Run python script in Java : Why do I get null output?

I'm trying to run a python script in Java. python script converts speech to text. But, after executing it in java, I get null output. The python script does not have any error and works fine as I run it in the terminal.

I tried "Thread.sleep()" in order to wait for process but It did not help. "SampleHandler" is my java class name.

Java:

try {
    java.net.URL location =  SampleHandler.class.getProtectionDomain().getCodeSource().getLocation();
    Process p = Runtime.getRuntime().exec(location.getFile() + "resources/speech_to_text.py");
    Thread.sleep(8000);
    BufferedReader in = new BufferedReader(new InputStreamReader(p.getInputStream()));
    String ret = "";
    ret = in.readLine();            
    System.out.println(ret);
} catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} catch (InterruptedException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} 

Python :

import os
import io
from google.cloud import speech
from google.cloud.speech import enums
from google.cloud.speech import types

os.environ["GOOGLE_APPLICATION_CREDENTIALS"]="key.json"
client = speech.SpeechClient()
file_name = os.path.join('audio.wav')
with io.open(file_name, 'rb') as audio_file:
    content = audio_file.read()
    audio = types.RecognitionAudio(content=content)

config = types.RecognitionConfig(
    encoding=enums.RecognitionConfig.AudioEncoding.LINEAR16,
    sample_rate_hertz=44100,
    audio_channel_count=2,
    language_code='en-US')

response = client.recognize(config, audio)

for result in response.results:
    print(format(result.alternatives[0].transcript))