Hadoop格式化namenode时候，出现Java异常：URI has an authority component问题的解决

在执行命令：

hdfs namenode -formate

时候，出现错误，提示：

17/07/06 10:07:39 INFO metrics.TopMetrics: NNTop conf: dfs.namenode.top.num.users = 10
17/07/06 10:07:39 INFO metrics.TopMetrics: NNTop conf: dfs.namenode.top.windows.minutes = 1,5,25
17/07/06 10:07:39 INFO namenode.FSNamesystem: Retry cache on namenode is enabled
17/07/06 10:07:39 INFO namenode.FSNamesystem: Retry cache will use 0.03 of total heap and retry cache entry expiry time is 600000 millis
17/07/06 10:07:39 INFO util.GSet: Computing capacity for map NameNodeRetryCache
17/07/06 10:07:39 INFO util.GSet: VM type       = 64-bit
17/07/06 10:07:39 INFO util.GSet: 0.029999999329447746% max memory 966.7 MB = 297.0 KB
17/07/06 10:07:39 INFO util.GSet: capacity      = 2^15 = 32768 entries
17/07/06 10:07:39 ERROR namenode.NameNode: Failed to start namenode.
java.lang.IllegalArgumentException: URI has an authority component
at java.io.File.<init>(File.java:423)
at org.apache.hadoop.hdfs.server.namenode.NNStorage.getStorageDirectory(NNStorage.java:329)
at org.apache.hadoop.hdfs.server.namenode.FSEditLog.initJournals(FSEditLog.java:276)
at org.apache.hadoop.hdfs.server.namenode.FSEditLog.initJournalsForWrite(FSEditLog.java:247)
at org.apache.hadoop.hdfs.server.namenode.NameNode.format(NameNode.java:986)
at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:1434)
at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:1559)

这个问题是因为配置hdfs-site.xml文件出现错误时候产生的：

默认的hdfs-site.xml的配置文件参数是：

<property>
<name>df
4000
s.namenode.name.dir</name>
<value>file://${hadoop.tmp.dir}/dfs/name</value>
<description>Determines where on the local filesystem the DFS name node
should store the name table(fsimage).  If this is a comma-delimited list
of directories then the name table is replicated in all of the
directories, for redundancy. </description>
</property>

将其改为具体的hadoop文件路径，想必这个大家也都知道，是在core-site.xml中配置的，默认的路径是在tmp文件夹下的，我们都会更改这个路径，很重要，也很基础的。

对于我的机器，改为

<property>
<name>dfs.namenode.name.dir</name>
<value>file:/~/hadoop_tmp/dfs/name</value>
<description>Determines where on the local filesystem the DFS name node
should store the name table(fsimage).  If this is a comma-delimited list
of directories then the name table is replicated in all of the
directories, for redundancy. </description>
</property>

这里file://原来是双斜杠，我仿照网上的博文改为单斜杠，双斜杠能不能用，我也不知道，大家可以自己试一试。