Download file from HTTPS server using Java

Question

I want to download a file from the server which is using the secured connection protocol HTTPS. I could do it in the normal server, But, how I can do it using the HTTPS. If anyone have used the sample API, please help me to find the useful resources.

Answer 1

Access an HTTPS url with Java is the same then access an HTTP url. You can always use the

URL url = new URL("https://hostname:port/file.txt");
URLConnection connection = url.openConnection();
InputStream is = connection.getInputStream();
// .. then download the file

But, you can have some problem when the server's certificate chain cannot be validated. So you may need to disable the validation of certificates for testing purposes and trust all certificates.

To do that write:

// Create a new trust manager that trust all certificates
TrustManager[] trustAllCerts = new TrustManager[]{
    new X509TrustManager() {
        public java.security.cert.X509Certificate[] getAcceptedIssuers() {
            return null;
        }
        public void checkClientTrusted(
            java.security.cert.X509Certificate[] certs, String authType) {
        }
        public void checkServerTrusted(
            java.security.cert.X509Certificate[] certs, String authType) {
        }
    }
};

// Activate the new trust manager
try {
    SSLContext sc = SSLContext.getInstance("SSL");
    sc.init(null, trustAllCerts, new java.security.SecureRandom());
    HttpsURLConnection.setDefaultSSLSocketFactory(sc.getSocketFactory());
} catch (Exception e) {
}

// And as before now you can use URL and URLConnection
URL url = new URL("https://hostname:port/file.txt");
URLConnection connection = url.openConnection();
InputStream is = connection.getInputStream();
// .. then download the file

Answer 2

Actually I had the similar problem. I was unable to download files from HTTPS server. Then I fixed this problem with this solution:

// But are u denied access?
// well here is the solution.
public static void TheKing_DownloadFileFromURL(String search, String path) throws IOException {

    // This will get input data from the server
    InputStream inputStream = null;

    // This will read the data from the server;
    OutputStream outputStream = null;

    try {
        // This will open a socket from client to server
        URL url = new URL(search);

        // This user agent is for if the server wants real humans to visit
        String USER_AGENT = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Safari/537.36";

        // This socket type will allow to set user_agent
        URLConnection con = url.openConnection();

        // Setting the user agent
        con.setRequestProperty("User-Agent", USER_AGENT);

        //Getting content Length
        int contentLength = con.getContentLength();
        System.out.println("File contentLength = " + contentLength + " bytes");


        // Requesting input data from server
        inputStream = con.getInputStream();

        // Open local file writer
        outputStream = new FileOutputStream(path);

        // Limiting byte written to file per loop
        byte[] buffer = new byte[2048];

        // Increments file size
        int length;
        int downloaded = 0; 

        // Looping until server finishes
        while ((length = inputStream.read(buffer)) != -1) 
        {
            // Writing data
            outputStream.write(buffer, 0, length);
            downloaded+=length;
            //System.out.println("Downlad Status: " + (downloaded * 100) / (contentLength * 1.0) + "%");


        }
    } catch (Exception ex) {
        //Logger.getLogger(WebCrawler.class.getName()).log(Level.SEVERE, null, ex);
    }

    // closing used resources
    // The computer will not be able to use the image
    // This is a must
    outputStream.close();
    inputStream.close();
}

Use this function... Hope you will get benefited with this easy solution.

Answer 3

You should be able to do it with exactly the same code, unless the SSL certifcate fails validations. This would normally happen if its a self-signed ceritifcate, or if the certificate is from a CA which your system doesn't know about.

In such case, you should handle the certificate validation in code. Only that part of your code would change. Everything else will remain the same.

First try out with the same code, and see if you get a Certificate Exception.

Answer 4

there's no difference downloading http vs https. open a HttpURLConnection to the correct URL and read the resulting stream.