来自于：http://blog.csdn.net/xiangxiaofeng12/article/details/5564756
String path="/index.jsp";//这是当前应用中一个绝对路径的url
servlet:
RequestDispatcher dispatcher=getServletContext().getRequestDispatcher(path);
jsp:
RequestDispatcher dispatcher=application.getRequestDispatcher(path);
all:
dispatcher.forward();//转到path这个页面（不可以在这之前或之后有其它输出）
dispatcher.include();//向浏览器输出path这个页面的执行结果（可以在这之前或之后有其它输出）
1、ServletRequest.getRequestDispatcher(String path)
path可是绝对路径也可以是相对路径
2、ServletContext.getRequestDispatcher(String path)
path必须以"/"开头，代表context root
3、另一个方法 ServletContext.getNameDispatcher(String name)
参数并不是路径，而是其名称，如果有多个Servlet名称一样的，在web.xml进行配置区别
4、以上方法回传一个RequestDispatcher对象，接着forward()或include()
5、forward()和include()区别在于include()方法将HTTP请求转送给其他Servlet或jsp后，这个Servlet或jsp虽然可以处理请求，但是主导权还是原来的Servlet或jsp，就是被调用的Servlet或jsp如果产生任何HTTP回应，将会并入原来的HttpResponse对象
<%@ page contentType="text/html; charset=utf-8" language="java"
import="java.sql.*" errorPage=""%>
<%@ page import="java.net.URLEncoder"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>下载</title>
</head>
<body>
<%
response.setContentType("application/x-download");
String fileDownload = "/bgqb_radio_select.png";
String filedisplay = "bgqb_radio_select.png";
response.addHeader("Content-Disposition", "attachment;filename="
+ URLEncoder.encode(filedisplay, "UTF-8"));
try {
RequestDispatcher dis = application
.getRequestDispatcher(fileDownload);
if (dis != null) {
dis.forward(request, response);
}
response.flushBuffer();
out.clear();
out = pageContext.pushBody();
} catch (Exception e) {
e.printStackTrace();
}
%>
</body>
</html>
void downLoaded(String fileName, HttpServletRequest request, HttpServletResponse response) throws IOException { response.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(fileName, "UTF-8")); response.setContentType("application/x-download;charset=UTF-8"); // response.setContentType("application/octet-stream;charset=UTF-8"); ServletOutputStream outputStream = response.getOutputStream(); BufferedInputStream inputStream = new BufferedInputStream( new FileInputStream(fileName)); int size = 2048; byte[] data = new byte[size]; while ((size = inputStream.read(data, 0, data.length)) != 0) { outputStream.write(data, 0, size); outputStream.flush(); } }
补充：
问题getOutputStream() has already been called for this response，详见：