Java ByteArrayOutputStream Tutorial with Examples

ByteArrayOutputStream
Constructors
Methods
Examples

1. ByteArrayOutputStream

ByteArrayOutputStream is a subclass of OutputStream. True to its name, ByteArrayOutputStream is used to write bytes to a byte array that manages in the way of an OutputStream.

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

bytes written to ByteArrayOutputStream will be assigned to elements of the byte array that ByteArrayOutputStream manages.

When the number of bytes written to ByteArrayOutputStream is greater than the length of array, ByteArrayOutputStream will create a new array with greater length and copy the bytes from the old array.

2. Constructors

Constructors

public ByteArrayOutputStream()  

public ByteArrayOutputStream(int initialSize)

ByteArrayOutputStream(int) constructor creates a ByteArrayOutputStream object with a byte array that has a specified initial size.
ByteArrayOutputStream() constructor creates a ByteArrayOutputStream object with a byte array of that has default size (32).

3. Methods

All methods of ByteArrayOutputStream are inherited from its parent class - OutputStream.

void close()  
void reset()  
int size()  

byte[] toByteArray()  
String toString()  
String toString(String charsetName)  
String toString(Charset charset)  

void write(byte[] b, int off, int len)  
void write(int b)  
void writeBytes(byte[] b)  

void writeTo(OutputStream out)

See the OutputStream article for more examples of these methods.

Java OutputStream

4. Examples

ByteArrayOutputStreamEx1.java

package org.o7planning.bytearrayoutputstream.ex;

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

public class ByteArrayOutputStreamEx1 {

    public static void main(String[] args) throws IOException {
        ByteArrayOutputStream baos = new ByteArrayOutputStream(1024);
        
        byte[] bytes1 = new byte[] {'H', 'e'};
        
        baos.write(bytes1);
        
        baos.write(108); // 'l'
        baos.write('l'); // code: 108
        baos.write('o'); // code: 111

        byte[] buffer = baos.toByteArray();
        
        for(byte b: buffer)  {
            System.out.println(b + " --> " + (char)b);
        }
    }
}

Output:

72 --> H
101 --> e
108 --> l
108 --> l
111 --> o

For example, add 2 byte arrays to create a new array.

ByteArrayOutputStreamEx3.java

package org.o7planning.bytearrayoutputstream.ex;

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

public class ByteArrayOutputStreamEx3 {

    public static void main(String[] args) throws IOException {
        byte[] arr1 = "Hello ".getBytes();
        byte[] arr2 = new byte[] {'W', 'o', 'r', 'l', 'd', '!'};
        
        byte[] result = add(arr1, arr2);
        
        for(byte b: result)  {
            System.out.println(b + " " + (char)b);
        }
    }

    public static byte[] add(byte[] arr1, byte[] arr2) {
        if (arr1 == null) {
            return arr2;
        }
        if (arr2 == null) {
            return arr1;
        }
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        try {
            baos.write(arr1);
            baos.write(arr2);
        } catch (Exception e) {
            // Never happened!
        }
        return baos.toByteArray();
    }
}