我有一个接受 InputStream 并从中读取数据的方法。我也想将此方法与 ByteBuffer 一起使用。有没有办法包装一个 ByteBuffer 以便它可以作为流访问？
【问题讨论】：
标签： java nio inputstream bytebuffer
JDK 中什么都没有，但是那里有很多实现，谷歌 ByteBufferInputStream。基本上，它们包装一个或多个 ByteBuffer 并跟踪其中的索引，该索引记录了已读取的内容。 like this 出现了很多，但显然是错误的，请参阅 @Mike Houston's answer for an improved version)。
【讨论】：
如果它由字节数组支持，您可以使用ByteArrayInputStream 并通过ByteBuffer.array() 获取字节数组。如果您在本机 ByteBuffer 上尝试，这将引发异常。
【讨论】：
Thilo 提到的实现似乎存在一些错误，并且还逐字复制并粘贴到其他网站上：
ByteBufferBackedInputStream.read() 返回它读取的字节的符号扩展 int 表示，这是错误的（值应在 [-1..255] 范围内）ByteBufferBackedInputStream.read(byte[], int, int) 不会返回 -1ByteBufferBackedOutputStream 似乎比较健全。
我在下面展示了一个“固定”版本。如果我发现更多错误（或有人指出），我会在这里更新。
更新：从读/写方法中删除了synchronized关键字
public class ByteBufferBackedInputStream extends InputStream {
ByteBuffer buf;
public ByteBufferBackedInputStream(ByteBuffer buf) {
this.buf = buf;
}
public int read() throws IOException {
if (!buf.hasRemaining()) {
return -1;
}
return buf.get() & 0xFF;
}
public int read(byte[] bytes, int off, int len)
throws IOException {
if (!buf.hasRemaining()) {
return -1;
}
len = Math.min(len, buf.remaining());
buf.get(bytes, off, len);
return len;
}
}
public class ByteBufferBackedOutputStream extends OutputStream {
ByteBuffer buf;
public ByteBufferBackedOutputStream(ByteBuffer buf) {
this.buf = buf;
}
public void write(int b) throws IOException {
buf.put((byte) b);
}
public void write(byte[] bytes, int off, int len)
throws IOException {
buf.put(bytes, off, len);
}
}
【讨论】：
flush 产生这种效果？似乎flip 会令人困惑，因为它会覆盖早期的数据，而flush() 通常不会这样做。我假设您正在尝试使用包装在输入和输出流中的单个缓冲区作为缓冲区？
for (int i = 0 ; i < len ; i++) { write(b[off + i]); } 为了提高效率，我们可以将字节数组直接传递到缓冲区，避免与 int 值相互转换并为每个字节调用一个函数。
throws IOException，因为实际实现从不抛出这些异常。
int available()。
如果可用，直接使用堆缓冲区（字节数组），否则使用包装的字节缓冲区（见答案 Mike Houston）
public static InputStream asInputStream(ByteBuffer buffer) {
if (buffer.hasArray()) {
// use heap buffer; no array is created; only the reference is used
return new ByteArrayInputStream(buffer.array());
}
return new ByteBufferInputStream(buffer);
}
还要注意，包装的缓冲区可以有效地支持标记/重置和跳过操作。
【讨论】：
.array() 是可选操作。它可能未实现（例如MappedByteBuffer），即使已实现，也会为只读缓冲区抛出异常。
buffer.hasArray() 存在的原因:)
InputStream 基于整个数组，这将是可以的，但不会为具有偏移量的流提供所需的结果。与您早 4 年提供的 this answer 相同的问题...
ByteBuffer 以作为流访问。 ByteBuffer 使用偏移量来控制调用者通常可以访问底层数组的哪个部分。这就是首先使用ByteBuffer 而不仅仅是byte[] 的部分原因。
这是我的InputStream & OutputStream 实现版本：
ByteBufferBackedInputStream:
public class ByteBufferBackedInputStream extends InputStream
{
private ByteBuffer backendBuffer;
public ByteBufferBackedInputStream(ByteBuffer backendBuffer) {
Objects.requireNonNull(backendBuffer, "Given backend buffer can not be null!");
this.backendBuffer = backendBuffer;
}
public void close() throws IOException {
this.backendBuffer = null;
}
private void ensureStreamAvailable() throws IOException {
if (this.backendBuffer == null) {
throw new IOException("read on a closed InputStream!");
}
}
@Override
public int read() throws IOException {
this.ensureStreamAvailable();
return this.backendBuffer.hasRemaining() ? this.backendBuffer.get() & 0xFF : -1;
}
@Override
public int read(@Nonnull byte[] buffer) throws IOException {
return this.read(buffer, 0, buffer.length);
}
@Override
public int read(@Nonnull byte[] buffer, int offset, int length) throws IOException {
this.ensureStreamAvailable();
Objects.requireNonNull(buffer, "Given buffer can not be null!");
if (offset >= 0 && length >= 0 && length <= buffer.length - offset) {
if (length == 0) {
return 0;
}
else {
int remainingSize = Math.min(this.backendBuffer.remaining(), length);
if (remainingSize == 0) {
return -1;
}
else {
this.backendBuffer.get(buffer, offset, remainingSize);
return remainingSize;
}
}
}
else {
throw new IndexOutOfBoundsException();
}
}
public long skip(long n) throws IOException {
this.ensureStreamAvailable();
if (n <= 0L) {
return 0L;
}
int length = (int) n;
int remainingSize = Math.min(this.backendBuffer.remaining(), length);
this.backendBuffer.position(this.backendBuffer.position() + remainingSize);
return (long) length;
}
public int available() throws IOException {
this.ensureStreamAvailable();
return this.backendBuffer.remaining();
}
public synchronized void mark(int var1) {
}
public synchronized void reset() throws IOException {
throw new IOException("mark/reset not supported");
}
public boolean markSupported() {
return false;
}
}
ByteBufferBackedOutputStream:
public class ByteBufferBackedOutputStream extends OutputStream
{
private ByteBuffer backendBuffer;
public ByteBufferBackedOutputStream(ByteBuffer backendBuffer) {
Objects.requireNonNull(backendBuffer, "Given backend buffer can not be null!");
this.backendBuffer = backendBuffer;
}
public void close() throws IOException {
this.backendBuffer = null;
}
private void ensureStreamAvailable() throws IOException {
if (this.backendBuffer == null) {
throw new IOException("write on a closed OutputStream");
}
}
@Override
public void write(int b) throws IOException {
this.ensureStreamAvailable();
backendBuffer.put((byte) b);
}
@Override
public void write(@Nonnull byte[] bytes) throws IOException {
this.write(bytes, 0, bytes.length);
}
@Override
public void write(@Nonnull byte[] bytes, int off, int len) throws IOException {
this.ensureStreamAvailable();
Objects.requireNonNull(bytes, "Given buffer can not be null!");
if ((off < 0) || (off > bytes.length) || (len < 0) ||
((off + len) > bytes.length) || ((off + len) < 0))
{
throw new IndexOutOfBoundsException();
}
else if (len == 0) {
return;
}
backendBuffer.put(bytes, off, len);
}
}
【讨论】：
基于 ByteArrayInputStream 代码的派生... 要求提供的 ByteBuffer 提前正确设置位置和限制。
public class ByteBufferInputStream extends InputStream
{
/**
* The input ByteBuffer that was provided.
* The ByteBuffer should be supplied with position and limit correctly set as appropriate
*/
protected ByteBuffer buf;
public ByteBufferInputStream(ByteBuffer buf)
{
this.buf = buf;
buf.mark(); // to prevent java.nio.InvalidMarkException on InputStream.reset() if mark had not been set
}
/**
* Reads the next byte of data from this ByteBuffer. The value byte is returned as an int in the range 0-255.
* If no byte is available because the end of the buffer has been reached, the value -1 is returned.
* @return the next byte of data, or -1 if the limit/end of the buffer has been reached.
*/
public int read()
{
return buf.hasRemaining()
? (buf.get() & 0xff)
: -1;
}
/**
* Reads up to len bytes of data into an array of bytes from this ByteBuffer.
* If the buffer has no remaining bytes, then -1 is returned to indicate end of file.
* Otherwise, the number k of bytes read is equal to the smaller of len and buffer remaining.
* @param b the buffer into which the data is read.
* @param off the start offset in the destination array b
* @param len the maximum number of bytes read.
* @return the total number of bytes read into the buffer, or -1 if there is no more data because the limit/end of
* the ByteBuffer has been reached.
* @exception NullPointerException If b is null.
* @exception IndexOutOfBoundsException If off is negative, len is negative, or len is greater than b.length - off
*/
public int read(byte b[], int off, int len)
{
if (b == null)
{
throw new NullPointerException();
}
else if (off < 0 || len < 0 || len > b.length - off)
{
throw new IndexOutOfBoundsException();
}
if (!buf.hasRemaining())
{
return -1;
}
int remaining = buf.remaining();
if (len > remaining)
{
len = remaining;
}
if (len <= 0)
{
return 0;
}
buf.get(b, off, len);
return len;
}
/**
* Skips n bytes of input from this ByteBuffer. Fewer bytes might be skipped if the limit is reached.
*
* @param n the number of bytes to be skipped.
* @return the actual number of bytes skipped.
*/
public long skip(long n)
{
int skipAmount = (n < 0)
? 0
: ((n > Integer.MAX_VALUE)
? Integer.MAX_VALUE
: (int) n);
if (skipAmount > buf.remaining())
{
skipAmount = buf.remaining();
}
int newPos = buf.position() + skipAmount;
buf.position(newPos);
return skipAmount;
}
/**
* Returns remaining bytes available in this ByteBuffer
* @return the number of remaining bytes that can be read (or skipped over) from this ByteBuffer.
*/
public int available()
{
return buf.remaining();
}
public boolean markSupported()
{
return true;
}
/**
* Set the current marked position in the ByteBuffer.
* <p> Note: The readAheadLimit for this class has no meaning.
*/
public void mark(int readAheadLimit)
{
buf.mark();
}
/**
* Resets the ByteBuffer to the marked position.
*/
public void reset()
{
buf.reset();
}
/**
* Closing a ByteBuffer has no effect.
* The methods in this class can be called after the stream has been closed without generating an IOException.
*/
public void close() throws IOException
{
}
}
【讨论】：