protected void createCookie(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    req.setCharacterEncoding("utf-8");
    resp.setContentType("text/html;charset=utf-8");
    //1. 創(chuàng)建Cookie對象
    Cookie cookie = new Cookie("key1", "value1");
    //2. 通知客戶端保存
    resp.addCookie(cookie);
    resp.getWriter().write("Cookie創(chuàng)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  (項(xiàng)目中會把這個(gè)寫成工具類)
    Cookie need = null;
    for (Cookie cookie : cookies) {
        if ("key2".equals(cookie.getName())) {
            need = cookie;
            break;
        }
    }
    if (need != null) { // 不等于null，說明賦過值
        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) {
    // 第一種
    // 修改需要先創(chuàng)建同key的Cookie對象，新值直接構(gòu)造傳入就行
    Cookie newCookie1 = new Cookie("key1", "newValue1"); 
    resp.addCookie(newCookie1); // 保存修改
    // 第二種
    Cookie newCookie2 = CookieUtils.findCookie(req.getCookies(), "key2");
    if (newCookie2 != null) {
        newCookie2.setValue("newValue2"); // !注意不支持中文和一些符號，需要的話可以使用BASE64編碼
        resp.addCookie(newCookie2);
    }
}

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

<form action="/dynamicobject/loginServlet" method="post">
    用戶名: <input type="text" name="username" value="${cookie.username.value}"> <br/>
    密碼: <input type="password" name="password" value="${cookie.password.value}"> <br/>
    <input type="submit" value="登錄">
</form>

public class LoginServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) {
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        // 這里可以去數(shù)據(jù)庫查找，我們這里寫死了
        if ("sutong".equals(username) && "123456".equals(password)) {
            Cookie c1 = new Cookie("username", username);
            c1.setMaxAge(60 * 60 * 24 * 7); // 一周內(nèi)有效
            resp.addCookie(c1);
            Cookie c2 = new Cookie("password", password); // 一般密碼都會加密的
            c2.setMaxAge(60 * 60 * 24 * 7);
            resp.addCookie(c2);
            System.out.println("登陸成功！");
        } else {
            System.out.println("登陸失敗！");
        }
    }
}

protected void createOrGetSession(HttpServletRequest req, HttpServletResponse resp) throws IOException {
    req.setCharacterEncoding("utf-8");
    resp.setContentType("text/html;charset=utf-8");
    HttpSession session = req.getSession(); // 創(chuàng)建或獲取Session
    boolean flag = session.isNew(); // 判斷是否剛創(chuàng)建
    String id = session.getId(); // id
    resp.getWriter().write("得到的Session的Id是" + id + "<br/>");
    resp.getWriter().write("這個(gè)Session是否剛創(chuàng)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> <!-- 分鐘為單位-->
</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>
    <!-- 注意這里改的訪問名(看起來像個(gè)圖片),這樣的話訪問這個(gè)就是自動生成驗(yàn)證碼和圖片，并保存到Session域--> 
    <url-pattern>/kaptcha.jpg</url-pattern> 
</servlet-mapping>

<form action="" method="post">
    用戶名：<input type="text" name="username"> <br/>
    密碼：<input type="password" name="password"> <br/>
    驗(yàn)證碼：<input type="text" name="code"> <br/>
    <img id="code_img" src="http://localhost:8080/book/kaptcha.jpg" alt="圖片找不到"> <br/>
    <input type="button" value="注冊">
</form>

// 給驗(yàn)證碼圖片綁定單機(jī)事件
$("#code_img").click(function () {
    // 但這樣每次發(fā)一樣的請求，可能會被瀏覽器的緩存導(dǎo)致驗(yàn)證碼無法改變，
    // 緩存是根據(jù)工程名后面的資源名和參數(shù)產(chǎn)生的，所以我們可以在后面加上一個(gè)隨機(jī)的參數(shù)跳過緩存
	//this.src = "http://localhost:8080/book/kaptcha.jpg"; 
    this.src = "http://localhost:8080/book/kaptcha.jpg?d=" + new Date(); // 可以加個(gè)時(shí)間戳
});