<!-- https://mvnrepository.com/artifact/com.github.penggle/kaptcha -->
<dependency>
 <groupId>com.github.penggle</groupId>
 <artifactId>kaptcha</artifactId>
 <version>2.3.2</version>
</dependency>

<servlet>
 <servlet-name>Kaptcha</servlet-name>
 <servlet-class>com.google.code.kaptcha.servlet.KaptchaServlet</servlet-class>
<!-- no border -->
<init-param>
 <param-name>kaptcha.border</param-name>
 <param-value>no</param-value>
</init-param>
<!-- font color is red -->
<init-param>
 <param-name>kaptcha.textproducer.font.color</param-name>
 <param-value>red</param-value>
</init-param>
<!-- font size is 43 -->
<init-param>
 <param-name>kaptcha.textproducer.font.size</param-name>
 <param-value>43</param-value>
</init-param>
<!-- noise color is black -->
<init-param>
 <param-name>kaptcha.noise.color</param-name>
 <param-value>black</param-value>
</init-param>
<!-- image width is 135 -->
<init-param>
 <param-name>kaptcha.image.width</param-name>
 <param-value>135</param-value>
</init-param>
<!-- image height is 50 -->
<init-param>
 <param-name>kaptcha.image.height</param-name>
 <param-value>50</param-value>
</init-param>
<!-- char[] -->
<init-param>
 <param-name>kaptcha.textproducer.char.string</param-name>
 <param-value>ACDEFGHIJKLMN235689</param-value>
</init-param>
<!-- char number -->
<init-param>
 <param-name>kaptcha.textproducer.char.length</param-name>
 <param-value>4</param-value>
</init-param>
<!-- font -->
<init-param>
 <param-name>kaptcha.textproducer.font.names</param-name>
 <param-value>Arial</param-value>
</init-param>
</servlet>
<servlet-mapping>
 <servlet-name>Kaptcha</servlet-name>
 <url-pattern>/Kaptcha</url-pattern>
</servlet-mapping>

<!-- 验证码 kaptcha -->
					<li>
						<div class="item-content">
							<div class="item-inner">
								<div class="item-title label">验证码</div>
								<input type="text" id="j_captcha" placeholder="验证码">
								<div class="item-input">
									<img id="captcha_img" alt="点击更换" title="点击更换"
										onclick="changeVerifyCode(this)" src="../Kaptcha">
								</div>
							</div>
						</div>
					</li>

function changeVerifyCode(img){
img.src="../Kaptcha?" + Math.floor(Math.random()*100);
alert('123');

var verfyCodeActual = $('#j_captcha').val();
				if(!verfyCodeActual){
					$.toast('请输入验证码!');
					return;
				}
				formData.append("verfyCodeActual",verfyCodeActual);

public static boolean checkVerifyCode(HttpServletRequest request) {
	String verifyCodeExpected = (String) request.getSession()
			.getAttribute(com.google.code.kaptcha.Constants.KAPTCHA_SESSION_KEY);
	String verfyCodeActual = HttpServletRequestUtil.getString(request, "verfyCodeActual");
	if (verfyCodeActual == null || !verfyCodeActual.equals(verifyCodeExpected)) {
		return false;	
	}
	return true;
}