JAVAWEB學習製作自己的小說管理網站-day02

Author AhahaGe

主要實現了創建驗證碼servlet,以及刷新驗證碼功能

創建驗證碼主要做以下幾個步驟：

• 建一個bufferedImage，來存放可改變的image
• 得到graphics2D來渲染2維的image，設置顏色setColor()和字體setFont()
• 用drawRect()方法畫矩形
• 用fillRect()方法填充矩形
• 用drawLine()方法畫干擾線
• 用drawString()方法畫驗證碼
• 瀏覽器設置不緩存
• 設置返回類型爲image
• 用ImageIO把bufferedImage寫入servletOutputStream

Step1:創建驗證碼servlet，類名爲ValidateCodeServlet

package 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.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;

/**
 * create a validateCode image and validate user's input
 * @author Ahaha_Ge
 *
 */
public class ValidateCodeServlet extends HttpServlet{

    private static final long serialVersionUID = 1L;

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        doPost(req,resp);
    }

    /**
     * generate validateCode image
     * image shape is rectangular with some lines and codes
     * codeCount is 4, code should contain 26 English chars and number
     */
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {

        int width = 160;
        int height = 40;
        int codeCount = 4;
        Random r = new Random();
        //create a buffered image instance
        BufferedImage bi = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        //create a graphics to render the image
        Graphics2D g = bi.createGraphics();
        //set context color and fill rectangular
        g.setColor(setRandomColor());
        g.fillRect(0, 0, width-1, height-1);
        //set context color and draw rectangular
        g.setColor(setRandomColor());
        g.drawRect(0, 0, width-1, height-1);
        //draw disturb lines
        for(int i=0; i<5; i++){
            g.setColor(setRandomColor());
            g.drawLine(r.nextInt(width), r.nextInt(height), r.nextInt(width), r.nextInt(height));
        }
        //set font
        Font font = new Font("font",Font.PLAIN,height*3/4);
        g.setFont(font);
        //create and draw codes
        String codes = generateCodes(codeCount);
        for(int i=0; i<codes.length(); i++){
            g.drawString(String.valueOf(codes.charAt(i)), width*(i+1)/(codeCount+1), height*7/8);
        }
        //put codes into session
        HttpSession session = req.getSession();
        session.setAttribute("validateCode", codes);
        //forbid cache
        resp.setHeader("Pragma", "no-cache");
        resp.setHeader("Cache-Control", "no-cache");
        resp.setDateHeader("expires", 0);
        resp.setContentType("image/jpeg");
        //send image to output stream
        ServletOutputStream sos = resp.getOutputStream();
        ImageIO.write(bi, "jpeg", sos);
        sos.close();
    }

    //set Random color
    private Color setRandomColor(){
        int r = new Random().nextInt(256);
        int g = new Random().nextInt(256);
        int b = new Random().nextInt(256);
        Color c = new Color(r,g,b);
        return c;
    }

    //create codes set
    private char[] createCodesSet(){
        char[] c = new char[62];
        for(int i=0; i<26; i++){
            //add A to Z
            c[i] = (char)(i+65);
            //add a to z
            c[26+i] = (char)(i+97);
        }
        for(int i=0; i<10; i++){
            //add 0 to 9
            c[52+i] = (char)(i+48);
        }
        return c;
    }

    //create n codes
    private String generateCodes(int n){
        //codes set
        char[] codes = createCodesSet();
        StringBuffer sb = new StringBuffer();
        for(int i=0;i<n;i++){
            sb.append(codes[new Random().nextInt(codes.length)]);
        }
        return sb.toString();
    }

    public static void main(String[] args){
        System.out.println(new ValidateCodeServlet().setRandomColor());
    }

}

Step2: 在web.xml中配置寫好的ValidateCodeServelt

<servlet>
    <servlet-name>validateCodeServlet</servlet-name>
    <servlet-class>servlet.ValidateCodeServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>validateCodeServlet</servlet-name>
    <url-pattern>/validateCodeServlet</url-pattern>
</servlet-mapping>

Step3: 在使用驗證碼的地方，創建一個image控件，再改變src爲ValidateCodeServlet

<input type="image" id="image" width="160" height="40" name="code" src="validateCodeServlet"/>

Step4: 用javascript來實現刷新驗證碼，寫一個按鈕，當點擊它時，定義一個方法，改變image控件的src，不要忘了newDate()，不然生成的驗證碼是一樣的。

<input type="button" name="fresh" value="fresh" onclick="freshValidateCode();"/>

<script type="text/javascript">
        function freshValidateCode()
        {
            document.getElementById("image").setAttribute("src","validateCodeServlet?"+new Date());
        }
    </script>

總結：這麼簡單的功能寫了兩天，第一天竟然被畫驗證碼給嚇住了，這麼多代碼，這麼多類，現在回過來看看，發現還是挺簡單的，主要是參考了網上的代碼，跟着理解了一遍，做了兩遍，做的時候總是會忘，總是會出小錯，終於作出來了，接着得寫上傳下載。