j2ee,jsp,servlet文件下载服务器端

来源：互联网发布：mac定妆喷雾编辑：程序博客网时间：2024/06/06 07:34

1.getOutputStream() has already been called for this response

报错的原因:

使用tomcat容器调用response.getOutputStream()方法的时候只能够写二进制文件.

但调用requonse.getWriter()方法时，则只能够在前台打印文本文件.

所以:

如果在jsp页面:

outPutStream.flush();outPutStream.close();outPutStream=null;response.flushBuffer();out.clear();out = pageContext.pushBody();

这里out和pageContext是jsp的内置对象;

如果在后台:

如果使用response.getWrter,那么前面只能用response.setContentType("text/html");

如果想用二进制流的方式输出,那么就不都够使用response.setContentType("text/html");

如果是想传输文件,推荐:

response.setContentType("application/x-msdownload;charset=utf-8");

同时为了防止乱码,response.setCharacterEncoding("utf-8");

filename = URLEncoder.encode(filename, "utf-8");

文件下载的代码:

public void getDownLoadBook() throws IOException{response.setCharacterEncoding("utf-8");String filepath=request.getSession().getServletContext().getRealPath("\\") + "upload\\books\\";//通过前台bookId,从数据库中取出文件保存的信息Book book=this.getBookService().getBook(bookId);if(book==null){       response.setContentType("text/html");PrintWriter writer=response.getWriter();writer.write("<html><body>");writer.write("此电子书不存在!");writer.write("</body></html>");writer.flush();writer.close();return;}String filename=book.getSaveName()+"";java.io.File file = new java.io.File(filepath + filename);if (!file.exists()) {         response.setContentType("text/html");         PrintWriter writer=response.getWriter();         writer.write("<html><body>"); writer.write("文件不存在!<br/>"+file.getAbsolutePath()+book.getOriginalName()+"不见了!"); writer.write("</body></html>"); writer.flush(); writer.close(); return;}response.setContentType("application/x-msdownload;charset=utf-8");response.setCharacterEncoding("utf-8");response.setContentLength((int) file.length());filename=book.getOriginalName();//编码文件名,防止乱码filename = URLEncoder.encode(filename, "utf-8");response.setHeader("Content-Disposition", "attachment; filename=" +filename);//得到输出流        javax.servlet.ServletOutputStream out = response.getOutputStream();// 读取文件流java.io.FileInputStream fileInputStream = new java.io.FileInputStream(file);// 下载文件, 设置响应头和下载保存的文件名filename=book.getOriginalName();if (filename != null && filename.length() > 0) {if (fileInputStream != null) {int filelen = fileInputStream.available();文件太大时内存不能一次读出,要循环int i=4096;   do{      byte a[] = new byte[4096];      i=fileInputStream.read(a);      out.write(a, 0, i);     }while(i>=4096);}fileInputStream.close();out.flush();out.close();}      }

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