给string写入指定的文件内，并换行。
File dirFile = new File("D://20110923.txt");
try
{
if ( dirFile.exists() == false)
{
dirFile.createNewFile();
}
FileWriter fw=new FileWriter("D://20110923.txt",true);
BufferedWriter bw=new BufferedWriter(fw);
bw.newLine();
bw.write("sss");
bw.close();
fw.close();

} catch (Exception ex)
{
}