我已经阅读了太阳指南和不同的类似问题。我想从 Socket 读取一些未知数量的字节到一个数组中。
我有两个选择，我可以在循环中使用 read(byte) 并将字节添加到字节数组，或者我可以使用 DataInputStream readFully(byte[]) 将所有字节读入字节数组。哪个更好，如何事先找到字节数组的大小进行分配？另外，如果我使用第一种方法，如何在字节数组中附加字节。
while(in.read(b) ! = -1)
{
//Add to byte array, but how to append at the end?
}
我可以使用 StringBuilder 接收数据，附加到它，然后执行toString().getBytes() 吗？
【问题讨论】：
分小块读取并写入ByteArrayOutputStream
ByteArrayOutputStream baos = new ByteArrayOutputStream();
byte buffer[] = new byte[1024];
for(int s; (s=in.read(buffer)) != -1; )
{
baos.write(buffer, 0, s);
}
byte result[] = baos.toByteArray();
【讨论】：
我有两个选择，我可以在循环中使用 read(byte) 并将字节添加到字节数组，或者我可以使用 DataInputStream readFully(byte[]) 将所有字节读入字节数组。哪个更好
两者都不能真正解决您的问题，因为...
如何事先找到字节数组的大小进行分配？
...您无法事先找到字节数组的大小，除非：
我可以使用StringBuilder来接收数据吗...
理论上可以使用StringBuilder。但是，它需要从字节转换为字符然后再转换回来……这可能有损耗。您也许可以找到一个无损的 8 位字符编码/解码……但我不会这样做。
我会简单地使用ByteArrayOutputStream 作为累积字节的缓冲区，然后使用toByteArray() 来提取它们。如@kan 的回答所示，您可以分块从套接字读取字节。
【讨论】：
先传大小，再传数据？
否则，您不能使用数组，但需要使用可调整大小的东西。
您不能追加到 Java 中的数组 - 它们不能增长。您可以设置一个缓冲区，并记住您当前使用它的位置。这实际上是 ArrayList 所做的：分配一个缓冲区，当超出其容量时，分配一个更大的缓冲区并将数据复制过来。重复。
【讨论】：
这应该可以解决问题。我不久前修改了它，以修复实现中的一些危险的同步错误。它不是 Java 类路径的一部分，但它很高效并且可以动态扩展。与其他解决方案相比，它有一些巧妙的技巧。
/*
* Circular Byte Buffer
* Copyright (C) 2002 Stephen Ostermiller
* http://ostermiller.org/contact.pl?regarding=Java+Utilities
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* See COPYING.TXT for details.
*/
package misc;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.BufferOverflowException;
import com.Ostermiller.util.CircularCharBuffer;
import com.Ostermiller.util.CircularObjectBuffer;
/**
* Implements the Circular Buffer producer/consumer model for bytes.
* More information about this class is available from <a target="_top" href=
* "http://ostermiller.org/utils/CircularByteBuffer.html">ostermiller.org</a>.
* <p>
* Using this class is a simpler alternative to using a PipedInputStream
* and a PipedOutputStream. PipedInputStreams and PipedOutputStreams don't support the
* mark operation, don't allow you to control buffer sizes that they use,
* and have a more complicated API that requires instantiating two
* classes and connecting them.
* <p>
* This class is thread safe.
*
* @see CircularCharBuffer
* @see CircularObjectBuffer
*
* @author Stephen Ostermiller http://ostermiller.org/contact.pl?regarding=Java+Utilities
* @since ostermillerutils 1.00.00
*/
public class CircularByteBuffer {
/**
* The default size for a circular byte buffer.
*
* @since ostermillerutils 1.00.00
*/
private final static int DEFAULT_SIZE = 1024;
/**
* A buffer that will grow as things are added.
*
* @since ostermillerutils 1.00.00
*/
public final static int INFINITE_SIZE = -1;
/**
* The circular buffer.
* <p>
* The actual capacity of the buffer is one less than the actual length
* of the buffer so that an empty and a full buffer can be
* distinguished. An empty buffer will have the markPostion and the
* writePosition equal to each other. A full buffer will have
* the writePosition one less than the markPostion.
* <p>
* There are three important indexes into the buffer:
* The readPosition, the writePosition, and the markPosition.
* If the InputStream has never been marked, the readPosition and
* the markPosition should always be the same. The bytes
* available to be read go from the readPosition to the writePosition,
* wrapping around the end of the buffer. The space available for writing
* goes from the write position to one less than the markPosition,
* wrapping around the end of the buffer. The bytes that have
* been saved to support a reset() of the InputStream go from markPosition
* to readPosition, wrapping around the end of the buffer.
*
* @since ostermillerutils 1.00.00
*/
protected byte[] buffer;
/**
* Index of the first byte available to be read.
*
* @since ostermillerutils 1.00.00
*/
protected volatile int readPosition = 0;
/**
* Index of the first byte available to be written.
*
* @since ostermillerutils 1.00.00
*/
protected volatile int writePosition = 0;
/**
* Index of the first saved byte. (To support stream marking.)
*
* @since ostermillerutils 1.00.00
*/
protected volatile int markPosition = 0;
/**
* Number of bytes that have to be saved
* to support mark() and reset() on the InputStream.
*
* @since ostermillerutils 1.00.00
*/
protected volatile int markSize = 0;
/**
* If this buffer is infinite (should resize itself when full)
*
* @since ostermillerutils 1.00.00
*/
protected volatile boolean infinite = false;
/**
* True if a write to a full buffer should block until the buffer
* has room, false if the write method should throw an IOException
*
* @since ostermillerutils 1.00.00
*/
protected boolean blockingWrite = true;
/**
* The InputStream that can empty this buffer.
*
* @since ostermillerutils 1.00.00
*/
protected InputStream in = new CircularByteBufferInputStream();
/**
* true if the close() method has been called on the InputStream
*
* @since ostermillerutils 1.00.00
*/
protected boolean inputStreamClosed = false;
/**
* The OutputStream that can fill this buffer.
*
* @since ostermillerutils 1.00.00
*/
protected OutputStream out = new CircularByteBufferOutputStream();
/**
* true if the close() method has been called on the OutputStream
*
* @since ostermillerutils 1.00.00
*/
protected boolean outputStreamClosed = false;
/**
* Make this buffer ready for reuse. The contents of the buffer
* will be cleared and the streams associated with this buffer
* will be reopened if they had been closed.
*
* @since ostermillerutils 1.00.00
*/
public void clear(){
synchronized (this){
readPosition = 0;
writePosition = 0;
markPosition = 0;
outputStreamClosed = false;
inputStreamClosed = false;
}
}
/**
* Retrieve a OutputStream that can be used to fill
* this buffer.
* <p>
* Write methods may throw a BufferOverflowException if
* the buffer is not large enough. A large enough buffer
* size must be chosen so that this does not happen or
* the caller must be prepared to catch the exception and
* try again once part of the buffer has been consumed.
*
*
* @return the producer for this buffer.
*
* @since ostermillerutils 1.00.00
*/
public OutputStream getOutputStream(){
return out;
}
/**
* Retrieve a InputStream that can be used to empty
* this buffer.
* <p>
* This InputStream supports marks at the expense
* of the buffer size.
*
* @return the consumer for this buffer.
*
* @since ostermillerutils 1.00.00
*/
public InputStream getInputStream(){
return in;
}
/**
* Get number of bytes that are available to be read.
* <p>
* Note that the number of bytes available plus
* the number of bytes free may not add up to the
* capacity of this buffer, as the buffer may reserve some
* space for other purposes.
*
* @return the size in bytes of this buffer
*
* @since ostermillerutils 1.00.00
*/
public int getAvailable(){
synchronized (this){
return available();
}
}
/**
* Get the number of bytes this buffer has free for
* writing.
* <p>
* Note that the number of bytes available plus
* the number of bytes free may not add up to the
* capacity of this buffer, as the buffer may reserve some
* space for other purposes.
*
* @return the available space in bytes of this buffer
*
* @since ostermillerutils 1.00.00
*/
public int getSpaceLeft(){
synchronized (this){
return spaceLeft();
}
}
/**
* Get the capacity of this buffer.
* <p>
* Note that the number of bytes available plus
* the number of bytes free may not add up to the
* capacity of this buffer, as the buffer may reserve some
* space for other purposes.
*
* @return the size in bytes of this buffer
*
* @since ostermillerutils 1.00.00
*/
public int getSize(){
synchronized (this){
return buffer.length;
}
}
/**
* double the size of the buffer
*
* @since ostermillerutils 1.00.00
*/
private void resize(){
synchronized (CircularByteBuffer.this) {
byte[] newBuffer = new byte[buffer.length * 2];
int marked = marked();
int available = available();
if (markPosition <= writePosition){
// any space between the mark and
// the first write needs to be saved.
// In this case it is all in one piece.
int length = writePosition - markPosition;
System.arraycopy(buffer, markPosition, newBuffer, 0, length);
} else {
int length1 = buffer.length - markPosition;
System.arraycopy(buffer, markPosition, newBuffer, 0, length1);
int length2 = writePosition;
System.arraycopy(buffer, 0, newBuffer, length1, length2);
}
buffer = newBuffer;
markPosition = 0;
readPosition = marked;
writePosition = marked + available;
CircularByteBuffer.this.notifyAll();
}
}
/**
* Space available in the buffer which can be written.
*
* @since ostermillerutils 1.00.00
*/
private int spaceLeft(){
if (writePosition < markPosition){
// any space between the first write and
// the mark except one byte is available.
// In this case it is all in one piece.
return (markPosition - writePosition - 1);
}
// space at the beginning and end.
return ((buffer.length - 1) - (writePosition - markPosition));
}
/**
* Bytes available for reading.
*
* @since ostermillerutils 1.00.00
*/
private int available(){
if (readPosition <= writePosition){
// any space between the first read and
// the first write is available. In this case i
// is all in one piece.
return (writePosition - readPosition);
}
// space at the beginning and end.
return (buffer.length - (readPosition - writePosition));
}
/**
* Bytes saved for supporting marks.
*
* @since ostermillerutils 1.00.00
*/
private int marked(){
if (markPosition <= readPosition){
// any space between the markPosition and
// the first write is marked. In this case i
// is all in one piece.
return (readPosition - markPosition);
}
// space at the beginning and end.
return (buffer.length - (markPosition - readPosition));
}
/**
* If we have passed the markSize reset the
* mark so that the space can be used.
*
* @since ostermillerutils 1.00.00
*/
private void ensureMark(){
if (marked() >= markSize){
markPosition = readPosition;
markSize = 0;
}
}
/**
* Create a new buffer with a default capacity.
* Writing to a full buffer will block until space
* is available rather than throw an exception.
*
* @since ostermillerutils 1.00.00
*/
public CircularByteBuffer(){
this (DEFAULT_SIZE, true);
}
/**
* Create a new buffer with given capacity.
* Writing to a full buffer will block until space
* is available rather than throw an exception.
* <p>
* Note that the buffer may reserve some bytes for
* special purposes and capacity number of bytes may
* not be able to be written to the buffer.
* <p>
* Note that if the buffer is of INFINITE_SIZE it will
* neither block or throw exceptions, but rather grow
* without bound.
*
* @param size desired capacity of the buffer in bytes or CircularByteBuffer.INFINITE_SIZE.
*
* @since ostermillerutils 1.00.00
*/
public CircularByteBuffer(int size){
this (size, true);
}
/**
* Create a new buffer with a default capacity and
* given blocking behavior.
*
* @param blockingWrite true writing to a full buffer should block
* until space is available, false if an exception should
* be thrown instead.
*
* @since ostermillerutils 1.00.00
*/
public CircularByteBuffer(boolean blockingWrite){
this (DEFAULT_SIZE, blockingWrite);
}
/**
* Create a new buffer with the given capacity and
* blocking behavior.
* <p>
* Note that the buffer may reserve some bytes for
* special purposes and capacity number of bytes may
* not be able to be written to the buffer.
* <p>
* Note that if the buffer is of INFINITE_SIZE it will
* neither block or throw exceptions, but rather grow
* without bound.
*
* @param size desired capacity of the buffer in bytes or CircularByteBuffer.INFINITE_SIZE.
* @param blockingWrite true writing to a full buffer should block
* until space is available, false if an exception should
* be thrown instead.
*
* @since ostermillerutils 1.00.00
*/
public CircularByteBuffer(int size, boolean blockingWrite){
if (size == INFINITE_SIZE){
buffer = new byte[DEFAULT_SIZE];
infinite = true;
} else {
buffer = new byte[size];
infinite = false;
}
this.blockingWrite = blockingWrite;
}
/**
* Class for reading from a circular byte buffer.
*
* @since ostermillerutils 1.00.00
*/
protected class CircularByteBufferInputStream extends InputStream {
/**
* Returns the number of bytes that can be read (or skipped over) from this
* input stream without blocking by the next caller of a method for this input
* stream. The next caller might be the same thread or or another thread.
*
* @return the number of bytes that can be read from this input stream without blocking.
* @throws IOException if the stream is closed.
*
* @since ostermillerutils 1.00.00
*/
@Override public int available() throws IOException {
synchronized (CircularByteBuffer.this){
if (inputStreamClosed) throw new IOException("InputStream has been closed, it is not ready.");
return (CircularByteBuffer.this.available());
}
}
/**
* Close the stream. Once a stream has been closed, further read(), available(),
* mark(), or reset() invocations will throw an IOException. Closing a
* previously-closed stream, however, has no effect.
*
* @throws IOException never.
*
* @since ostermillerutils 1.00.00
*/
@Override public void close() throws IOException {
synchronized (CircularByteBuffer.this){
inputStreamClosed = true;
}
}
/**
* Mark the present position in the stream. Subsequent calls to reset() will
* attempt to reposition the stream to this point.
* <p>
* The readAheadLimit must be less than the size of circular buffer, otherwise
* this method has no effect.
*
* @param readAheadLimit Limit on the number of bytes that may be read while
* still preserving the mark. After reading this many bytes, attempting to
* reset the stream will fail.
*
* @since ostermillerutils 1.00.00
*/
@Override public void mark(int readAheadLimit) {
synchronized (CircularByteBuffer.this){
//if (inputStreamClosed) throw new IOException("InputStream has been closed; cannot mark a closed InputStream.");
if (buffer.length - 1 > readAheadLimit) {
markSize = readAheadLimit;
markPosition = readPosition;
}
}
}
/**
* Tell whether this stream supports the mark() operation.
*
* @return true, mark is supported.
*
* @since ostermillerutils 1.00.00
*/
@Override public boolean markSupported() {
return true;
}
/**
* Read a single byte.
* This method will block until a byte is available, an I/O error occurs,
* or the end of the stream is reached.
*
* @return The byte read, as an integer in the range 0 to 255 (0x00-0xff),
* or -1 if the end of the stream has been reached
* @throws IOException if the stream is closed.
*
* @since ostermillerutils 1.00.00
*/
@Override public int read() throws IOException {
synchronized (CircularByteBuffer.this){
while (true) {
if (inputStreamClosed) throw new IOException("InputStream has been closed; cannot read from a closed InputStream.");
int available = CircularByteBuffer.this.available();
if (available > 0){
int result = buffer[readPosition] & 0xff;
readPosition++;
if (readPosition == buffer.length){
readPosition = 0;
}
ensureMark();
return result;
} else if (outputStreamClosed){
return -1;
} else {
try {
CircularByteBuffer.this.wait();
} catch(Exception x){
throw new IOException("Blocking read operation interrupted.");
}
}
}
}
}
/**
* Read bytes into an array.
* This method will block until some input is available,
* an I/O error occurs, or the end of the stream is reached.
*
* @param cbuf Destination buffer.
* @return The number of bytes read, or -1 if the end of
* the stream has been reached
* @throws IOException if the stream is closed.
*
* @since ostermillerutils 1.00.00
*/
@Override public int read(byte[] cbuf) throws IOException {
return read(cbuf, 0, cbuf.length);
}
/**
* Read bytes into a portion of an array.
* This method will block until some input is available,
* an I/O error occurs, or the end of the stream is reached.
*
* @param cbuf Destination buffer.
* @param off Offset at which to start storing bytes.
* @param len Maximum number of bytes to read.
* @return The number of bytes read, or -1 if the end of
* the stream has been reached
* @throws IOException if the stream is closed.
*
* @since ostermillerutils 1.00.00
*/
@Override public int read(byte[] cbuf, int off, int len) throws IOException {
synchronized (CircularByteBuffer.this){
while (true){
if (inputStreamClosed) throw new IOException("InputStream has been closed; cannot read from a closed InputStream.");
int available = CircularByteBuffer.this.available();
if (available > 0){
int length = Math.min(len, available);
int firstLen = Math.min(length, buffer.length - readPosition);
int secondLen = length - firstLen;
System.arraycopy(buffer, readPosition, cbuf, off, firstLen);
if (secondLen > 0){
System.arraycopy(buffer, 0, cbuf, off+firstLen, secondLen);
readPosition = secondLen;
} else {
readPosition += length;
}
if (readPosition == buffer.length) {
readPosition = 0;
}
ensureMark();
return length;
} else if (outputStreamClosed){
return -1;
} else {
try {
CircularByteBuffer.this.wait();
} catch(Exception x){
throw new IOException("Blocking read operation interrupted.");
}
}
}
}
}
/**
* Reset the stream.
* If the stream has been marked, then attempt to reposition i
* at the mark. If the stream has not been marked, or more bytes
* than the readAheadLimit have been read, this method has no effect.
*
* @throws IOException if the stream is closed.
*
* @since ostermillerutils 1.00.00
*/
@Override public void reset() throws IOException {
synchronized (CircularByteBuffer.this){
if (inputStreamClosed) throw new IOException("InputStream has been closed; cannot reset a closed InputStream.");
readPosition = markPosition;
}
}
/**
* Skip bytes.
* This method will block until some bytes are available,
* an I/O error occurs, or the end of the stream is reached.
*
* @param n The number of bytes to skip
* @return The number of bytes actually skipped
* @throws IllegalArgumentException if n is negative.
* @throws IOException if the stream is closed.
*
* @since ostermillerutils 1.00.00
*/
@Override public long skip(long n) throws IOException, IllegalArgumentException {
synchronized (CircularByteBuffer.this){
while (true){
if (inputStreamClosed) throw new IOException("InputStream has been closed; cannot skip bytes on a closed InputStream.");
int available = CircularByteBuffer.this.available();
if (available > 0){
int length = Math.min((int)n, available);
int firstLen = Math.min(length, buffer.length - readPosition);
int secondLen = length - firstLen;
if (secondLen > 0){
readPosition = secondLen;
} else {
readPosition += length;
}
if (readPosition == buffer.length) {
readPosition = 0;
}
ensureMark();
return length;
} else if (outputStreamClosed){
return 0;
} else {
try {
CircularByteBuffer.this.wait();
} catch(Exception x){
throw new IOException("Blocking read operation interrupted.");
}
}
}
}
}
}
/**
* Class for writing to a circular byte buffer.
* If the buffer is full, the writes will either block
* until there is some space available or throw an IOException
* based on the CircularByteBuffer's preference.
*
* @since ostermillerutils 1.00.00
*/
protected class CircularByteBufferOutputStream extends OutputStream {
/**
* Close the stream, flushing it first.
* This will cause the InputStream associated with this circular buffer
* to read its last bytes once it empties the buffer.
* Once a stream has been closed, further write() or flush() invocations
* will cause an IOException to be thrown. Closing a previously-closed stream,
* however, has no effect.
*
* @throws IOException never.
*
* @since ostermillerutils 1.00.00
*/
@Override public void close() throws IOException {
synchronized (CircularByteBuffer.this){
if (!outputStreamClosed){
flush();
}
outputStreamClosed = true;
}
}
/**
* Flush the stream.
*
* @throws IOException if the stream is closed.
*
* @since ostermillerutils 1.00.00
*/
@Override public void flush() throws IOException {
synchronized (CircularByteBuffer.this) {
// this method needs to do nothing
CircularByteBuffer.this.notifyAll();
}
}
/**
* Write an array of bytes.
* If the buffer allows blocking writes, this method will block until
* all the data has been written rather than throw an IOException.
*
* @param cbuf Array of bytes to be written
* @throws BufferOverflowException if buffer does not allow blocking writes
* and the buffer is full. If the exception is thrown, no data
* will have been written since the buffer was set to be non-blocking.
* @throws IOException if the stream is closed, or the write is interrupted.
*
* @since ostermillerutils 1.00.00
*/
@Override public void write(byte[] cbuf) throws IOException {
write(cbuf, 0, cbuf.length);
}
/**
* Write a portion of an array of bytes.
* If the buffer allows blocking writes, this method will block until
* all the data has been written rather than throw an IOException.
*
* @param cbuf Array of bytes
* @param off Offset from which to start writing bytes
* @param len - Number of bytes to write
* @throws BufferOverflowException if buffer does not allow blocking writes
* and the buffer is full. If the exception is thrown, no data
* will have been written since the buffer was set to be non-blocking.
* @throws IOException if the stream is closed, or the write is interrupted.
*
* @since ostermillerutils 1.00.00
*/
@Override public void write(byte[] cbuf, int off, int len) throws IOException {
synchronized (CircularByteBuffer.this){
while (len > 0){
if (outputStreamClosed) throw new IOException("OutputStream has been closed; cannot write to a closed OutputStream.");
if (inputStreamClosed) throw new IOException("Buffer closed by InputStream; cannot write to a closed buffer.");
while (infinite && spaceLeft() < len){
resize();
}
while (!infinite && spaceLeft() < len) {
// wait for space to become available
try {
CircularByteBuffer.this.wait();
} catch (InterruptedException e) {
}
}
if (!blockingWrite && spaceLeft() < len) throw new BufferOverflowException();
int realLen = Math.min(len, spaceLeft());
int firstLen = Math.min(realLen, buffer.length - writePosition);
int secondLen = Math.min(realLen - firstLen, buffer.length - markPosition - 1);
int written = firstLen + secondLen;
if (firstLen > 0){
System.arraycopy(cbuf, off, buffer, writePosition, firstLen);
}
if (secondLen > 0){
System.arraycopy(cbuf, off+firstLen, buffer, 0, secondLen);
writePosition = secondLen;
} else {
writePosition += written;
}
if (writePosition == buffer.length) {
writePosition = 0;
}
off += written;
len -= written;
}
CircularByteBuffer.this.notifyAll();
}
}
/**
* Write a single byte.
* The byte to be written is contained in the 8 low-order bits of the
* given integer value; the 24 high-order bits are ignored.
* If the buffer allows blocking writes, this method will block until
* all the data has been written rather than throw an IOException.
*
* @param c number of bytes to be written
* @throws BufferOverflowException if buffer does not allow blocking writes
* and the buffer is full.
* @throws IOException if the stream is closed, or the write is interrupted.
*
* @since ostermillerutils 1.00.00
*/
@Override public void write(int c) throws IOException {
boolean written = false;
synchronized (CircularByteBuffer.this){
while (!written){
if (outputStreamClosed) throw new IOException("OutputStream has been closed; cannot write to a closed OutputStream.");
if (inputStreamClosed) throw new IOException("Buffer closed by InputStream; cannot write to a closed buffer.");
int spaceLeft = spaceLeft();
while (infinite && spaceLeft < 1){
resize();
spaceLeft = spaceLeft();
}
if (!blockingWrite && spaceLeft < 1) throw new BufferOverflowException();
if (spaceLeft > 0){
buffer[writePosition] = (byte)(c & 0xff);
writePosition++;
if (writePosition == buffer.length) {
writePosition = 0;
}
written = true;
}
}
if (!written){
try {
CircularByteBuffer.this.wait(100);
} catch(Exception x){
throw new IOException("Waiting for available space in buffer interrupted.");
}
}
CircularByteBuffer.this.notifyAll();
}
}
}
}
从ostermiller.org 获取 jar 并将其添加到您的项目库中，以获取其他缺少的类。
【讨论】：