Note- Facebook provides 25 latest message conversation.

To get Facebook chat messages in Android, following steps are used:

1. Define the 'read_mailbox' property as below:

   private static final List PERMISSIONS = Arrays.asList("read_mailbox");
   

2. Write the following code to get messages from Facebook:

Session.openActiveSession(createNewTextShareFromFacebookActivity, true, new Session.StatusCallback() {

            // callback when session changes state
            @Override
            public void call(final Session session, SessionState state, Exception exception) {
                if (session.isOpened()) {
                    List permissions = session.getPermissions();        
                    // If permission is not already provided then it will provide the 'read_mailbox' permission to read inbox messages from facebokk
                    if (!isSubsetOf(PERMISSIONS, permissions)) {
                        Session.NewPermissionsRequest newPermissionsRequest = new Session
                                .NewPermissionsRequest(createNewTextShareFromFacebookActivity, PERMISSIONS);
                        session.requestNewReadPermissions(newPermissionsRequest);
                        return;
                    }
                    Request req = new Request(session, "/me/inbox",null, HttpMethod.GET,
                            new Callback() {

                        @Override
                        public void onCompleted(Response response) {

                            if(response.getGraphObject() != null)
                            {
                                JSONObject graphResponse = response
                                        .getGraphObject()
                                        .getInnerJSONObject();
                                // Here we can print the graphResponse object to see the messages given by facebook
                            }
                        }
                    });
                    Request.executeBatchAsync(req);
                }
            }
        });
    

Check permission is provided or not:

// Check the permission is already provided or not
    private boolean isSubsetOf(Collection subset, Collection superset) {
        for (String string : subset) {
            if (!superset.contains(string)) {
                return false;
            }
        }
        return true;
    }

Hope this will help you. Good luck :)