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8139206: Add InputStream readNBytes(int len)

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Reviewed-by: alanb, chegar, plevart, apetcher, rriggs, weijun
This commit is contained in:
Brian Burkhalter 2018-02-01 09:40:38 -08:00
parent 482ff9cfdf
commit 697c3fc073
3 changed files with 170 additions and 26 deletions
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97
src/java.base/share/classes/java/io/InputStream.java
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@ -63,7 +63,8 @@ public abstract class InputStream implements Closeable {
*
* <p> While the stream is open, the {@code available()}, {@code read()},
* {@code read(byte[])}, {@code read(byte[], int, int)},
* {@code readAllBytes()}, {@code readNBytes()}, {@code skip()}, and
* {@code readAllBytes()}, {@code readNBytes(byte[], int, int)},
* {@code readNBytes(int)}, {@code skip(long)}, and
* {@code transferTo()} methods all behave as if end of stream has been
* reached. After the stream has been closed, these methods all throw
* {@code IOException}.
@ -122,6 +123,15 @@ public abstract class InputStream implements Closeable {
return 0;
}
@Override
public byte[] readNBytes(int len) throws IOException {
if (len < 0) {
throw new IllegalArgumentException("len < 0");
}
ensureOpen();
return new byte[0];
}
@Override
public long skip(long n) throws IOException {
ensureOpen();
@ -233,8 +243,8 @@ public abstract class InputStream implements Closeable {
* <code>b</code> and the number of bytes read before the exception
* occurred is returned. The default implementation of this method blocks
* until the requested amount of input data <code>len</code> has been read,
* end of file is detected, or an exception is thrown. Subclasses are encouraged
* to provide a more efficient implementation of this method.
* end of file is detected, or an exception is thrown. Subclasses are
* encouraged to provide a more efficient implementation of this method.
*
* @param b the buffer into which the data is read.
* @param off the start offset in array <code>b</code>
@ -308,26 +318,85 @@ public abstract class InputStream implements Closeable {
* It is strongly recommended that the stream be promptly closed if an I/O
* error occurs.
*
* @implSpec
* This method invokes {@link #readNBytes(int)} with a length of
* {@link Integer#MAX_VALUE}.
*
* @return a byte array containing the bytes read from this input stream
* @throws IOException if an I/O error occurs
* @throws OutOfMemoryError if an array of the required size cannot be
* allocated. For example, if an array larger than {@code 2GB} would
* be required to store the bytes.
* allocated.
*
* @since 9
*/
public byte[] readAllBytes() throws IOException {
return readNBytes(Integer.MAX_VALUE);
}
/**
* Reads up to a specified number of bytes from the input stream. This
* method blocks until the requested number of bytes have been read, end
* of stream is detected, or an exception is thrown. This method does not
* close the input stream.
*
* <p> The length of the returned array equals the number of bytes read
* from the stream. If {@code len} is zero, then no bytes are read and
* an empty byte array is returned. Otherwise, up to {@code len} bytes
* are read from the stream. Fewer than {@code len} bytes may be read if
* end of stream is encountered.
*
* <p> When this stream reaches end of stream, further invocations of this
* method will return an empty byte array.
*
* <p> Note that this method is intended for simple cases where it is
* convenient to read the specified number of bytes into a byte array. The
* total amount of memory allocated by this method is proportional to the
* number of bytes read from the stream which is bounded by {@code len}.
* Therefore, the method may be safely called with very large values of
* {@code len} provided sufficient memory is available.
*
* <p> The behavior for the case where the input stream is <i>asynchronously
* closed</i>, or the thread interrupted during the read, is highly input
* stream specific, and therefore not specified.
*
* <p> If an I/O error occurs reading from the input stream, then it may do
* so after some, but not all, bytes have been read. Consequently the input
* stream may not be at end of stream and may be in an inconsistent state.
* It is strongly recommended that the stream be promptly closed if an I/O
* error occurs.
*
* @implNote
* The number of bytes allocated to read data from this stream and return
* the result is bounded by {@code 2*(long)len}, inclusive.
*
* @param len the maximum number of bytes to read
* @return a byte array containing the bytes read from this input stream
* @throws IllegalArgumentException if {@code length} is negative
* @throws IOException if an I/O error occurs
* @throws OutOfMemoryError if an array of the required size cannot be
* allocated.
*
* @since 11
*/
public byte[] readNBytes(int len) throws IOException {
if (len < 0) {
throw new IllegalArgumentException("len < 0");
}
List<byte[]> bufs = null;
byte[] result = null;
int total = 0;
int remaining = len;
int n;
do {
byte[] buf = new byte[DEFAULT_BUFFER_SIZE];
byte[] buf = new byte[Math.min(remaining, DEFAULT_BUFFER_SIZE)];
int nread = 0;
// read to EOF which may read more or less than buffer size
while ((n = read(buf, nread, buf.length - nread)) > 0) {
while ((n = read(buf, nread,
Math.min(buf.length - nread, remaining))) > 0) {
nread += n;
remaining -= n;
}
if (nread > 0) {
@ -345,7 +414,9 @@ public abstract class InputStream implements Closeable {
bufs.add(buf);
}
}
} while (n >= 0); // if the last call to read returned -1, then break
// if the last call to read returned -1 or the number of bytes
// requested have been read then break
} while (n >= 0 && remaining > 0);
if (bufs == null) {
if (result == null) {
@ -357,12 +428,12 @@ public abstract class InputStream implements Closeable {
result = new byte[total];
int offset = 0;
int remaining = total;
remaining = total;
for (byte[] b : bufs) {
int len = Math.min(b.length, remaining);
System.arraycopy(b, 0, result, offset, len);
offset += len;
remaining -= len;
int count = Math.min(b.length, remaining);
System.arraycopy(b, 0, result, offset, count);
offset += count;
remaining -= count;
}
return result;