ZetCode

Java FileWriter

last modified July 6, 2020

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:

Note: In the past, FileWriter relied on the default platform's encoding. Since Java 11, the issue was corrected. It is possible now to explicitly specify the encoding. Always specify the encoding when using FileWriter.

Java FileWriter example

The following example writes a line to a file.

com/zetcode/JavaFileWriterEx.java
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.

com/zetcode/JavaFileWritterAppend.java
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.

FileWriter with 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.

com/zetcode/JavaFileWriterBuffered.java
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.

com/zetcode/JavaFileOutputStreamEx.java
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.

In this tutorial, we have presented the Java FileWriter class.

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