文章目錄

• ServletContext
• • 1.共享數據
  • 2.獲取初始化參數
  • 3.請求轉發
  • 4.讀取資源文件

ServletContext

• web容器在啟動的時候，它會為每個web程序都創建一個對應的ServletContext對象，它代表了當前的web應用；

1.共享數據

Servlet1可以將數據存放在ServletContext中，Servlet2和Servlet3可以在ServletContext中取得Servlet1在ServletContext中存放的數據。

在HelloServlet中存放String數據 伊澤瑞爾。

public class HelloServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//獲取servletContext對象ServletContext servletContext = this.getServletContext();String name = "伊澤瑞爾";//以鍵值對的形式將數據放入servletContext對象中servletContext.setAttribute("name",name);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);} }

在GetNameServlet中取得數據并顯示在網站上

public class GetNameServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//獲取ServletContext對象ServletContext servletContext = this.getServletContext();//獲取HelloServlet中在獲取ServletContext對象中存放的數據String name = (String) servletContext.getAttribute("name");//設置響應信息為中文resp.setContentType("text/html");resp.setCharacterEncoding("utf-8");resp.getWriter().write(name);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);} }

先訪問HelloServlet頁面將數據存放在ServletContext中，再訪問GetNameServlet拿出數據并顯示在網頁。

2.獲取初始化參數

<!--配置一些web應用初始化參數--><context-param><param-name>url</param-name><param-value>jdbc:mysql://localhost:3306/mybatis</param-value></context-param> protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {ServletContext context = this.getServletContext();String url = context.getInitParameter("url");resp.getWriter().print(url); }

3.請求轉發

public class ServletDemo01 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//創建servletContext對象ServletContext servletContext = this.getServletContext();//請求轉發servletContext.getRequestDispatcher("/getName").forward(req,resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);} }

運行，顯示的是GetNameServlet的頁面，這里null是由于沒有訪問hello的緣故。

顯示的是GetNameServlet的頁面，但是路徑卻還是自己的。

如圖，A向B請求資源，B向C請求資源，B將C返回的資源再返回給A，A自始至終沒有接觸C，所以顯示的還是B的路徑。

4.讀取資源文件

Properties

• 在resources目錄下新建db.properties文件

username=ez password=123456 public class ServletDemo02 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//創建servletContext對象ServletContext servletContext = this.getServletContext();//獲取properties文件的字節輸入流對象InputStream is = servletContext.getResourceAsStream("/WEB-INF/classes/db.properties");//創建properies對象Properties prop = new Properties();//加載流prop.load(is);String user = prop.getProperty("username");String pwd = prop.getProperty("password");//顯示resp.getWriter().write(user+":"+pwd);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);} }

總結

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