//String转inputStream
1. String --> InputStream
InputStream String2InputStream(String str){
    ByteArrayInputStream stream = new ByteArrayInputStream(str.getBytes());
    return stream;
}

2. 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();
}