什么时间使用高级应用？
- 针对一个消息读取多次
- 在一个process中，仅仅处理一个topic中的一组partitions
- 使用事务，确保每个消息只被处理一次
使用高级应用（调用较底层函数）的缺点？
SimpleConsumer需要做很多额外的工作（在以groups方式进行消息处理时不需要）
- 在应用程序中跟踪上次消息处理的offset
- 确定一个topic partition的lead broker
- 手工处理broker leander的改变
使用底层函数（SimpleConsumer）开发的步骤
- 通过active broker,确定topic partition的lead broker
- 确定topic partition的replicat brokers
- 根据需要，创建数据请求
- 抓取数据
- 识别lead brokder改变并进行恢复
代码示例
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import kafka.api.FetchRequest;
import kafka.api.FetchRequestBuilder;
import kafka.api.PartitionOffsetRequestInfo;
import kafka.cluster.Broker;
import kafka.common.ErrorMapping;
import kafka.common.TopicAndPartition;
import kafka.javaapi.FetchResponse;
import kafka.javaapi.OffsetResponse;
import kafka.javaapi.PartitionMetadata;
import kafka.javaapi.TopicMetadata;
import kafka.javaapi.TopicMetadataRequest;
import kafka.javaapi.TopicMetadataResponse;
import kafka.javaapi.consumer.SimpleConsumer;
import kafka.message.MessageAndOffset;
/**
* https://cwiki.apache.org/confluence/display/KAFKA/0.8.0+SimpleConsumer+Example
* @author Fung
*
*/
public class ConsumerSimpleExample {
public static void main(String arg[]) {
String[] args={"20","page_visits","2","172.168.63.233","9092"};
ConsumerSimpleExample example = new ConsumerSimpleExample();
long maxReads = Long.parseLong(args[0]);
String topic = args[1];
int partition = Integer.parseInt(args[2]);
List<String> seeds = new ArrayList<String>();
seeds.add(args[3]);
int port = Integer.parseInt(args[4]);
try {
example.run(maxReads, topic, partition, seeds, port);
} catch (Exception e) {
System.out.println("Oops:" + e);
e.printStackTrace();
}
}
private List<String> m_replicaBrokers = new ArrayList<String>();
public ConsumerSimpleExample() {
m_replicaBrokers = new ArrayList<String>();
}
public void run(long a_maxReads, String a_topic, int a_partition,
List<String> a_seedBrokers, int a_port) throws Exception {
// find the meta data about the topic and partition we are interested in
//
PartitionMetadata metadata = findLeader(a_seedBrokers, a_port, a_topic,
a_partition);
if (metadata == null) {
System.out
.println("Can't find metadata for Topic and Partition. Exiting");
return;
}
if (metadata.leader() == null) {
System.out
.println("Can't find Leader for Topic and Partition. Exiting");
return;
}
String leadBroker = metadata.leader().host();
String clientName = "Client_" + a_topic + "_" + a_partition;
SimpleConsumer consumer = new SimpleConsumer(leadBroker, a_port,
100000, 64 * 1024, clientName);
long readOffset = getLastOffset(consumer, a_topic, a_partition,
kafka.api.OffsetRequest.LatestTime(), clientName);
int numErrors = 0;
while (a_maxReads > 0) {
if (consumer == null) {
consumer = new SimpleConsumer(leadBroker, a_port, 100000,
64 * 1024, clientName);
}
// Note: this fetchSize of 100000 might need to be increased if
// large batches are written to Kafka
FetchRequest req = new FetchRequestBuilder().clientId(clientName)
.addFetch(a_topic, a_partition, readOffset, 100000).build();
FetchResponse fetchResponse = consumer.fetch(req);
if (fetchResponse.hasError()) {
numErrors++;
// Something went wrong!
short code = fetchResponse.errorCode(a_topic, a_partition);
System.out.println("Error fetching data from the Broker:"
+ leadBroker + " Reason: " + code);
if (numErrors > 5)
break;
if (code == ErrorMapping.OffsetOutOfRangeCode()) {
// We asked for an invalid offset. For simple case ask for
// the last element to reset
readOffset = getLastOffset(consumer, a_topic, a_partition,
kafka.api.OffsetRequest.LatestTime(), clientName);
continue;
}
consumer.close();
consumer = null;
leadBroker = findNewLeader(leadBroker, a_topic, a_partition,
a_port);
continue;
}
numErrors = 0;
long numRead = 0;
for (MessageAndOffset messageAndOffset : fetchResponse.messageSet(
a_topic, a_partition)) {
long currentOffset = messageAndOffset.offset();
if (currentOffset < readOffset) {
System.out.println("Found an old offset: " + currentOffset
+ " Expecting: " + readOffset);
continue;
}
readOffset = messageAndOffset.nextOffset();
ByteBuffer payload = messageAndOffset.message().payload();
byte[] bytes = new byte[payload.limit()];
payload.get(bytes);
System.out.println(String.valueOf(messageAndOffset.offset())
+ ": " + new String(bytes, "UTF-8"));
numRead++;
a_maxReads--;
}
if (numRead == 0) {
try {
Thread.sleep(1000);
} catch (InterruptedException ie) {
}
}
}
if (consumer != null)
consumer.close();
}
public static long getLastOffset(SimpleConsumer consumer, String topic,
int partition, long whichTime, String clientName) {
TopicAndPartition topicAndPartition = new TopicAndPartition(topic,
partition);
Map<TopicAndPartition, PartitionOffsetRequestInfo> requestInfo = new HashMap<TopicAndPartition, PartitionOffsetRequestInfo>();
requestInfo.put(topicAndPartition, new PartitionOffsetRequestInfo(
whichTime, 1));
kafka.javaapi.OffsetRequest request = new kafka.javaapi.OffsetRequest(
requestInfo, kafka.api.OffsetRequest.CurrentVersion(),
clientName);
OffsetResponse response = consumer.getOffsetsBefore(request);
if (response.hasError()) {
System.out
.println("Error fetching data Offset Data the Broker. Reason: "
+ response.errorCode(topic, partition));
return 0;
}
long[] offsets = response.offsets(topic, partition);
return offsets[0];
}
private String findNewLeader(String a_oldLeader, String a_topic,
int a_partition, int a_port) throws Exception {
for (int i = 0; i < 3; i++) {
boolean goToSleep = false;
PartitionMetadata metadata = findLeader(m_replicaBrokers, a_port,
a_topic, a_partition);
if (metadata == null) {
goToSleep = true;
} else if (metadata.leader() == null) {
goToSleep = true;
} else if (a_oldLeader.equalsIgnoreCase(metadata.leader().host())
&& i == 0) {
// first time through if the leader hasn't changed give
// ZooKeeper a second to recover
// second time, assume the broker did recover before failover,
// or it was a non-Broker issue
//
goToSleep = true;
} else {
return metadata.leader().host();
}
if (goToSleep) {
try {
Thread.sleep(1000);
} catch (InterruptedException ie) {
}
}
}
System.out
.println("Unable to find new leader after Broker failure. Exiting");
throw new Exception(
"Unable to find new leader after Broker failure. Exiting");
}
private PartitionMetadata findLeader(List<String> a_seedBrokers,
int a_port, String a_topic, int a_partition) {
PartitionMetadata returnMetaData = null;
loop: for (String seed : a_seedBrokers) {
SimpleConsumer consumer = null;
try {
consumer = new SimpleConsumer(seed, a_port, 100000, 64 * 1024,
"leaderLookup");
List<String> topics = Collections.singletonList(a_topic);
TopicMetadataRequest req = new TopicMetadataRequest(topics);
TopicMetadataResponse resp = consumer.send(req);
List<TopicMetadata> metaData = resp.topicsMetadata();
for (TopicMetadata item : metaData) {
for (PartitionMetadata part : item.partitionsMetadata()) {
if (part.partitionId() == a_partition) {
returnMetaData = part;
break loop;
}
}
}
} catch (Exception e) {
System.out.println("Error communicating with Broker [" + seed
+ "] to find Leader for [" + a_topic + ", "
+ a_partition + "] Reason: " + e);
} finally {
if (consumer != null)
consumer.close();
}
}
if (returnMetaData != null) {
m_replicaBrokers.clear();
for (Broker replica : returnMetaData.replicas()) {
m_replicaBrokers.add(replica.host());
}
}
return returnMetaData;
}
}参考
https://cwiki.apache.org/confluence/display/KAFKA/0.8.0+SimpleConsumer+Example
