import java.io.IOException;

import java.nio.file.Files;

import java.nio.file.Path;

import java.nio.file.Paths;

import java.util.ArrayList;

import java.util.List;

import java.util.regex.Matcher;

import java.util.regex.Pattern;

public class LogSearch {

/**

* Searches log files for a given pattern.

* @param filePath The path to the log file.

* @param searchPattern The regular expression pattern to search for.

* @return A list of lines containing the search pattern. Returns an empty list if no match or error.

* @throws IOException If an I/O error occurs while reading the file.

*/

public List<String> searchLogFile(String filePath, String searchPattern) throws IOException {

List<String> results = new ArrayList<>();

// Defensive check: Validate input

if (filePath == null || filePath.trim().isEmpty()) {

System.err.println("Error: File path cannot be null or empty.");

return results; // Return empty list

}

if (searchPattern == null || searchPattern.trim().isEmpty()) {

System.err.println("Error: Search pattern cannot be null or empty.");

return results; // Return empty list

}

Path path = Paths.get(filePath);

try {

String fileContent = new String(Files.readAllBytes(path));

Pattern pattern = Pattern.compile(searchPattern);

Matcher matcher = pattern.matcher(fileContent);

while (matcher.find()) {

results.add(fileContent.substring(matcher.start(), matcher.end())); // Extract matching line

}

} catch (IOException e) {

System.err.println("Error reading file: " + e.getMessage());

return results; // Return empty list

}

return results;

}

public static void main(String[] args) throws IOException {

LogSearch searcher = new LogSearch();

// Example usage:

String filePath = "example.log"; // Replace with your log file path

String searchPattern = "ERROR"; // Replace with your search pattern

//Create a dummy log file for testing

try {

Files.write(Paths.get(filePath), "This is a log line.\n".getBytes());

Files.write(Paths.get(filePath), "Another log line.\n".getBytes());

Files.write(Paths.get(filePath), "ERROR: Something went wrong.\n".getBytes());

Files.write(Paths.get(filePath), "Just a normal line.\n".getBytes());

Files.write(Paths.get(filePath), "ERROR: Another error occurred.\n".getBytes());

} catch (IOException e) {

System.err.println("Error creating dummy log file: " + e.getMessage());

return;

}

List<String> results = searcher.searchLogFile(filePath, searchPattern);

if (results.isEmpty()) {

System.out.println("No matches found.");

} else {

System.out.println("Matches found:");

for (String line : results) {

System.out.println(line);

}

}

}

}