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();

}

http://blog.sina.com.cn/s/blog_a000da9d010121bl.html