Apache POI生成Excel

public InputStream getInputStream()
	{
		HSSFWorkbook wb = new HSSFWorkbook();
		HSSFSheet sheet = wb.createSheet("sheet1");

		HSSFRow row = sheet.createRow(0);

		HSSFCell cell = row.createCell((short) 0);
		cell.setEncoding(HSSFCell.ENCODING_UTF_16);
		cell.setCellValue("序号");

		cell = row.createCell((short) 1);
		cell.setEncoding(HSSFCell.ENCODING_UTF_16);
		cell.setCellValue("姓");

		cell = row.createCell((short) 2);
		cell.setEncoding(HSSFCell.ENCODING_UTF_16);
		cell.setCellValue("名");

		cell = row.createCell((short) 3);
		cell.setEncoding(HSSFCell.ENCODING_UTF_16);
		cell.setCellValue("年龄");

		List<User> list = this.findAll();

		for (int i = 0; i < list.size(); ++i)
		{
			User user = list.get(i);

			row = sheet.createRow(i + 1);

			cell = row.createCell((short) 0);
			cell.setEncoding(HSSFCell.ENCODING_UTF_16);
			cell.setCellValue(i + 1);

			cell = row.createCell((short) 1);
			cell.setEncoding(HSSFCell.ENCODING_UTF_16);
			cell.setCellValue(user.getFirstname());

			cell = row.createCell((short) 2);
			cell.setEncoding(HSSFCell.ENCODING_UTF_16);
			cell.setCellValue(user.getLastname());

			cell = row.createCell((short) 3);
			cell.setEncoding(HSSFCell.ENCODING_UTF_16);
			cell.setCellValue(user.getAge());
		}

		File file = new File("test.xls");

		try
		{
			OutputStream os = new FileOutputStream(file);
			wb.write(os);
			os.close();
		}
		catch (Exception e)
		{
			e.printStackTrace();
		}

		InputStream is = null;
		try
		{
			is = new FileInputStream(file);
		}
		catch (FileNotFoundException e)
		{
			e.printStackTrace();
		}

		return is;

	}

上面在服务器端生成test.xls时这样会造成多用户不同步的情况。

解决办法：
1.让每个用户产生一个随机名字的文件
bug：多个用户的话，这样的垃圾文件会越来越多。
所以，当用户下载完后，过一段时间就将他删掉。
生成一个文件后通过线程将文件删除。

new Thread(new Runnable()
		{
			public void run()
			{
				try
				{
					Thread.sleep(15000);
				}
				catch (InterruptedException e)
				{
					e.printStackTrace();
				}
				
				file.delete();//删除临时文件 
			}
		}).start();

或者服务器启动就删除
web.xml

  <servlet>
    <servlet-name>DeleteFilesServlet</servlet-name>
    <servlet-class>com.test.servlet.DeleteFilesServlet</servlet-class>
    <!-- 这个是用来server自动访问,不需要urlmapping -->
    <load-on-startup>8</load-on-startup>
  </servlet>

public class DeleteFilesServlet extends HttpServlet
{

	public void destroy()
	{
		
	}

	public void init() throws ServletException
	{
//		File file = new File(".");
//		
//		File[] subFiles = file.listFiles();
//		
//		for(File f : subFiles)
//		{
//			if(f.getName().endsWith("xls"))
//			{
//				f.delete();
//			}
//		}
		
		File file = new File(".");
		
		File[] subFiles = file.listFiles(new FileFilter()
		{
			public boolean accept(File pathname)
			{
				if(pathname.getName().endsWith("xls"))
				{
					return true;
				}
				
				return false;
			}
		}
		);
		
		for(File f : subFiles)
		{
			f.delete();
		}
	}

}

2.将构造好的流放到内存里，不会在服务

器端产生大量的临时文件。