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Java(TM) 2 Platform, Standard Edition, v1.2.2 API Specification: Class DigestInputStream - JDK 5 Documentation v1.2.2, Java 2 SDK 英文文档

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java.security
Class DigestInputStream

java.lang.Object
  |
  +--java.io.InputStream
        |
        +--java.io.FilterInputStream
              |
              +--java.security.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.
 
Fields inherited from class java.io.FilterInputStream
in
 
Constructor Summary
DigestInputStream(InputStream stream, MessageDigest digest)
          Creates a digest input stream, using the specified input stream and message digest.
 
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.
 
Methods inherited from class java.io.FilterInputStream
available, close, mark, markSupported, read, reset, skip
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Field Detail

digest

protected MessageDigest digest
The message digest associated with this stream.
Constructor Detail

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 Detail

getMessageDigest

public MessageDigest getMessageDigest()
Returns the message digest associated with this stream.
Returns:
the message digest associated with this stream.

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.

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
Tags copied from class: Object
Returns:
a string representation of the object.
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