The Byte Streams ByteArrayInputStream

ByteArrayInputStream is an implementation of an input stream that uses a byte array as the source.

ByteArrayInputStream Constructors

• ByteArrayInputStream(byte[] buf) - Creates a ByteArrayInputStream so that it uses buf as its buffer array.
• ByteArrayInputStream(byte[] buf, int offset, int length) - Creates ByteArrayInputStream that uses buf as its buffer array.

ByteArrayInputStream Methods

• int available() - Returns the number of remaining bytes that can be read (or skipped over) from this input stream.
• void close() - Closing a ByteArrayInputStream has no effect.
• void mark(int readAheadLimit) - Set the current marked position in the stream.
• boolean markSupported() - Tests if this InputStream supports mark/reset.
• int read() - Reads the next byte of data from this input stream.
• int read(byte[] b, int off, int len) - Reads up to len bytes of data into an array of bytes from this input stream.
• void reset() - Resets the buffer to the marked position.
• long skip(long n) - Skips n bytes of input from this input stream.

The close( ) method has no effect on a ByteArrayInputStream. Therefore, it is not necessary to call close( ) on a ByteArrayInputStream, but doing so is not an error.

ByteArrayInputStream Example 1

The following example creates a pair of ByteArrayInputStreams, initializing them with the byte representation of the alphabet:

// Demonstrate ByteArrayInputStream.
import java.io.*;
class ByteArrayInputStreamDemo {
    public static void main(String args[]) {
        String tmp = "abcdefghijklmnopqrstuvwxyz";
        byte b[] = tmp.getBytes();
        ByteArrayInputStream input1 = new ByteArrayInputStream(b);
        ByteArrayInputStream input2 = new ByteArrayInputStream(b, 0, 3);
    }
}

The input1 object contains the entire lowercase alphabet, whereas input2 contains only the first three letters. A ByteArrayInputStream implements both mark( ) and reset( ). However, if mark( ) has not been called, then reset( ) sets the stream pointer to the start of the stream—which, in this case, is the start of the byte array passed to the constructor.

ByteArrayInputStream Example 2

This example shows how to use the reset( ) method to read the same input twice. In this case, the program reads and prints the letters "abc" once in lowercase and then again in uppercase.

import java.io.*;
class ByteArrayInputStreamReset {
    public static void main(String args[]) {
        String tmp = "abc";
        byte b[] = tmp.getBytes();
        ByteArrayInputStream in = new ByteArrayInputStream(b);
        for (int i = 0; i < 2; i++) {
            int c;
            while ((c = in .read()) != -1) {
                if (i == 0) {
                    System.out.print((char) c);
                } else {
                    System.out.print(Character.toUpperCase((char) c));
                }
            }
            System.out.println(); in .reset();
        }
    }
}

Output:

abc
ABC

This example first reads each character from the stream and prints it as-is in lowercase. It then resets the stream and begins reading again, this time converting each character to uppercase before printing.

Reference

ByteArrayInputStream Javadoc 8