工作需要把Exception的內容列印到日誌裡，也就是把printStackTrace()輸出的內容轉到文字檔案內。這個方法放在平時用的寫log的靜態類裡方便使用。

public class LogUtil
{
	public static void writeLog(final String str, final String name) throws IOException
	{
		final SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");  
		final SimpleDateFormat sdfFile = new SimpleDateFormat("yyyy-MM-dd");

		final String logFile = System.getProperty("java.io.tmpdir");
		final Date date = new Date();
		final String _dateFile = sdfFile.format(date);
		final String _date = sdf.format(date);

		final String logName = logFile + File.separator + _dateFile + " " + name + ".log";
		final File txt = new File(logName);

		if (!txt.exists())
		{
			txt.createNewFile();
		}
		final FileOutputStream fos = new FileOutputStream(txt, true);
		final OutputStreamWriter write = new OutputStreamWriter(fos, "UTF-8");
		final BufferedWriter writer = new BufferedWriter(write);
		writer.write(_date + " | ");
		writer.write(str);
		writer.close();
	}

	public static String logToString(final Exception e)
	{
		//將出錯的棧資訊輸出到printWriter中
		StringWriter stringWriter = null;
		PrintWriter printWriter = null;
		try
		{
			stringWriter = new StringWriter();
			printWriter = new PrintWriter(stringWriter);

			e.printStackTrace(printWriter);
			printWriter.flush();
			stringWriter.flush();
		}
		finally
		{
			if (stringWriter != null)
			{
				try
				{
					stringWriter.close();
				}
				catch (final IOException e1)
				{
					e1.printStackTrace();
				}
			}
			if (printWriter != null)
			{
				printWriter.close();
			}
		}
		return stringWriter.toString();
	}
}