在本地执行示例Flink程序

Question

我试图在本地模式下在Apache Flink中执行示例程序.

import org.apache.flink.api.common.functions.FlatMapFunction;
import org.apache.flink.api.java.DataSet;
import org.apache.flink.api.java.ExecutionEnvironment;
import org.apache.flink.api.java.tuple.Tuple2;
import org.apache.flink.util.Collector;


public class WordCountExample {
    public static void main(String[] args) throws Exception {
        final ExecutionEnvironment env = ExecutionEnvironment.getExecutionEnvironment();

        DataSet<String> text = env.fromElements(
            "Who's there?",
            "I think I hear them. Stand, ho! Who's there?");
        //DataSet<String> text1 = env.readTextFile(args[0]);

        DataSet<Tuple2<String, Integer>> wordCounts = text
            .flatMap(new LineSplitter())
            .groupBy(0)
            .sum(1);

        wordCounts.print();
        env.execute();

        env.execute("Word Count Example");
    }

    public static class LineSplitter implements FlatMapFunction<String, Tuple2<String, Integer>> {
        @Override
        public void flatMap(String line, Collector<Tuple2<String, Integer>> out) {
            for (String word : line.split(" ")) {
                out.collect(new Tuple2<String, Integer>(word, 1));
            }
        }
    }
}

它给了我例外:

    Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/hadoop/mapreduce/InputFormat
    at WordCountExample.main(WordCountExample.java:10)
Caused by: java.lang.ClassNotFoundException: org.apache.hadoop.mapreduce.InputFormat
    at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
    ... 1 more

我究竟做错了什么？

我也使用过正确的罐子. flink-java-0.9.0-milestone-1.jar flink-clients-0.9.0-milestone-1.jar flink-core-0.9.0-milestone-1.jar

Answer 1

在项目中添加三个Flink Jar文件作为依赖项是不够的,因为它们具有其他传递依赖性,例如在Hadoop上.

获得开发(和本地执行)Flink程序的工作设置的最简单方法是遵循使用Maven原型配置Maven项目的快速入门指南.可以将此Maven项目导入IDE.

Answer 2

NoClassDefFoundError 扩展了 LinkageError

如果 Java 虚拟机或 ClassLoader 实例尝试加载类的定义（作为普通方法调用的一部分或作为使用 new 表达式创建新实例的一部分）并且找不到该类的定义，则抛出此异常。搜索到的类定义在编译当前执行的类时就已存在，但无法再找到该定义。

您的代码/jar 依赖于 hadoop。在这里找到它下载 jar 文件并将其添加到您的类路径org.apache.hadoop.mapreduce.InputFormat中