There are multiple ways of writing and reading a text file in Java. this is required while dealing with many applications. There are several ways to read a plain text file in Java e.g. you can use FileReader, BufferedReader, or Scanner to read a text file. Every utility provides something special e.g. BufferedReader provides buffering of data for fast reading, and Scanner provides parsing ability.
Methods:
- Using BufferedReader class
- Using Scanner class
- Using File Reader class
- Reading the whole file in a List
- Read a text file as String
We can also use both BufferReader and Scanner to read a text file line by line in Java. Then Java SE 8 introduces another Stream class java.util.stream.Stream which provides a lazy and more efficient way to read a file.
Tip Note: Practices of writing good code like flushing/closing streams, Exception-Handling etc, have been avoided for better understanding of codes by beginners as well.
Let us discuss each of the above methods to a deeper depth and most importantly by implementing them via a clean java program.
1. BufferedReader class for Reading text file
This method reads text from a character-input stream. It does buffer for efficient reading of characters, arrays, and lines. The buffer size may be specified, or the default size may be used. The default is large enough for most purposes. In general, each read request made of a Reader causes a corresponding read request to be made of the underlying character or byte stream. It is therefore advisable to wrap a BufferedReader around any Reader whose read() operations may be costly, such as FileReaders and InputStreamReaders as shown below as follows:
Syntax
BufferedReader in = new BufferedReader(Reader in, int size);
Example
Java
import java.io.*;
public class GFG {
public static void main(String[] args) throws Exception
{
File file = new File(
"C:\\Users\\pankaj\\Desktop\\test.txt");
BufferedReader br
= new BufferedReader(new FileReader(file));
String st;
while ((st = br.readLine()) != null)
System.out.println(st);
}
}
|
Output
If you want to code refer to GeeksforGeeks
2. FileReader class for Reading text file
Convenience class for reading character files. The constructors of this class assume that the default character encoding and the default byte-buffer size are appropriate.
Constructors defined in this class are as follows:
- FileReader(File file): Creates a new FileReader, given the File to read from
- FileReader(FileDescriptor fd): Creates a new FileReader, given the FileDescriptor to read from
- FileReader(String fileName): Creates a new FileReader, given the name of the file to read from
Example
Java
import java.io.*;
public class GFG {
public static void main(String[] args) throws Exception
{
FileReader fr = new FileReader(
"C:\\Users\\pankaj\\Desktop\\test.txt");
int i;
while ((i = fr.read()) != -1)
System.out.print((char)i);
}
}
|
Output
If you want to code refer to GeeksforGeeks
3. Scanner class for reading text file
A simple text scanner that can parse primitive types and strings using regular expressions. A Scanner breaks its input into tokens using a delimiter pattern, which by default matches whitespace. The resulting tokens may then be converted into values of different types using the various next methods.
Example 1: With using loops
Java
import java.io.File;
import java.util.Scanner;
public class ReadFromFileUsingScanner {
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());
}
}
|
Output
If you want to code refer to GeeksforGeeks
Example 2: Without using loops
Java
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class ReadingEntireFileWithoutLoop {
public static void main(String[] args)
throws FileNotFoundException
{
File file = new File(
"C:\\Users\\pankaj\\Desktop\\test.txt");
Scanner sc = new Scanner(file);
sc.useDelimiter("\\Z");
System.out.println(sc.next());
}
}
|
Output
If you want to code refer to GeeksforGeeks
4. Reading the whole file in a List
Read all lines from a file. This method ensures that the file is closed when all bytes have been read or an I/O error, or other runtime exception, is thrown. Bytes from the file are decoded into characters using the specified charset.
Syntax:
public static List readAllLines(Path path,Charset cs)throws IOException
This method recognizes the following as line terminators:
\u000D followed by \u000A, CARRIAGE RETURN followed by LINE FEED
\u000A, LINE FEED
\u000D, CARRIAGE RETURN
Example
Java
import java.io.*;
import java.nio.charset.StandardCharsets;
import java.nio.file.*;
import java.util.*;
public class ReadFileIntoList {
public static List<String>
readFileInList(String fileName)
{
List<String> lines = Collections.emptyList();
try {
lines = Files.readAllLines(
Paths.get(fileName),
StandardCharsets.UTF_8);
}
catch (IOException e) {
e.printStackTrace();
}
return lines;
}
public static void main(String[] args)
{
List l = readFileInList(
"C:\\Users\\pankaj\\Desktop\\test.java");
Iterator<String> itr = l.iterator();
while (itr.hasNext())
System.out.println(itr.next());
}
}
|
Output
If you want to code refer to GeeksforGeeks
5. Read a text file as String
Example
Java
package io;
import java.nio.file.*;
;
public class ReadTextAsString {
public static String readFileAsString(String fileName)
throws Exception
{
String data = "";
data = new String(
Files.readAllBytes(Paths.get(fileName)));
return data;
}
public static void main(String[] args) throws Exception
{
String data = readFileAsString(
"C:\\Users\\pankaj\\Desktop\\test.java");
System.out.println(data);
}
}
|
Output
If you want to code refer to GeeksforGeeks
This article is contributed by Pankaj Kumar. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.