来自于：
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"%>下载 <% 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(); } %>
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：