javaWeb中Cookie，Session原理

一.概述

初步了解javaweb项目的Cookie、Session，重点认识其原理。

二、示例

1.Cookie

1.1 服务器往客户端写入Cookie，ServeltSetCookies

@WebServlet("/ServeltSetCookies")
public class ServeltSetCookies extends HttpServlet {
    private static final long serialVersionUID = 1L;

public ServeltSetCookies() {
super();
}

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        Cookie cookie = new Cookie("cache-cookie", "cache");
        response.addCookie(cookie);
        Cookie cookie2 = new Cookie("file-cookie", "file");
        cookie2.setMaxAge(3600);
        response.addCookie(cookie2);
        response.setContentType("text/html");
        PrintWriter pw = response.getWriter();
        pw.print("addCookie Ok");
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

1.2 显示写入的Cookie ServeltShowCookies

@WebServlet("/ServeltShowCookies")
public class ServeltShowCookies extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public ServeltShowCookies() {
        super();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        response.setContentType("text/html");
        PrintWriter pw = response.getWriter();
        pw.print("<html><head>");
        pw.print("<title>Cookie Info</title>");
        pw.print("</head><body>");
        pw.print("<h2>Cookie Information</h2>");

        Cookie[] cookies = request.getCookies();
        pw.print("<table  border='1'>");
        pw.print("<tr>");
        pw.print("<th>");
        pw.print("CookieName");
        pw.print("</th>");
        pw.print("<th>");
        pw.print("CookieValue");
        pw.print("</th>");
        pw.print("</tr>");
        if(cookies!=null&&cookies.length>0)
        {
            for (Cookie cookie : cookies) {
                pw.print("<tr>");
                pw.print("<td>");
                pw.print(cookie.getName());
                pw.print("</td>");
                pw.print("<td>");
                pw.print(cookie.getValue());
                pw.print("</td>");
                pw.print("</tr>");
            }
        }
        pw.print("</table>");
        pw.print("</body></html>");
    }

protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    doGet(request, response);
}

2.Session

2.1 客户端获取服务器的Session，ServeltInfoSession

@WebServlet("/ServeltInfoSession")
public class ServeltInfoSession extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public ServeltInfoSession() {
        super();
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
     *  response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        HttpSession mysession = request.getSession(true);

        response.setContentType("text/html");
        PrintWriter pw = response.getWriter();
        pw.print("<html><head>");
        pw.print("<title>Session Info</title>");
        pw.print("</head><body>");
        pw.print("<h2>Session Information</h2>");
        pw.print("New Session: " + mysession.isNew());
        pw.print("<br />SessionID:" + mysession.getId());
        pw.print("<br />Session created time:" + new Date(mysession.getCreationTime()));
        pw.print("<br />Session last access time:" + new Date(mysession.getLastAccessedTime()));
        pw.print("<h2>Request Information</h2>");
        pw.print("<br />SessionID from request:" + request.getRequestedSessionId());
        pw.print("<br />SessionID via cookie:" + request.isRequestedSessionIdFromCookie());
        pw.print("<br /> SessionID via rewrite URL" + request.isRequestedSessionIdFromURL());
        pw.print("<br /> Valid Session" + request.isRequestedSessionIdValid());

        pw.print("<br /> <a href = 'ServeltInfoSession'>refresh</a>");
        // 重写url encodeURL括号里面写的是类名。
        pw.print("<br /> <a href =" + response.encodeURL("ServeltInfoSession") + ">refresh</a>");
        pw.print("</body></html>");
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }

2.2 显示Session，ServeltShowSession

@WebServlet("/ServeltShowSession")
public class ServeltShowSession extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public ServeltShowSession() {
        super();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        HttpSession session = request.getSession(true);
        String head;

        response.setContentType("text/html");
        PrintWriter pw = response.getWriter();

        Integer count = (Integer) session.getAttribute("access");

        if (count == null) {
            count = new Integer(0);
            head = "hi,newcommer!";
        } else {
            count = new Integer(count.intValue() + 1);
            head = "welcome back";
        }
        session.setAttribute("access", count);
        pw.print("<html><body><h2>" + head + "</h2>" + count + "</body></html>");

    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }

三、总结

Cookie存在于客户端，Session存在于服务器。

Cookie：

服务器可以往客户端写入数据

只能是key-value的键值对的文本内容

客户端可以阻止服务器写入

不同的webApplication只能拿自己写入的内容

Cookie有两种类型：属于窗口（内容），属于文本（文件）

一个servlet/jsp设置的cookie能够被同一路径下面或者子路径下面的servlet/jsp读到（路径=URL）（路径！=真实文件路径）

Session：

两种方式实现（客户端可获取Session）：session-id写在临时cookie中，重写URL(response.encodeURL())

Session有过期时间，服务器根据session-timeout时间判断是否清除该Session，tomcat中的通用session过期时间设置为：conf–>web.xml里面的里面的（时间单位为分钟）。

<session-config>  
    <session-timeout>30</session-timeout>  
</session-config>

Session不像Cookie拥有路径访问的问题，同一个application下的servlet/jsp可以共享同一个session，前提是同一个客户端窗口。

javaWeb中Cookie，Session原理

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