0、創建module

請參考Day05創建module

一、Scope Object

Scope Object就是用來共享數據，想想你從前端接收使用者的數據，你希望再轉發給另一個Servlet協助處理;或是你希望記住使用者接下來一連串操作中會共用的訊息;或是你有著希望所有Servlet都知道的事，就讓我們來看看這三大域對象吧

• ServletRequest：一次的請求範圍內及請求轉發
• HttpSession：一次會話內，可以跨多個請求
• ServletContext：作用範圍在此WebApp內，可以跨多個會話，因作用範圍是全域有時也會稱Application Context
  

二、Scope Object API

• void setAttribute(String name,String value)設值
• Object getAttribute(String name)取值
• removeAttribute(String name)移除

Demo

SetAttributeServlet

@WebServlet("/SetAttributeServlet")
public class SetAttributeServlet extends HttpServlet {
    public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
        req.setAttribute("request","request-information");
        req.getSession().setAttribute("session","session-information");
        req.getServletContext().setAttribute("application","servlet-information");
        //case1 請求轉發
        req.getRequestDispatcher("GetAttributeServlet").forward(req,res);
    }
}

GetAttributeServlet

@WebServlet("/GetAttributeServlet")
public class GetAttributeServlet extends HttpServlet {
    public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException {
        PrintWriter writer = res.getWriter();
        //case1
        writer.println("request data："+req.getAttribute("request"));
        writer.println("session data："+req.getSession().getAttribute("request"));
        writer.println("application data"+req.getServletContext().getAttribute("application"));
    }
}

訪問SetAttributeServlet

註解請求轉發，先訪問SetAttributeServlet，再訪問GetAttributeServlet

Reference

• Sharing Information - The Java EE6 Tutorial