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
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.
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 Program to illustrate Reading
from FileReader
// using BufferedReader Class
// Importing input output classes
import java.io.*;
// Main class
public class GFG {
// main driver method
public static void main(String[] args)
throws Exception
{
// File path is passed as parameter
File file = new File(
"C:\\Users\\pankaj\\Desktop\\test.txt");
// Note: Double backquote is to avoid compiler
// interpret words
// like \test as \t (ie. as a escape sequence)
// Creating an object of BufferedReader class
BufferedReader br
= new BufferedReader(new FileReader(file));
// Declaring a string variable
String st;
// Condition holds true till
// there is character in a string
while ((st = br.readLine()) != null)
// Print the string
System.out.println(st);
}
}
Output
If you want to code refer to javaprogramer
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 Program to Illustrate reading from
// FileReader using FileReader class
// Importing input output classes
import java.io.*;
// Main class
// ReadingFromFile
public class GFG {
// Main driver method
public static void main(String[] args)
throws Exception
{
// Passing the path to the file as a parameter
FileReader fr = new FileReader(
"C:\\Users\\pankaj\\Desktop\\test.txt");
// Declaring loop variable
int i;
// Holds true till there is nothing to read
while ((i = fr.read()) != -1)
// Print all the content of a file
System.out.print((char)i);
}
}
Output
If you want to code refer to javaprogramer
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
Example
// Java Program to illustrate
// reading from Text File
// using Scanner Class
import java.io.File;
import java.util.Scanner;
public class ReadFromFileUsingScanner {
public static void main(String[] args)
throws Exception
{
// pass the path to the file as a parameter
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 javaprogramer
Example 2: Without using loops
// Java Program to illustrate reading
from FileReader
// using Scanner Class reading entire File
// without using loop
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);
// we just need to use \\Z as delimiter
sc.useDelimiter("\\Z");
System.out.println(sc.next());
}
}
Output
If you want to code refer to javaprogramer
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<br>
\u000A, LINE FEED
\u000D, CARRIAGE RETURN
Example
// Java program to illustrate reading
data from file
// using nio.File
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) {
// do something
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 javaprogramer
5. Read a text file as String
Example
// Java Program to illustrate
// reading from text file
// as string in 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 javaprogramer
