Download files from google drive using REST API

Question

Currently I'm working on Google Drive integration with Salesforce. I was able to connect to Google Drive and retrieve a list of file information. now I need to download some files from Google Drive. For that I'm using following method:

public PageReference downloadFile(FileWrapper file){
    //webContentLink
    if(file == null || file.id == null){
        return null;
    }

    Http http = new Http();
    HttpRequest req = new HttpRequest();
    req.setMethod('GET');
    req.setEndpoint('https://www.googleapis.com/drive/v2/files/'+ file.id+'?alt=media');
    req.setHeader('Content-Type', 'application/json');
    req.setHeader('Authorization', 'Bearer ' + accessToken);
    req.setTimeout(60 * 1000);

    HttpResponse resp = null;
    resp = http.send(req);
    test = resp.getBody();

    if(resp.getStatusCode() == 200){
        PageReference pageref = new PageReference(resp.getBody());
        return pageref;
    }

    return null;
}

When I run this method I'm getting Maximum view state size limit (135KB) exceeded. Actual view state size for this page was 189.844KB. Is there are any other way to download file other than using PageReference? Please help me to sort out this problem. If you guys have any other better way please suggest.

Answer 1

You're giving the PageReference constructor the file content, rather than the URL it wants, but the key here is to not get the file content in Apex at all.

You should be able to have the browser do the work for you by returning a PageReference for the file's webViewLink URL (I think it's webViewLink, but if that doesn't work you might want to try webContentLink) and passing the access token in a URL parameter. Your code would be something like this:

public PageReference downloadFile(FileWrapper file){
    if(file == null || file.webViewLink == null){
        return null;
    }

    String url = file.webViewLink + '?access_token=' + accessToken;

    PageReference pageref = new PageReference(url);
    return pageref;
}