DigestInputStream (Java Platform SE 7 ) (original) (raw)

• 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 thedigest methods on the associated message digest after your calls to one of this digest input stream'sread methods.
It is possible to turn this stream on or off (seeon). When it is on, a call to one of theread 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 (seeMessageDigest), 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

  Fields

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

     * ### Fields inherited from class java.io.[FilterInputStream](../../java/io/FilterInputStream.html "class in java.io")  
     `[in](../../java/io/FilterInputStream.html#in)`  

  • Constructor Summary

  Constructors

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

  • Method Summary

  Methods

  Modifier and Type	Method and 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 inherited from class java.io.[FilterInputStream](../../java/io/FilterInputStream.html "class in java.io")  
     `[available](../../java/io/FilterInputStream.html#available%28%29), [close](../../java/io/FilterInputStream.html#close%28%29), [mark](../../java/io/FilterInputStream.html#mark%28int%29), [markSupported](../../java/io/FilterInputStream.html#markSupported%28%29), [read](../../java/io/FilterInputStream.html#read%28byte[]%29), [reset](../../java/io/FilterInputStream.html#reset%28%29), [skip](../../java/io/FilterInputStream.html#skip%28long%29)`  
     * ### Methods inherited from class java.lang.[Object](../../java/lang/Object.html "class in java.lang")  
     `[clone](../../java/lang/Object.html#clone%28%29), [equals](../../java/lang/Object.html#equals%28java.lang.Object%29), [finalize](../../java/lang/Object.html#finalize%28%29), [getClass](../../java/lang/Object.html#getClass%28%29), [hashCode](../../java/lang/Object.html#hashCode%28%29), [notify](../../java/lang/Object.html#notify%28%29), [notifyAll](../../java/lang/Object.html#notifyAll%28%29), [wait](../../java/lang/Object.html#wait%28%29), [wait](../../java/lang/Object.html#wait%28long%29), [wait](../../java/lang/Object.html#wait%28long,%20int%29)`

• • Field Detail

     * #### digest  
     protected [MessageDigest](../../java/security/MessageDigest.html "class in java.security") digest  
     The message digest associated with this stream.  

  • Constructor Detail

    * #### DigestInputStream  
    public DigestInputStream([InputStream](../../java/io/InputStream.html "class in java.io") stream,  
                     [MessageDigest](../../java/security/MessageDigest.html "class in java.security") 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](../../java/security/MessageDigest.html "class in java.security") getMessageDigest()  
    Returns the message digest associated with this stream.  
    Returns:  
    the message digest associated with this stream.  
    See Also:  
    [setMessageDigest(java.security.MessageDigest)](../../java/security/DigestInputStream.html#setMessageDigest%28java.security.MessageDigest%29)  
    * #### setMessageDigest  
    public void setMessageDigest([MessageDigest](../../java/security/MessageDigest.html "class in java.security") digest)  
    Associates the specified message digest with this stream.  
    Parameters:  
    `digest` \- the message digest to be associated with this stream.  
    See Also:  
    [getMessageDigest()](../../java/security/DigestInputStream.html#getMessageDigest%28%29)  
    * #### read  
    public int read()  
             throws [IOException](../../java/io/IOException.html "class in java.io")  
    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](../../java/security/DigestInputStream.html#on%28boolean%29)), this method will then call `update` on the message digest associated with this stream, passing it the byte read.  
    **Overrides:**  
    `[read](../../java/io/FilterInputStream.html#read%28%29)` in class `[FilterInputStream](../../java/io/FilterInputStream.html "class in java.io")`  
    Returns:  
    the byte read.  
    Throws:  
    `[IOException](../../java/io/IOException.html "class in java.io")` \- if an I/O error occurs.  
    See Also:  
    [MessageDigest.update(byte)](../../java/security/MessageDigest.html#update%28byte%29)  
    * #### read  
    public int read(byte[] b,  
           int off,  
           int len)  
             throws [IOException](../../java/io/IOException.html "class in java.io")  
    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](../../java/security/DigestInputStream.html#on%28boolean%29)), this method will then call `update` on the message digest associated with this stream, passing it the data.  
    **Overrides:**  
    `[read](../../java/io/FilterInputStream.html#read%28byte[],%20int,%20int%29)` in class `[FilterInputStream](../../java/io/FilterInputStream.html "class in java.io")`  
    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](../../java/io/IOException.html "class in java.io")` \- if an I/O error occurs.  
    See Also:  
    [MessageDigest.update(byte\[\], int, int)](../../java/security/MessageDigest.html#update%28byte[],%20int,%20int%29)  
    * #### 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](../../java/lang/String.html "class in java.lang") toString()  
    Prints a string representation of this digest input stream and its associated message digest object.  
    **Overrides:**  
    `[toString](../../java/lang/Object.html#toString%28%29)` in class `[Object](../../java/lang/Object.html "class in java.lang")`  
    Returns:  
    a string representation of the object.

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