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Class FilterInputStream

java.lang.Object

java.io.InputStream

java.io.FilterInputStream

All Implemented Interfaces:: Closeable, AutoCloseable

Direct Known Subclasses:: BufferedInputStream, CheckedInputStream, CipherInputStream, DataInputStream, DeflaterInputStream, DigestInputStream, InflaterInputStream, LineNumberInputStream, ProgressMonitorInputStream, PushbackInputStream

public class FilterInputStream extends InputStream

A FilterInputStream wraps some other input stream, which it uses as its basic source of data, possibly transforming the data along the way or providing additional functionality. The class FilterInputStream itself simply overrides select methods of InputStream with versions that pass all requests to the wrapped input stream. Subclasses of FilterInputStream may of course override any methods declared or inherited by FilterInputStream, and may also provide additional fields and methods.

Since:: 1.0

Field Summary

Modifier and Type	Field	Description
`protected InputStream`	`in`	The input stream to be filtered.

Constructor Summary

FilterInputStream(InputStream in)

Modifier	Constructor	Description
`protected`	Creates a `FilterInputStream` by assigning the argument `in` to the field `this.in` so as to remember it for later use.

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 by the next caller of a method for this input stream.
`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.
`int`	`read()`	Reads the next byte of data from the input stream.
`int`	`read(byte[] b)`	Reads up to `b.length` bytes of data from this input stream into an array of bytes.
`int`	`read(byte[] b, int off, int len)`	Reads up to `len` bytes of data from this input stream into an array of bytes.
`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 the input stream.

Methods declared in class java.io.InputStream

nullInputStream, readAllBytes, readNBytes, readNBytes, skipNBytes, transferTo

Methods declared in class java.lang.Object

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

Field Details

in

protected volatile InputStream in

The input stream to be filtered.

Constructor Details

FilterInputStream

protected FilterInputStream(InputStream in)

Creates a FilterInputStream by assigning the argument in to the field this.in so as to remember it for later use.

Parameters:: in - the underlying input stream, or null if this instance is to be created without an underlying stream.

Method Details

read

public 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.

Specified by:

read in class InputStream

Implementation Requirements:

This method simply performs in.read() and returns the result.

Returns:

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

Throws:

IOException - if an I/O error occurs.

See Also:

read

public int read(byte[] b) throws IOException

Reads up to b.length bytes of data from this input stream into an array of bytes. This method blocks until some input is available.

Overrides:

read in class InputStream

Implementation Requirements:

This method simply performs the call read(b, 0, b.length) and returns the result. It is important that it does not do in.read(b) instead; certain subclasses of FilterInputStream depend on the implementation strategy actually used.

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 an I/O error occurs.

See Also:

read

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

Reads up to len bytes of data from this input stream into an array of bytes. If len is not zero, the method blocks until some input is available; otherwise, no bytes are read and 0 is returned.

Overrides:

read in class InputStream

Implementation Requirements:

This method simply performs in.read(b, off, len) and returns the result.

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:

NullPointerException - If b is null.

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

IOException - if an I/O error occurs.

See Also:

skip

public long skip(long n) throws IOException

Skips over and discards n bytes of data from the input stream. The skip method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly 0. The actual number of bytes skipped is returned.

Overrides:

skip in class InputStream

Implementation Requirements:

This method simply performs in.skip(n) and returns the result.

Parameters:

n - the number of bytes to be skipped.

Returns:

the actual number of bytes skipped.

Throws:

IOException - if in.skip(n) throws an IOException.

See Also:

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 by the next caller of a method for this input stream. The next caller might be 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.

Overrides:: available in class InputStream
Implementation Requirements:: This method returns the result of in.available().
Returns:: an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking.
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

Overrides:

close in class InputStream

Implementation Requirements:

This method simply performs in.close().

Throws:

IOException - if an I/O error occurs.

See Also:

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

Overrides:

mark in class InputStream

Implementation Requirements:

This method simply performs in.mark(readlimit).

Parameters:

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

See Also:

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.

Stream marks are intended to be used in situations where you need to read ahead a little to see what's in the stream. Often this is most easily done by invoking some general parser. If the stream is of the type handled by the parse, it just chugs along happily. If the stream is not of that type, the parser should toss an exception when it fails. If this happens within readlimit bytes, it allows the outer code to reset the stream and try another parser.

Overrides:

reset in class InputStream

Implementation Requirements:

This method simply performs in.reset().

Throws:

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

See Also:

markSupported

public boolean markSupported()

Tests if this input stream supports the mark and reset methods.

Overrides:

markSupported in class InputStream

Implementation Requirements:

This method simply performs in.markSupported().

Returns:

true if this stream type supports the mark and reset method; false otherwise.

See Also:

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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/io/FilterInputStream.html