5.ServletContext

web容器啟動時，會為每個web程式建立一個對應的ServletContext物件，代表了當前的web應用，即在一個web應用中ServletContext是共有的(唯一)

1.共享資料

在一個Servlet中儲存的資料能在另一個Servlet中獲取到

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        this.getServletContext()  servlet上下文
//        this.getInitParameterNames()  初始化引數
//        this.getServletConfig()  servlet配置
        ServletContext context = this.getServletContext();
        String userName = "meeseek";
        context.setAttribute("name",userName);
        System.out.println(" hello");
    }

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

public class GetServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //解決中文亂碼問題
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        
        ServletContext servletContext = this.getServletContext();
        String username = (String) servletContext.getAttribute("name");
        resp.getWriter().print("名字為" + username);
    }

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

<servlet>
    <servlet-name>hello</servlet-name>
    <servlet-class>com.shida.servlet.HelloServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>hello</servlet-name>
    <url-pattern>/hello</url-pattern>
  </servlet-mapping>

  <servlet>
    <servlet-name>getc</servlet-name>
    <servlet-class>com.shida.servlet.GetServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>getc</servlet-name>
    <url-pattern>/getc</url-pattern>
  </servlet-mapping>
 

測試訪問結果即可

2.獲取初始化引數

<!--  配置一些web初始引數-->
  <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);
    }

<servlet>
    <servlet-name>sd3</servlet-name>
    <servlet-class>com.shida.servlet.ServletDemo03</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>sd3</servlet-name>
    <url-pattern>/sd3</url-pattern>
  </servlet-mapping>

啟動測試結果：