Java 8- How to replace word in a File using Stream

By Atul Rai | Last Updated: October 13, 2018 Previous       Next

On this page, you will learn how to find and replace words in a file using Java Stream. Java introduced Stream interface under the java.util.stream package in the JDK 8 version.

Here we have a simple text file named info.txt which contains some information about the user.

Hi, My name is Atul Rai and my favorite color is Blue.
I have completed my master's in 2014.

And you want to replace the user information like favorite color Blue with Black and master’s year 2014 with 2016.

Step 1:  Create a method which the contain the combination of old word and the new word.

public static Map<String, String> replaceWith() {

	Map<String, String> map = new HashMap<>();
	map.put("Blue", "Black");
	map.put("2014", "2016");

	return map;
}

Step 2: Create another method which loops the Map key, replace with its value and assign to the String.

public static String replaceWords(String str, Map<String, String> map) {
	for (Map.Entry<String, String> entry : map.entrySet()) {

		if (str.contains(entry.getKey())) {
			str = str.replace(entry.getKey(), entry.getValue());
		}
	}
	return str;
}

Step 3: Read the file location, instantiate the Stream and call these methods in the main method.

Map<String, String> m = replaceWith();
Path filePath = Paths.get("F:\\text\\info.txt");

Stream<String> lines = Files.lines(filePath, Charset.forName("UTF-8"));
List<String> replacedLine = lines.map(line -> replaceWords(line, m)).collect(Collectors.toList());
Files.write(filePath, replacedLine, Charset.forName("UTF-8"));
lines.close();

Let’s see the complete example.

package org.websparrow;

import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class StreamReplaceWordtDemo {

	public static void main(String[] args) {

		Map<String, String> m = replaceWith();
		Path filePath = Paths.get("F:\\text\\info.txt");

		try {
			Stream<String> lines = Files.lines(filePath, Charset.forName("UTF-8"));
			List<String> replacedLine = lines.map(line -> replaceWords(line, m)).collect(Collectors.toList());
			Files.write(filePath, replacedLine, Charset.forName("UTF-8"));
			lines.close();
			System.out.println("Done");
		} catch (IOException e) {

			e.printStackTrace();
		}

	}

	public static Map<String, String> replaceWith() {

		Map<String, String> map = new HashMap<>();
		map.put("Blue", "Black");
		map.put("2014", "2016");

		return map;

	}

	public static String replaceWords(String str, Map<String, String> map) {
		for (Map.Entry<String, String> entry : map.entrySet()) {

			if (str.contains(entry.getKey())) {
				str = str.replace(entry.getKey(), entry.getValue());
			}
		}
		return str;
	}

}

Output: Now you can see that old words replaced with new words.

Hi, My name is Atul Rai and my favorite color is Black.
I have completed my master's in 2016.

If you want to store the modified user information into a new file. Create a new file path object and pass it to Files.write() method.

Path newFilePath = Paths.get("F:\\text\\new_info.txt");
Files.write(newFilePath, replacedLine, Charset.forName("UTF-8"));

References

1. Interface Stream<T>
2. Class Collectors