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

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java.security
Class DigestOutputStream

java.lang.Object
  |
  +--java.io.OutputStream
        |
        +--java.io.FilterOutputStream
              |
              +--java.security.DigestOutputStream
public class DigestOutputStream
extends FilterOutputStream

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 ouput stream's write methods.

It is possible to turn this stream on or off (see on). When it is on, a call to one of the write 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.

See Also:
MessageDigest, DigestInputStream

Field Summary
protected  MessageDigest digest
          The message digest associated with this stream.
 
Fields inherited from class java.io.FilterOutputStream
out
 
Constructor Summary
DigestOutputStream(OutputStream stream, MessageDigest digest)
          Creates a digest output stream, using the specified output 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.
 void setMessageDigest(MessageDigest digest)
          Associates the specified message digest with this stream.
 String toString()
          Prints a string representation of this digest output stream and its associated message digest object.
 void write(byte[] b, int off, int len)
          Updates the message digest (if the digest function is on) using the specified subarray, and in any case writes the subarray to the output stream.
 void write(int b)
          Updates the message digest (if the digest function is on) using the specified byte, and in any case writes the byte to the output stream.
 
Methods inherited from class java.io.FilterOutputStream
close, flush, write
 
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

DigestOutputStream

public DigestOutputStream(OutputStream stream,
                          MessageDigest digest)
Creates a digest output stream, using the specified output stream and message digest.
Parameters:
stream - the output 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.

write

public void write(int b)
           throws IOException
Updates the message digest (if the digest function is on) using the specified byte, and in any case writes the byte to the output stream. That is, if the digest function is on (see on), this method calls update on the message digest associated with this stream, passing it the byte b. This method then writes the byte to the output stream, blocking until the byte is actually written.
Overrides:
write in class FilterOutputStream
Parameters:
b - the byte to be used for updating and writing to the output stream.
Throws:
IOException - if an I/O error occurs.
See Also:
MessageDigest.update(byte)

write

public void write(byte[] b,
                  int off,
                  int len)
           throws IOException
Updates the message digest (if the digest function is on) using the specified subarray, and in any case writes the subarray to the output stream. That is, if the digest function is on (see on), this method calls update on the message digest associated with this stream, passing it the subarray specifications. This method then writes the subarray bytes to the output stream, blocking until the bytes are actually written.
Overrides:
write in class FilterOutputStream
Parameters:
b - the array containing the subarray to be used for updating and writing to the output stream.
off - the offset into b of the first byte to be updated and written.
len - the number of bytes of data to be updated and written from b, starting at offset off.
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 write 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 output 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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