Module java.base

Package java.io

Class InputStream

java.lang.Object

java.io.InputStream

All Implemented Interfaces:

Closeable, AutoCloseable

Direct Known Subclasses:

AudioInputStream, ByteArrayInputStream, FileInputStream, FilterInputStream, ObjectInputStream, PipedInputStream, SequenceInputStream, StringBufferInputStream

public abstract class InputStream
extends Object
implements Closeable

This abstract class is the superclass of all classes representing an input stream of bytes.

Applications that need to define a subclass of InputStream must always provide a method that returns the next byte of input.

Since:

1.0

See Also:

• BufferedInputStream
• ByteArrayInputStream
• DataInputStream
• FilterInputStream
• read()
• OutputStream
• PushbackInputStream

Constructor Summary

Constructors

Constructor	Description
InputStream()	Constructor for subclasses to call.

Method Summary

Modifier and Type	Method	Description
int	available()	Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking, which may be 0, or 0 when end of stream is detected.
void	close()	Closes this input stream and releases any system resources associated with the stream.
void	mark(int readlimit)	Marks the current position in this input stream.
boolean	markSupported()	Tests if this input stream supports the mark and reset methods.
static InputStream	nullInputStream()	Returns a new InputStream that reads no bytes.
abstract int	read()	Reads the next byte of data from the input stream.
int	read(byte[] b)	Reads some number of bytes from the input stream and stores them into the buffer array b.
int	read(byte[] b, int off, int len)	Reads up to len bytes of data from the input stream into an array of bytes.
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()	Repositions this stream to the position at the time the mark method was last called on this input stream.
long	skip(long n)	Skips over and discards n bytes of data from this input stream.
void	skipNBytes(long n)	Skips over and discards exactly n bytes of data from this input 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 declared in class java.lang.Object

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

Constructor Details

InputStream

public InputStream()

Constructor for subclasses to call.

Method Details

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), skipNBytes(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

read

public abstract int read()
                  throws IOException

Reads the next byte of data from the input stream. The value byte is returned as an int in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value -1 is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown.

Returns:

the next byte of data, or -1 if the end of the stream is reached.

Throws:

IOException - if an I/O error occurs.

read

public int read(byte[] b)
         throws IOException

Reads some number of bytes from the input stream and stores them into the buffer array b. The number of bytes actually read is returned as an integer. This method blocks until input data is available, end of file is detected, or an exception is thrown.

If the length of b is zero, then no bytes are read and 0 is returned; otherwise, there is an attempt to read at least one byte. If no byte is available because the stream is at the end of the file, the value -1 is returned; otherwise, at least one byte is read and stored into b.

The first byte read is stored into element b[0], the next one into b[1], and so on. The number of bytes read is, at most, equal to the length of b. Let k be the number of bytes actually read; these bytes will be stored in elements b[0] through b[k-1], leaving elements b[k] through b[b.length-1] unaffected.

Implementation Requirements:

The read(b) method for class InputStream has the same effect as:

    read(b, 0, b.length)

Parameters:

b - the buffer into which the data is read.

Returns:

the total number of bytes read into the buffer, or -1 if there is no more data because the end of the stream has been reached.

Throws:

IOException - If the first byte cannot be read for any reason other than the end of the file, if the input stream has been closed, or if some other I/O error occurs.

NullPointerException - if b is null.

See Also:

• read(byte[], int, int)

read

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

Reads up to len bytes of data from the input stream into an array of bytes. An attempt is made to read as many as len bytes, but a smaller number may be read. The number of bytes actually read is returned as an integer.

This method blocks until input data is available, end of file is detected, or an exception is thrown.

If len is zero, then no bytes are read and 0 is returned; otherwise, there is an attempt to read at least one byte. If no byte is available because the stream is at end of file, the value -1 is returned; otherwise, at least one byte is read and stored into b.

The first byte read is stored into element b[off], the next one into 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.

In every case, elements b[0] through b[off-1] and elements b[off+len] through b[b.length-1] are unaffected.

Implementation Requirements:

The read(b, off, len) method for class InputStream simply calls the method read() repeatedly. If the first such call results in an IOException, that exception is returned from the call to the read(b, off, len) method. If any subsequent call to read() results in a IOException, the exception is caught and treated as if it were end of file; the bytes read up to that point are stored into b and the number of bytes read before the exception occurred is returned. The default implementation of this method blocks until the requested amount of input data len has been read, end of file is detected, or an exception is thrown. Subclasses are encouraged to provide a more efficient implementation of this method.

Parameters:

b - the buffer into which the data is read.

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

len - the maximum number of bytes to read.

Returns:

the total number of bytes read into the buffer, or -1 if there is no more data because the end of the stream has been reached.

Throws:

IOException - If the first byte cannot be read for any reason other than end of file, or if the input stream has been closed, or if some other 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

See Also:

• read()

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.

Implementation Requirements:

This method invokes readNBytes(int) with a length of Integer.MAX_VALUE.

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 has 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.

Implementation Note:

The number of bytes allocated to read data from this stream and return the result is bounded by 2*(long)len, inclusive.

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

skip

public long skip(long n)
          throws IOException

Skips over and discards n bytes of data from this input stream. The skip method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly 0. This may result from any of a number of conditions; reaching end of file before n bytes have been skipped is only one possibility. The actual number of bytes skipped is returned. If n is negative, the skip method for class InputStream always returns 0, and no bytes are skipped. Subclasses may handle the negative value differently.

Implementation Requirements:

The skip method implementation of this class creates a byte array and then repeatedly reads into it until n bytes have been read or the end of the stream has been reached. Subclasses are encouraged to provide a more efficient implementation of this method. For instance, the implementation may depend on the ability to seek.

Parameters:

n - the number of bytes to be skipped.

Returns:

the actual number of bytes skipped which might be zero.

Throws:

IOException - if an I/O error occurs.

See Also:

• skipNBytes(long)

skipNBytes

public void skipNBytes(long n)
                throws IOException

Skips over and discards exactly n bytes of data from this input stream. If n is zero, then no bytes are skipped. If n is negative, then no bytes are skipped. Subclasses may handle the negative value differently.

This method blocks until the requested number of bytes has been skipped, end of file is reached, or an exception is thrown.

If end of stream is reached before the stream is at the desired position, then an EOFException is thrown.

If an I/O error occurs, then the input stream may be in an inconsistent state. It is strongly recommended that the stream be promptly closed if an I/O error occurs.

Implementation Requirements:

If n is zero or negative, then no bytes are skipped. If n is positive, the default implementation of this method invokes skip() repeatedly with its parameter equal to the remaining number of bytes to skip until the requested number of bytes has been skipped or an error condition occurs. If at any point the return value of skip() is negative or greater than the remaining number of bytes to be skipped, then an IOException is thrown. If skip() ever returns zero, then read() is invoked to read a single byte, and if it returns -1, then an EOFException is thrown. Any exception thrown by skip() or read() will be propagated.

Implementation Note:

Subclasses are encouraged to provide a more efficient implementation of this method.

Parameters:

n - the number of bytes to be skipped.

Throws:

EOFException - if end of stream is encountered before the stream can be positioned n bytes beyond its position when this method was invoked.

IOException - if the stream cannot be positioned properly or if an I/O error occurs.

Since:

12

See Also:

• skip(long)

available

public int available()
              throws IOException

Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking, which may be 0, or 0 when end of stream is detected. The read might be on the same thread or another thread. A single read or skip of this many bytes will not block, but may read or skip fewer bytes.

Note that while some implementations of InputStream will return the total number of bytes in the stream, many will not. It is never correct to use the return value of this method to allocate a buffer intended to hold all data in this stream.

A subclass's implementation of this method may choose to throw an IOException if this input stream has been closed by invoking the close() method.

API Note:

This method should be overridden by subclasses.

Implementation Requirements:

The available method of InputStream always returns 0.

Returns:

an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking or 0 when it reaches the end of the input stream.

Throws:

IOException - if an I/O error occurs.

close

public void close()
           throws IOException

Closes this input stream and releases any system resources associated with the stream.

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Implementation Requirements:

The close method of InputStream does nothing.

Throws:

IOException - if an I/O error occurs.

mark

public void mark(int readlimit)

Marks the current position in this input stream. A subsequent call to the reset method repositions this stream at the last marked position so that subsequent reads re-read the same bytes.

The readlimit arguments tells this input stream to allow that many bytes to be read before the mark position gets invalidated.

The general contract of mark is that, if the method markSupported returns true, the stream somehow remembers all the bytes read after the call to mark and stands ready to supply those same bytes again if and whenever the method reset is called. However, the stream is not required to remember any data at all if more than readlimit bytes are read from the stream before reset is called.

Marking a closed stream should not have any effect on the stream.

Implementation Requirements:

The mark method of InputStream does nothing.

Parameters:

readlimit - the maximum limit of bytes that can be read before the mark position becomes invalid.

See Also:

• reset()

reset

public void reset()
           throws IOException

Repositions this stream to the position at the time the mark method was last called on this input stream.

The general contract of reset is:

• If the method markSupported returns true, then:
  • If the method mark has not been called since the stream was created, or the number of bytes read from the stream since mark was last called is larger than the argument to mark at that last call, then an IOException might be thrown.
  • If such an IOException is not thrown, then the stream is reset to a state such that all the bytes read since the most recent call to mark (or since the start of the file, if mark has not been called) will be resupplied to subsequent callers of the read method, followed by any bytes that otherwise would have been the next input data as of the time of the call to reset.
• If the method markSupported returns false, then:
  • The call to reset may throw an IOException.
  • If an IOException is not thrown, then the stream is reset to a fixed state that depends on the particular type of the input stream and how it was created. The bytes that will be supplied to subsequent callers of the read method depend on the particular type of the input stream.

Implementation Requirements:

The method reset for class InputStream does nothing except throw an IOException.

Throws:

IOException - if this stream has not been marked or if the mark has been invalidated.

See Also:

• mark(int)
• IOException

markSupported

public boolean markSupported()

Tests if this input stream supports the mark and reset methods. Whether or not mark and reset are supported is an invariant property of a particular input stream instance.

Implementation Requirements:

The markSupported method of InputStream returns false.

Returns:

true if this stream instance supports the mark and reset methods; false otherwise.

See Also:

• mark(int)
• reset()

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 the total number of bytes transferred is greater than Long.MAX_VALUE, then Long.MAX_VALUE will be returned.

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