How to get access token using gmail api?
Ans: As per your following tutorial, you are using OAuth 2.0. So there is a basic pattern for accessing a Google API using OAuth 2.0. It follows 4 steps:
- Obtain OAuth 2.0 credentials from the Google Developers Console.
- Obtain an access token from the Google Authorization Server.
- Send the access token to an API.
- Refresh the access token, if necessary.
For details, you can follow the tutorial - Using OAuth 2.0 to Access Google APIs
You have to visit the Google Developers Console to obtain OAuth 2.0 credentials such as a client ID and client secret that are known to both Google and your application
Root Cause Analysis:
Issue-1:
After studying your code, some lacking are found. If your code runs smoothly, then the code always give an empty string. Because your AccessToken() method always return return "";
Issue-2:
catch (Exception e)
{
System.out.println("Error.");
}
Your try catch block is going exception block. Because, it seems that you have not completed your code properly. You have missed encoding as well as using JSONObject which prepares the access token. So it is giving output as
Error.
Solution:
I got that your code is similar with this tutorial
As your code needs more changes to solve your issue. So I offer you to use LinkedHashMap or ArrayList. Those will provide easier way to make solution. So I give you 2 sample code to make your life easier. You can choose any of them. You need to change refresh_token, client id, client secret and grant type as yours.
private String getAccessToken()
{
try
{
Map<String,Object> params = new LinkedHashMap<>();
params.put("grant_type","refresh_token");
params.put("client_id",[YOUR CLIENT ID]);
params.put("client_secret",[YOUR CLIENT SECRET]);
params.put("refresh_token",[YOUR REFRESH TOKEN]);
StringBuilder postData = new StringBuilder();
for(Map.Entry<String,Object> param : params.entrySet())
{
if(postData.length() != 0)
{
postData.append('&');
}
postData.append(URLEncoder.encode(param.getKey(),"UTF-8"));
postData.append('=');
postData.append(URLEncoder.encode(String.valueOf(param.getValue()),"UTF-8"));
}
byte[] postDataBytes = postData.toString().getBytes("UTF-8");
URL url = new URL("https://accounts.google.com/o/oauth2/token");
HttpURLConnection con = (HttpURLConnection)url.openConnection();
con.setDoOutput(true);
con.setUseCaches(false);
con.setRequestMethod("POST");
con.getOutputStream().write(postDataBytes);
BufferedReader reader = new BufferedReader(new InputStreamReader(con.getInputStream()));
StringBuffer buffer = new StringBuffer();
for (String line = reader.readLine(); line != null; line = reader.readLine())
{
buffer.append(line);
}
JSONObject json = new JSONObject(buffer.toString());
String accessToken = json.getString("access_token");
return accessToken;
}
catch (Exception ex)
{
ex.printStackTrace();
}
return null;
}
For accessing google play android developer api, you need to pass the
previous refresh token to get access token
private String getAccessToken(String refreshToken){
HttpClient client = new DefaultHttpClient();
HttpPost post = new HttpPost("https://accounts.google.com/o/oauth2/token");
try
{
List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(4);
nameValuePairs.add(new BasicNameValuePair("grant_type", "refresh_token"));
nameValuePairs.add(new BasicNameValuePair("client_id", GOOGLE_CLIENT_ID));
nameValuePairs.add(new BasicNameValuePair("client_secret", GOOGLE_CLIENT_SECRET));
nameValuePairs.add(new BasicNameValuePair("refresh_token", refreshToken));
post.setEntity(new UrlEncodedFormEntity(nameValuePairs));
org.apache.http.HttpResponse response = client.execute(post);
BufferedReader reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
StringBuffer buffer = new StringBuffer();
for (String line = reader.readLine(); line != null; line = reader.readLine())
{
buffer.append(line);
}
JSONObject json = new JSONObject(buffer.toString());
String accessToken = json.getString("access_token");
return accessToken;
}
catch (IOException e) { e.printStackTrace(); }
return null;
}
Resource Link:
Hope that, this samples and resource link will help you to solve your issue and get access of access token.
Ans: It indicates that the query was invalid. Parent ID was missing or the combination of dimensions or metrics requested was not valid.
Recommended Action: You need to make changes to the API query in order for it to work.
For HTTP/1.1 400 Bad Request error, you can go through my another
answer. It will help you to make sense about which host you
need to use and which conditions you need to apply.
A token might stop working for one of these reasons:
- The user has
revoked access.
- The token has not been used for
six months.
- The
user changed passwords and the token contains Gmail, Calendar,
Contacts, or Hangouts scopes.
- The user account has
exceeded a certain number of token requests.
There is currently a limit of 25 refresh tokens per user account per client. If the limit is reached, creating a new token automatically invalidates the oldest token without warning. This limit does not apply to service accounts.
Which precautions should be followed?
Precautions - 1:
Some requests require an authentication step where the user logs in
with their Google account. After logging in, the user is asked whether
they are willing to grant the permissions that your application is
requesting. This process is called user consent.
If the user grants the permission, the Google Authorization Server
sends your application an access token (or an authorization code that
your application can use to obtain an access token). If the user does
not grant the permission, the server returns an error.
Precautions - 2:
If an access token is issued for the Google+ API, it does not grant
access to the Google Contacts API. You can, however, send that access
token to the Google+ API multiple times for similar operations.
Precautions - 3:
An access token typically has an expiration date of 1 hour, after
which you will get an error if you try to use it. Google Credential
takes care of automatically "refreshing" the token, which simply means
getting a new access token.
Save refresh tokens in secure long-term storage and continue to use
them as long as they remain valid. Limits apply to the number of
refresh tokens that are issued per client-user combination, and per
user across all clients, and these limits are different. If your
application requests enough refresh tokens to go over one of the
limits, older refresh tokens stop working.
