Java ByteArrayOutputStream Class

The ByteArrayOutputStream class of the java.io package can be used to write an array of output data (in bytes).

It extends the OutputStream abstract class.

Note: In ByteArrayOutputStream maintains an internal array of bytes to store the data.

Create a ByteArrayOutputStream

In order to create a byte array output stream, we must import the java.io.ByteArrayOutputStream package first. Once we import the package, here is how we can create an output stream.

// Creates a ByteArrayOutputStream with default size
ByteArrayOutputStream out = new ByteArrayOutputStream();

Here, we have created an output stream that will write data to an array of bytes with default size 32 bytes. However, we can change the default size of the array.

// Creating a ByteArrayOutputStream with specified size
ByteArrayOutputStream out = new ByteArrayOutputStream(int size);

Here, the size specifies the length of the array.

Methods of ByteArrayOutputStream

The ByteArrayOutputStream class provides the implementation of the different methods present in the OutputStream class.

write() Method

• write(int byte) - writes the specified byte to the output stream
• write(byte[] array) - writes the bytes from the specified array to the output stream
• write(byte[] arr, int start, int length) - writes the number of bytes equal to length to the output stream from an array starting from the position start
• writeTo(ByteArrayOutputStream out1) - writes the entire data of the current output stream to the specified output stream

Example: ByteArrayOutputStream to write data

import java.io.ByteArrayOutputStream;

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

    String data = "This is a line of text inside the string.";

    try {
      // Creates an output stream
      ByteArrayOutputStream out = new ByteArrayOutputStream();
      byte[] array = data.getBytes();

      // Writes data to the output stream
      out.write(array);

      // Retrieves data from the output stream in string format
      String streamData = out.toString();
      System.out.println("Output stream: " + streamData);

      out.close();
    }

    catch(Exception e) {
      e.getStackTrace();
    }
  }
}

Output

Output stream: This is a line of text inside the string.

In the above example, we have created a byte array output stream named output.

ByteArrayOutputStream output = new ByteArrayOutputStream();

To write the data to the output stream, we have used the write() method.

Note: The getBytes() method used in the program converts a string into an array of bytes.

Access Data from ByteArrayOutputStream

• toByteArray() - returns the array present inside the output stream
• toString() - returns the entire data of the output stream in string form

For example,

import java.io.ByteArrayOutputStream;

class Main {
  public static void main(String[] args) {
    String data = "This is data.";

    try {
      // Creates an output stream
      ByteArrayOutputStream out = new ByteArrayOutputStream();

      // Writes data to the output stream
      out.write(data.getBytes());

      // Returns an array of bytes
      byte[] byteData = out.toByteArray();
      System.out.print("Data using toByteArray(): ");
      for(int i=0; i<byteData.length; i++) {
        System.out.print((char)byteData[i]);
      }

      // Returns a string
      String stringData = out.toString();
      System.out.println("\nData using toString(): " + stringData);

      out.close();
    }

    catch(Exception e) {
      e.getStackTrace();
    }
  }
}

Output

Data using toByteArray(): This is data.
Data using toString(): This is data.

In the above example, we have created an array of bytes to store the data returned by the toByteArray() method.

We then have used the for loop to access each byte from the array. Here, each byte is converted into the corresponding character using typecasting.

close() Method

To close the output stream, we can use the close() method.

However, the close() method has no effect in ByteArrayOutputStream class. We can use the methods of this class even after the close() method is called.

Other Methods of ByteArrayOutputStream

To learn more, visit Java ByteArrayOutputStream (official Java documentation).