Problem:
How to write text file in Java? java.io have a number of useful classes for working with files, one of them is FileWriter that we’re going to show in this post. Read on!
Solution:
In the following program we’re going to generate some data and write them into a CSV file. To write text file in Java use FileWriter. For better performance always wrap it in BufferedWriter like in the example.
The program is using FileWriter in two ways:
- To create a “highscores.csv” file with generated data
- To reopen the file for appending to add some more data.
package com.farenda.java.io;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
import java.util.AbstractMap.SimpleImmutableEntry;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Random;
public class WriteTextFileExample {
private static final Random rand = new Random();
public static void main(String[] args) throws IOException {
Map<String,Integer> playersPoints = generateSampleData();
String scoreFile = "highscores.csv";
// Create a new file and override when already exists:
try (Writer output = openWriter(scoreFile)) {
writeHeader(output);
for (Entry<String, Integer> player : playersPoints.entrySet()) {
output.write(formatRow(player));
}
}
Entry<String, Integer> newUser =
new SimpleImmutableEntry<>("newUser", generatePoints());
// Reopen the file but for appending:
try (Writer output = openWriter(scoreFile, true)) {
output.write(formatRow(newUser));
}
}
private static Map<String,Integer> generateSampleData() {
Map<String,Integer> playersPoints = new LinkedHashMap<>();
for (int i = 1; i <= 5; ++i) {
playersPoints.put("user" + i, generatePoints());
}
return playersPoints;
}
private static int generatePoints() {
return rand.nextInt(1000) + 1;
}
private static void writeHeader(Writer output) throws IOException {
output.append("#name,points").append(System.lineSeparator());
}
private static BufferedWriter openWriter(String fileName)
throws IOException {
return openWriter(fileName, false);
}
private static BufferedWriter openWriter(String fileName, boolean append)
throws IOException {
// Don't forget to add buffering to have better performance!
return new BufferedWriter(new FileWriter(fileName, append));
}
private static String formatRow(Entry<String, Integer> player) {
String row = String.format("%s,%s%n",
player.getKey(), player.getValue());
System.out.print("Adding row: " + row);
return row;
}
}
The result of running the above program:
Adding row: user1,757 Adding row: user2,482 Adding row: user3,155 Adding row: user4,269 Adding row: user5,31 Adding row: newUser,680
And the contents of the created file:
$> cat highscores.csv #name,points user1,757 user2,482 user3,155 user4,269 user5,31 newUser,680
