什么时间使用高级应用？

1. 针对一个消息读取多次
2. 在一个process中，仅仅处理一个topic中的一组partitions
3. 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）

1. 在应用程序中跟踪上次消息处理的offset
2. 确定一个topic partition的lead broker
3. 手工处理broker leander的改变

使用底层函数（SimpleConsumer）开发的步骤

1.  通过active broker,确定topic partition的lead broker
2. 确定topic partition的replicat brokers
3. 根据需要，创建数据请求
4. 抓取数据
5. 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 = http://www.mamicode.com/findLeader(a_seedBrokers, a_port, a_topic,> 

 参考 
 
 https://cwiki.apache.org/confluence/display/KAFKA/0.8.0+SimpleConsumer+Example