In this post we’ll see a Java program to read a file in HDFS. You can read a file in HDFS in two ways-
- Create an object of FSDataInputStream and use that object to read data from file. See example.
- You can use IOUtils class provided by Hadoop framework. See example.
Reading HDFS file Using FSDataInputStream
import java.io.IOException;
import java.io.OutputStream;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
public class HDFSFileRead {
public static void main(String[] args) {
Configuration conf = new Configuration();
FSDataInputStream in = null;
OutputStream out = null;
try {
FileSystem fs = FileSystem.get(conf);
// Input file path
Path inFile = new Path(args[0]);
// Check if file exists at the given location
if (!fs.exists(inFile)) {
System.out.println("Input file not found");
throw new IOException("Input file not found");
}
// open and read from file
in = fs.open(inFile);
//displaying file content on terminal
out = System.out;
byte buffer[] = new byte[256];
int bytesRead = 0;
while ((bytesRead = in.read(buffer)) > 0) {
out.write(buffer, 0, bytesRead);
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally {
// Closing streams
try {
if(in != null) {
in.close();
}
if(out != null) {
out.close();
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
In order to execute this program you need to add the class path to the Hadoop’s classpath.
export HADOOP_CLASSPATH=<PATH TO .class FILE>
To run program- hadoop org.netjs.HDFSFileRead /user/process/display.txt
Reading HDFS file Using IOUtils class
import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IOUtils;
public class HDFSFileRead {
public static void main(String[] args) {
Configuration conf = new Configuration();
FSDataInputStream in = null;
//OutputStream out = null;
try {
FileSystem fs = FileSystem.get(conf);
// Input file path
Path inFile = new Path(args[0]);
// Check if file exists at the given location
if (!fs.exists(inFile)) {
System.out.println("Input file not found");
throw new IOException("Input file not found");
}
in = fs.open(inFile);
IOUtils.copyBytes(in, System.out, 512, false);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally {
IOUtils.closeStream(in);
}
}
}
That's all for this topic Java Program to Read File in HDFS. If you have any doubt or any suggestions to make please drop a comment. Thanks!
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