Small Java library to easily connect to Google API, whether your authenticating with a user account using OAuth2 or with a service account.

This library basically authenticates with the Google API using the method described on the Java Quickstart for Google Developers . (whether you're connecting to Google Drive, Google Spreadsheets or other API's ; ex. Google Drive).

However, these quickstart guides always use user based OAuth2 authentication. Although well documented, I found it very cumbersome to do the same thing using a Google Cloud Service Account. There's a guide specifically for that, but it does not contain any practical examples like the other guides do. It actually took me almost a day to get the same thing up & running with a service account and without using deprecated stuff.

So if you run into the same problem, feel free to use this library. Basically, you create a GoogleAPISocket with given authentication type (user based auth / service account), some parameters that tell the system where to find your keyfile and a list of scopes that identify the specific API you want to use (e.g. Google Spreadsheets).

This library will presume you have a keyfile present in <USER HOME>\.googleauth\<PROJECT FOLDER>\

This library depends on four other libraries:

• com.google.api-client:google-api-client:1.32.1
• com.google.api-client:google-api-client-jackson2:1.28.1
• com.google.auth:google-auth-library-oauth2-http:1.0.0
• com.google.oauth-client:google-oauth-client-jetty:1.30.6

Let's say we have a service account and downloaded the keyfile from https://console.cloud.google.com/apis/credentials to a file called thermal-springs-1540545.json. We first need to set some parameters before constructing the GoogleAPISocket:

• Connection Type: Service account
• Project Name: My Google Sheets Interface
• Project Folder: gsheetsconnection
• Auth file: thermal-springs-1540545.json

On a Windows machine, the library will look for the keyfile with following path: C:\Users\username\.googleauth\gsheetsconnection\thermal-springs-1540545.json Or on Linux: /home/username/.googleauth/gsheetsconnection/thermal-springs-1540545.json

Be sure to put your keyfile in the right place before using the library. To authenticate with Google API, call:

GoogleAPISocket socket = GoogleAPISocketFactory.createSocket(GoogleAPISocketFactory.CONNECTION_TYPE_SERVICE_ACCOUNT, "My Google Sheets Interface", "gsheetsconnection", "thermal-springs-1540545.json");

Next, we want to connect to a specific API, e.g. Google Spreadsheets, to read some data from a sheet. This means we first have to load the right scope:

import com.google.api.services.sheets.v4.SheetsScopes;
...
socket.setScopes(SheetsScopes.SPREADSHEETS_READONLY)

If you need to use more scopes at once, setScopes(...) takes up to four parameters. Finally, call:

socket.connect();

The socket will now provide the necessary parameters to connect to a specific API. In our example, call

new Sheets.Builder(socket.HTTP_TRANSPORT, socket.JSON_FACTORY, socket.getCredentials())
                .setApplicationName(socket.getApplicationName())
                .build();

to get a Sheets object.