[转载]RequestDispatcher.include(String str)用法。

只是在书上看到了RequestDispatcher对象的Include方法可以将多个单功能的文件例如.jsp文件整合成一个Servlet文件

今天上网找到一个很好的实例来说明这一点。很感谢此作者！^_^

 

public

  class  TestDispatcher  extends  javax.servlet.http.HttpServlet  implements

        javax.servlet.Servlet ...

{

    public TestDispatcher() ...{

        super();

    }

    protected void doGet(HttpServletRequest request,

            HttpServletResponse response) throws ServletException, IOException ...{

        doPost(request, response);

    }

    protected void doPost(HttpServletRequest request,

            HttpServletResponse response) throws ServletException, IOException ...{

            RequestDispatcher rd ;

        rd = request.getRequestDispatcher("TestDispatcher1");

        rd.include(request, response);

        //String hello = (String) request.getAttribute("hello");

        //System.out.println(hello);

        rd = request.getRequestDispatcher("/test/test51.jsp");

        rd.include(request, response);

        rd = request.getRequestDispatcher("/test/test5.jsp");

        rd.include(request, response);

    }

}

 

public

  class  TestDispatcher1  extends  javax.servlet.http.HttpServlet  implements

        javax.servlet.Servlet ...

{

    public TestDispatcher1() ...{

        super();

    }

    protected void doGet(HttpServletRequest request,

            HttpServletResponse response) throws ServletException, IOException ...{

        doPost(request, response);

    }

    protected void doPost(HttpServletRequest request,

            HttpServletResponse response) throws ServletException, IOException ...{

            request.setAttribute("hello", "hello");

            response.getWriter().write("this is servlet2<br>");

            response.sendRedirect();

    }

}

 <% ...@ page language = " java "  contentType = " text/html; charset=ISO-8859-1 "
    pageEncoding = " ISO-8859-1 " %>
     <% ...@ taglib uri = " /WEB-INF/c.tld "  prefix = " c "   %>
 <! DOCTYPE html PUBLIC  " -//W3C//DTD HTML 4.01 Transitional//EN "   " http://www.w3.org/TR/html4/loose.dtd " >
 < html >
 < head >
 < meta http - equiv = " Content-Type "  content = " text/html; charset=ISO-8859-1 " >
 < title > Insert title here </ title >
 </ head >
 < body >
     < c:out value = " ${hello} " ></ c:out >
         < br >
     this  is test51.jsp.
         < br >
 </ body >
 </ html >

 

 

 <% ...@ page language = " java "  contentType = " text/html; charset=ISO-8859-1 "
    pageEncoding = " ISO-8859-1 " %>
 <! DOCTYPE html PUBLIC  " -//W3C//DTD HTML 4.01 Transitional//EN "   " http://www.w3.org/TR/html4/loose.dtd " >
 < html >
 < head >
 < meta http - equiv = " Content-Type "  content = " text/html; charset=ISO-8859-1 " >
 < title > Insert title here </ title >
 </ head >
 < body >
 this  is test5.jsp.
 </ body >
 </ html >

输出结果：     this is servlet2
                    hello
                    this is test51.jsp 
                    this is test5.jsp

总结：servlet1中include另外一个servlet2,会计算servlet2,最终转向servlet1决定，servlet2中的request和response对象中存储的数据被和并到servlet1的request和response对象中。

servlet中include一个jsp页，相当于：jsp中<%@ include file="XXX.jsp" %>

都表示要跳转到其他资源，不同的是，如果使用forward跳转则后面的response输出则不会执行，而用include
来跳转，则include的servlet执行完后，再返回到原来的servlet执行response的输出（如果有）。如：
servlet A
RequestDispatcher disp = request.getRequestDispatcher("B");
disp.forward(request, response);
System.out.println("servlet A completed");
PrintWriter pw = response.getWriter();
pw.println("servlet A");

servlet B
PrintWriter pw = response.getWriter();
pw.println("servlet B");

输出结果：
控制台：servlet A completed
页面：servlet B
如果将forward换成include的话，则结果为：
控制台：servlet A completed
页面：servlet B servlet A
PS：如果在servlet B里吧pw给close掉了的话，那servlet A 这里就无法输出了，则结果就和第一个一样。

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