如何把文件流变成的字符串变回文件

怎么把文件流变成的字符串变回文件？
也就是以下过程的逆过程：
public String selfReadFile(String strFileName){  
StringBuffer buf=null; 
BufferedReader breader = null;//reader for the template files  
try  
{  
breader = new BufferedReader(new InputStreamReader(new FileInputStream((strFileName)),Charset.forName("utf-8")));  
buf = new StringBuffer();  
while(breader.ready())  
buf.append((char)breader.read());  
breader.close();  
}//try  
catch(Exception e)  
{  
e.printStackTrace();  
}//catch  
return buf.toString();  
}

------解决方案--------------------
output stream
------解决方案--------------------
InputStream is=null;
BufferedReader br=null;

try {
is=asset.open("airport.txt");
br=new BufferedReader(new InputStreamReader(is,"GBK"));
fos=new FileOutputStream("/data/data/com.tarena.android/airport_1.txt");
String str=null;
while((str=br.readLine())!=null){
fos.write(str.getBytes());
fos.flush();
}catch (IOException e) {
// TODO: handle exception
}finally{
if(br!=null)try{br.close();}catch(IOException e){}
if(is!=null)try{is.close();}catch(IOException e){}
if(fos!=null)try{fos.close();}catch(IOException e){}
}