Java I/O 深入学习（ 二）之数组类输入输出流

1. ByteArrayOutputStream

在实例化的时候会创建一个byte 类型的数组缓冲区，默认 32 个字节，可以无限增长。可以将内存中的对象读到该数组中。其中 write() 方法负责往数组中写数据。

实例化时的代码：

/**
     * Creates a new byte array output stream. The buffer capacity is 
     * initially 32 bytes, though its size increases if necessary. 
     */
    public ByteArrayOutputStream() {
	this(32);
    }

    /**
     * Creates a new byte array output stream, with a buffer capacity of 
     * the specified size, in bytes. 
     *
     * @param   size   the initial size.
     * @exception  IllegalArgumentException if size is negative.
     */
    public ByteArrayOutputStream(int size) {
        if (size < 0) {
            throw new IllegalArgumentException("Negative initial size: "
                                               + size);
        }
	buf = new byte[size];
    }

 写入数据时的代码：

/**
     * Writes the specified byte to this byte array output stream. 
     *
     * @param   b   the byte to be written.
     */
    public synchronized void write(int b) {
	int newcount = count + 1;
	if (newcount > buf.length) {
            buf = Arrays.copyOf(buf, Math.max(buf.length << 1, newcount));
	}
	buf[count] = (byte)b;
	count = newcount;
    }

    /**
     * Writes <code>len</code> bytes from the specified byte array 
     * starting at offset <code>off</code> to this byte array output stream.
     *
     * @param   b     the data.
     * @param   off   the start offset in the data.
     * @param   len   the number of bytes to write.
     */
    public synchronized void write(byte b[], int off, int len) {
	if ((off < 0) || (off > b.length) || (len < 0) ||
            ((off + len) > b.length) || ((off + len) < 0)) {
	    throw new IndexOutOfBoundsException();
	} else if (len == 0) {
	    return;
	}
        int newcount = count + len;
        if (newcount > buf.length) {
            buf = Arrays.copyOf(buf, Math.max(buf.length << 1, newcount));
        }
        System.arraycopy(b, off, buf, count, len);
        count = newcount;
    }

2.ByteArrayInputStream

负责把字节数组中的字节以流的形式读出,实现了对同一个字节数组的操作，因此在实例化时需要传入一个byte类型的数据。

实例化代码：

/**
     * Creates a <code>ByteArrayInputStream</code>
     * so that it  uses <code>buf</code> as its
     * buffer array. 
     * The buffer array is not copied. 
     * The initial value of <code>pos</code>
     * is <code>0</code> and the initial value
     * of  <code>count</code> is the length of
     * <code>buf</code>.
     *
     * @param   buf   the input buffer.
     */
    public ByteArrayInputStream(byte buf[]) {
	this.buf = buf;
        this.pos = 0;
	this.count = buf.length;
    }

    /**
     * Creates <code>ByteArrayInputStream</code>
     * that uses <code>buf</code> as its
     * buffer array. The initial value of <code>pos</code>
     * is <code>offset</code> and the initial value
     * of <code>count</code> is the minimum of <code>offset+length</code>
     * and <code>buf.length</code>.
     * The buffer array is not copied. The buffer's mark is
     * set to the specified offset.
     *
     * @param   buf      the input buffer.
     * @param   offset   the offset in the buffer of the first byte to read.
     * @param   length   the maximum number of bytes to read from the buffer.
     */
    public ByteArrayInputStream(byte buf[], int offset, int length) {
	this.buf = buf;
        this.pos = offset;
	this.count = Math.min(offset + length, buf.length);
        this.mark = offset;
    }

 一般情况下我们可以ByteArrayOutputStream和ByteArrayInputStream与ObjectInputStream/ObjectOutputStream或者DataInputStream/DataOutputStream结合使用，在读取对象或者数据类型数据时可以使用，例如以前在设计模式中讲过的原型模式中就有例子。

 

public User deepClone(){
		try {
			ByteArrayOutputStream baos = new ByteArrayOutputStream();
			ObjectOutputStream oos = new ObjectOutputStream(baos);
			oos.writeObject(this);
			ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
			ObjectInputStream ois = new ObjectInputStream(bais);
			return (User)ois.readObject();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return null;
	}