[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("http://www.csdn.net");
    }
}

 

 

<% ...@ 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" %>

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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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