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SequenceInputStream.javaAPI DocAndroid 1.5 API8149Wed May 06 22:41:04 BST 2009java.io

SequenceInputStream

public class SequenceInputStream extends InputStream
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.
since
Android 1.0

Fields Summary
private Enumeration
e
An enumeration which will return types of InputStream.
private InputStream
in
The current input stream.
Constructors Summary
public SequenceInputStream(InputStream s1, InputStream s2)
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}.
since
Android 1.0

        if (s1 == null) {
            throw new NullPointerException();
        }
        Vector<InputStream> inVector = new Vector<InputStream>(1);
        inVector.addElement(s2);
        e = inVector.elements();
        in = s1;
public SequenceInputStream(Enumeration e)
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}.
since
Android 1.0

        this.e = e;
        if (e.hasMoreElements()) {
            in = e.nextElement();
            if (in == null) {
                throw new NullPointerException();
            }
        }
Methods Summary
public intavailable()
Returns the number of bytes that are available before the current input stream will block.

return
the number of bytes available in the current input stream before blocking.
throws
IOException if an I/O error occurs in the current input stream.
since
Android 1.0

        if (e != null && in != null) {
            return in.available();
        }
        return 0;
public voidclose()
Closes all streams in this sequence of input stream.

throws
IOException if an error occurs while closing any of the input streams.
since
Android 1.0

        while (in != null) {
            nextStream();
        }
        e = null;
private voidnextStream()
Sets up the next InputStream or leaves it alone if there are none left.

throws
IOException

        if (in != null) {
            in.close();
        }
        if (e.hasMoreElements()) {
            in = e.nextElement();
            if (in == null) {
                throw new NullPointerException();
            }
        } else {
            in = null;
        }
public intread()
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.
since
Android 1.0

        while (in != null) {
            int result = in.read();
            if (result >= 0) {
                return result;
            }
            nextStream();
        }
        return -1;
public intread(byte[] buffer, int offset, int count)
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.

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.

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}.
since
Android 1.0

        if (in == null) {
            return -1;
        }
        // BEGIN android-changed
        if (buffer == null) {
            throw new NullPointerException(Msg.getString("K0047")); //$NON-NLS-1$
        }
        // avoid int overflow
        // Exception priorities (in case of multiple errors) differ from
        // RI, but are spec-compliant.
        // used (offset | count) < 0 instead of (offset < 0) || (count < 0)
        // to safe one operation
        if ((offset | count) < 0 || offset > buffer.length - count) {
            throw new IndexOutOfBoundsException(Msg.getString("K002f")); //$NON-NLS-1$
        }
        // END android-changed
        while (in != null) {
            int result = in.read(buffer, offset, count);
            if (result >= 0) {
                return result;
            }
            nextStream();
        }
        return -1;