Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.commons.io.output; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.io.UnsupportedEncodingException; import java.util.ArrayList; import java.util.List; /** * This class implements an output stream in which the data is * written into a byte array. The buffer automatically grows as data * is written to it. * <p> * The data can be retrieved using <code>toByteArray()</code> and * <code>toString()</code>. * <p> * Closing a <tt>ByteArrayOutputStream</tt> has no effect. The methods in * this class can be called after the stream has been closed without * generating an <tt>IOException</tt>. * <p> * This is an alternative implementation of the java.io.ByteArrayOutputStream * class. The original implementation only allocates 32 bytes at the beginning. * As this class is designed for heavy duty it starts at 1024 bytes. In contrast * to the original it doesn't reallocate the whole memory block but allocates * additional buffers. This way no buffers need to be garbage collected and * the contents don't have to be copied to the new buffer. This class is * designed to behave exactly like the original. The only exception is the * deprecated toString(int) method that has been ignored. * * @author <a href="mailto:jeremias@apache.org">Jeremias Maerki</a> * @author Holger Hoffstatte * @version $Id: ByteArrayOutputStream.java 610010 2008-01-08 14:50:59Z niallp $ */ public class ByteArrayOutputStream extends OutputStream { /** A singleton empty byte array. */ private static final byte[] EMPTY_BYTE_ARRAY = new byte[0]; /** The list of buffers, which grows and never reduces. */ private List buffers = new ArrayList(); /** The index of the current buffer. */ private int currentBufferIndex; /** The total count of bytes in all the filled buffers. */ private int filledBufferSum; /** The current buffer. */ private byte[] currentBuffer; /** The total count of bytes written. */ private int count; /** * Creates a new byte array output stream. The buffer capacity is * initially 1024 bytes, though its size increases if necessary. */ public ByteArrayOutputStream() { this(1024); } /** * Creates a new byte array output stream, with a buffer capacity of * the specified size, in bytes. * * @param size the initial size * @throws IllegalArgumentException if size is negative */ public ByteArrayOutputStream(int size) { if (size < 0) { throw new IllegalArgumentException("Negative initial size: " + size); } needNewBuffer(size); } /** * Return the appropriate <code>byte[]</code> buffer * specified by index. * * @param index the index of the buffer required * @return the buffer */ private byte[] getBuffer(int index) { return (byte[]) buffers.get(index); } /** * Makes a new buffer available either by allocating * a new one or re-cycling an existing one. * * @param newcount the size of the buffer if one is created */ private void needNewBuffer(int newcount) { if (currentBufferIndex < buffers.size() - 1) { //Recycling old buffer filledBufferSum += currentBuffer.length; currentBufferIndex++; currentBuffer = getBuffer(currentBufferIndex); } else { //Creating new buffer int newBufferSize; if (currentBuffer == null) { newBufferSize = newcount; filledBufferSum = 0; } else { newBufferSize = Math.max(currentBuffer.length << 1, newcount - filledBufferSum); filledBufferSum += currentBuffer.length; } currentBufferIndex++; currentBuffer = new byte[newBufferSize]; buffers.add(currentBuffer); } } /** * Write the bytes to byte array. * @param b the bytes to write * @param off The start offset * @param len The number of bytes to write */ public 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; } synchronized (this) { int newcount = count + len; int remaining = len; int inBufferPos = count - filledBufferSum; while (remaining > 0) { int part = Math.min(remaining, currentBuffer.length - inBufferPos); System.arraycopy(b, off + len - remaining, currentBuffer, inBufferPos, part); remaining -= part; if (remaining > 0) { needNewBuffer(newcount); inBufferPos = 0; } } count = newcount; } } /** * Write a byte to byte array. * @param b the byte to write */ public synchronized void write(int b) { int inBufferPos = count - filledBufferSum; if (inBufferPos == currentBuffer.length) { needNewBuffer(count + 1); inBufferPos = 0; } currentBuffer[inBufferPos] = (byte) b; count++; } /** * Writes the entire contents of the specified input stream to this * byte stream. Bytes from the input stream are read directly into the * internal buffers of this streams. * * @param in the input stream to read from * @return total number of bytes read from the input stream * (and written to this stream) * @throws IOException if an I/O error occurs while reading the input stream * @since Commons IO 1.4 */ public synchronized int write(InputStream in) throws IOException { int readCount = 0; int inBufferPos = count - filledBufferSum; int n = in.read(currentBuffer, inBufferPos, currentBuffer.length - inBufferPos); while (n != -1) { readCount += n; inBufferPos += n; count += n; if (inBufferPos == currentBuffer.length) { needNewBuffer(currentBuffer.length); inBufferPos = 0; } n = in.read(currentBuffer, inBufferPos, currentBuffer.length - inBufferPos); } return readCount; } /** * Return the current size of the byte array. * @return the current size of the byte array */ public synchronized int size() { return count; } /** * Closing a <tt>ByteArrayOutputStream</tt> has no effect. The methods in * this class can be called after the stream has been closed without * generating an <tt>IOException</tt>. * * @throws IOException never (this method should not declare this exception * but it has to now due to backwards compatability) */ public void close() throws IOException { //nop } /** * @see java.io.ByteArrayOutputStream#reset() */ public synchronized void reset() { count = 0; filledBufferSum = 0; currentBufferIndex = 0; currentBuffer = getBuffer(currentBufferIndex); } /** * Writes the entire contents of this byte stream to the * specified output stream. * * @param out the output stream to write to * @throws IOException if an I/O error occurs, such as if the stream is closed * @see java.io.ByteArrayOutputStream#writeTo(OutputStream) */ public synchronized void writeTo(OutputStream out) throws IOException { int remaining = count; for (int i = 0; i < buffers.size(); i++) { byte[] buf = getBuffer(i); int c = Math.min(buf.length, remaining); out.write(buf, 0, c); remaining -= c; if (remaining == 0) { break; } } } /** * Gets the curent contents of this byte stream as a byte array. * The result is independent of this stream. * * @return the current contents of this output stream, as a byte array * @see java.io.ByteArrayOutputStream#toByteArray() */ public synchronized byte[] toByteArray() { int remaining = count; if (remaining == 0) { return EMPTY_BYTE_ARRAY; } byte newbuf[] = new byte[remaining]; int pos = 0; for (int i = 0; i < buffers.size(); i++) { byte[] buf = getBuffer(i); int c = Math.min(buf.length, remaining); System.arraycopy(buf, 0, newbuf, pos, c); pos += c; remaining -= c; if (remaining == 0) { break; } } return newbuf; } /** * Gets the curent contents of this byte stream as a string. * @return the contents of the byte array as a String * @see java.io.ByteArrayOutputStream#toString() */ public String toString() { return new String(toByteArray()); } /** * Gets the curent contents of this byte stream as a string * using the specified encoding. * * @param enc the name of the character encoding * @return the string converted from the byte array * @throws UnsupportedEncodingException if the encoding is not supported * @see java.io.ByteArrayOutputStream#toString(String) */ public String toString(String enc) throws UnsupportedEncodingException { return new String(toByteArray(), enc); } }