Servlet程序开发-- 取得其他内置对象

servlet本身提供的只有request和response对象，如果要取得session对象，只能依靠request对象，因为session属于HTTP协议范畴，而且在每次发送请求的时候，服务器都会自动为客户端设置一个cookie，所以，很自然的，session中要使用cookie机制，但是cookie又只能通过request取得，所以自然session也只能通过request取得。

取得session对象：

package org.lxh.servletdemo ;
import java.io.* ;
import javax.servlet.* ;
import javax.servlet.http.* ;
public class HttpSessionDemoServlet extends HttpServlet {
    public void doGet(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException{
        HttpSession ses = req.getSession() ;
        System.out.println("SESSION ID --> " + ses.getId()) ;
        ses.setAttribute("username","李兴华") ;     // 设置session属性
        System.out.println("username属性内容：" + ses.getAttribute("username")) ;
    }
    public void doPost(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException{
        this.doGet(req,resp) ;
    }
}

 web.xml:

<servlet>
        <servlet-name>sessiondemo</servlet-name>
        <servlet-class>
            org.lxh.servletdemo.HttpSessionDemoServlet
        </servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>sessiondemo</servlet-name>
        <url-pattern>/HttpSessionDemoServlet</url-pattern>
    </servlet-mapping>

2. 取得application：

package org.lxh.servletdemo ;
import java.io.* ;
import javax.servlet.* ;
import javax.servlet.http.* ;
public class ServletContextDemoServlet extends HttpServlet {
    public void doGet(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException{
        ServletContext app = super.getServletContext() ;
        System.out.println("真实路径：" + app.getRealPath("/")) ;
    }
    public void doPost(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException{
        this.doGet(req,resp) ;
    }
}

web.xml：

    <servlet>
        <servlet-name>applicationdemo</servlet-name>
        <servlet-class>
            org.lxh.servletdemo.ServletContextDemoServlet
        </servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>applicationdemo</servlet-name>
        <url-pattern>/ServletContextDemoServlet</url-pattern>
    </servlet-mapping>

总结：

1. 通过req.getSession() 可以取得session，可以进行登录验证操作

2. 通过getServletContext()取得application