login.java

private CallbackManager mCallbackManager;
private AccessToken mToken = null;

@Override
protected void onCreate(Bundle savedInstanceState){
  super.onCreate(savedInstanceState);
  FacebokSdk.sdkInitialize(getApplicationContext());
  mCallbackManager = CallbackManager.Factory.create();
  mToken = AccessToken.getCurrentAccessToken();
  
  if(mToken == null){
    LoginButton loginButton = (LoginButton)findViewById(R.id.login_button);
    if(loginButton != null) {
      loginButton.setReadPermissions("public_profile", "user_friends", "email");
      loginButton.registerCallback(mCallbackManager, new FacebookCallback<LoginResult>() {
        @Override
        public void onSuccess(final LoginResult loginResult) {
          GraphRequest request;
          mToken = loginResult.getAccessToken();
          request = GraphRequest.newMeRequest(mToken, jsonObjectCallback);
          Bundle parameters = new Bundle();
          parameters.putString("fields", "id,name,email,gender,birthday,cover");
          request.setParameters(parameters);
          request.executeAsync();
        }

        @Override
        public void onCancel() {}

        @Override
        public void onError(FacebookException error) {}
      });
    }
  }else{
    GraphRequest request;
    request = GraphRequest.newMeRequest(mToken, jsonObjectCallback);
    Bundle parameters = new Bundle();
    parameters.putString("fields", "id,name,email,gender,birthday,cover");
    request.setParameters(parameters);
    request.executeAsync();
  }
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data){
  super.onActivityResult(requestCode, resultCode, data);
  mCallbackManager.onActivityResult(requestCode, resultCode, data);
}
    
GraphRequest.GraphJSONObjectCallback jsonObjectCallback = new GraphRequest.GraphJSONObjectCallback() {
  @Override
  public void onCompleted(final JSONObject user, GraphResponse response) {
    if (response.getError() == null) {
      setResult(RESULT_OK);
    }
  }
};