Java全面细致讲解Cookie与Session及kaptcha验证码的使用

protected void createCookie(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    req.setCharacterEncoding("utf-8");
    resp.setContentType("text/html;charset=utf-8");
    //1. 创建Cookie对象
    Cookie cookie = new Cookie("key1", "value1");
    //2. 通知客户端保存
    resp.addCookie(cookie);
    resp.getWriter().write("Cookie创建成功");
}

protected void getCookie(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    req.setCharacterEncoding("utf-8");
    resp.setContentType("text/html;charset=utf-8");
    Cookie[] cookies = req.getCookies();
    for (Cookie cookie : cookies) {
        //System.out.println(cookie);
        resp.getWriter().write("Cookie["+ cookie.getName() + " = " + cookie.getValue() + "] <br/>");
    }
    // 查找特定的Cookie  (项目中会把这个写成工具类)
    Cookie need = null;
    for (Cookie cookie : cookies) {
        if ("key2".equals(cookie.getName())) {
            need = cookie;
            break;
        }
    }
    if (need != null) { // 不等于null，说明赋过值
        resp.getWriter().write("找到了需要的Cookie");
    }
}

// 查找特定的Cookie
public static Cookie findCookie(Cookie[] cookies, String name) {
    if (cookies == null || name == null || cookies.length == 0) {
        return null;
    }
    for (Cookie cookie : cookies) {
        if (name.equals(cookie.getName())) {
            return cookie;
        }
    }
    return null;
}

protected void updateCookie(HttpServletRequest req, HttpServletResponse resp) {
    // 第一种
    // 修改需要先创建同key的Cookie对象，新值直接构造传入就行
    Cookie newCookie1 = new Cookie("key1", "newValue1"); 
    resp.addCookie(newCookie1); // 保存修改
    // 第二种
    Cookie newCookie2 = CookieUtils.findCookie(req.getCookies(), "key2");
    if (newCookie2 != null) {
        newCookie2.setValue("newValue2"); // !注意不支持中文和一些符号，需要的话可以使用BASE64编码
        resp.addCookie(newCookie2);
    }
}

Cookie cookie = new Cookie("path1", "path1");
cookie.setPath(req.getContextPath() + "/abc"); //  ->  /工程路径/abc

<form action="/dynamicobject/loginServlet" method="post">
    用户名: <input type="text" name="username" value="${cookie.username.value}"> <br/>
    密码: <input type="password" name="password" value="${cookie.password.value}"> <br/>
    <input type="submit" value="登录">
</form>

public class LoginServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) {
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        // 这里可以去数据库查找，我们这里写死了
        if ("sutong".equals(username) && "123456".equals(password)) {
            Cookie c1 = new Cookie("username", username);
            c1.setMaxAge(60 * 60 * 24 * 7); // 一周内有效
            resp.addCookie(c1);
            Cookie c2 = new Cookie("password", password); // 一般密码都会加密的
            c2.setMaxAge(60 * 60 * 24 * 7);
            resp.addCookie(c2);
            System.out.println("登陆成功！");
        } else {
            System.out.println("登陆失败！");
        }
    }
}

protected void createOrGetSession(HttpServletRequest req, HttpServletResponse resp) throws IOException {
    req.setCharacterEncoding("utf-8");
    resp.setContentType("text/html;charset=utf-8");
    HttpSession session = req.getSession(); // 创建或获取Session
    boolean flag = session.isNew(); // 判断是否刚创建
    String id = session.getId(); // id
    resp.getWriter().write("得到的Session的Id是" + id + "<br/>");
    resp.getWriter().write("这个Session是否刚创建" + flag);
}

HttpSession session = req.getSession();
session.setAttribute("key1", "value1");

String att = (String) req.getSession().getAttribute("key1");  // 返回的是Object

<session-config>
    <session-timeout>20</session-timeout> <!-- 分钟为单位-->
</session-config>

<servlet>
    <servlet-name>KaptchaServlet</servlet-name>
    <servlet-class>com.google.code.kaptcha.servlet.KaptchaServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>KaptchaServlet</servlet-name>
    <!-- 注意这里改的访问名(看起来像个图片),这样的话访问这个就是自动生成验证码和图片，并保存到Session域--> 
    <url-pattern>/kaptcha.jpg</url-pattern> 
</servlet-mapping>

<form action="" method="post">
    用户名：<input type="text" name="username"> <br/>
    密码：<input type="password" name="password"> <br/>
    验证码：<input type="text" name="code"> <br/>
    <img id="code_img" src="http://localhost:8080/book/kaptcha.jpg" alt="图片找不到"> <br/>
    <input type="button" value="注册">
</form>

// 给验证码图片绑定单机事件
$("#code_img").click(function () {
    // 但这样每次发一样的请求，可能会被浏览器的缓存导致验证码无法改变，
    // 缓存是根据工程名后面的资源名和参数产生的，所以我们可以在后面加上一个随机的参数跳过缓存
	//this.src = "http://localhost:8080/book/kaptcha.jpg"; 
    this.src = "http://localhost:8080/book/kaptcha.jpg?d=" + new Date(); // 可以加个时间戳
});