String query = "SELECT CampaignId, CampaignName, Clicks, Impressions FROM CAMPAIGN_PERFORMANCE_REPORT";
ReportDownloadResponse response =
new ReportDownloader(session).downloadReport(query, DownloadFormat.CSV);
Comment out the save to file line
//response.saveToFile(reportFile);
String responseAsString = response.getAsString();
You may then parse the String object as needed