您收到“ java.lang.NoClassDefFoundError：org / apache / spark / sql /
Dataset”错误，因为pom.xml文件中缺少“ spark-sql”依赖项。
如果要使用Spark 2.0.0读取Cassandra表，则需要以下最低依赖项。
<dependency> <groupId>org.apache.spark</groupId> <artifactId>spark-core_2.11</artifactId> <version>2.0.0</version></dependency><dependency> <groupId>org.apache.spark</groupId> <artifactId>spark-sql_2.11</artifactId> <version>2.0.0</version></dependency><dependency> <groupId>com.datastax.spark</groupId> <artifactId>spark-cassandra-connector_2.11</artifactId> <version>2.0.0-M3</version></dependency>
Spark 2.0.0提供了SparkSession和数据集API。下面是读取Cassandra表并打印记录的示例程序。
public class SparkCassandraDatasetApplication { public static void main(String[] args) { SparkSession spark = SparkSession .builder() .appName("SparkCassandraDatasetApplication") .config("spark.sql.warehouse.dir", "/file:C:/temp") .config("spark.cassandra.connection.host", "127.0.0.1") .config("spark.cassandra.connection.port", "9042") .master("local[2]") .getOrCreate(); //Read data Dataset<Row> dataset = spark.read().format("org.apache.spark.sql.cassandra") .options(new HashMap<String, String>() { { put("keyspace", "mykeyspace"); put("table", "mytable"); } }).load(); //Print data dataset.show(); spark.stop(); } }如果仍然要使用RDD，请使用下面的示例程序。
public class SparkCassandraRDDApplication {public static void main(String[] args) { SparkConf conf = new SparkConf() .setAppName("SparkCassandraRDDApplication") .setMaster("local[2]") .set("spark.cassandra.connection.host", "127.0.0.1") .set("spark.cassandra.connection.port", "9042"); JavaSparkContext sc = new JavaSparkContext(conf); //Read JavaRDD<UserData> resultsRDD = javaFunctions(sc).cassandraTable("mykeyspace", "mytable",CassandraJavaUtil.mapRowTo(UserData.class)); //Print resultsRDD.foreach(data -> { System.out.println(data.id); System.out.println(data.username); }); sc.stop(); }}上面程序中使用的Javabean（UserData）如下。
public class UserData implements Serializable{ String id; String username; public String getId() { return id; } public void setId(String id) { this.id = id; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } }
