Java Program to Read a text file and Write to Another file

package com.demo.file;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class CopyExample {
	public static void main(String[] args) {
		FileInputStream instream = null;
		FileOutputStream outstream = null;

		try {
			File infile = new File("C://java_examples//input.txt");
			File outfile = new File("C://java_examples//output.txt");

			instream = new FileInputStream(infile);
			outstream = new FileOutputStream(outfile);

			byte[] buffer = new byte[1024];

			int length;
			/*
			 * copying the contents from input stream to output stream using
			 * read and write methods
			 */
			while ((length = instream.read(buffer)) > 0) {
				outstream.write(buffer, 0, length);
			}
			

			// Closing the input stream
			instream.close();
			// Closing the output stream			
			outstream.close();

			System.out.println("File copied successfully!!");

		} catch (IOException e) {
			//print Exception
			e.printStackTrace();
		}
	}
}

Output :

File copied successfully!!

Read method

public int read(byte b[]) throws IOException

This reads up to b.length bytes of data from this input stream into an array of bytes. This method blocks until some input is available.

Parameters: buffer b into which the data is read.
Returns: it is return total number of bytes read into the buffer, otherwise -1 if there is no more data because the end of the file has been reached.
It is throws IOException if an I/O error occurs.

Write() Method

public void write(byte b[], int off, int len) throws IOException

This method writes len bytes from the specified byte array starting at offset off to this file output stream.

Copy one file to another Using Using BufferedReader and BufferedWriter

We read content of file using readLine() method of BufferedReader . We will write copy content into another file using write() method of BufferedWriter.

package com.demo.file;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;

public class CopyExample2 {
	public static void main(String[] args) {
		String source = "C://java_examples//input.txt";
		String dest = "C://java_examples//output.txt";
		try {
			File inputfile = new File(source);
			FileInputStream fileInputStream = new FileInputStream(inputfile);
			BufferedReader bufferedReader = new BufferedReader(
					new InputStreamReader(fileInputStream));

			FileWriter fileWriter = new FileWriter(dest, true);
			BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);

			String aLine = null;
			while ((aLine = bufferedReader.readLine()) != null) {
				// Process each line and add output to Dest.txt file
				bufferedWriter.write(aLine);
				bufferedWriter.newLine();
			}

			// do not forget to close the buffer reader
			bufferedReader.close();

			// close buffer writer
			bufferedWriter.close();
			System.out.println("File copied successfully!!");
		} catch (IOException e) {
			// print Exception
			e.printStackTrace();
		}
	}
}

readLine() method

public String readLine() throws IOException

Returns a string containing the contents of the line, not including any line-termination characters, or null if the end of the stream has been reached . it throws IOException  If an I/O error occurs .

write() method

public void write(String str) throws IOException

This method use to writes a string. It takes parameter  str String to be written and throws:IOException , If an I/O error occurs .

In this tutorial we have learned how  to copy the contents of one file to another using java. You can see more file handling java example .