Append a String to the end of the existing String with specific position in a text file in Java - bufferedreader

Question

Exp -
In a text file we have the following topics with some description.
#Repeat the annotation
It is the major topic for .....
#Vector analysis
It covers all the aspects of sequential....
#Cloud Computing
Create header accounts for all the users
We have to add / append new Tags to the Topics in specific line
For exp-
#Repeat the annotation #Maven build
#Cloud Computing #SecondYear
File f = new File("/user/imp/value/GSTR.txt");
FileReader fr = new FileReader(f);
Object fr1;
while((fr1 = fr.read()) != null) {
if(fr1.equals("#Repeat the annotation")) {
FileWriter fw = new FileWriter(f,true);
fw.write("#Maven build");
fw.close();
}
}
****** #Maven is getting added to the last line of the text file but not at the specific position next to the topic

Answer 1

The output is written to the file GSTR_modified.txt. The code along with an example input file is also available here. The code in the github repository reads the file "input.txt" and writes to the file "output.txt".
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
public class Main {
public static void main(String[] args) throws IOException {
// Create a list to store the file content.
ArrayList<String> list = new ArrayList<>();
// Store the file content in the list. Each line becomes an element in the list.
try (BufferedReader br = new BufferedReader(new FileReader("/user/imp/value/GSTR.txt""))) {
String line;
while ((line = br.readLine()) != null) {
list.add(line);
}
}
// Iterate the list of lines.
for (int i = 0; i < list.size(); i++) {
// line is the element at the index i.
String line = list.get(i);
// Check if a line is equal to "#Repeat the annotation"
if (line.contains("#Repeat the annotation")){
// Set the list element at index i to the line itself concatenated with
// the string " #Maven build".
list.set(i,line.concat(" #Maven build"));
}
// Same pattern as above.
if (line.contains("#Cloud Computing")){
list.set(i,line.concat(" #SecondYear"));
}
}
// Write the contents of the list to a file.
FileWriter writer = new FileWriter("GSTR_modified.txt");
for(String str: list) {
// Append newline character \n to each element
// and write it to file.
writer.write(str+"\n");
}
writer.close();
}
}