Cage小巧，好用。這里在官方基礎例子基礎上做了擴展：

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package?com.lavasoft.ntv.web.common; import?com.github.cage.IGenerator; import?java.util.Random; /** ?* 驗證碼生成器 ?* ?* @author leizhimin 14-5-5 下午2:42 ?*/ public?class?MyTokenGenerator?implements?IGenerator<String> { ????private?int?length =?4; ????private?String charsetdir =?"23456789abcdefghigkmnpqrstuvwxyzABCDEFGHIGKLMNPQRSTUVWXYZ"; ????private?static?final?Random r =?new?Random(); ????public?MyTokenGenerator() { ????} ????public?MyTokenGenerator(int?length, String charsetdir) { ????????this.length = length; ????????this.charsetdir = charsetdir; ????} ????@Override ????public?String next() { ????????StringBuffer sb =?new?StringBuffer(); ????????int?len = charsetdir.length(); ????????for?(int?i =?0; i < length; i++) { ????????????sb.append(charsetdir.charAt(r.nextInt(len -?1))); ????????} ????????return?sb.toString(); ????} ????public?static?void?main(String[] args) { ????????MyTokenGenerator t =?new?MyTokenGenerator(); ????????for?(int?i =?0; i <?100; i++) { ????????????System.out.println(t.next()); ????????} ????} }

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package?com.lavasoft.ntv.web.servlet; import?com.github.cage.Cage; import?com.lavasoft.ntv.web.common.MyTokenGenerator; import?javax.servlet.ServletException; import?javax.servlet.http.HttpServlet; import?javax.servlet.http.HttpServletRequest; import?javax.servlet.http.HttpServletResponse; import?javax.servlet.http.HttpSession; import?java.io.IOException; public?class?CaptchaServlet?extends?HttpServlet { ????private?static?final?long?serialVersionUID = 1490947492185481844L; ????private?static?final?Cage cage =?new?Cage(null,null,null,null,null,?new?MyTokenGenerator(),null); ????/** ?????* Generates a captcha token and stores it in the session. ?????* ?????* @param session where to store the captcha. ?????*/ ????public?static?void?generateToken(HttpSession session) { ????????String token = cage.getTokenGenerator().next(); ????????session.setAttribute("captchaToken", token); ????????markTokenUsed(session,?false); ????} ????/** ?????* Used to retrieve previously stored captcha token from session. ?????* ?????* @param session where the token is possibly stored. ?????* @return token or null if there was none ?????*/ ????public?static?String getToken(HttpSession session) { ????????Object val = session.getAttribute("captchaToken"); ????????return?val !=?null?? val.toString() :?null; ????} ????/** ?????* Marks token as used/unused for image generation. ?????* ?????* @param session where the token usage flag is possibly stored. ?????* @param used??? false if the token is not yet used for image generation ?????*/ ????protected?static?void?markTokenUsed(HttpSession session,?boolean?used) { ????????session.setAttribute("captchaTokenUsed", used); ????} ????/** ?????* Checks if the token was used/unused for image generation. ?????* ?????* @param session where the token usage flag is possibly stored. ?????* @return true if the token was marked as unused in the session ?????*/ ????protected?static?boolean?isTokenUsed(HttpSession session) { ????????return?!Boolean.FALSE.equals(session.getAttribute("captchaTokenUsed")); ????} ????@Override ????protected?void?doGet(HttpServletRequest req, HttpServletResponse resp) ????????????throws?ServletException, IOException { ????????HttpSession session = req.getSession(false); ????????String token = session !=?null?? getToken(session) :?null; ????????if?(token ==?null?|| isTokenUsed(session)) { ????????????resp.sendError(HttpServletResponse.SC_NOT_FOUND,"Captcha not found."); ????????????return; ????????} ????????setResponseHeaders(resp); ????????markTokenUsed(session,?true); ????????cage.draw(token, resp.getOutputStream()); ????} ????/** ?????* Helper method, disables HTTP caching. ?????* ?????* @param resp response object to be modified ?????*/ ????protected?void?setResponseHeaders(HttpServletResponse resp) { ????????resp.setContentType("image/"?+ cage.getFormat()); ????????resp.setHeader("Cache-Control",?"no-cache, no-store"); ????????resp.setHeader("Pragma",?"no-cache"); ????????long?time = System.currentTimeMillis(); ????????resp.setDateHeader("Last-Modified", time); ????????resp.setDateHeader("Date", time); ????????resp.setDateHeader("Expires", time); ????} }

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<%-- ??Created by IntelliJ IDEA. ??User: leizhimin 14-5-5 下午12:18 --%> <%@page import="com.lavasoft.ntv.web.servlet.CaptchaServlet"%><%@ ????????page contentType="text/html" pageEncoding="UTF-8"%><% ????boolean showGoodResult; ????boolean showBadResult; ????if ("POST".equals(request.getMethod())) { ????????String sessionToken = CaptchaServlet.getToken(session); ????????String requestToken = request.getParameter("captcha"); ????????showGoodResult = sessionToken != null && sessionToken.equals(requestToken); ????????showBadResult = !showGoodResult; ????} else { ????????showGoodResult = showBadResult = false; ????} ????CaptchaServlet.generateToken(session); %><!DOCTYPE html> <html?xmlns="http://www.w3.org/1999/xhtml"> <head> ????<meta?charset="UTF-8"?/> ????<title>Captcha Reader</title> </head> <body> <%? if (showGoodResult) {%> <h1?style="color: green;">Your kung fu is good!</h1> <%? } else if (showBadResult) {%> <h1?style="color: red;">This is not right. Try again!</h1> <%? } %> <p>Type in the word seen on the picture</p> <form?action=""?method="post"> ????<input?name="captcha"?type="text"?autocomplete="off"?/> ????<input?type="submit"?/> </form> <img?alt="captcha image"?src="/ntv/captcha"?width="120px"?height="30px"/> </body> </html>

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<servlet> ????<servlet-name>captcha</servlet-name> ????<servlet-class>com.lavasoft.ntv.web.servlet.CaptchaServlet</servlet-class> </servlet> <servlet-mapping> ????<servlet-name>captcha</servlet-name> ????<url-pattern>/captcha</url-pattern> </servlet-mapping>

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本文轉自 leizhimin 51CTO博客，原文鏈接：http://blog.51cto.com/lavasoft/1406702，如需轉載請自行聯系原作者

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