Java FileWriter

last modified January 27, 2024

Java FileWriter tutorial shows how to use FileWriter class to write text to files in Java.

Java FileWriter

FileWriter is a Java convenience class for writing text data to files. FileWriter extends OutputStreamWriter and creates the FileOutputStream.

Java FileWriter constructors

These are FileWriter constructors:

• FileWriter(File file) — constructs a FileWriter to a File
• FileWriter(File file, boolean append) — constructs a FileWriter to a File; allows appending mode
• FileWriter(FileDescriptor fd) — constructs a FileWriter to a FileDescriptor
• FileWriter(File file, Charset charset) — constructs a FileWriter given the File to write and charset
• FileWriter(File file, Charset charset, boolean append) — constructs a FileWriter given the File to write, charset and a boolean indicating whether to append the data written
• FileWriter(String fileName) — constructs a FileWriter to a file name
• FileWriter(String fileName, boolean append) — constructs a FileWriter to a file name; allows appending mode
• FileWriter(String fileName, Charset charset) — constructs a FileWriter given a file name and charset
• FileWriter(String fileName, Charset charset, boolean append) — constructs a FileWriter given a file name, charset and a boolean indicating whether to append the data written

Java FileWriter example

The following example writes a line to a file.

package com.zetcode;

import java.io.FileWriter;
import java.io.IOException;

public class JavaFileWriterEx {

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

        var fileName = "src/resources/myfile.txt";

        try (var fr = new FileWriter(fileName, StandardCharsets.UTF_8)) {

            fr.write("Today is a sunny day");
        }
    }
}

The example writes text data to a file with FileWriter.

try (var fr = new FileWriter(fileName, StandardCharsets.UTF_8)) {

The first parameter of the FileWriter is the file name. The second is the encoding used. We use try-with-resources construct to clean resources after we have finished writing.

writer.write("Today is a sunny day");

The FileWriter's write method writes text to the file.

Java FileWriter append to file

With FileWriter it is possible to append text to a file. The typical usage for appending is logging.

package com.zetcode;

import java.io.FileWriter;
import java.io.IOException;
import java.nio.charset.StandardCharsets;

public class JavaFileWritterAppend {

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

        var fileName = "src/resources/myfile.txt";

        try (var fr = new FileWriter(fileName, StandardCharsets.UTF_8, true)) {

            fr.write("Tomorrow will be cloudy.");
        }
    }
}

The code example appends text to file.

try (var fr = new FileWriter(fileName, StandardCharsets.UTF_8, true)) {

The second parameter of FileWriter tells that we will append to the file.

Java FileWriter & BufferedWriter

FileWriter's performance can be improved with BufferedWriter. BufferedWriter writes text to a character-output stream, buffering characters to improve the performance of writing single characters, arrays, and strings. The buffer size may be specified, or the default size may be accepted; the default is large enough for most purposes.

package com.zetcode;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;
import java.nio.charset.StandardCharsets;

public class JavaFileWriterBuffered {

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

        String text = readText();

        var fileName = "src/resources/wikipedia_home_page.txt";

        try (var fr = new FileWriter(fileName, StandardCharsets.UTF_8);
             var bufWriter = new BufferedWriter(fr)) {

            bufWriter.write(text);
        }
    }

    public static String readText() throws IOException {

        StringBuilder sb;

        var url = new URL("https://www.wikipedia.org");

        try (var br = new BufferedReader(new InputStreamReader(url.openStream(),
                StandardCharsets.UTF_8))) {

            String line;
            sb = new StringBuilder();

            while ((line = br.readLine()) != null) {

                sb.append(line);
                sb.append(System.lineSeparator());
            }
        }

        return sb.toString();
    }
}

In the example, we read Wikipedia's home page (its HTML code) and write it to a file. The home page is large enough to consider buffering.

try (var fr = new FileWriter(fileName, StandardCharsets.UTF_8);
    var bufWriter = new BufferedWriter(fr)) {

   bufWriter.write(text);
}

The FileWriter is passed to the BufferedWriter as a parameter. Then we call the BufferedWriter's write method to write the text.

try (var br = new BufferedReader(new InputStreamReader(url.openStream(),
    StandardCharsets.UTF_8))) {

The reading operation is buffered as well with the BufferedReader class.

Specifying encoding with pre-Java 11

A workaround with pre-Java 11 FileWriter encoding issue was to use the OutputStreamWriter and FileOutputStream instead.

package com.zetcode;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.nio.charset.StandardCharsets;

public class JavaFileOutputStreamEx {

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

        String fileName = "src/resources/myfile.txt";

        try (var osw = new OutputStreamWriter(new FileOutputStream(fileName),
                StandardCharsets.UTF_8)) {
            osw.write("Сегодня был прекрасный день.");
        }
    }
}

The example writes text to a file with OutputStreamWriter. The second parameter is the charset to be used.

Source

Java FileWriter - language reference

In this article we have presented the Java FileWriter class.

Author

My name is Jan Bodnar and I am a passionate programmer with many years of programming experience. I have been writing programming articles since 2007. So far, I have written over 1400 articles and 8 e-books. I have over eight years of experience in teaching programming.

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