java.security

## Class DigestOutputStream

- java.lang.Object
- - java.io.OutputStream
  - - java.io.FilterOutputStream
    - - java.security.DigestOutputStream

- All Implemented Interfaces:
    Closeable, Flushable

      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

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected MessageDigest` | `digest` The message digest associated with this stream.

    - ### Fields inherited from class java.io.FilterOutputStream

      `out`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `DigestOutputStream(OutputStream stream, MessageDigest digest)` Creates a digest output stream, using the specified output 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.
    `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.
      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()`

    - #### 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`
      Returns:
        a string representation of the object.

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