文章目錄

• ServletContext
• • 1.共享數(shù)據(jù)
  • 2.獲取初始化參數(shù)
  • 3.請求轉(zhuǎn)發(fā)
  • 4.讀取資源文件

ServletContext

• web容器在啟動(dòng)的時(shí)候，它會(huì)為每個(gè)web程序都創(chuàng)建一個(gè)對應(yīng)的ServletContext對象，它代表了當(dāng)前的web應(yīng)用；

1.共享數(shù)據(jù)

Servlet1可以將數(shù)據(jù)存放在ServletContext中，Servlet2和Servlet3可以在ServletContext中取得Servlet1在ServletContext中存放的數(shù)據(jù)。

在HelloServlet中存放String數(shù)據(jù) 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(shù)據(jù)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(shù)據(jù)并顯示在網(wǎng)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(shù)據(jù)String name = (String) servletContext.getAttribute("name");//設(shè)置響應(yīng)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(shù)據(jù)存放在ServletContext中，再訪問GetNameServlet拿出數(shù)據(jù)并顯示在網(wǎng)頁。

2.獲取初始化參數(shù)

<!--配置一些web應(yīng)用初始化參數(shù)--><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(zhuǎn)發(fā)

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

運(yùn)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(chuàng)建servletContext對象ServletContext servletContext = this.getServletContext();//獲取properties文件的字節(jié)輸入流對象InputStream is = servletContext.getResourceAsStream("/WEB-INF/classes/db.properties");//創(chuàng)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);} }

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