Maven中配置Hadoop 2.x版本

这几天在学习Hadoop，下载的是2.9.0的版本。期间，遇到了很多问题，其中有一个问题是在Intellij IDEA中配置Maven依赖项时遇到的。在网上的教程里，配置方式如下：

<dependencies>
    <dependency>
        <groupId>org.apache.hadoopgroupId>
        <artifactId>hadoop-coreartifactId>
        <version>1.2.1version>
    dependency>
    <dependency>
        <groupId>org.apache.hadoopgroupId>
        <artifactId>hadoop-commonartifactId>
        <version>2.7.2version>
    dependency>
dependencies>

但是这样的配置在运行时报了如下错误：

Exception in thread "main" org.apache.hadoop.ipc.RemoteException: Server IPC version 9 cannot communicate with client version 4
    at org.apache.hadoop.ipc.Client.call(Client.java:1113)
    at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:229)
    at com.sun.proxy.$Proxy1.getProtocolVersion(Unknown Source)
    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:498)
    at com.sun.proxy.$Proxy1.getProtocolVersion(Unknown Source)
    at org.apache.hadoop.ipc.RPC.checkVersion(RPC.java:422)
    at org.apache.hadoop.hdfs.DFSClient.createNamenode(DFSClient.java:183)
    at org.apache.hadoop.hdfs.DFSClient.(DFSClient.java:281)
    at org.apache.hadoop.hdfs.DFSClient.(DFSClient.java:245)
    at org.apache.hadoop.hdfs.DistributedFileSystem.initialize(DistributedFileSystem.java:100)
    at org.apache.hadoop.fs.FileSystem.createFileSystem(FileSystem.java:1446)
    at org.apache.hadoop.fs.FileSystem.access$200(FileSystem.java:67)
    at org.apache.hadoop.fs.FileSystem$Cache.get(FileSystem.java:1464)
    at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:263)
    at org.apache.hadoop.fs.Path.getFileSystem(Path.java:187)
    at Main.main(Main.java:20)

这是因为，我在配置中使用的hadoop-core项还是1.2.1版本的，早已不支持Hadoop 2.9.0。而且由于Hadoop配置方式变更，上述问题不能通过改变hadoop-core版本解决。正确方式是使用hadoop-client和hadoop-hdfs两个依赖项取代hadoop-core。配置方式如下:

<dependencies>
    <dependency>
        <groupId>org.apache.hadoopgroupId>
        <artifactId>hadoop-hdfsartifactId>
        <version>2.9.0version>
    dependency>

    <dependency>
        <groupId>org.apache.hadoopgroupId>
        <artifactId>hadoop-clientartifactId>
        <version>2.9.0version>
    dependency>

    <dependency>
        <groupId>org.apache.hadoopgroupId>
        <artifactId>hadoop-commonartifactId>
        <version>2.9.0version>
    dependency>
dependencies>

这下子就不会出以上问题了。