第一步:

首先先寫一個驗證碼圖片生成類CreateAuthCode

package com.sunsheng.commons;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.util.Random;

public class CreateAuthCode extends BufferedImage {

	private Graphics graphics;
	private int width;
	private int height;

	public CreateAuthCode(int width, int height, int imageType) {
		super(width, height, imageType);
		this.width = width;
		this.height = height;

		graphics = getGraphics();

		//設定圖片的背景顏色
		setBgColor();
		
		//給圖片設定一個邊框
		setBorder();
		
		//往圖片中寫入字串
		setText();
	}

	private void setBorder() {
		//設定邊框的顏色
		graphics.setColor(Color.RED);
		
		//為了防止邊框寫到圖片外面,所以處理一下
		graphics.drawRect(1, 1, width - 2, height - 2);

	}

	private void setBgColor() {

		graphics.setColor(Color.WHITE);
		
		//往矩形區域填充設定的顏色
		graphics.fillRect(0, 0, width, height);
	}

	private void setText() {

		graphics.setColor(Color.BLUE);
		
		//設定檔案的字型
		graphics.setFont(new Font("宋體", Font.BOLD, 60));
		
		// graphics.drawString("中國", 10, 80);

		int x = 10;
		//往圖片中寫入4個隨機的整數(0~9)
		for (int i = 0; i < 4; i++) {

			int num = new Random().nextInt(10);
			//座標是字串左下角的那個點
			graphics.drawString(String.valueOf(num), x, 65);
			
			//數字字串是半形格式佔30個畫素,每個字串之間距離10個畫素,所以x軸要右移40畫素
			x += 40;
		}
	}

}
 

在Servlet中輸入圖片

package com.sunsheng;

import java.awt.image.BufferedImage;
import java.io.IOException;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.sunsheng.commons.CreateAuthCode;

public class AuthCode extends HttpServlet {

	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		
		//設定http響應頭,告訴瀏覽器伺服器傳送的是一個jpeg格式的圖片
		resp.setHeader("content-type", "image/jpeg");
		
		
		//在記憶體中建立一個圖片
		//呼叫ImageIO工具的write方法把圖片從記憶體寫到Response的OutputStream中
		ImageIO.write(new CreateAuthCode(180, 80, BufferedImage.TYPE_INT_RGB)
						, "jpg"
						, resp.getOutputStream());
	}

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

}