Class DigestInputStream

java.lang.Object

java.io.InputStream

java.io.FilterInputStream

java.security.DigestInputStream

All Implemented Interfaces:

Closeable, AutoCloseable

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 original digest untouched.

Implementation Note:

This implementation only updates the message digest with data actually read from the input stream when it is turned on. This includes the various read methods, transferTo, readAllBytes, and readNBytes. Please note that data bypassed by the skip method are ignored. On the other hand, if the underlying stream supports the mark and reset methods, and the same data is read again after reset, then the message digest is updated again.

Since:

1.2

See Also:

• MessageDigest
• DigestOutputStream

Field Summary

Fields

Modifier and Type	Field	Description
protected MessageDigest	digest	The message digest associated with this stream.

Fields declared in class FilterInputStream

in

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

Constructor Summary

Constructors

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

Method Summary

Modifier and Type	Method	Description
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.

Methods declared in class FilterInputStream

available, close, mark, markSupported, read, reset, skip

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(byte[] b)	Reads up to b.length 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 InputStream

nullInputStream, readAllBytes, readNBytes, readNBytes, skipNBytes, transferTo

Modifier and Type	Method	Description
static InputStream	nullInputStream()	Returns a new InputStream that reads no 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	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 Object

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

Modifier and Type	Method	Description
protected Object	clone()	Answers a new instance of the same class as the receiver, whose slots have been filled in with the values in the slots of the receiver.
boolean	equals(Object o)	Compares the argument to the receiver, and answers true if they represent the same object using a class specific comparison.
protected void	finalize()	Deprecated, for removal: This API element is subject to removal in a future version. May cause performance issues, deadlocks and hangs.
final Class<? extends Object>	getClass()	Answers the unique instance of java.lang.Class which represents the class of the receiver.
int	hashCode()	Answers an integer hash code for the receiver.
final void	notify()	Causes one thread which is waiting on the receiver to be made ready to run.
final void	notifyAll()	Causes all threads which are waiting on the receiver to be made ready to run.
final void	wait()	Causes the thread which sent this message to be made not ready to run pending some change in the receiver (as indicated by notify or notifyAll).
final void	wait(long time)	Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.
final void	wait(long time, int frac)	Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.

Field Details

digest

protected MessageDigest digest

The message digest associated with this stream.

Constructor Details

DigestInputStream

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.

Method Details

getMessageDigest

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)

setMessageDigest

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()

read

public int read()
         throws IOException

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.

Overrides:

read in class FilterInputStream

Returns:

the byte read.

Throws:

IOException - if an I/O error occurs.

See Also:

• MessageDigest.update(byte)

read

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

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.

Overrides:

read in class FilterInputStream

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)

on

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.

toString

public String toString()

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

Overrides:

toString in class Object

Returns:

String a printable representation for the receiver.