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？
问问题
63161 次
6 回答
83
Thilo 提到的实现似乎存在一些错误，并且还逐字复制并粘贴在其他网站上：
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)根据 API 规范，当缓冲区中没有剩余字节时不返回 -1
ByteBufferBackedOutputStream 似乎相对健全。
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：synchronized从读/写方法中删除了关键字
输入流
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;
}
}
输出流
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);
}
}
于 2011-07-06T21:08:52.717 回答
15
JDK 中什么都没有，但是那里有很多实现，谷歌搜索 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。这样的事情经常出现，但显然是错误的，请参阅@Mike Houston 对改进版本的回答）。
于 2010-12-02T06:26:38.310 回答
7
如果它由字节数组支持，则可以使用 aByteArrayInputStream并通过ByteBuffer.array(). 如果您在本机 ByteBuffer 上尝试，这将引发异常。
于 2010-12-02T06:50:38.973 回答
2
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);
}
另请注意，包装缓冲区可以有效地支持标记/重置和跳过操作。
于 2014-09-29T15:04:02.993 回答
2
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);
}
}
于 2015-12-09T07:41:35.930 回答
1
基于 ByteArrayInputStream 代码的派生... 要求提供的 ByteBuffer 在适当的情况下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
{
}
}
于 2020-04-17T14:50:17.197 回答