Servlet三大域物件與會話

阿新 • • 發佈：2021-10-08

1 servlet域物件

在指定區域內實現資料共享的物件
域物件的統一方法：
   Object getAttribute(String aName);
   void removeAttribute(String aName);
   void setAttribute(String aName,Object vObj);
   Enumeration<String> getAttributeNames();

1 request域物件

requet域物件的共享區域：同一個請求鏈（請求轉發或者請求包含涉及的多個資源）

程式碼1：/s0101

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //設定request域屬性
    request.setAttribute("aa", "aa"+System.currentTimeMillis());
    request.setAttribute("bb", "bb"+System.currentTimeMillis());
    request.getRequestDispatcher("/s0100").forward(request, response);
}

程式碼2：/s0100

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/html;charset=utf-8");
    PrintWriter out=response.getWriter();
    //獲取request域屬性
    out.print("request域屬性aa="+request.getAttribute("aa")+"<br/>");
    out.print("request域屬性bb="+request.getAttribute("bb")+"<br/>");
}

2 session域物件

session：回話： 同一個瀏覽器對伺服器發出的幾個連貫(預設時間差不能大於30分鐘)的請求
回話跟蹤技術：解決http協議的無狀態（兩次請求之間不能實現資料共享）

程式碼1：/s0102

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //設定session域屬性
    HttpSession session=request.getSession();
    session.setAttribute("aa", "aa_session_"+System.currentTimeMillis());
    session.setAttribute("bb", "bb_session_"+System.currentTimeMillis());
    response.getWriter().print("<a href='http://localhost:8080/java37_ee_06_servlet/s0100'>請求/s0100</a><br/>");
}

程式碼2：/s0100

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/html;charset=utf-8");
    PrintWriter out=response.getWriter();
    //獲取request域屬性
    out.print("request域屬性aa="+request.getAttribute("aa")+"<br/>");
    out.print("request域屬性bb="+request.getAttribute("bb")+"<br/>");
    //獲取session域屬性
    HttpSession session=request.getSession();
    out.print("session域屬性aa="+session.getAttribute("aa")+"<br/>");
    out.print("session域屬性bb="+session.getAttribute("bb")+"<br/>");
}

3 application(servletContext)域物件

servletContext上下文物件：同一個專案的所有請求之間實現資料共享

程式碼1：/s0103

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //獲取servletcontext:上下文物件
    ServletContext context=request.getServletContext();
    context=this.getServletContext();
    context=request.getSession().getServletContext();
    //新增servletcontext的域屬性
    context.setAttribute("aa", "aa_context_"+System.currentTimeMillis());
    context.setAttribute("bb", "bb_context_"+System.currentTimeMillis());
    response.getWriter().print("<a href='http://localhost:8080/java37_ee_06_servlet/s0100'>請求/s0100</a><br/>");

}

程式碼2 :/s0100

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/html;charset=utf-8");
    PrintWriter out=response.getWriter();
    //獲取request域屬性
    out.print("request域屬性aa="+request.getAttribute("aa")+"<br/>");
    out.print("request域屬性bb="+request.getAttribute("bb")+"<br/>");
    //獲取session域屬性
    HttpSession session=request.getSession();
    out.print("session域屬性aa="+session.getAttribute("aa")+"<br/>");
    out.print("session域屬性bb="+session.getAttribute("bb")+"<br/>");
    //獲取servletcontext:上下文物件
    ServletContext context=request.getServletContext();
    out.print("servletContext域屬性aa="+context.getAttribute("aa")+"<br/>");
    out.print("servletContext域屬性aa="+context.getAttribute("aa")+"<br/>");
}

2 會話跟蹤技術之cookie

cookie:由伺服器端建立和客戶端儲存 並通過請求頭和響應頭傳遞的鍵值對物件

程式碼1：在響應頭中新增cookie :::/s0201

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //建立cookie
    Cookie c1=new Cookie("c1", "c1_v");
    Cookie c2=new Cookie("c2", "c2_v");

    //設定cookie的生命週期：
    c1.setMaxAge(-1);//如果值為負數：：等價於瀏覽器記憶體 瀏覽器不關閉 cookie一值存在,瀏覽器關閉 cookie消失
    c1.setMaxAge(0);//如果值為零：：刪除cookie
    c1.setMaxAge(20);//如果值為正數：：cookie儲存在硬碟中指定秒：：與瀏覽器記憶體無關

    //設定cookie的儲存目錄：預設是當前資源：：/java37_ee_06_servlet/s0201
    c1.setPath("/");

    //把cookie新增到響應頭 傳遞給客戶端瀏覽器
    response.setHeader("Set-Cookie", "c3=c3_v");
    response.addCookie(c1);
    response.addCookie(c2);

    response.setCharacterEncoding("utf-8");
    response.setContentType("text/html;charset=utf-8");
    response.getWriter().print("<a href='http://localhost:8080/java37_ee_06_servlet/s0200'>請求/s0200</a><br/>");

}

程式碼2：通過請求頭獲取cookie:::/s0200

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //獲取cookie
    Cookie[] arr=request.getCookies();

    response.setCharacterEncoding("utf-8");
    response.setContentType("text/html;charset=utf-8");
    response.getWriter().print("接收到的cookie是："+Arrays.toString(arr));
}

測試請求/s0201

測試請求/s0200

原理解釋

3 會話跟蹤技術之session

回話：同一個瀏覽器發出的幾個連貫(預設是30分鐘)的請求

程式碼1：在session中新增資料

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //在session中新增屬性
    HttpSession session=request.getSession();
    session.setAttribute("aa", "aa_session_v");
    session.setAttribute("bb", "bb_session_v");

    //session.invalidate();//銷燬session
    //session.setMaxInactiveInterval(arg0);//設定session過期間隔 預設是30分鐘
    //session.getMaxInactiveInterval();//獲取session過期間隔
    // session.setMaxInactiveInterval(10);
    session.getId();//獲取sessionid：：：當前回話的session物件的ip地址


    response.setCharacterEncoding("utf-8");
    response.setContentType("text/html;charset=utf-8");
    PrintWriter out=response.getWriter();
    out.print("session.getId()="+session.getId()+"<br/>");
    out.print("session.getMaxInactiveInterval()="+session.getMaxInactiveInterval()+"<br/>");
    out.print("<a href='http://localhost:8080/java37_ee_06_servlet/s0200'>請求/s0200</a><br/>");
}

程式碼2：獲取session中的資料

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		//獲取cookie
		Cookie[] arr=request.getCookies();
		String message="";
		for (Cookie c : arr) {
			message+=c.getName()+"="+c.getValue()+"<br/>";
		}
		//獲取session
		HttpSession session=request.getSession();
		response.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out=response.getWriter();
		out.print("接收到的cookie是："+message);
		out.print("session域屬性aa="+session.getAttribute("aa")+"<br/>");
		out.print("session域屬性bb="+session.getAttribute("bb")+"<br/>");
		out.print("session.getId()="+session.getId()+"<br/>");
		out.print("session.getMaxInactiveInterval()="+session.getMaxInactiveInterval()+"<br/>");	
	}

訪問/s0202

session原理

4 cookie和session的區別

參考：https://www.jianshu.com/p/2f7031a69f43

概念

cookie：符合http協議規範的 由伺服器建立 客戶端儲存的 通過請求頭和響應頭傳遞的鍵值對物件
session：由伺服器建立和儲存 但依賴於名為JSESSIONID的cookie的 用於儲存回話資料的物件

相同之處

1 都是解決http無狀態的回話跟蹤技術
2 都是伺服器端建立 都依賴http協議的請求頭和響應頭

不同之處

1 儲存位置不同
   cookie由客戶端儲存
   session伺服器儲存
2 預設有效時間不同
   cookie生命週期預設是瀏覽器記憶體
   session預設請求間隔是30分鐘
3 隱私策略不同
   cookie對客戶端可見  不安全
   session對客戶端是透明的  不存在敏感資訊的安全問題
4 依賴關係
    session依賴名為JSESSIONID的cookie
5 儲存容量不同
    cookie單個數據<=4kb 單個站點只能有20個cookie
    sesion沒有限制
6 儲存的資料格式
    cookie只能儲存asicc碼資訊+二進位制
    session可以儲存任意資料