Java FileOutputStream

Input/Output: Exploring java.io > Byte Streams >
Siva Nookala - 20 Feb 2017

A FileOutputStream is an output stream for writing data to a File or to a FileDescriptor. Whether or not a file is available or may be created depends upon the underlying platform. Some platforms, in particular, allow a file to be opened for writing by only one FileOutputStream(or other file-writing object) at a time. In such situations the constructors in this class will fail if the file involved is already open.

FileOutputStream is meant for writing streams of raw bytes such as image data. For writing streams of characters, consider using Java FileWriter.

FileOutputStream Constructors:

Constructor	Description
`FileOutputStream(File file)`	Creates a file output stream to write to the file represented by the specified `File` object.
`FileOutputStream(File file, boolean append)`	Creates a file output stream to write to the file represented by the specified `File` object.
`FileOutputStream(FileDescriptor fdObj)`	Creates a file output stream to write to the specified file descriptor, which represents an existing connection to an actual file in the file system.
`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.

FileOutputStream Method:

Methods	Description
`void close()`	Closes this file output stream and releases any system resources associated with this stream.
`protected void finalize()`	Cleans up the connection to the file, and ensures that the `close` method of this file output stream is called when there are no more references to this stream.
`FileChannel getChannel()`	Returns the unique `FileChannel` object associated with this file output stream.
`FileDescriptor getFD()`	Returns the file descriptor associated with this stream.
`void write(byte[] b)`	Writes `b.length` bytes from the specified byte array to this file output stream.
`void write(byte[] b, int off, int len)`	Writes `len` bytes from the specified byte array starting at offset `off` to this file output stream.
`void write(int b)`	Writes the specified byte to this file output stream.

Example Program:

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.GradientPaint;
import java.awt.Graphics2D;
import java.awt.geom.Ellipse2D;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import javax.imageio.ImageIO;

public class Test {
    public static void main(String[] args) {

        File file = new File("MeritCampus.txt");

        try (FileOutputStream fop = new FileOutputStream(file)) {

            // if file doesn't exists, then create it
            if (!file.exists()) {
                file.createNewFile();
            }

            // writes byte to the output stream
            fop.write(65);
            // flushes the content to the underlying stream
            fop.flush();
            fop.close();        

            System.out.println("File created.");

        } catch (IOException e) {
            e.printStackTrace();
        }

        int width = 300;
        int height = 300;
        BufferedImage bi = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        Graphics2D g2 = bi.createGraphics();
        g2.setColor(Color.black);
        g2.fillRect(0,0, width, height);
        g2.setStroke(new BasicStroke(10.0f));
        g2.setPaint(new GradientPaint(10,10, Color.green, 50,50, Color.blue, true));
        g2.fill(new Ellipse2D.Float(50,50,200,200));

        try (FileOutputStream out = new FileOutputStream("image.jpg")) {    
            ImageIO.write(bi, "jpg", out);
        } catch (IOException ex) {
            ex.printStackTrace();
        }

        System.out.println("Image created.");
    }
}

Output:

File created.
Image created. 

//the following text file is created
/* This is the content of file : MeritCampus.txt
A
*/ 

//the following image is written on the system

Image: Fileoutputstream_output

Description:
A file MeritCampus.txt is created if it does not exist already. Byte is written on the FileOutputStream and the content is flushed to the underlying stream. An image is written on the second FileOutputStream and created. Note that the full path is to be given if the file or image is not to be created in the same folder as the java file on the system and this is a JDK7 example, where the new “try resource close” method to handle the file easily is used.

Things to try:

Try to write the data from an array into the FileOutputStream using write(byte[] b) method instead of using write(int b).

Try to write the data from an array starting at the offset into the FileOutputStream using write(byte[] b, int off, int len) method instead of using write(int b).

Try writing different images in different formats by using FileOutputStream.

Java FileInputStream

Java ByteArrayInputStream