How to use HttpClient libraries to download a file from Google Drive? - google-drive-api

Question

I am attempting to integrate Google Picker on a page. The user uses the picker to sign in into his google account and picks a file. I am trying to use Apache HttpClient libraries to download this file.
Here are the implementation details :
I used Client Side Auth on Javascript as highlighted on this Google Tutorial. Once I got the 'fileId' of the file, I performed an authenticated GET using Google Drive API to retrieve the file metadata - name, user, dates, downloadUrl, exportLinks etc. You can use the above link to test the end point and see the responses if you have a fileId.
function postDownload (resp) {
var link;
var data = $.parseJSON (resp);
console.log (data.webContentLink);
if (data.mimeType == "application/pdf"){
link = data.downloadUrl;
} else {
link = (data.exportLinks)['application/pdf'];
}
//I wish to use the below link to download the file on server side
//using HttpClient libraries.
console.log ("Download Link - " +link);
}
//Call back after a file is selected on the picker
function pickerCallback(data) {
if (data.action == google.picker.Action.PICKED) {
var id = data.docs[0].id;
var accessToken = gapi.auth.getToken().access_token;
console.log (id);
var xhr = new XMLHttpRequest();
xhr.open('GET', 'https://www.googleapis.com/drive/v2/files/' + id);
xhr.setRequestHeader('Authorization', 'Bearer ' + accessToken);
xhr.onload = function() {
postDownload(xhr.responseText);
};
xhr.onerror = function() {
checkAuth();
};
xhr.send();
}
}
Download Code:
import java.io.IOException;
import org.apache.http.Header;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
public class DownloadFile {
public static void main(String[] args) throws IOException {
String link = "https://docs.google.com/uc? id=0ByJwoNOQMrO_S3hlWGRfa2JwVWM&export=download";
DefaultHttpClient httpclient = new DefaultHttpClient();
HttpGet get = new HttpGet(link);
HttpResponse response = httpclient.execute(get);
Header[] headers = response.getAllHeaders();
for (Header header : headers) {
System.out.println("Key : " + header.getName() + " ,Value : " + header.getValue());
}
}
}
If I use the link on the browser or the POSTMAN Chrome Extension, I am able to download the file correctly. The REST clients reports the incoming data correctly as 'application/pdf'.
However, when I use the above Snippet to perform a HttpGet on the URL, the incoming data has a content type of 'text/html' . No clue about this behavior. I don't think the final URL needs to be treated any differently to download the file.
Has anybody faced this issue? Thanks in advance.

Answer 1

I was able to solve the issue by adding an authentication header. I guess the auth token is stored in the user's session on the browser and hence I was able to download the file by hitting the URL. For a standalone Java program, we may have to pass the authentication token too.
The below code worked.
import java.io.IOException;
import org.apache.http.Header;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
public class DownloadFile {
public static void main(String[] args) throws IOException {
String link = "https://docs.google.com/feeds/download/documents/export/Export?id=1vE4GVvVVipwMjKsc1q9p75LYWrRy8DZz0APjVFiHL9A";
DefaultHttpClient httpclient = new DefaultHttpClient();
HttpGet get = new HttpGet(link);
// get.addHeader("Content-Type", "application/pdf");
get.addHeader("Authorization", "Bearer 1vE4GVvVVipwMjKsc1q9p75LYWrRy8DZz0APjVFiHL9A");
HttpResponse response = httpclient.execute(get);
Header[] headers = response.getAllHeaders();
for (Header header : headers) {
System.out.println("Key : " + header.getName() + " ,Value : " + header.getValue());
}
}
}