forward是否共享一个request，能否通过getParameter取得参数

Request的getParameter和getAttribute的区别：

/article/1988708.html

本人依然很困惑，因为两个Servlet之间是共享一个Request的 为什么要先取出来getParameter得到值之后 setAttribute 在新的Servlet又getAttribute

难道新的Servlet里面无法获取共享的Request里面的patameter吗？

于是做了个实验：

第一个servlet

package com.silvia;

import java.io.IOException;

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

public class MyFirstServlet extends HttpServlet {

    public void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        System.out.println(req.getParameter("a"));
        req.getRequestDispatcher("/servlet2").forward(req,resp);
    }
}

第二个servlet

package com.silvia;

import java.io.IOException;

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

public class Servlet2 extends HttpServlet {

    public void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        System.out.println("servlet2");
        System.out.println(req.getParameter("a"));
    }
}

web.xml

<web-app xmlns="http://java.sun.com/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
                      http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"   version="3.0"
  metadata-complete="true">

  <display-name>Welcome to Tomcat</display-name>
  <description>
     Welcome to Tomcat
  </description>

  <servlet>
      <servlet-name>myFirstServlet</servlet-name>
      <servlet-class>com.silvia.MyFirstServlet</servlet-class>
  </servlet>
    
    <servlet-mapping>
      <servlet-name>myFirstServlet</servlet-name>
      <url-pattern>/hello</url-pattern>
    </servlet-mapping>

    <servlet>
      <servlet-name>servlet2</servlet-name>
      <servlet-class>com.silvia.Servlet2</servlet-class>
    </servlet>
    <servlet-mapping>
      <servlet-name>servlet2</servlet-name>
      <url-pattern>/servlet2</url-pattern>
    </servlet-mapping>

</web-app>

放到tomcat的webapp下面



编译会报错



只要将tomcat下lib里面的servlet-api.jar加入CLASSPATH里面即可

编译成功后启动tomcat



以http://localhost:8080/myTest/hello?a=1 去访问下



看结果我们发现其实是可以取到的！

至于为什么 研究下tomcat源码之后再来进一步解释