Java OutputStream Tutorial with Examples

OutputStream
write(int)
write(byte[])
write(byte[], int, int)
close()
flush()

1. OutputStream

No ADS

OutputStream is a class in java.io package, which is a base class representing a stream of bytes to write bytes to a target, such as file.

public abstract class OutputStream implements Closeable, Flushable

ByteArrayOutputStream
FileOutputStream
FilterOutputStream
ObjectOutputStream
PipedOutputStream
BufferedOutputStream
DataOutputStream
PrintStream
CheckedOutputStream
CipherOutputStream
DeflaterOutputStream
DigestOutputStream
InflaterOutputStream

Basically, you cannot use OutputStream class directly because it is an abstract class. But in a particular case you can use one of its subclasses.

OutputStream methods

public static OutputStream nullOutputStream()   
 
public abstract void write(int b) throws IOException
public void write(byte b[]) throws IOException  
public void write(byte b[], int off, int len) throws IOException  

public void flush() throws IOException  
public void close() throws IOException

2. write(int)

No ADS

public abstract void write(int b) throws IOException

Writes one byte to OutputStream. b parameter is the unsigned code of byte, which is an integer between 0 and 255. If value of b is out of the above range, it will be ignored.

OutputStream_write_ex1.java

package org.o7planning.outputstream.ex;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;

public class OutputStream_write_ex1 {

    // Windows path: C:/Somedirectory/out-file.txt
    private static final String file_path = "/Volumes/Data/test/out-file.txt";

    public static void main(String[] args) throws IOException {
        File file = new File(file_path);
        // Create parent folder:
        file.getParentFile().mkdirs();

        // FileOutputStream  
        OutputStream os = new FileOutputStream(file);
       
        // 'J'
        os.write((int)'J'); // 74
        
        // 'P'
        os.write('P'); // 80 (Automatically converted to int)
        
        // '日' = 3 bytes UTF-8: [230, 151, 165]
        os.write(230);  
        os.write(151);  
        os.write(165);  
        
        // '本' = 3 bytes UTF-8: [230, 156, 172]
        os.write(230);    
        os.write(156);     
        os.write(172);     
        
        // '-'
        os.write('-');  // 45 (Automatically converted to int)
        
        // '八' = 3 bytes UTF-8: [229, 133, 171]
        os.write(229);    
        os.write(133);    
        os.write(171);    
        
        // '洲' = 3 bytes UTF-8: [230, 180, 178]
        os.write(230);  
        os.write(180);  
        os.write(178);   
        
        // Close
        os.close();
    }
}

Output:

out-file.txt

JP日本-八洲

UTF-8 files use 1, 2, 3 or 4 bytes to store a character. The image below shows the bytes on the newly created file.

3. write(byte[])

No ADS

public void write(byte[] b) throws IOException

Writes a byte array to OutputStream.

OutputStream_write_ex2.java

package org.o7planning.outputstream.ex;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;

public class OutputStream_write_ex2 {

    // Windows path: C:/Somedirectory/out-file.txt
    private static final String file_path = "/Volumes/Data/test/out-file.txt";

    public static void main(String[] args) throws IOException {
        File file = new File(file_path);
        // Create parent folder:
        file.getParentFile().mkdirs();

        // FileOutputStream
        OutputStream writer = new FileOutputStream(file);  
        
        byte[] bytes = new byte[] { 'J', 'P', //
                         (byte)230, (byte)151, (byte)165, // '日' = 3 bytes UTF-8: [230, 151, 165]
                         (byte)230, (byte)156, (byte)172, // '本' = 3 bytes UTF-8: [230, 156, 172]
                         '-', //
                         (byte)229, (byte)133, (byte)171, // '八' = 3 bytes UTF-8: [229, 133, 171]
                         (byte)230, (byte)180, (byte)178, // '洲' = 3 bytes UTF-8: [230, 180, 178]
                         };  
        
        writer.write(bytes);  
        // Close
        writer.close();
    }
}

Output:

out-file.txt

JP日本-八洲

4. write(byte[], int, int)

public void write(byte b[], int offset, int len) throws IOException

Write part of a byte array to OutputStream. Write bytes from offset index to offset+len index.

OutputStream_write_ex3.java

package org.o7planning.outputstream.ex;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;

public class OutputStream_write_ex3 {

    public static void main(String[] args) throws IOException {
        
        // ByteArrayOutputStream is a subclass of OutputStream.
        OutputStream outputStream = new ByteArrayOutputStream();  
        
        byte[] bytes = new byte[] {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9'};
        
        outputStream.write(bytes, 2, 5); // '2', ...'6'
        
        String s = outputStream.toString();
        System.out.println(s);
        
        outputStream.close();
    }
}

Output:

5. close()

No ADS

public void close() throws IOException

The close() method is used to close this stream, the flush() method will be called first. Once the stream has been closed, further write() or flush() invocations will cause an IOException to be thrown. Closing a previously closed stream has no effect.

public interface Closeable extends AutoCloseable

Writer class implements Closeable interface. If you write code according to the rules of AutoCloseable, system will automatically close the stream for you without having to call close() method directly.

OutputStream_close_ex1.java

package org.o7planning.outputstream.ex;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;

public class OutputStream_close_ex1 {

    // Windows path: C:/Somedirectory/out-file.txt
    private static final String file_path = "/Volumes/Data/test/out-file.txt";

    public static void main(String[] args) throws IOException {
        File file = new File(file_path);
        // Create parent folder:
        file.getParentFile().mkdirs();

        try (OutputStream writer = new FileOutputStream(file)) {
            writer.write((int) '1');
            writer.write('2');
            writer.write((int) '3');
        }
    }
}

Java Closeable

6. flush()

public void flush() throws IOException

The data that you write to OutputStream is sometimes temporarily stored on the buffer. flush() method is used to flush the data into the target.

You can read BufferedOutputStream article below to understand more about flush() method.

Java BufferedOutputStream

If the intended destination of this OutputStream is an abstraction provided by the underlying operating system, for example a file, then flushing the stream guarantees only that bytes previously written to the stream are passed to the operating system for writing; it does not guarantee that they are actually written to a physical device such as a disk drive.

No ADS

Java OutputStream Tutorial with Examples

1. OutputStream

2. write(int)

3. write(byte[])

4. write(byte[], int, int)

5. close()

6. flush()

Java IO Tutorials

Java IO Tutorials

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