風人園

JSP文件下載及出現getOutputStream() has already been called for this response的解決方法

http://iamin.blogdriver.com/iamin/1072546.html

一、采用RequestDispatcher的方式進行

1、web.xml文件中增加
? <mime-mapping>
??? <extension>doc</extension>
??? <mime-type>application/vnd.ms-word</mime-type>
? </mime-mapping>


2、程序如下：

<%@page language="java" import="java.net.*" pageEncoding="gb2312"%>
<%
??? response.setContentType("application/x-download");//設置為下載application/x-download
??? String filenamedownload = "/系統解決方案.doc";//即將下載的文件的相對路徑
??? String filenamedisplay = "系統解決方案.doc";//下載文件時顯示的文件保存名稱
??? filenamedisplay = URLEncoder.encode(filenamedisplay,"UTF-8");
??? response.addHeader("Content-Disposition","attachment;filename=" + filenamedisplay);
???
??? try
??? {
??????? RequestDispatcher dispatcher = application.getRequestDispatcher(filenamedownload);
??????? if(dispatcher != null)
??????? {
??????????? dispatcher.forward(request,response);
??????? }
??????? response.flushBuffer();
??? }
??? catch(Exception e)
??? {
??????? e.printStackTrace();
??? }
??? finally
??? {
???
??? }
%>


二、采用文件流輸出的方式下載

1、web.xml文件中增加
? <mime-mapping>
??? <extension>doc</extension>
??? <mime-type>application/vnd.ms-word</mime-type>
? </mime-mapping>


2、程序如下：

<%@page language="java" contentType="application/x-msdownload" import="java.io.*,java.net.*" pageEncoding="gb2312"%><%
??? //關于文件下載時采用文件流輸出的方式處理：
??? //加上response.reset()，并且所有的％>后面不要換行，包括最后一個；
??? //因為Application Server在處理編譯jsp時對于％>和<％之間的內容一般是原樣輸出，而且默認是PrintWriter，
??? //而你卻要進行流輸出：ServletOutputStream，這樣做相當于試圖在Servlet中使用兩種輸出機制，
??? //就會發生：getOutputStream() has already been called for this response的錯誤
??? //詳細請見《More Java Pitfill》一書的第二部分 Web層Item 33：試圖在Servlet中使用兩種輸出機制 270
??? //而且如果有換行，對于文本文件沒有什么問題，但是對于其它格式，比如AutoCAD、Word、Excel等文件
??? //下載下來的文件中就會多出一些換行符0x0d和0x0a，這樣可能導致某些格式的文件無法打開，有些也可以正常打開。

??? response.reset();//可以加也可以不加
??? response.setContentType("application/x-download");//設置為下載application/x-download
??? // /../../退WEB-INF/classes兩級到應用的根目錄下去，注意Tomcat與WebLogic下面這一句得到的路徑不同，WebLogic中路徑最后沒有/
??? System.out.println(this.getClass().getClassLoader().getResource("/").getPath());
??? String filenamedownload = this.getClass().getClassLoader().getResource("/").getPath() + "/../../系統解決方案.doc";
??? String filenamedisplay = "系統解決方案.doc";//系統解決方案.txt
??? filenamedisplay = URLEncoder.encode(filenamedisplay,"UTF-8");
??? response.addHeader("Content-Disposition","attachment;filename=" + filenamedisplay);

??? OutputStream output = null;
??? FileInputStream fis = null;
??? try
??? {
??????? output? = response.getOutputStream();
??????? fis = new FileInputStream(filenamedownload);

??????? byte[] b = new byte[1024];
??????? int i = 0;

??????? while((i = fis.read(b)) > 0)
??????? {
??????????? output.write(b, 0, i);
??????? }
??????? output.flush();
??? }
??? catch(Exception e)
??? {
??????? System.out.println("Error!");
??????? e.printStackTrace();
??? }
??? finally
??? {
??????? if(fis != null)
??????? {
??????????? fis.close();
??????????? fis = null;
??????? }
??????? if(output != null)
??????? {
??????????? output.close();
??????????? output = null;
??????? }
??? }
%>