j2ee,jsp,servlet文件下载server端

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

报错的原因:

使用tomcat容器调用response.getOutputStream()方法的时候仅仅可以写二进制文件.

但调用requonse.getWriter()方法时，则仅仅可以在前台打印文本文件.

所以:

假设在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;

假设在后台:

假设使用response.getWrter,那么前面仅仅能用response.setContentType("text/html");

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

假设是想传输文件,推荐:

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

同一时候为了防止乱码,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();

	//编码文件名称,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称

	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();

		}

     }

巴特西

j2ee,jsp,servlet文件下载server端

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