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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package java.io;
import java.util.Arrays;
import java.util.Enumeration;
import java.util.Vector;
/**
* Concatenates two or more existing {@link InputStream}s. Reads are taken from
* the first stream until it ends, then the next stream is used, until the last
* stream returns end of file.
*/
public class SequenceInputStream extends InputStream {
/**
* An enumeration which will return types of InputStream.
*/
private Enumeration<? extends InputStream> e;
/**
* The current input stream.
*/
private InputStream in;
/**
* Constructs a new {@code SequenceInputStream} using the two streams
* {@code s1} and {@code s2} as the sequence of streams to read from.
*
* @param s1
* the first stream to get bytes from.
* @param s2
* the second stream to get bytes from.
* @throws NullPointerException
* if {@code s1} is {@code null}.
*/
public SequenceInputStream(InputStream s1, InputStream s2) {
if (s1 == null) {
throw new NullPointerException("s1 == null");
}
Vector<InputStream> inVector = new Vector<InputStream>(1);
inVector.addElement(s2);
e = inVector.elements();
in = s1;
}
/**
* Constructs a new SequenceInputStream using the elements returned from
* Enumeration {@code e} as the stream sequence. The instances returned by
* {@code e.nextElement()} must be of type {@link InputStream}.
*
* @param e
* the enumeration of {@code InputStreams} to get bytes from.
* @throws NullPointerException
* if any of the elements in {@code e} is {@code null}.
*/
public SequenceInputStream(Enumeration<? extends InputStream> e) {
this.e = e;
if (e.hasMoreElements()) {
in = e.nextElement();
if (in == null) {
throw new NullPointerException("element is null");
}
}
}
@Override
public int available() throws IOException {
if (e != null && in != null) {
return in.available();
}
return 0;
}
/**
* Closes all streams in this sequence of input stream.
*
* @throws IOException
* if an error occurs while closing any of the input streams.
*/
@Override
public void close() throws IOException {
while (in != null) {
nextStream();
}
e = null;
}
/**
* Sets up the next InputStream or leaves it alone if there are none left.
*
* @throws IOException
*/
private void nextStream() throws IOException {
if (in != null) {
in.close();
}
if (e.hasMoreElements()) {
in = e.nextElement();
if (in == null) {
throw new NullPointerException("element is null");
}
} else {
in = null;
}
}
/**
* Reads a single byte from this sequence of input streams and returns it as
* an integer in the range from 0 to 255. It tries to read from the current
* stream first; if the end of this stream has been reached, it reads from
* the next one. Blocks until one byte has been read, the end of the last
* input stream in the sequence has been reached, or an exception is thrown.
*
* @return the byte read or -1 if either the end of the last stream in the
* sequence has been reached or this input stream sequence is
* closed.
* @throws IOException
* if an error occurs while reading the current source input
* stream.
*/
@Override
public int read() throws IOException {
while (in != null) {
int result = in.read();
if (result >= 0) {
return result;
}
nextStream();
}
return -1;
}
/**
* Reads at most {@code count} bytes from this sequence of input streams and
* stores them in the byte array {@code buffer} starting at {@code offset}.
* Blocks only until at least 1 byte has been read, the end of the stream
* has been reached, or an exception is thrown.
* <p>
* This SequenceInputStream shows the same behavior as other InputStreams.
* To do this it will read only as many bytes as a call to read on the
* current substream returns. If that call does not return as many bytes as
* requested by {@code count}, it will not retry to read more on its own
* because subsequent reads might block. This would violate the rule that
* it will only block until at least one byte has been read.
* <p>
* If a substream has already reached the end when this call is made, it
* will close that substream and start with the next one. If there are no
* more substreams it will return -1.
*
* @param buffer
* the array in which to store the bytes read.
* @param offset
* the initial position in {@code buffer} to store the bytes read
* from this stream.
* @param count
* the maximum number of bytes to store in {@code buffer}.
* @return the number of bytes actually read; -1 if this sequence of streams
* is closed or if the end of the last stream in the sequence has
* been reached.
* @throws IndexOutOfBoundsException
* if {@code offset < 0} or {@code count < 0}, or if {@code
* offset + count} is greater than the size of {@code buffer}.
* @throws IOException
* if an I/O error occurs.
* @throws NullPointerException
* if {@code buffer} is {@code null}.
*/
@Override
public int read(byte[] buffer, int offset, int count) throws IOException {
if (in == null) {
return -1;
}
Arrays.checkOffsetAndCount(buffer.length, offset, count);
while (in != null) {
int result = in.read(buffer, offset, count);
if (result >= 0) {
return result;
}
nextStream();
}
return -1;
}
}
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