Hadoop 学习笔记（二） HDFS API

4.删除HDFS上的文件

package proj;



import java.io.IOException;



import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.fs.FileSystem;

import org.apache.hadoop.fs.Path;



public class DeleteFile {



    public static void main(String[] args) throws IOException {

        Configuration conf = new Configuration();

        //要点：没有这句会传到本地文件系统，而不是hdfs

        conf.set("fs.default.name","hdfs://localhost:9000");

        FileSystem hdfs = FileSystem.get(conf);

        Path delef = new Path("in/test3.txt");

        boolean isDeleted = hdfs.delete(delef, false);

        //递归删除

        //boolean isDelete = hdfs.delete(delef, true);

        System.out.println("delete? "+ isDeleted);

    }



}

 

检查文件是否存在
package proj;



import java.io.IOException;



import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.fs.FileSystem;

import org.apache.hadoop.fs.Path;



public class CheckFile {



    public static void main(String[] args) throws IOException {

        Configuration conf = new Configuration();

        //要点：没有这句会传到本地文件系统，而不是hdfs

        conf.set("fs.default.name","hdfs://localhost:9000");

        FileSystem hdfs = FileSystem.get(conf);

        Path findf = new Path("in/hello.c");

        boolean exist = hdfs.exists(findf);

        System.out.println("exist ? " + exist);

        

    }



}

 

查找某个文件在HDFS集群的位置
package proj;



import java.io.IOException;



import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.fs.BlockLocation;

import org.apache.hadoop.fs.FileStatus;

import org.apache.hadoop.fs.FileSystem;

import org.apache.hadoop.fs.Path;



public class FileLocal {

    public static void main(String[] args) throws IOException{

        Configuration conf = new Configuration();

        //要点：没有这句会传到本地文件系统，而不是hdfs

        conf.set("fs.default.name","hdfs://localhost:9000");

        FileSystem hdfs = FileSystem.get(conf);

        Path fpath = new Path("in/hello.c");

        

        FileStatus filestatus = hdfs.getFileStatus(fpath);

        BlockLocation[] blkLocations = hdfs.getFileBlockLocations(filestatus, 0, filestatus.getLen());

        int blockLen = blkLocations.length;

        for (int i = 0; i < blockLen; i++) {

            String[] hosts = blkLocations[i].getHosts();

            System.out.println("block "+i+" location "+ hosts[i]);

        }

    }

}

获取HDFS集群上所有节点名称
package proj;



import java.io.IOException;



import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.fs.FileSystem;

import org.apache.hadoop.fs.Path;

import org.apache.hadoop.hdfs.DistributedFileSystem;

import org.apache.hadoop.hdfs.protocol.DatanodeInfo;



public class GetList {



    public static void main(String[] args) throws IOException {



        Configuration conf = new Configuration();

        //要点：没有这句会传到本地文件系统，而不是hdfs

        conf.set("fs.default.name","hdfs://localhost:9000");

        FileSystem fs = FileSystem.get(conf);

        DistributedFileSystem hdfs = (DistributedFileSystem)fs;

        DatanodeInfo[] dataNodeStats = hdfs.getDataNodeStats();

        String[] names = new String[dataNodeStats.length];

        for (int i = 0; i < dataNodeStats.length; i++) {

            names[i] = dataNodeStats[i].getHostName();

            System.out.println("node " + i + " name " + names[i]);

        }

    }



}