Java Web學習Day02 ServletContext物件

1.ServletContext

​ web容器在啟動的時候，它會為每個web程式都建立一個對應的ServletContext物件，它代表了我當前的web應用

1、共享資料

• 我在這個Servlet儲存的應用，可以在另一個servlet中拿到：

  //設定資料
  public class HelloServlet extends HttpServlet {
      @Override
      protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  //        this.getInitParameter();  初始化引數
  //        this.getServletConfig();  Servlet配置
  //        this.getServletContext(); Servlet上下文
          ServletContext context = this.getServletContext();
          String username = "藍天";
          context.setAttribute("username",username);  //將一個數據儲存在ServletContext中，名字為：username 值為username
          System.out.println("Hello！");
      }
  
      @Override
      protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          doGet(req, resp);
      }
  }
   
  

  //拿取資料
  public class GetServlet extends HttpServlet {
      @Override
      protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          ServletContext context = this.getServletContext();
          String username = (String)context.getAttribute("username");
          resp.setContentType("text/html");
          resp.setCharacterEncoding("utf-8");
          resp.getWriter().print("名字"+username);
      }
      @Override
      protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          doGet(req, resp);
      }
  }
   
  

      <!--HelloServlet註冊-->
      <servlet>
          <servlet-name>hello</servlet-name>
          <servlet-class>com.lantian.servlet.HelloServlet</servlet-class>
      </servlet>
      <servlet-mapping>
          <servlet-name>hello</servlet-name>
          <url-pattern>/hello</url-pattern>
      </servlet-mapping>
  
      <!--GetServlet註冊-->
      <servlet>
          <servlet-name>getc</servlet-name>
          <servlet-class>com.lantian.servlet.GetServlet</servlet-class>
      </servlet>
      <servlet-mapping>
          <servlet-name>getc</servlet-name>
          <url-pattern>/getc</url-pattern>
      </servlet-mapping>
   
  

  測試訪問結果：直接訪問getc會返回null 因為此時hello中setAttribute還會設定資料；訪問hello後再此訪問getc得到返回資料 名字藍天

2、獲取初始化引數

    <!--配置一些web應用初始化引數-->
    <context-param>
        <param-name>url</param-name>
        <param-value>jdbc:mysql://localhost:3306/mybatis</param-value>
    </context-param>
    <!--ServletDemo03註冊-->
    <servlet>
        <servlet-name>demo3</servlet-name>
        <servlet-class>com.lantian.servlet.ServletDemo03</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>demo3</servlet-name>
        <url-pattern>/demo3</url-pattern>
    </servlet-mapping>

public class ServletDemo03 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();  //建立ServletContext物件
       String url = context.getInitParameter("url");		//獲取初始化引數
       resp.getWriter().print(url);
    }
}

3、請求轉發

public class ServletDemo04 extends HelloServlet{
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        System.out.println("進入方法Demo04");
/*      RequestDispatcher redis = context.getRequestDispatcher("/demo3");       //轉發的請求路徑
        redis.forward(req,resp);        //呼叫forward實現請求轉發；
        */
        context.getRequestDispatcher("/demo3").forward(req,resp);

    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

4、讀取資原始檔

​ Properties

• 在java目錄下新建properties
• 在resources目錄下新建properties

發現： 都被打包到同一路徑下：classes， 稱這個路徑為 類路徑

思路： 需要一個檔案流

username=root
password=123456

public class ServletDemo05 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        InputStream  is =this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
        Properties prop = new Properties();
        prop.load(is);
        String user = prop.getProperty("username");
        String pwd = prop.getProperty("password");
        resp.getWriter().print("使用者名稱: "+user+"\n"+"密碼："+pwd);

    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

訪問測試