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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
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*
* This code 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
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
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package java.io;
import java.io.InputStream;
import java.util.Enumeration;
import java.util.Vector;
/**
* A {@code SequenceInputStream} represents
* the logical concatenation of other input
* streams. It starts out with an ordered
* collection of input streams and reads from
* the first one until end of file is reached,
* whereupon it reads from the second one,
* and so on, until end of file is reached
* on the last of the contained input streams.
*
* @author Author van Hoff
* @since 1.0
*/
public class SequenceInputStream extends InputStream {
Enumeration e;
InputStream in;
/**
* Initializes a newly created {@code SequenceInputStream}
* by remembering the argument, which must
* be an {@code Enumeration} that produces
* objects whose run-time type is {@code InputStream}.
* The input streams that are produced by
* the enumeration will be read, in order,
* to provide the bytes to be read from this
* {@code SequenceInputStream}. After
* each input stream from the enumeration
* is exhausted, it is closed by calling its
* {@code close} method.
*
* @param e an enumeration of input streams.
* @see java.util.Enumeration
*/
public SequenceInputStream(Enumeration e) {
this.e = e;
peekNextStream();
}
/**
* Initializes a newly
* created {@code SequenceInputStream}
* by remembering the two arguments, which
* will be read in order, first {@code s1}
* and then {@code s2}, to provide the
* bytes to be read from this {@code SequenceInputStream}.
*
* @param s1 the first input stream to read.
* @param s2 the second input stream to read.
*/
public SequenceInputStream(InputStream s1, InputStream s2) {
Vector v = new Vector<>(2);
v.addElement(s1);
v.addElement(s2);
e = v.elements();
peekNextStream();
}
/**
* Continues reading in the next stream if an EOF is reached.
*/
final void nextStream() throws IOException {
if (in != null) {
in.close();
}
peekNextStream();
}
private void peekNextStream() {
if (e.hasMoreElements()) {
in = (InputStream) e.nextElement();
if (in == null)
throw new NullPointerException();
} else {
in = null;
}
}
/**
* Returns an estimate of the number of bytes that can be read (or
* skipped over) from the current underlying input stream without
* blocking by the next invocation of a method for the current
* underlying input stream. The next invocation might be
* the same thread or another thread. A single read or skip of this
* many bytes will not block, but may read or skip fewer bytes.
*
* This method simply calls {@code available} of the current underlying
* input stream and returns the result.
*
* @return an estimate of the number of bytes that can be read (or
* skipped over) from the current underlying input stream
* without blocking or {@code 0} if this input stream
* has been closed by invoking its {@link #close()} method
* @throws IOException if an I/O error occurs.
*
* @since 1.1
*/
public int available() throws IOException {
if (in == null) {
return 0; // no way to signal EOF from available()
}
return in.available();
}
/**
* Reads the next byte of data from this input stream. The byte is
* returned as an {@code int} in the range {@code 0} to
* {@code 255}. If no byte is available because the end of the
* stream has been reached, the value {@code -1} is returned.
* This method blocks until input data is available, the end of the
* stream is detected, or an exception is thrown.
*
* This method
* tries to read one character from the current substream. If it
* reaches the end of the stream, it calls the {@code close}
* method of the current substream and begins reading from the next
* substream.
*
* @return the next byte of data, or {@code -1} if the end of the
* stream is reached.
* @throws IOException if an I/O error occurs.
*/
public int read() throws IOException {
while (in != null) {
int c = in.read();
if (c != -1) {
return c;
}
nextStream();
}
return -1;
}
/**
* Reads up to {@code len} bytes of data from this input stream
* into an array of bytes. If {@code len} is not zero, the method
* blocks until at least 1 byte of input is available; otherwise, no
* bytes are read and {@code 0} is returned.
*
* The {@code read} method of {@code SequenceInputStream}
* tries to read the data from the current substream. If it fails to
* read any characters because the substream has reached the end of
* the stream, it calls the {@code close} method of the current
* substream and begins reading from the next substream.
*
* @param b the buffer into which the data is read.
* @param off the start offset in array {@code b}
* at which the data is written.
* @param len the maximum number of bytes read.
* @return int the number of bytes read.
* @throws NullPointerException If {@code b} is {@code null}.
* @throws IndexOutOfBoundsException If {@code off} is negative,
* {@code len} is negative, or {@code len} is
* greater than {@code b.length - off}
* @throws IOException if an I/O error occurs.
*/
public int read(byte b[], int off, int len) throws IOException {
if (in == null) {
return -1;
} else if (b == null) {
throw new NullPointerException();
} else if (off < 0 || len < 0 || len > b.length - off) {
throw new IndexOutOfBoundsException();
} else if (len == 0) {
return 0;
}
do {
int n = in.read(b, off, len);
if (n > 0) {
return n;
}
nextStream();
} while (in != null);
return -1;
}
/**
* Closes this input stream and releases any system resources
* associated with the stream.
* A closed {@code SequenceInputStream}
* cannot perform input operations and cannot
* be reopened.
*
* If this stream was created
* from an enumeration, all remaining elements
* are requested from the enumeration and closed
* before the {@code close} method returns.
*
* @throws IOException if an I/O error occurs.
*/
public void close() throws IOException {
IOException ioe = null;
while (in != null) {
try {
in.close();
} catch (IOException e) {
if (ioe == null) {
ioe = e;
} else {
ioe.addSuppressed(e);
}
}
peekNextStream();
}
if (ioe != null) {
throw ioe;
}
}
}