利用Kafka发送/消费消息-Java示例
当使用命令行工具把基本的组件运行起来后，再使用Java client就很简单，这里是入门的第一个Java客户端程序，有很多需要深入理解的地方。
依赖配置
<dependency>
<groupId>org.apache.kafka</groupId>
<artifactId>kafka_2.11</artifactId>
<version>0.8.2.1</version>
</dependency>注意kafka的artifact_Id（比如我用的kafka_2.11）后面的版本号一定要和本机装的Scala版本一致，否则会报以下错误。
Exception in thread "main" java.lang.NoClassDefFoundError: scala/collection/GenTraversableOnce$class
at kafka.utils.Pool.<init>(Pool.scala:28)
at kafka.consumer.ZookeeperConsumerConnector.<init>(ZookeeperConsumerConnector.scala:91)
at kafka.javaapi.consumer.ZookeeperConsumerConnector.<init>(ZookeeperConsumerConnector.scala:66)
at kafka.javaapi.consumer.ZookeeperConsumerConnector.<init>(ZookeeperConsumerConnector.scala:69)
at kafka.consumer.Consumer$.createJavaConsumerConnector(ConsumerConnector.scala:105)
at kafka.consumer.Consumer.createJavaConsumerConnector(ConsumerConnector.scala)
at com.vonzhou.learn.message.KafkaConsumer.<init>(KafkaConsumer.java:23)
at com.vonzhou.learn.message.KafkaConsumer.main(KafkaConsumer.java:72)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
Caused by: java.lang.ClassNotFoundException: scala.collection.GenTraversableOnce$class
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 13 moreProducer发送消息
public class MessageProducer {
private Producer<String,String> producer;
public static void main(String[] args) {
new MessageProducer().start();
}
public void init(){
Properties props = new Properties();
/**
* 用于自举（bootstrapping ），producer只是用它来获得元数据（topic, partition, replicas）
* 实际用户发送消息的socket会根据返回的元数据来确定
*/
props.put("metadata.broker.list", "localhost:9092");
/**
* 消息的序列化类
* 默认是 kafka.serializer.DefaultEncoder， 输入时 byte[] 返回是同样的字节数组
*/
props.put("serializer.class", "kafka.serializer.StringEncoder");
/**
* producer发送消息后是否等待broker的ACK，默认是0
* 1 表示等待ACK，保证消息的可靠性
*/
props.put("request.required.acks", "1");
ProducerConfig config = new ProducerConfig(props);
// 泛型参数分别表示 The first is the type of the Partition key, the second the type of the message
producer = new Producer<String, String>(config);
}
public void produceMsg(){
// 构建发送的消息
long timestamp = System.currentTimeMillis();
String msg = "Msg" + timestamp;
String topic = "test"; // 确保有这个topic
System.out.println("发送消息" + msg);
String key = "Msg-Key" + timestamp;
/**
* topic: 消息的主题
* key：消息的key，同时也会作为partition的key
* message:发送的消息
*/
KeyedMessage<String, String> data = new KeyedMessage<String, String>(topic, key, msg);
producer.send(data);
}
public void start() {
System.out.println("开始发送消息 ...");
Executors.newSingleThreadExecutor().execute(new Runnable() {
public void run() {
init();
while (true) {
try {
produceMsg();
Thread.sleep(2000);
} catch (Throwable e) {
if (producer != null) {
try {
producer.close();
} catch (Throwable e1) {
System.out.println("Turn off Kafka producer error! " + e);
}
}
}
}
}
});
}
}Consumer消费消息
public class MessageConsumer {
private ConsumerConnector consumer;
private String topic;
public static void main(String[] arg) {
new MessageConsumer().start();
}
public void init(){
// 指定 zookeeper 的地址
String zookeeper = "localhost:2181";
String topic = "test";
String groupId = "test-group";
Properties props = new Properties();
/**
* 必须的配置
*/
props.put("zookeeper.connect", zookeeper);
/**
* 必须的配置， 代表该消费者所属的 consumer group
*/
props.put("group.id", groupId);
/**
* 多长时间没有发送心跳信息到zookeeper就会认为其挂掉了，默认是6000
*/
props.put("zookeeper.session.timeout.ms", "6000");
/**
* 可以允许zookeeper follower 比 leader慢的时长
*/
props.put("zookeeper.sync.time.ms", "200");
/**
* 控制consumer offsets提交到zookeeper的频率， 默认是60 * 1000
*/
props.put("auto.commit.interval.ms", "1000");
consumer = Consumer.createJavaConsumerConnector(new ConsumerConfig(props));
this.topic = topic;
}
public void consume() {
Map<String, Integer> topicCountMap = new HashMap<String, Integer>();
topicCountMap.put(topic, 1);
/**
* createMessageStreams 为每个topic创建 message stream
*/
Map<String, List<KafkaStream<byte[], byte[]>>> messageStreams = consumer.createMessageStreams(topicCountMap);
KafkaStream<byte[], byte[]> stream = messageStreams.get(topic).get(0);
ConsumerIterator<byte[], byte[]> iterator = stream.iterator();
while (iterator.hasNext()) {
try {
String message = new String(iterator.next().message());
System.out.println("收到消息" + message);
} catch (Throwable e) {
System.out.println(e.getCause());
}
}
}
public void start() {
System.out.println("开始消费消息...");
Executors.newSingleThreadExecutor().execute(new Runnable() {
public void run() {
init();
while (true) {
try {
consume();
} catch (Throwable e) {
if (consumer != null) {
try {
consumer.shutdown();
} catch (Throwable e1) {
System.out.println("Turn off Kafka consumer error! " + e);
}
}
}
}
}
});
}
}