我正在嘗試將推文從 twitter 保存到 MongoDb 數(shù)據(jù)庫。我有RDD<Status>，我正在嘗試借助 ObjectMapper 將其轉(zhuǎn)換為 JSON 格式。但是這種轉(zhuǎn)換存在一些問題（public class Main {    //set system credentials for access to twitter    private static void setTwitterOAuth() {        System.setProperty("twitter4j.oauth.consumerKey", TwitterCredentials.consumerKey);        System.setProperty("twitter4j.oauth.consumerSecret", TwitterCredentials.consumerSecret);        System.setProperty("twitter4j.oauth.accessToken", TwitterCredentials.accessToken);        System.setProperty("twitter4j.oauth.accessTokenSecret", TwitterCredentials.accessTokenSecret);    }    public static void main(String [] args) {        setTwitterOAuth();        SparkConf conf = new SparkConf().setMaster("local[2]")                                        .setAppName("SparkTwitter");        JavaSparkContext sparkContext = new JavaSparkContext(conf);        JavaStreamingContext jssc = new JavaStreamingContext(sparkContext, new Duration(1000));        JavaReceiverInputDStream<Status> twitterStream = TwitterUtils.createStream(jssc);        //Stream that contains just tweets in english        JavaDStream<Status> enTweetsDStream=twitterStream.filter((status) -> "en".equalsIgnoreCase(status.getLang()));        enTweetsDStream.persist(StorageLevel.MEMORY_AND_DISK());        enTweetsDStream.print();        jssc.start();        jssc.awaitTermination();    }    static void saveRawTweetsToMondoDb(JavaRDD<Status> rdd,JavaSparkContext sparkContext) {     try {            ObjectMapper objectMapper = new ObjectMapper();            SQLContext sqlContext = new SQLContext(sparkContext);            JavaRDD<String> tweet =  rdd.map(status -> objectMapper.writeValueAsString(status));            DataFrame dataFrame = sqlContext.read().json(tweet);        } catch (Exception e) {            System.out.println("Error saving to database");        }    }JavaRDD<String> tweet =  rdd.map(status -> objectMapper.writeValueAsString(status));這是一個(gè)問題。需要不兼容的類型JavaRDD<String>，但地圖被推斷為javaRDD<R>