Java InputStream、String、File相互转化

String --> InputStream  
ByteArrayInputStream stream = new ByteArrayInputStream(str.getBytes());  
InputStream --> String  
String inputStream2String(InputStream is){  
   BufferedReader in = new BufferedReader(new InputStreamReader(is));  
   StringBuffer buffer = new StringBuffer();  
   String line = "";  
   while ((line = in.readLine()) != null){  
     buffer.append(line);  
   }  
   return buffer.toString();  
}  
  
File --> InputStream  
InputStream in = new FileInputStream(file);  
   
InputStream --> File  
public void inputstreamtofile(InputStream ins,File file){  
   OutputStream os = new FileOutputStream(file);  
   int bytesRead = 0;  
   byte[] buffer = new byte[8192];  
   while ((bytesRead = ins.read(buffer, 0, 8192)) != -1) {  
      os.write(buffer, 0, bytesRead);  
   }  
   os.close();  
   ins.close();  
}