Hadoop实验：用java直接使用FileSystem以标准输出格式显示Hadoop文件系统中的文件

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《Haoop权威指南》实验3.2

1.设置Hadoop的类目录，hadoop-env.sh

[hadoop@Master conf]$ cd /usr/hadoop/conf
[hadoop@Master conf]$ vim hadoop-env.sh

增加 export HADOOP_CLASSPATH=/usr/hadoop/myclass

2.设置搜索目录：使到运行javac，jps等程序时，省去打入一长串路径

[hadoop@Master hadoop]$ cd /home/hadoop/
[hadoop@Master ~]$ ls -a |grep .bash_profile
.bash_profile

[hadoop@Master ~]$ vim .bash_profile

3.编写java
[hadoop@Master ~]$ cd /usr/hadoop/myclass

[hadoop@Master myclass]$ vim FileSystemCat.java

import java.io.InputStream;import java.net.URI;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.FileSystem;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.IOUtils;public class FileSystemCat {        public static void main(String[] args) throws Exception {                String uri = args[0];                Configuration conf = new Configuration();                FileSystem fs = FileSystem.get(URI.create(uri), conf);                InputStream in = null;                try {                        in = fs.open(new Path(uri));                        IOUtils.copyBytes(in, System.out,4096,false);                } finally  {                IOUtils.closeStream(in);                }        }}

4.编译java

[hadoop@Master myclass]$ javac -classpath /usr/hadoop/hadoop-core-1.2.1.jar FileSystemCat.java

5.用java把hdfs系统里的文件内容读取出来，显示到屏幕

[hadoop@Master myclass]$ hadoop FileSystemCat hdfs://192.168.150.2:9000/user/hadoop/in/test1.txt

hello world

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