How To Read from a Text File in Java

BufferedReader reader = null;
try {
    reader = new BufferedReader(new InputStreamReader(new FileInputStream("filename.txt"), "UTF-8"));
    String string = reader.readLine();
} finally {
    if (reader != null) {
        reader.close();
    }
}

How To Write to a Text File in Java

Writer writer = null;
try {
    writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream("filename.txt"), "UTF-8"));
    writer.write(string);
} finally {
    if (writer != null) {
        writer.close();
    }
}

How to use Client Certificate Authentication in iOS App

http://stackoverflow.com/questions/3749429/how-to-use-client-certificate-authentication-in-ios-app

http://stackoverflow.com/questions/25924881/ios-client-certificates-and-mobile-device-management

https://developer.apple.com/library/ios/qa/qa1745/_index.html