03-请求转发和request共享数据

        3. 共享数据：* 域对象：一个有作用范围的对象，可以在范围内共享数据
            * request 域：代表一次请求的范围，一般用于请求转发的多个资源中共享数据
            * 方法：1. void setAttribute(String name,Object obj): 存储数据
                2. Object getAttitude(String name): 通过键获取值
                3. void removeAttribute(String name): 通过键移除键值对 

package cn.itcast.web.request;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.Enumeration;
import java.util.Map;
import java.util.Set;

@WebServlet(“/requestDemo7”)
public class RequestDemo7 extends HttpServlet {

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //1. 设置流的编码
    request.setCharacterEncoding("utf-8");

    // 获取请求参数 username
    String username = request.getParameter("username");

    System.out.println(username);
}

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

}
package cn.itcast.web.request;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet(“/requestDemo8”)
public class RequestDemo8 extends HttpServlet {

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("demo8888 被访问了。。。");
    // 转发到 demo9 资源 

/*

    RequestDispatcher requestDispatcher = request.getRequestDispatcher("/requestDemo9");
    requestDispatcher.forward(request,response);
    */

    // 存储数据到 request 域中
    request.setAttribute("msg","hello");

    request.getRequestDispatcher("/requestDemo9").forward(request,response);
    //request.getRequestDispatcher("http://www.itcast.cn").forward(request,response);

}

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

}
package cn.itcast.web.request;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet(“/requestDemo9”)
public class RequestDemo9 extends HttpServlet {

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    // 获取数据
    Object msg = request.getAttribute("msg");
    System.out.println(msg);

    System.out.println("demo9999 被访问了。。。");

}

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

}