我正在使用Java在Spark Streaming中编写一个简单的数据管道,从Kafka中提取JSON数据,将JSON解析为自定义类( Transaction
),然后将该数据插入到Cassandra表中,但我无法获得 mapToRow()
函数上班 .
我已经看到很多例子说你需要做的就是这样:
JavaPairInputDStream<String, String> stream = KafkaUtils.createDirectStream(
streamingContext,
String.class,
String.class,
StringDecoder.class,
StringDecoder.class,
kafkaParams,
topicsSet
);
JavaDStream<String> lines = stream.map(
new Function<Tuple2<String,String>, String>(){
@Override
public String call(Tuple2<String,String> tuple2) {
return tuple2._2();
}
}
);
javaFunctions(lines).writerBuilder("myKeyspace", "myTableName", mapToRow(Transaction.class)).saveToCassandra();
但是,当我这样做时,我收到错误:
The method mapToRow(Class<Transaction>) is undefined for the type SaveTransactions
我认为我所缺乏的是我班上的某种装饰,但我还没有成功找出哪一个 . 我试过裸骨,基本上让这个类成为一个属性包:
public class Transaction implements java.io.Serializable{
public int TransactionId;
...
public Transaction(){}
}
我已经尝试了所有的DataStax映射注释:
@Table(keyspace = "myKeyspace", name = "myTableName",
readConsistency = "QUORUM",
writeConsistency = "QUORUM",
caseSensitiveKeyspace = false,
caseSensitiveTable = false)
public class Transaction implements java.io.Serializable{
@PartitionKey(0)
@Column(name="transaction_id")
public int TransactionId;
...
public Transaction(){}
}
我还尝试为每个属性 Build 公共get / set方法并将属性设置为private:
public class Transaction implements java.io.Serializable{
private int transactionId;
...
public Transaction(){}
public int getTransactionId() {
return transactionId;
}
public void setTransactionId(int transactionId) {
this.transactionId = transactionId;
}
}
我已经能够使用下面的类将 DStream
解析为 RDD
的 Transactions
:
public class Transaction implements java.io.Serializable{
...
public static class ParseJSON implements FlatMapFunction<Iterator<String>, Transaction> {
public Iterable<Transaction> call(Iterator<String> lines) throws Exception {
ArrayList<Transaction> transactions = new ArrayList<Transaction>();
ObjectMapper mapper = new ObjectMapper();
while (lines.hasNext()) {
String line = lines.next();
try {
transactions.add(mapper.readValue(line, Transaction.class));
} catch (Exception e) {
System.out.println("Skipped:" + e);
}
}
return transactions;
}
}
}
结合以下代码,从上面作用于 lines
对象:
JavaDStream<Transaction> events = lines.mapPartitions(new Transaction.ParseJSON());
但是,一旦我从中获得它仍然无法使用writeBuilder() . saveToCassandra()链 .
非常感谢任何帮助 .
1 回答
事实证明这个问题只是一个导入问题 . 我导入
com.datastax.spark.connector.japi.CassandraStreamingJavaUtil.*
认为它会给我我需要的一切但是我还需要为.mapToRow()函数引入com.datastax.spark.connector.japi.CassandraJavaUtil.*
.一旦我解决了这个问题,我就开始收到以下错误:
通过引入spark-sql项目解决了这个问题:
希望这有助于下一个人/加仑 .