application内置对象是ServletContext接口的实例，表示的是Servlet上下文。如果要在一个Servlet中使用此对象。直接通过GenericServlet类提供的方法即可。

ServletContextDemoServlet.java

package im.weitang;

import java.io.IOException;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ServletContextDemoServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext app = super.getServletContext();
        System.out.println("真实路径：" + app.getRealPath("/"));
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request, response);
    }
}

修改Web.xml，添加如下代码：

<servlet>
    <description></description>
    <display-name>ServletContextDemoServlet</display-name>
    <servlet-name>ServletContextDemoServlet</servlet-name>
    <servlet-class>im.weitang.ServletContextDemoServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>ServletContextDemoServlet</servlet-name>
    <url-pattern>/ServletContextDemoServlet</url-pattern>
</servlet-mapping>

程序运行后，tomca后台输出：

真实路径：D:\JavaWeb\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\servlet\