DaggerStep1_GetFeedHandler.java

public class GetFeedHandler implements RequestHandler<GetFeedRequest, GetFeedResponse> {
    @Inject DynamoDB mDynamoDB;
    @Inject LambdaLogger mLambdaLogger;

    public GetFeedResponse handleRequest(final GetFeedRequest input, final Context context) {
        Injector.getInjector(context).inject(this);
        
        final List<String> activityIds = getActivitiesForUser(input.getUserId());
        return new GetFeedResponse(activityIds);
    }

    private List<String> getActivitiesForUser(final String userId) {
        final List<String> activityIds = new ArrayList<>();

        mLambdaLogger.log(String.format("Querying activities for user %s", userId));
        final Table table = mDynamoDB.getTable(TableConstants.FEED_TABLE_NAME);
        final Index index = table.getIndex(TableConstants.FEED_USERID_CREATED_AT_INDEX);

        final QuerySpec spec = new QuerySpec()
                .withKeyConditionExpression("#U = :userId")
                .withValueMap(new ValueMap()
                        .withString(":userId", userId))
                .withNameMap(new NameMap()
                        .with("#U", TableConstants.FEED_USERID_COLUMN))
                .withScanIndexForward(false);

        final ItemCollection<QueryOutcome> items = index.query(spec);
        for (final Item activity : items) {
            final String activityId = (String) activity.get(TableConstants.FEED_ID_COLUMN);

            mLambdaLogger.log(String.format("Found activity %s", activityId));
            activityIds.add(activityId);
        }

        return activityIds;
    }
}