本篇文章为大家展示了在Spark Streaming job中如何读取Kafka messages及其offsetRange，内容简明扼要并且容易理解，绝对能使你眼前一亮，通过这篇文章的详细介绍希望你能有所收获。
创新互联是一家集网站建设,红安企业网站建设,红安品牌网站建设,网站定制,红安网站建设报价,网络营销,网络优化,红安网站推广为一体的创新建站企业，帮助传统企业提升企业形象加强企业竞争力。可充分满足这一群体相比中小企业更为丰富、高端、多元的互联网需求。同时我们时刻保持专业、时尚、前沿，时刻以成就客户成长自我，坚持不断学习、思考、沉淀、净化自己，让我们为更多的企业打造出实用型网站。
在Spark Streaming job中读取Kafka topic(s)中的messages时，有时我们会需要同步记录下每次读取的messages的offsetRange。要达到这一目的，下面这两段代码（代码1和代码2）都是正确的，而且是等价的。
代码1（正确）：
-----------------------
JavaPairInputDStream messages = KafkaUtils.createDirectStream(
jssc,
String.class,
String.class,
StringDecoder.class,
StringDecoder.class,
kafkaParams,
topicsSet
);
messages.foreachRDD(
new Function, Void>() {
@Override
public Void call(JavaPairRDD rdd) throws Exception {
OffsetRange[] offsets = ((HasOffsetRanges) rdd.rdd()).offsetRanges();
JavaRDD valueRDD = rdd.values();
long msgNum = processEachRDD(valueRDD, outputFolderPath, definedDuration);
if (msgNum > 0 && zkPathRoot!= null) {
writeOffsetToZookeeper(zkClient, zkPathRoot, offsets);
}
return null;
}
});
代码2（正确）：
-----------------------
JavaPairInputDStream messages = KafkaUtils.createDirectStream(
jssc,
String.class,
String.class,
StringDecoder.class,
StringDecoder.class,
kafkaParams,
topicsSet
);
final AtomicReference offsetRanges=new AtomicReference();
lines = messages.transformToPair(new Function, JavaPairRDD>() {
@Override
public JavaPairRDD call(JavaPairRDD rdd) throws Exception {
OffsetRange[] offsets = ((HasOffsetRanges) rdd.rdd()).offsetRanges();
offsetRanges.set(offsets);
return rdd;
}
}).map(new Function, String>() {
@Override
public String call(Tuple2 tuple2) {
return tuple2._2();
}
});
lines.foreachRDD(new Function, Void>() {
@Override
public Void call(JavaRDD rdd) throws Exception {
long msgNum = processEachRDD(rdd, outputFolderPath, definedDuration);
if (msgNum > 0 && zkPathRoot!= null) {
OffsetRange[] offsets = offsetRanges.get();
writeOffsetToZookeeper(zkClient, zkPathRoot, offsets);
}
return null;
}
});
但是要注意，下面这两段代码（代码3和代码4）是错误的，它们都会抛出一个exception：java.lang.ClassCastException: org.apache.spark.rdd.MapPartitionsRDD cannot be cast to org.apache.spark.streaming.kafka.HasOffsetRanges
代码3（错误）：
-----------------------
JavaPairInputDStream messages = KafkaUtils.createDirectStream(
jssc,
String.class,
String.class,
StringDecoder.class,
StringDecoder.class,
kafkaParams,
topicsSet
);
messages.transform(new Function, JavaRDD>() {
@Override
public JavaRDD call(JavaPairRDD rdd) throws Exception {
return rdd.values（）;
}
}).foreachRDD(new Function, Void>() {
@Override
public Void call(JavaRDD rdd) throws Exception {
long msgNum = processEachRDD(rdd, outputFolderPath, definedDuration);
if (msgNum > 0 && zkPathRoot!= null) {
OffsetRange[] offsets = offsetRanges.get();
writeOffsetToZookeeper(zkClient, zkPathRoot, offsets);
}
return null;
}
});
代码4（错误）：
-----------------------
JavaPairInputDStream messages = KafkaUtils.createDirectStream(
jssc,
String.class,
String.class,
StringDecoder.class,
StringDecoder.class,
kafkaParams,
topicsSet
);
messages.map(new Function, String>() {
@Override
public String call(Tuple2 tuple2) {
return tuple2._2();
}
}).foreachRDD(new Function, Void>() {
@Override
public Void call(JavaRDD rdd) throws Exception {
long msgNum = processEachRDD(rdd, outputFolderPath, definedDuration);
if (msgNum > 0 && zkPathRoot!= null) {
OffsetRange[] offsets = offsetRanges.get();
writeOffsetToZookeeper(zkClient, zkPathRoot, offsets);
}
return null;
}
});
上述内容就是在Spark Streaming job中如何读取Kafka messages及其offsetRange，你们学到知识或技能了吗？如果还想学到更多技能或者丰富自己的知识储备，欢迎关注创新互联行业资讯频道。
当前标题：在SparkStreamingjob中如何读取Kafkamessages及其offsetRange
网站网址：
http://cdkjz.cn/article/gejdho.html
