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 and Description
InputStream() This constructor does nothing.

Method Summary

Modifier and Type	Method and 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.
static InputStream	nullInputStream() Returns a new InputStream that reads no bytes.
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.
byte[]	readAllBytes() Reads all remaining bytes from the input stream.
int	readNBytes(byte[] b, int off, int len) Reads the requested number of bytes from the input stream into the given byte array.
byte[]	readNBytes(int len) Reads up to a specified number of bytes from the input stream.
void	reset() Resets this stream to the last marked location.
long	skip(long byteCount) Skips at most byteCount bytes in this stream.
long	transferTo(OutputStream out) Reads all bytes from this input stream and writes the bytes to the given output stream in the order that they are read.

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

nullInputStream

public static InputStream nullInputStream()

Returns a new InputStream that reads no bytes. The returned stream is initially open. The stream is closed by calling the close() method. Subsequent calls to close() have no effect.

While the stream is open, the available(), read(), read(byte[]), read(byte[], int, int), readAllBytes(), readNBytes(byte[], int, int), readNBytes(int), skip(long), and transferTo() methods all behave as if end of stream has been reached. After the stream has been closed, these methods all throw IOException.

The markSupported() method returns false. The mark() method does nothing, and the reset() method throws IOException.

Returns:

an InputStream which contains no bytes

Since:

11

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 Closeable

Specified by:

close in interface AutoCloseable

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.

readAllBytes

public byte[] readAllBytes()
                    throws IOException

Reads all remaining bytes from the input stream. This method blocks until all remaining bytes have been read and end of stream is detected, or an exception is thrown. This method does not close the input stream.

When this stream reaches end of stream, further invocations of this method will return an empty byte array.

Note that this method is intended for simple cases where it is convenient to read all bytes into a byte array. It is not intended for reading input streams with large amounts of data.

The behavior for the case where the input stream is asynchronously closed, or the thread interrupted during the read, is highly input stream specific, and therefore not specified.

If an I/O error occurs reading from the input stream, then it may do so after some, but not all, bytes have been read. Consequently the input stream may not be at end of stream and may be in an inconsistent state. It is strongly recommended that the stream be promptly closed if an I/O error occurs.

Returns:

a byte array containing the bytes read from this input stream

Throws:

IOException - if an I/O error occurs

OutOfMemoryError - if an array of the required size cannot be allocated.

Since:

9

readNBytes

public byte[] readNBytes(int len)
                  throws IOException

Reads up to a specified number of bytes from the input stream. This method blocks until the requested number of bytes have been read, end of stream is detected, or an exception is thrown. This method does not close the input stream.

The length of the returned array equals the number of bytes read from the stream. If len is zero, then no bytes are read and an empty byte array is returned. Otherwise, up to len bytes are read from the stream. Fewer than len bytes may be read if end of stream is encountered.

When this stream reaches end of stream, further invocations of this method will return an empty byte array.

Note that this method is intended for simple cases where it is convenient to read the specified number of bytes into a byte array. The total amount of memory allocated by this method is proportional to the number of bytes read from the stream which is bounded by len. Therefore, the method may be safely called with very large values of len provided sufficient memory is available.

The behavior for the case where the input stream is asynchronously closed, or the thread interrupted during the read, is highly input stream specific, and therefore not specified.

If an I/O error occurs reading from the input stream, then it may do so after some, but not all, bytes have been read. Consequently the input stream may not be at end of stream and may be in an inconsistent state. It is strongly recommended that the stream be promptly closed if an I/O error occurs.

Parameters:

len - the maximum number of bytes to read

Returns:

a byte array containing the bytes read from this input stream

Throws:

IllegalArgumentException - if length is negative

IOException - if an I/O error occurs

OutOfMemoryError - if an array of the required size cannot be allocated.

Since:

11

readNBytes

public int readNBytes(byte[] b,
                      int off,
                      int len)
               throws IOException

Reads the requested number of bytes from the input stream into the given byte array. This method blocks until len bytes of input data have been read, end of stream is detected, or an exception is thrown. The number of bytes actually read, possibly zero, is returned. This method does not close the input stream.

In the case where end of stream is reached before len bytes have been read, then the actual number of bytes read will be returned. When this stream reaches end of stream, further invocations of this method will return zero.

If len is zero, then no bytes are read and 0 is returned; otherwise, there is an attempt to read up to len bytes.

The first byte read is stored into element b[off], the next one in to b[off+1], and so on. The number of bytes read is, at most, equal to len. Let k be the number of bytes actually read; these bytes will be stored in elements b[off] through b[off+k-1], leaving elements b[off+k ] through b[off+len-1] unaffected.

The behavior for the case where the input stream is asynchronously closed, or the thread interrupted during the read, is highly input stream specific, and therefore not specified.

If an I/O error occurs reading from the input stream, then it may do so after some, but not all, bytes of b have been updated with data from the input stream. Consequently the input stream and b may be in an inconsistent state. It is strongly recommended that the stream be promptly closed if an I/O error occurs.

Parameters:

b - the byte array into which the data is read

off - the start offset in b at which the data is written

len - the maximum number of bytes to read

Returns:

the actual number of bytes read into the buffer

Throws:

IOException - if an I/O error occurs

NullPointerException - if b is null

IndexOutOfBoundsException - If off is negative, len is negative, or len is greater than b.length - off

Since:

9

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.

transferTo

public long transferTo(OutputStream out)
                throws IOException

Reads all bytes from this input stream and writes the bytes to the given output stream in the order that they are read. On return, this input stream will be at end of stream. This method does not close either stream.

This method may block indefinitely reading from the input stream, or writing to the output stream. The behavior for the case where the input and/or output stream is asynchronously closed, or the thread interrupted during the transfer, is highly input and output stream specific, and therefore not specified.

If an I/O error occurs reading from the input stream or writing to the output stream, then it may do so after some bytes have been read or written. Consequently the input stream may not be at end of stream and one, or both, streams may be in an inconsistent state. It is strongly recommended that both streams be promptly closed if an I/O error occurs.

Parameters:

out - the output stream, non-null

Returns:

the number of bytes transferred

Throws:

IOException - if an I/O error occurs when reading or writing

NullPointerException - if out is null

Since:

9