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请求转发
访问指定url路径可以到达HttpServlet的doGet方法。所以基本上全部逻辑都是写在这个方法上，这样的话，一个方法（也可以说一个Servlet）要处理的东西太多了。请求转发的目的就是把请求转发给别一个Servlet，从而分担一些任务。
1.步骤
（1）通过request对象获取请求转发器对象：RequestDispatcher getRequestDispatcher(String path)
（2）使用RequestDispatcher对象来进行转发：forward(ServletRequest request, ServletResponse response)
2.示例
（1）
@WebServlet("/servletdemo1")
public class ServletDemo1 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println("servletdemo1被访问了");
req.getRequestDispatcher("/servletdemo2").forward(req,resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
}
}
（2）
@WebServlet("/servletdemo2")
public class ServletDemo2 extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("servletdemo2被访问了");
}
}
控制台输出结果：
servletdemo1被访问了
servletdemo2被访问了
3.请求转发的特点
1. 浏览器地址栏路径不发生变化
2. 只能转发到当前服务器内部资源中。
3. 转发是一次请求
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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
示例：
（1）
@WebServlet("/servletdemo1")
public class ServletDemo1 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
req.setAttribute("message","Hello");
req.getRequestDispatcher("/servletdemo2").forward(req,resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
}
}
（2）
@WebServlet("/servletdemo2")
public class ServletDemo2 extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
Object o = request.getAttribute("message");
System.out.println(o);
}
}
输出结果：
Hello
说明实现了共享数据。