hadoop通过java输出HAFS上的文件内容

package org.apache.hadoop.book;
import java.io.InputStream;
import java.net.URL;
import org.apache.hadoop.fs.FsUrlStreamHandlerFactory;
import org.apache.hadoop.io.IOUtils;
 
public class URLCat {
 
  static {
    URL.setURLStreamHandlerFactory(new FsUrlStreamHandlerFactory());
  }
 
  public static void main(String[] args) throws Exception {
    InputStream in = null;
    try {
      in = new URL(args[0]).openStream();
      IOUtils.copyBytes(in, System.out, 4096, false);
    } finally {
      IOUtils.closeStream(in);
    }
  }
}
/*1，创建目录class，并编译

[root@centos7 class]# pwd
    root/hadoop-2.9.2/class　　　　注:class一般在hadoop的安装目录下
    [root@centos7 java]#javac -classpath /home/hdc/user/hadoop-2.9.1/share/hadoop/common/hadoop-common-2.9.1.jar -d ${HADOOP_HOME}/class URLCat.java

　　　　　　　　　　 (javac -classpath /home/hdc/user/hadoop-2.9.1/share/hadoop/common/hadoop-common-2.9.1.jar:/home/hdc/user/hadoop-2.9.1/share/hadoop/mapreduce/hadoop-mapreduce-client-core-2.9.1.jar:/home/hdc/user/hadoop-2.9.1/share/hadoop/common/lib/commons-cli-1.2.jar -d ${HADOOP_HOME}/class *.java )
 2，打包
     jar -cvf URLCat.jar ./org/apache/hadoop/book/URLCat.class
 3,配置环境
     export HADOOP_CLASSPATH=/home/hdc/user/hadoop-2.9.1/class
 4,执行
     hadoop org.apache.hadoop.book.URLCat hdfs://localhost:9000/hdc/test

　 (hadoop jar MaxTemperature.jar temperature.MaxTemperature /program/maxtemperature/input /program/maxtemperature/output)

　(

　　　　jar -cvf WordCount.jar ~/eclipse-workspace/WordCount/bin/WordCount*.class　　//有三个.class文件分别是WordCount.class，WordCountMapper.class，WordCountReducer.class

　　　　hadoop jar ~/eclipse-workspace/WordCount/bin/WordCount.jar WordCount /hdc/input_1/word /program_output/wordcount_out

　　　　主要参考教程：http://dblab.xmu.edu.cn/blog/hadoop-build-project-by-shell/

　)
 */