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Added in API level 1

SequenceInputStream

public class SequenceInputStream
extends InputStream

java.lang.Object
   ↳ java.io.InputStream
     ↳ java.io.SequenceInputStream


Concatenates two or more existing InputStreams. Reads are taken from the first stream until it ends, then the next stream is used, until the last stream returns end of file.

Summary

Public constructors

SequenceInputStream(InputStream s1, InputStream s2)

Constructs a new SequenceInputStream using the two streams s1 and s2 as the sequence of streams to read from.

SequenceInputStream(Enumeration<? extends InputStream> e)

Constructs a new SequenceInputStream using the elements returned from Enumeration e as the stream sequence.

Public methods

int available()

Returns an estimated number of bytes that can be read or skipped without blocking for more input.

void close()

Closes all streams in this sequence of input stream.

int read()

Reads a single byte from this sequence of input streams and returns it as an integer in the range from 0 to 255.

int read(byte[] buffer, int byteOffset, int byteCount)

Reads up to byteCount bytes from this sequence of input streams and stores them in the byte array buffer starting at byteOffset.

Inherited methods

From class java.io.InputStream
From class java.lang.Object
From interface java.io.Closeable
From interface java.lang.AutoCloseable

Public constructors

SequenceInputStream

Added in API level 1
SequenceInputStream (InputStream s1, 
                InputStream s2)

Constructs a new SequenceInputStream using the two streams s1 and s2 as the sequence of streams to read from.

Parameters
s1 InputStream: the first stream to get bytes from.
s2 InputStream: the second stream to get bytes from.
Throws
NullPointerException if s1 is null.

SequenceInputStream

Added in API level 1
SequenceInputStream (Enumeration<? extends InputStream> e)

Constructs a new SequenceInputStream using the elements returned from Enumeration e as the stream sequence. The instances returned by e.nextElement() must be of type InputStream.

Parameters
e Enumeration: the enumeration of InputStreams to get bytes from.
Throws
NullPointerException if any of the elements in e is null.

Public methods

available

Added in API level 1
int available ()

Returns an estimated number of bytes that can be read or skipped without blocking for more input.

Note that this method provides such a weak guarantee that it is not very useful in practice.

Firstly, the guarantee is "without blocking for more input" rather than "without blocking": a read may still block waiting for I/O to complete — the guarantee is merely that it won't have to wait indefinitely for data to be written. The result of this method should not be used as a license to do I/O on a thread that shouldn't be blocked.

Secondly, the result is a conservative estimate and may be significantly smaller than the actual number of bytes available. In particular, an implementation that always returns 0 would be correct. In general, callers should only use this method if they'd be satisfied with treating the result as a boolean yes or no answer to the question "is there definitely data ready?".

Thirdly, the fact that a given number of bytes is "available" does not guarantee that a read or skip will actually read or skip that many bytes: they may read or skip fewer.

It is particularly important to realize that you must not use this method to size a container and assume that you can read the entirety of the stream without needing to resize the container. Such callers should probably write everything they read to a ByteArrayOutputStream and convert that to a byte array. Alternatively, if you're reading from a file, length() returns the current length of the file (though assuming the file's length can't change may be incorrect, reading a file is inherently racy).

The default implementation of this method in InputStream always returns 0. Subclasses should override this method if they are able to indicate the number of bytes available.

Returns
int the estimated number of bytes available
Throws
IOException

close

Added in API level 1
void close ()

Closes all streams in this sequence of input stream.

Throws
IOException if an error occurs while closing any of the input streams.

read

Added in API level 1
int read ()

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.

Returns
int 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.

read

Added in API level 1
int read (byte[] buffer, 
                int byteOffset, 
                int byteCount)

Reads up to byteCount bytes from this sequence of input streams and stores them in the byte array buffer starting at byteOffset. 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 byteCount, 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.

Parameters
buffer byte
byteOffset int
byteCount int
Returns
int
Throws
IndexOutOfBoundsException if byteOffset < 0 || byteCount < 0 || byteOffset + byteCount > buffer.length.
IOException if an I/O error occurs.
NullPointerException if buffer == null.
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