Java FileOutputStream

last modified January 27, 2024

Java FileOutputStream tutorial shows how to use FileOutputStream class to write to files in Java.

Java FileOutputStream

FileOutputStream is an output stream for writing data to a File or to a FileDescriptor. FileOutputStream is a subclass of OutputStream, which accepts output bytes and sends them to some sink. In case of FileOutputStream, the sink is a file object.

Java FileOutputStream constructors

These are FileOutputStream constructors:

• FileOutputStream(File file) — creates a file output stream to write to a File object.
• FileOutputStream(File file, boolean append) — creates a file output stream to write to a File object; allows appending mode.
• FileOutputStream(FileDescriptor fdObj) — creates a file output stream to write to the specified file descriptor.
• FileOutputStream(String name) — creates a file output stream to write to the file with the specified name.
• FileOutputStream(String name, boolean append) — creates a file output stream to write to the file with the specified name; allows appending mode.

Java FileOutputStream close

The FileOutputStream's close method closes file output stream and releases any system resources associated with this stream. In our examples we use try-with-resources statement, which ensures that each resource is closed at the end of the statement.

Java FileOutputStream write

FileOutputStream writes bytes with the following write methods :

• write(byte[] b) — writes array of bytes to the file output stream.
• write(byte[] b, int off, int len) — writes len bytes from the specified byte array starting at offset off to the file output stream.
• write(int b) — writes one byte to the file output stream.

Java FileOutputStream example

The following example uses FileOutputStream to write text to a file.

package com.zetcode;

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

public class FileOutputStreamEx {

    public static void main(String[] args) throws FileNotFoundException, IOException {
        
        String fileName = "/home/janbodnar/tmp/newfile.txt";
        
        try (FileOutputStream fos = new FileOutputStream(fileName)) {
            
            String text = "Today is a beautiful day";
            byte[] mybytes = text.getBytes();
            
            fos.write(mybytes);
        }
    }
}

The code example writes one line to a file.

try (FileOutputStream fos = new FileOutputStream(fileName)) {

The FileOutputStream constructor takes a string as a parameter; it is the file name to which we write. We use try-with-resources construct to clean resources after we have finished writing.

String text = "Today is a beautiful day";
byte[] mybytes = text.getBytes();

FileOutputStream write bytes to the file; we get bytes from a string with the getBytes method.

fos.write(mybytes);

The bytes are written to the file.

$ cat newfile.txt 
Today is a beautiful day

We show the contents of the file with the cat command.

Java FileOutputStream append to file

With FileOutputStream it is possible to append data to a file. The typical usage for appending is logging.

package com.zetcode;

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

public class FileOutputStreamAppend {

    public static void main(String[] args) throws FileNotFoundException, IOException {        
        
        String fileName = "/home/janbodnar/tmp/newfile.txt";
        
        try (FileOutputStream fos = new FileOutputStream(fileName, true)) {
            
            String text = "Today is a beautiful day";
            byte[] mybytes = text.getBytes();
            
            fos.write(mybytes);
        }
    }
}

The code example appends text to file.

try (FileOutputStream fos = new FileOutputStream(fileName, true)) {

The second parameter of FileOutputStream indicates that we will append to the file.

Java FileOutputStream specifying encoding

FileWriter class, which is a Java convenience class for writing character files, has a serious limitation: it uses the default encoding and does not allow us to explicitly specify the encoding. If we have to set the encoding, we can use OutputStreamWriter and FileOutputStream.

package com.zetcode;

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

public class FileOutputStreamEncoding {

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

        String fileName = "/home/janbodnar/tmp/newfile.txt";

        FileOutputStream fos = new FileOutputStream(fileName);
        
        try (OutputStreamWriter osw =  new OutputStreamWriter(fos, 
                StandardCharsets.UTF_8)) {

            String text = "Сегодня был прекрасный день.";

            osw.write(text);
        }
    }
}

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

$ cat newwfile.txt 
Сегодня был прекрасный день.

We show the contents of the file.

Source

Java FileOutputStream - language reference

In this article we have presented the Java FileOutputStream 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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