Question

我正在尝试从包含json数据的kafka主题中读取并根据字段“entity”的值写入新主题。我正在使用以下代码从kafka读取和写入

import org.apache.kafka.common.serialization.Serde;
import org.apache.kafka.common.serialization.Serdes;
import org.apache.kafka.streams.KafkaStreams;
import org.apache.kafka.streams.KeyValue;
import org.apache.kafka.streams.StreamsConfig;
import org.apache.kafka.streams.kstream.KStream;
import org.apache.kafka.streams.kstream.KStreamBuilder;
import java.util.Properties;

public class entityDataLoader {
public static void main(final String[] args) throws Exception {
final Properties streamsConfiguration = new Properties();
streamsConfiguration.put(StreamsConfig.APPLICATION_ID_CONFIG, "map-function-lambda-example");
streamsConfiguration.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
streamsConfiguration.put(StreamsConfig.KEY_SERDE_CLASS_CONFIG, Serdes.ByteArray().getClass().getName());
streamsConfiguration.put(StreamsConfig.VALUE_SERDE_CLASS_CONFIG, Serdes.String().getClass().getName());

// Set up serializers and deserializers, which we will use for overriding the default serdes
// specified above.
final Serde<String> stringSerde = Serdes.String();
final Serde<byte[]> byteArraySerde = Serdes.ByteArray();

// In the subsequent lines we define the processing topology of the Streams application.
final KStreamBuilder builder = new KStreamBuilder();

// Read the input Kafka topic into a KStream instance.
final KStream<byte[], String> textLines = builder.stream(byteArraySerde, stringSerde, "postilion-events");

String content = textLines.toString();
String entity = JSONExtractor.returnJSONValue(content, "entity");
System.out.println(entity);

textLines.to(entity);

final KafkaStreams streams = new KafkaStreams(builder, streamsConfiguration);
streams.cleanUp();
streams.start();

// Add shutdown hook to respond to SIGTERM and gracefully close Kafka Streams
Runtime.getRuntime().addShutdownHook(new Thread(streams::close));
}
}

如何成功运行此应用程序？

使用Netbeans，我使用依赖项构建并将jar文件放在/ home / kafka路径中，并尝试将其作为类路径运行并指定我创建的类（使用命令java -cp mavenproject.jar postilionkafka.entityDataLoader）。我收到以下错误

Error: A JNI error has occurred, please check your installation and try again
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/kafka/streams/processor/TopologyBuilder
    at java.lang.Class.getDeclaredMethods0(Native Method)
    at java.lang.Class.privateGetDeclaredMethods(Class.java:2701)
    at java.lang.Class.privateGetMethodRecursive(Class.java:3048)
    at java.lang.Class.getMethod0(Class.java:3018)
    at java.lang.Class.getMethod(Class.java:1784)
    at sun.launcher.LauncherHelper.validateMainClass(LauncherHelper.java:544)
    at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:526)
Caused by: java.lang.ClassNotFoundException: org.apache.kafka.streams.processor.TopologyBuilder
    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)
    ... 7 more

感谢@James，我已经能够解决这个问题了。我无法从主题中的记录中提取实体数据。主题中的记录是JSON，示例是{"date":{"string":"2017-03-20"},"time":{"string":"20:04:13:563"},"event_nr":1572470,"interface":"Transaction Manager","event_id":5001,"date_time":1490040253563,"entity":"Transaction Manager","state":0,"msg_param_1":{"string":"ISWSnk"},"msg_param_2":{"string":"Application startup"},"msg_param_3":null,"msg_param_4":null,"msg_param_5":null,"msg_param_6":null,"msg_param_7":null,"msg_param_8":null,"msg_param_9":null,"long_msg_param_1":null,"long_msg_param_2":null,"long_msg_param_3":null,"long_msg_param_4":null,"long_msg_param_5":null,"long_msg_param_6":null,"long_msg_param_7":null,"long_msg_param_8":null,"long_msg_param_9":null,"last_sent":{"long":1490040253563},"transmit_count":{"int":1},"team_id":null,"app_id":{"int":4},"logged_by_app_id":{"int":4},"entity_type":{"int":3},"binary_data":null}

我想根据实体字段的值写一个主题（对于下面的json示例，它应该写入主题事务管理器。如果我运行我当前的代码，我会得到以下错误

SLF4J：无法加载类“org.slf4j.impl.StaticLoggerBinder”。 SLF4J：默认为无操作（NOP）记录器实现 SLF4J：有关详细信息，请参阅http://www.slf4j.org/codes.html#StaticLoggerBinder。 org.apache.kafka.streams.kstream.internals.KStreamImpl@568db2f2 找不到对象位置0处的意外字符（o）。空值线程“main”中的异常java.lang.NullPointerException：topic不能为null at java.util.Objects.requireNonNull（Objects.java:228）在org.apache.kafka.streams.kstream.internals.KStreamImpl.to（KStreamImpl.java:353）在org.apache.kafka.streams.kstream.internals.KStreamImpl.to（KStreamImpl.java:337） at postilionkafka.dataload.main（dataload.java:35）

JSONExtractor类定义为

import org.json.simple.JSONObject;
import org.json.simple.parser.ParseException;
import org.json.simple.parser.JSONParser;
class JSONExtractor {

/**
 *
 */
public static String returnJSONValue(String args, String value){
    JSONParser parser = new JSONParser();
    String app= null;
    System.out.println(args);
    try{
        Object obj = parser.parse(args);
        JSONObject JObj = (JSONObject)obj;
        app= (String) JObj.get(value);
        return app;
    }
    catch(ParseException pe){
        System.out.println("No Object found");
        System.out.println(pe);
    }
    return app;
}
}

Answer 1

这看起来像一个简单的类路径问题，尝试在classpath参数中添加非标准java的所有jar，例如：

java -cp kafka-stream.jar:mavenproject.jar postilionkafka.entityDataLoader

这很快就会变得过于复杂，这也是我们使用Maven来管理依赖关系的原因之一。我通常直接从IDE运行我正在处理的任何应用程序，这也是一种更简单的调试方法。如果我必须在我的IDE之外启动，我仍然会尝试从我的IDE，IntelliJ注销包含所需依赖项的执行命令，并节省我重新建立那些可能是什么以及如何从我的提取它们的时间当地的maven回购。

如果从IDE运行的替代方法对您不起作用，则使用Maven exec。请参阅running a project from maven上的此答案。

运行自定义构建的Kafka流DSL应用程序返回java.lang.ClassNotFoundException

1 个答案: