;Color color=getRandomColor();Color reverseColor=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(reverseColor);g.drawString(randomString, 18, 20);for(int i=0,n=random.nextInt(100);i<n;i++){g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1);}ServletOutputStream sout=response.getOutputStream();JPEGImageEncoder endocer=JPEGCodec.createJPEGEncoder(sout);endocer.encode(bi);sout.flush();}public void init() throws ServletException {// Put your code here}}</span>

效果图：