How to Search for a String in a File and Write Matched Lines to Another File in Java?

How can I search for a specific string in a file and write the lines that match to another file using Java?

BufferedReader reader = new BufferedReader(new FileReader("input.txt")); PrintWriter writer = new PrintWriter(new FileWriter("output.txt"));

Searching for a string in a file and writing the matched lines to another file is a common task in Java. This process involves reading a file line by line, checking if each line contains the specified string, and then writing those lines to a new file if a match is found.

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.PrintWriter;

public class StringSearcher {
    public static void main(String[] args) {
        String searchString = "your_search_string";
        try (BufferedReader reader = new BufferedReader(new FileReader("input.txt")); 
             PrintWriter writer = new PrintWriter(new FileWriter("output.txt"))) {
            String line;
            while ((line = reader.readLine()) != null) {
                if (line.contains(searchString)) {
                    writer.println(line);
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Causes

• The source file does not exist or is improperly formatted.
• The search string is not found in any line of the file.
• Improper handling of file I/O exceptions.

Solutions

• Use `BufferedReader` to read the file efficiently line by line.
• Utilize `PrintWriter` to create and write to the output file easily.
• Implement exception handling to manage potential file I/O errors.

Mistake: Forgetting to close file resources which can lead to memory leaks.

Solution: Use try-with-resources to automatically manage closing files.

Mistake: Trying to read a non-existent file without handling exceptions.

Solution: Always check if the file exists or wrap file operations in a try-catch block.