java.io.InputStream Class Reference

Inheritance diagram for java.io.InputStream:

Public Member Functions
	InputStream ()
int	available () throws IOException
void	close () throws IOException
void	mark (int readlimit)
boolean	markSupported ()
abstract int	read () throws IOException
int	read (byte[] buffer) throws IOException
int	read (byte[] buffer, int offset, int length) throws IOException
synchronized void	reset () throws IOException
long	skip (long byteCount) throws IOException

Detailed Description

A readable source of bytes.

Most clients will use input streams that read data from the file system (FileInputStream), the network (java.net.Socket#getInputStream()/java.net.HttpURLConnection#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 & Destructor Documentation

InputStream()

java.io.InputStream.InputStream ( )

inline

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

Member Function Documentation

available()

int java.io.InputStream.available ( ) throws IOException

inline

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

Exceptions

IOException

if this stream is closed or an error occurs

close()

void java.io.InputStream.close ( ) throws IOException

inline

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

Exceptions

IOException

if an error occurs while closing this stream.

mark()

void java.io.InputStream.mark ( int  readlimit )

inline

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()

boolean java.io.InputStream.markSupported ( )

inline

Indicates whether this stream supports the

mark() 

and

reset() 

methods. The default implementation returns

false 

.

Returns

always

false 

.

See also

mark(int)

reset()

read() [1/3]

abstract int java.io.InputStream.read ( ) throws IOException

abstract

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.

Returns

the byte read or -1 if the end of stream has been reached.

Exceptions

IOException

if the stream is closed or another IOException occurs.

read() [2/3]

int java.io.InputStream.read ( byte []  buffer ) throws IOException

inline

Equivalent to

read(buffer, 0, buffer.length) 

.

read() [3/3]

int java.io.InputStream.read ( byte []  buffer, int  offset, int  length  ) throws IOException

inline

Reads at most

length 

bytes from this stream and stores them in the byte array

b 

starting at

offset 

.

Parameters

buffer	the byte array in which to store the bytes read.
offset	the initial position in buffer to store the bytes read from this stream.
length	the maximum number of bytes to store in b .

Returns

the number of bytes actually read or -1 if the end of the stream has been reached.

Exceptions

IndexOutOfBoundsException	if offset < 0 or length < 0 , or if offset + length is greater than the length of b .
IOException	if the stream is closed or another IOException occurs.

reset()

synchronized void java.io.InputStream.reset ( ) throws IOException

inline

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.

Exceptions

IOException

if this stream is closed or another IOException occurs.

skip()

long java.io.InputStream.skip ( long  byteCount ) throws IOException

inline

Skips at most

n 

bytes in this stream. This method does nothing and returns 0 if

n 

is negative, 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.

Parameters

byteCount

the number of bytes to skip.

Returns

the number of bytes actually skipped.

Exceptions

IOException

if this stream is closed or another IOException occurs.

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The documentation for this class was generated from the following file:

• src/java/io/InputStream.java