报错：Exception in thread "main" java.lang.NoClassDefFoundError: Lorg/apache/hadoop/fs/FileSystem

报错现象：

Exception in thread "main" java.lang.NoClassDefFoundError: Lorg/apache/hadoop/fs/FileSystem;
    at java.lang.Class.getDeclaredFields0(Native Method)
    at java.lang.Class.privateGetDeclaredFields(Class.java:2583)
    at java.lang.Class.getDeclaredFields(Class.java:1916)
    at org.apache.flink.api.java.ClosureCleaner.clean(ClosureCleaner.java:72)
    at org.apache.flink.streaming.api.environment.StreamExecutionEnvironment.clean(StreamExecutionEnvironment.java:1560)
    at org.apache.flink.streaming.api.datastream.DataStream.clean(DataStream.java:185)
    at org.apache.flink.streaming.api.datastream.DataStream.addSink(DataStream.java:1191)
    at KafkaHadoop.main(KafkaHadoop.java:46)
Caused by: java.lang.ClassNotFoundException: org.apache.hadoop.fs.FileSystem
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:335)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 8 more

过程解释：

当时我是在做kafka+flink+hadoop数据存取的功能，一直在报这个错，代码也没有问题，困扰了很长时间。

解决过程:

第一步：我怀疑是依赖冲突问题，于是将关于hadoop的pom依赖给一一注释掉，发现做完之后还是报错；

第二步：我开始怀疑是没有这个jar包，但是当我去MVNREPOSITORY网站搜索关于org.apache.hadoop.fs.FileSystem的依赖时，搜索到了一下几个依赖：

　　       hadoop-hdfs、flink-connector-filesystem_2.11、flink-hadoop-fs 相关的，但是放上去之后发现并没有什么卵用；

第三步：于是我就开始百度 org.apache.hadoop.fs.FileSystem 相关信息，

（1）找到了下面这个网站入口：

（2）点进去发现：

（3）然后点了进去：

 

虽然看不懂，但是我感觉很有可能就是在下面这几个jar包中，于是我就去MVNREPOSITORY网站搜索hadoop-core,

        <!-- https://mvnrepository.com/artifact/org.apache.hadoop/hadoop-core -->
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-core</artifactId>
            <version>1.1.0</version>
        </dependency>

将这个依赖加了进去，然后报错解决。

完整pom：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>yk.bigdate</groupId>
    <artifactId>flinkHDFS</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <flink.version>1.6.1</flink.version>
        <slf4j.version>1.7.7</slf4j.version>
        <log4j.version>1.2.17</log4j.version>
    </properties>

    <dependencies>
        <!--******************* flink *******************-->
        <dependency>
            <groupId>org.apache.flink</groupId>
            <artifactId>flink-java</artifactId>
            <version>${flink.version}</version>
        </dependency>
        <dependency>
            <groupId>org.apache.flink</groupId>
            <artifactId>flink-streaming-java_2.11</artifactId>
            <version>${flink.version}</version>
        </dependency>
<!--        <dependency>
            <groupId>org.apache.flink</groupId>
            <artifactId>flink-clients_2.11</artifactId>
            <version>${flink.version}</version>
        </dependency>-->
        <dependency>
            <groupId>org.apache.flink</groupId>
            <artifactId>flink-connector-kafka-0.11_2.11</artifactId>
            <version>${flink.version}</version>
            <scope> compile</scope>
        </dependency>
        <dependency>
            <groupId>org.apache.flink</groupId>
            <artifactId>flink-connector-filesystem_2.11</artifactId>
            <version>${flink.version}</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.apache.hadoop/hadoop-core -->
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-core</artifactId>
            <version>1.1.0</version>
        </dependency>
        <!--******************* kafka *******************-->
        <dependency>
            <groupId>org.apache.kafka</groupId>
            <artifactId>kafka-clients</artifactId>
            <version>1.1.1</version>
        </dependency>

    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.3</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
            <!--打jar包-->
            <plugin>
                <artifactId>maven-assembly-plugin</artifactId>
                <configuration>
                    <archive>
                        <manifest>
                            <mainClass>com.allen.capturewebdata.Main</mainClass>
                        </manifest>
                    </archive>
                    <descriptorRefs>
                        <descriptorRef>jar-with-dependencies</descriptorRef>
                    </descriptorRefs>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>