DigestInputStream

public class DigestInputStream extends FilterInputStream

A transparent stream that updates the associated message digest using the bits going through the stream.

To complete the message digest computation, call one of the digest methods on the associated message digest after your calls to one of this digest input stream's read methods.

It is possible to turn this stream on or off (see on). When it is on, a call to one of the read methods results in an update on the message digest. But when it is off, the message digest is not updated. The default is for the stream to be on.

Note that digest objects can compute only one digest (see MessageDigest), so that in order to compute intermediate digests, a caller should retain a handle onto the digest object, and clone it for each digest to be computed, leaving the orginal digest untouched.

See Also

• MessageDigest
• DigestOutputStream

Field Summary

protected MessageDigest

digest

The message digest associated with this stream.

Inherited Field Summary

From class java.io.FilterInputStream

protected InputStream

in

The input stream to be filtered.

Public Constructor Summary

DigestInputStream(InputStream stream, MessageDigest digest) Creates a digest input stream, using the specified input stream and message digest.

Public Method Summary

MessageDigest	getMessageDigest() Returns the message digest associated with this stream.
void	on(boolean on) Turns the digest function on or off.
int	read() Reads a byte, and updates the message digest (if the digest function is on).
int	read(byte[] b, int off, int len) Reads into a byte array, and updates the message digest (if the digest function is on).
void	setMessageDigest(MessageDigest digest) Associates the specified message digest with this stream.
String	toString() Prints a string representation of this digest input stream and its associated message digest object.

Inherited Method Summary

From class java.io.FilterInputStream

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.
synchronized 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 this input stream.
int	read(byte[] b, int off, int len) Reads up to len bytes of data from this input stream into an array of bytes.
int	read(byte[] b) Reads up to byte.length bytes of data from this input stream into an array of bytes.
synchronized 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.

From class java.io.InputStream

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 invocation of a method for this input stream.
void	close() Closes this input stream and releases any system resources associated with the stream.
synchronized 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.
abstract int	read() Reads the next byte of data from the input stream.
int	read(byte[] b, int off, int len) Reads up to len bytes of data from the input stream into an array of bytes.
int	read(byte[] b) Reads some number of bytes from the input stream and stores them into the buffer array b.
synchronized 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.

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

From interface java.io.Closeable

abstract void

close() Closes this stream and releases any system resources associated with it.

From interface java.lang.AutoCloseable

abstract void

close() Closes this resource, relinquishing any underlying resources.

Fields

protected MessageDigest digest

The message digest associated with this stream.

Public Constructors

public DigestInputStream (InputStream stream, MessageDigest digest)

Creates a digest input stream, using the specified input stream and message digest.

Parameters

stream	the input stream.
digest	the message digest to associate with this stream.

Public Methods

public MessageDigest getMessageDigest ()

Returns the message digest associated with this stream.

Returns

• the message digest associated with this stream.

See Also

• setMessageDigest(java.security.MessageDigest)

public void on (boolean on)

Turns the digest function on or off. The default is on. When it is on, a call to one of the read methods results in an update on the message digest. But when it is off, the message digest is not updated.

Parameters

on	true to turn the digest function on, false to turn it off.

public int read ()

Reads a byte, and updates the message digest (if the digest function is on). That is, this method reads a byte from the input stream, blocking until the byte is actually read. If the digest function is on (see on), this method will then call update on the message digest associated with this stream, passing it the byte read.

Returns

• the byte read.

Throws

IOException	if an I/O error occurs.

See Also

• MessageDigest.update(byte)

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

Reads into a byte array, and updates the message digest (if the digest function is on). That is, this method reads up to len bytes from the input stream into the array b, starting at offset off. This method blocks until the data is actually read. If the digest function is on (see on), this method will then call update on the message digest associated with this stream, passing it the data.

Parameters

b	the array into which the data is read.
off	the starting offset into b of where the data should be placed.
len	the maximum number of bytes to be read from the input stream into b, starting at offset off.

Returns

• the actual number of bytes read. This is less than len if the end of the stream is reached prior to reading len bytes. -1 is returned if no bytes were read because the end of the stream had already been reached when the call was made.

Throws

IOException	if an I/O error occurs.

See Also

• MessageDigest.update(byte[], int, int)

public void setMessageDigest (MessageDigest digest)

Associates the specified message digest with this stream.

Parameters

digest	the message digest to be associated with this stream.

See Also

• getMessageDigest()

public String toString ()

Prints a string representation of this digest input stream and its associated message digest object.

Returns

• a printable representation of this object.