hdfs文件操作基本方法(1)

import org.apache.hadoop.conf.*;
import org.apache.hadoop.fs.*;
import org.apache.hadoop.hdfs.*;
import org.apache.hadoop.hdfs.protocol.*;
import java.util.Date;
public class DFSOperater {
/**
* @param args
*/
public static void main(String[] args) {
Configuration conf = new Configuration();
try {
// Get a list of all the nodes host names in the HDFS cluster
FileSystem fs = FileSystem.get(conf);
DistributedFileSystem hdfs = (DistributedFileSystem) fs;
DatanodeInfo[] dataNodeStats = hdfs.getDataNodeStats();
String[] names = new String[dataNodeStats.length];
System.out.println("list of all the nodes in HDFS cluster:"); // print
// info
for (int i = 0; i < dataNodeStats.length; i++) {
names[i] = dataNodeStats[i].getHostName();
System.out.println(names[i]); // print info
}
Path f = new Path("/user/cluster/dfs.txt");
// check if a file exists in HDFS
boolean isExists = fs.exists(f);
System.out.println("The file exists? [" + isExists + "]");
// if the file exist, delete it
if (isExists) {
boolean isDeleted = hdfs.delete(f, false);// fase : not
// recursive
if (isDeleted)
System.out.println("now delete " + f.getName());
}
// create and write
System.out.println("create and write [" + f.getName()
+ "] to hdfs:");
FSDataOutputStream os = fs.create(f, true, 0);
for (int i = 0; i < 10; i++) {
os.writeChars("test hdfs ");
}
os.writeChars("/n");
os.close();
// get the locations of a file in HDFS
System.out.println("locations of file in HDFS:");
FileStatus filestatus = fs.getFileStatus(f);
BlockLocation[] blkLocations = fs.getFileBlockLocations(filestatus,
0, filestatus.getLen());
int blkCount = blkLocations.length;
for (int i = 0; i < blkCount; i++) {
String[] hosts = blkLocations[i].getHosts();
// Do sth with the block hosts
System.out.println(hosts);
}
// get HDFS file last modification time
long modificationTime = filestatus.getModificationTime(); // measured
// in
// milliseconds
// since
// the
// epoch
Date d = new Date(modificationTime);
System.out.println(d);
// reading from HDFS
System.out.println("read [" + f.getName() + "] from hdfs:");
FSDataInputStream dis = fs.open(f);
System.out.println(dis.readUTF());
dis.close();
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
}
}
}