Program to insert/write content at specific position in file in java



Let’s say c:/myFile.txt looks like this >
you learning file io from javaMadeSoEasy

Write a Program to insert/write content at specific position in file in java, such that after execution of program file must look like this -

you ARE learning file io from javaMadeSoEasy



Java does not allow you to insert in file, so follow these steps >
  • 1) Read from file in String.
  • 2) Insert content at specified position in String, as per your requirement.
  • 3) write updated String in file.


RandomAccessFile allows us to read/write at random positions by using seek method but when we try to write at random position, data is not inserted, in fact it’s overridden. See How to Read/write from file using RandomAccessFile.


Program to insert/write content at specific position in file in java >

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
public class InsertInFileAtSpecifiedPosition {
public static void main(String[] args) throws IOException {
     String fileName = "c:/myFile.txt";
     FileReader fr = new FileReader("c:/myFile.txt");
     BufferedReader br = new BufferedReader(fr);
     // 1) Read from file in String
     String str = br.readLine();
     // 2) Insert content at specified position in String, as per your
     // requirement
     String updatedStr = str.substring(0, 4) + "ARE " + str.substring(4);
     br.close();
     // 3) write updated String in file
     FileWriter writer = new FileWriter(fileName);
     writer.write(updatedStr);
     writer.close();
}
}



After executing above program c:/myFile.txt will look like this >
you ARE learning file io from javaMadeSoEasy


RELATED LINKS>

Create File using createNewFile() method in java file IO


Copy a file in java 2 in ways


Find current directory or current path in java


Directory operations - create, identify, delete, copy, traverse

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