There are many times during our project work we need to read a text file in java. There are many ways to read a text file in java. One can use FileReader, BufferedReader and Scanner to read a text file.
Java 8 introduced Stream class java.util.stream.Stream which gives a lazy and more efficient way to read a file line by line.
BufferedReader uses buffering of data for very fast reading.
Reading a text file using BufferedReader
BufferedReader is very simple and high performance technique of reading text files in Java. It reads the text from a character input stream. It does the buffering of characters, arrays and lines for efficient reading.
The buffer size can be specified or the default size can be used.
package ReadFile;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
public class BufferedReaderExample
{
public static void main(String[] args)throws Exception
{
//place where file is located. double backward slash should be used.
File file = new File("C:\\Users\\Desktop\\test.txt");
BufferedReader br = new BufferedReader(new FileReader(file));
String string;
while ((string = br.readLine()) != null)
System.out.println(string);
}
}Using try with resource and nio
package ReadFile;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
public class BufferedReaderExample {
public static void main(String[] args) throws Exception {
//using class of nio file package
Path filePath = Paths.get("C:\\Users\\Desktop\\test.txt");
//converting to UTF 8
Charset charset = StandardCharsets.UTF_8;
//try with resource
try (BufferedReader bufferedReader = Files.newBufferedReader(filePath, charset)) {
String line;
while ((line = bufferedReader.readLine()) != null) {
System.out.println(line);
}
} catch (IOException ex) {
System.out.format("I/O exception: ", ex);
}
}
}Reading a text file using FileReader
FileReader is used for reading streams of characters. For reading streams of raw bytes, try using a FileInputStream.
package ReadFile;
import java.io.FileReader;
public class FileReaderExample {
public static void main(String[] args) throws Exception {
FileReader fileReader = new FileReader("C:\\Users\\Desktop\\test.txt");
int i;
while ((i = fileReader.read()) != -1)
System.out.print((char) i);
}
}Reading a text file using Scanner
package ReadFile;
import java.io.File;
import java.io.FileReader;
import java.util.Scanner;
public class ScannerReaderExample {
public static void main(String[] args) throws Exception {
File file = new File("C:\\Users\\pankaj\\Desktop\\test.txt");
Scanner sc = new Scanner(file);
while (sc.hasNextLine())
System.out.println(sc.nextLine());
}
}Java read file line by line using Files.readAllLines()
Files.readAllLines() is a method of the Java NIO Files class which reads all the lines of a file and then returns a List<String> containing each line. Internally it uses BufferedReader to read the file.
package ReadFile;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.List;
public class ReaderExample {
public static void main(String[] args) throws Exception {
Path filePath = Paths.get("c://test.txt");
Charset charset = StandardCharsets.UTF_8;
try {
List<String> lines = Files.readAllLines(filePath, charset);
for (String line : lines) {
System.out.println(line);
}
} catch (IOException ex) {
System.out.format("I/O Exception", ex);
}
}
}Java read file line by line using Files.lines()
Files.lines() method reads all the lines from the file as Stream. Stream API methods can be used like forEach, map to get record with each line of the file.
package ReadFile;
import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
public class ReaderExample {
public static void main(String[] args) throws Exception {
Path filePath = Paths.get("c://demo.txt");
Charset charset = StandardCharsets.UTF_8;
try {
//converting to stream
Files.lines(filePath, charset).forEach(System.out::println);
} catch (IOException ex) {
System.out.format("I/O Exception:", ex);
}
}
}Java read file into byte using Files.readAllBytes()
It reads all bytes from a file.
This method ensures that file is closed when all bytes had been read or an I/O error, or other runtime exception, is thrown.
This method should be used for simple needs where it is easy to read all bytes into a byte array. It should not be used for reading in large files.
It throws
IOException – if an I/O error occurs while reading from the stream
OutOfMemoryError – If file size is more than 2 GB then this error will be thrown.
SecurityException –checkRead method will be invoked to check read access to the file.
package ReadFile;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
public class ReaderExample {
public static void main(String[] args) throws Exception {try {
byte[] data = Files.readAllBytes(Paths.get("C:\\Users\\Desktop\\test.txt"));
// Use byte data
System.out.println(new String(data));
} catch (IOException ex) {
System.out.format("I/O Exception ", ex);
}}
}Conclusion
That’s all readers. You have learned how to read a text file in java.
