1、创建Servlet类
（1）主要目的为返回生成随机字符串的图片
@WebServlet("/newCode")
public class NewCode extends HttpServlet {
private Random random = new Random(); // 随机数对象
private int width = 80; // 宽度
private int height = 30; // 高度
private int fontsize = 12; // 字体大小
private String str = "0123456789abcdef"; // 字体大小
//生成最少4个字符的随机字符串
private String randCode(int len){
if(len < 4) {
len = 4;
}
//更改宽度
width = 5 + fontsize*len;
//生成字符串
String code = "";
for (int i = 0; i < len; i++) {
code += str.charAt(random.nextInt(str.length()));
}
return code;
}
// 返回随机颜色
private Color randColor() {
int r = random.nextInt(256);
int g = random.nextInt(256);
int b = random.nextInt(256);
return new Color(r, g, b);
}
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// 1.创建画板
BufferedImage img = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
// 2.创建画笔
Graphics2D pen = (Graphics2D) img.getGraphics();
// 3.生成随机内容
String code = randCode(4);
request.getSession().setAttribute("valiCode", code);
// 4.绘制内容
// 4.1设置绘制区域
pen.fillRect(0, 0, width, height);
// 4.2设置字体
pen.setFont(new Font("微软雅黑", Font.BOLD, fontsize));
// 4.3按顺序逐个绘制字符
for (int i = 0; i < code.length(); i++) {
pen.setColor(randColor());
// 绘制字符
pen.drawString(code.charAt(i) + "", 5 + i * fontsize, (fontsize + height) / 2);
}
// 4.4绘制噪音线
for (int i = 0; i < 2; i++) {
pen.setColor(randColor());
pen.setStroke(new BasicStroke(3));
pen.drawLine(random.nextInt(width/2), random.nextInt(height),
random.nextInt(width), random.nextInt(height));
}
// 5、存为图片并发送
ServletOutputStream out = response.getOutputStream();
ImageIO.write(img, "png", out);
out.flush();
out.close();
}
}
（2）主要目的是判断用户输入的字符串是否与session中的字符串（图片验证码）一致，若一致则跳转到正确页面，否则提示重新输入。
@WebServlet("/valiCode")
public class ValiCode extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
this.doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// 1、得到数据
String inCode = request.getParameter("inCode").toString().toLowerCase();
String valiCode = request.getSession().getAttribute("valiCode").toString().toLowerCase();
// 2、验证是否正确
if (inCode.equals(valiCode)) {
response.sendRedirect("index.jsp");
} else {
request.getSession().setAttribute("err", "验证码输入错误，请重新输入!");
// 返回上一页
String url = request.getHeader("Referer");
response.sendRedirect(url);
}
}
}
2、创建JSP页面
（1）目的为验证码匹配成功后跳转到正确响应页面
<body>
This is my JSP page.
</body>
（2）用户输入界面
<style type="text/css">
.code_a {
color: #0000ff;
font-size: 12px;
text-decoration: none;
cursor: pointer;
}
#imgCode {
cursor: pointer;
}
</style>
<script type="text/javascript">
function changeCode() {
var imgCode = document.getElementById("imgCode");
imgCode.src = "newCode?" + Math.random();
}
</script>
</head>
<body>
<form action="valiCode" method="post">
<label>验证码:</label> <input type="text" id="inCode" name="inCode" /> <img
alt="" src="newCode" align="center" id="imgCode"
onclick="changeCode()"> <a class="code_a"
onclick="changeCode()">换一张</a><br /> <input type="submit" value="登录" />
</form>
<div style="color: red;">${err}</div>
</body>
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