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() + \"] 
\");
    }
    // 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

    用户名:  

    密码:  

    

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 + \"
\");
    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

    20 

    KaptchaServlet
    com.google.code.kaptcha.servlet.KaptchaServlet


    KaptchaServlet
     
    /kaptcha.jpg 

    用户名： 

    密码： 

    验证码： 

     

    

// 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
});