Package java.io

Class InputStream

java.lang.Object

java.io.InputStream

All Implemented Interfaces:

Closeable, AutoCloseable

Direct Known Subclasses:

AssetManager.AssetInputStream, ByteArrayInputStream, FileInputStream, FilterInputStream, ObjectInputStream, PipedInputStream, SequenceInputStream, StringBufferInputStream, TeeInputStream, ZipFile.RAFStream

public abstract class InputStream
extends Object
implements Closeable

A readable source of bytes.

Most clients will use input streams that read data from the file system (FileInputStream), the network (Socket.getInputStream()/URLConnection.getInputStream()), or from an in-memory byte array (ByteArrayInputStream).

Use InputStreamReader to adapt a byte stream like this one into a character stream.

Most clients should wrap their input stream with BufferedInputStream. Callers that do only bulk reads may omit buffering.

Some implementations support marking a position in the input stream and resetting back to this position later. Implementations that don't return false from markSupported() and throw an IOException when reset() is called.

Subclassing InputStream

Subclasses that decorate another input stream should consider subclassing FilterInputStream, which delegates all calls to the source input stream.

All input stream subclasses should override both read() and read(byte[],int,int). The three argument overload is necessary for bulk access to the data. This is much more efficient than byte-by-byte access.

See Also:

OutputStream

Constructor Summary

Constructors

Constructor	Description
InputStream()	This constructor does nothing.

Method Summary

Modifier and Type	Method	Description
int	available()	Returns an estimated number of bytes that can be read or skipped without blocking for more input.
void	close()	Closes this stream.
void	mark(int readlimit)	Sets a mark position in this InputStream.
boolean	markSupported()	Indicates whether this stream supports the mark() and reset() methods.
abstract int	read()	Reads a single byte from this stream and returns it as an integer in the range from 0 to 255.
int	read(byte[] buffer)	Equivalent to read(buffer, 0, buffer.length).
int	read(byte[] buffer, int byteOffset, int byteCount)	Reads up to byteCount bytes from this stream and stores them in the byte array buffer starting at byteOffset.
void	reset()	Resets this stream to the last marked location.
long	skip(long byteCount)	Skips at most byteCount bytes in this stream.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

InputStream

public InputStream()

This constructor does nothing. It is provided for signature compatibility.

Method Detail

available

public int available()
              throws IOException

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, 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:

the estimated number of bytes available

Throws:

IOException - if this stream is closed or an error occurs

close

public void close()
           throws IOException

Closes this stream. Concrete implementations of this class should free any resources during close. This implementation does nothing.

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Throws:

IOException - if an error occurs while closing this stream.

mark

public void mark(int readlimit)

Sets a mark position in this InputStream. The parameter readlimit indicates how many bytes can be read before the mark is invalidated. Sending reset() will reposition the stream back to the marked position provided readLimit has not been surpassed.

This default implementation does nothing and concrete subclasses must provide their own implementation.

Parameters:

readlimit - the number of bytes that can be read from this stream before the mark is invalidated.

See Also:

markSupported(), reset()

markSupported

public boolean markSupported()

Indicates whether this stream supports the mark() and reset() methods. The default implementation returns false.

Returns:

always false.

See Also:

mark(int), reset()

read

public abstract int read()
                  throws IOException

Reads a single byte from this stream and returns it as an integer in the range from 0 to 255. Returns -1 if the end of the stream has been reached. Blocks until one byte has been read, the end of the source stream is detected or an exception is thrown.

Throws:

IOException - if the stream is closed or another IOException occurs.

read

public int read(byte[] buffer)
         throws IOException

Equivalent to read(buffer, 0, buffer.length).

Throws:

IOException

read

public int read(byte[] buffer,
                int byteOffset,
                int byteCount)
         throws IOException

Reads up to byteCount bytes from this stream and stores them in the byte array buffer starting at byteOffset. Returns the number of bytes actually read or -1 if the end of the stream has been reached.

Throws:

IndexOutOfBoundsException - if byteOffset < 0 || byteCount < 0 || byteOffset + byteCount > buffer.length.

IOException - if the stream is closed or another IOException occurs.

reset

public void reset()
           throws IOException

Resets this stream to the last marked location. Throws an IOException if the number of bytes read since the mark has been set is greater than the limit provided to mark, or if no mark has been set.

This implementation always throws an IOException and concrete subclasses should provide the proper implementation.

Throws:

IOException - if this stream is closed or another IOException occurs.

skip

public long skip(long byteCount)
          throws IOException

Skips at most byteCount bytes in this stream. The number of actual bytes skipped may be anywhere between 0 and byteCount. If byteCount is negative, this method does nothing and returns 0, but some subclasses may throw.

Note the "at most" in the description of this method: this method may choose to skip fewer bytes than requested. Callers should always check the return value.

This default implementation reads bytes into a temporary buffer. Concrete subclasses should provide their own implementation.

Returns:

the number of bytes actually skipped.

Throws:

IOException - if this stream is closed or another IOException occurs.