JavaWeb学习笔记2——生成图片验证码

首先创建一个名为identity的JavaWeb项目，并在其下面新建一个Servlet，名为IdentityServlet，如果不会创建项目和Servlet请参考我上节笔记：https://blog.csdn.net/h2503652646/article/details/82555695

下面是IdentityServlet.java的源代码

package com.test.identity;

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 IdentityServlet extends HttpServlet {
	
	
	public 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','U','V','W','X','Y','P','Q','R',
			'S','T','Z'};         //这些是随机在图片上生成的验证码内容
	
	
	public static Random random=new Random();
	
	
	
	//获取6位随机字符验证码的方法
	public static String getRandomString(){
		StringBuffer buffer=new StringBuffer();
		
		for(int i=0;i<6;i++){
			buffer.append(CHARS[random.nextInt(CHARS.length)]);
		}
		return buffer.toString();
	}
	
	//随机颜色
	public static Color getRandomColor(){
		return new Color(random.nextInt(255),random.nextInt(255),random.nextInt(255));
	}
	
	
	//某颜色的反色，用于前景色
	public static Color getReverseColor(Color c){
		return new Color(255-c.getRed(),255-c.getGreen(),255-c.getBlue());
	}

	/**
		 * Constructor of the object.
		 */
	public IdentityServlet() {
		super();
	}

	/**
		 * Destruction of the servlet. <br>
		 */
	public void destroy() {
		super.destroy(); // Just puts "destroy" string in log
		// Put your code here
	}

	/**
		 * The doGet method of the servlet. <br>
		 *
		 * This method is called when a form has its tag value method equals to get.
		 * 
		 * @param request the request send by the client to the server
		 * @param response the response send by the server to the client
		 * @throws ServletException if an error occurred
		 * @throws IOException if an error occurred
		 */
	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

		response.setContentType("image/jpeg");
		
		String randomString=getRandomString();   //随机字符串
		request.getSession(true).setAttribute("randomString", randomString);
		
		int width=100;
		int height=30;
		
		Color color=getRandomColor();
		Color reverse=getReverseColor(color);       //反色，用于前景色
		
		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);    //绘制随机字符
		for(int i=0, n=random.nextInt(100);i<n;i++){
			                                   //画最多100个噪音点
			g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1);  //噪音点在图片上随机选择位置产生
		}
		
		
		ServletOutputStream out=response.getOutputStream();
		
		JPEGImageEncoder encoder=JPEGCodec.createJPEGEncoder(out);  //转成JPEG格式
		
		
		encoder.encode(bi);  //对图片进行编码
		out.flush();
	}

	/**
		 * The doPost method of the servlet. <br>
		 *
		 * This method is called when a form has its tag value method equals to post.
		 * 
		 * @param request the request send by the client to the server
		 * @param response the response send by the server to the client
		 * @throws ServletException if an error occurred
		 * @throws IOException if an error occurred
		 */
	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();
	}

	/**
		 * Initialization of the servlet. <br>
		 *
		 * @throws ServletException if an error occurs
		 */
	public void init() throws ServletException {
		// Put your code here
	}

}

接下来我们建立一个HTML文件来引用这个图片验证码，创建方法是：在项目Iidentity上右键选择New—HTML（Advanced Templatets），在弹出框中设置名字为identity，然后Finish，下面是identity.html的代码：

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">   
<script>
function reloadImage(){

     document.getElementById('btn').disable=true;
     document.getElementById('identity').src='servlet/IdentityServlet?ts='+new Date().getTime();

}
</script>
<img src="servlet/IdentityServlet" id="identity" onload="btn.disabled =false; "/>
<input type=button value="换个图片" onclick="reloadImage()" id="btn">

代码工作全部完成，然后将项目部署在自己的Tomcat上（部署方法参考上节笔记），启动Tomcat，在浏览器中输入：

http://localhost:8080/identity/identity.html 回车，效果如下：

可以点击按钮进行验证码的刷新更换。

JavaWeb学习笔记2——生成图片验证码

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