# Class CipherOutputStream

java.lang.Object
java.io.OutputStream
java.io.FilterOutputStream
javax.crypto.CipherOutputStream

All Implemented Interfaces:
  `Closeable, Flushable, AutoCloseable`

public class CipherOutputStream extends FilterOutputStream
A `CipherOutputStream` is composed of an `OutputStream` and a `Cipher` object so that write() methods first process the data before writing them out to the underlying `OutputStream`. The `Cipher` object must be fully initialized before being used by a `CipherOutputStream`.

For example, if the `Cipher` object is initialized for encryption, the `CipherOutputStream` will attempt to encrypt data before writing out the encrypted data.

This class adheres strictly to the semantics, especially the failure semantics, of its ancestor classes `java.io.OutputStream` and `java.io.FilterOutputStream`. This class has exactly those methods specified in its ancestor classes, and overrides them all. Moreover, this class catches all exceptions that are not thrown by its ancestor classes. In particular, this class catches `BadPaddingException` and other exceptions thrown by failed integrity checks during decryption. These exceptions are not re-thrown, so the client will not be informed that integrity checks failed. Because of this behavior, this class may not be suitable for use with decryption in an authenticated mode of operation (e.g. GCM) if the application requires explicit notification when authentication fails. Such an application can use the `Cipher` API directly as an alternative to using this class.

It is crucial for a programmer using this class not to use methods that are not defined or overridden in this class (such as a new method or constructor that is later added to one of the super classes), because the design and implementation of those methods are unlikely to have considered security impact with regard to `CipherOutputStream`.

Since:
  1.4
See Also:
  - `OutputStream`
  - `FilterOutputStream`
  - `Cipher`
  - `CipherInputStream`

- ## Field Summary

  ### Fields declared in class FilterOutputStream

  `out`
  Modifier and Type
  Field
  Description
  `protected OutputStream`
  `out`
  The underlying output stream to be filtered.

- ## Constructor Summary

  Constructors
  Modifier
  Constructor
  Description
  `protected`
  `CipherOutputStream(OutputStream os)`
  Constructs a `CipherOutputStream` from an `OutputStream` without specifying a `Cipher` object.
  ``
  `CipherOutputStream(OutputStream os, Cipher c)`
  Constructs a `CipherOutputStream` from an `OutputStream` and a `Cipher` object.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `close()`
  Closes this output stream and releases any system resources associated with this stream.
  `void`
  `flush()`
  Flushes this output stream by forcing any buffered output bytes that have already been processed by the encapsulated `Cipher` object to be written out.
  `void`
  `write(byte[] b)`
  Writes `b.length` bytes from the specified byte array to this output stream.
  `void`
  `write(byte[] b, int off, int len)`
  Writes `len` bytes from the specified byte array starting at offset `off` to this output stream.
  `void`
  `write(int b)`
  Writes the specified byte to this output stream.

  ### Methods declared in class OutputStream

  `nullOutputStream`
  Modifier and Type
  Method
  Description
  `static OutputStream`
  `nullOutputStream()`
  Returns a new `OutputStream` which discards all bytes.

  ### Methods declared in class Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`
  Modifier and Type
  Method
  Description
  `protected Object`
  `clone()`
  Creates and returns a copy of this object.
  `boolean`
  `equals(Object obj)`
  Indicates whether some other object is "equal to" this one.
  `protected void`
  `finalize()`
  Deprecated, for removal: This API element is subject to removal in a future version.
  Finalization is deprecated and subject to removal in a future release.
  `final Class<?>`
  `getClass()`
  Returns the runtime class of this `Object`.
  `int`
  `hashCode()`
  Returns a hash code value for this object.
  `final void`
  `notify()`
  Wakes up a single thread that is waiting on this object's monitor.
  `final void`
  `notifyAll()`
  Wakes up all threads that are waiting on this object's monitor.
  `String`
  `toString()`
  Returns a string representation of the object.
  `final void`
  `wait()`
  Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
  `final void`
  `wait(long timeoutMillis)`
  Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
  `final void`
  `wait(long timeoutMillis, int nanos)`
  Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

- ## Constructor Details

  - ### CipherOutputStream

    public CipherOutputStream(OutputStream os, Cipher c)
    Constructs a `CipherOutputStream` from an `OutputStream` and a `Cipher` object.
    Note: if the specified output stream or cipher is `null`, `a NullPointerException` may be thrown later when they are used.
    Parameters:
      `os` - the `OutputStream` object
      `c` - an initialized `Cipher` object

  - ### CipherOutputStream

    protected CipherOutputStream(OutputStream os)
    Constructs a `CipherOutputStream` from an `OutputStream` without specifying a `Cipher` object. This has the effect of constructing a `CipherOutputStream` using a `NullCipher`.
    Note: if the specified output stream is `null`, a `NullPointerException` may be thrown later when it is used.
    Parameters:
      `os` - the `OutputStream` object

- ## Method Details

  - ### write

    public void write(int b) throws IOException
    Writes the specified byte to this output stream.
    Overrides:
      `write` in class `FilterOutputStream`
    Parameters:
      `b` - the `byte`.
    Throws:
      `IOException` - if an I/O error occurs.

  - ### write

    public void write(byte[] b) throws IOException
    Writes `b.length` bytes from the specified byte array to this output stream.

    The `write` method of `CipherOutputStream` calls the `write` method of three arguments with the three arguments `b`, `0`, and `b.length`.

    Overrides:
      `write` in class `FilterOutputStream`
    Parameters:
      `b` - the data.
    Throws:
      `NullPointerException` - if `b` is `null`.
      `IOException` - if an I/O error occurs.
    See Also:
      - `write(byte[], int, int)`

  - ### write

    public void write(byte[] b, int off, int len) throws IOException
    Writes `len` bytes from the specified byte array starting at offset `off` to this output stream.
    Overrides:
      `write` in class `FilterOutputStream`
    Parameters:
      `b` - the data.
      `off` - the start offset in the data.
      `len` - the number of bytes to write.
    Throws:
      `IOException` - if an I/O error occurs.
    See Also:
      - `FilterOutputStream.write(int)`

  - ### flush

    public void flush() throws IOException
    Flushes this output stream by forcing any buffered output bytes that have already been processed by the encapsulated `Cipher` object to be written out.

    Any bytes buffered by the encapsulated `Cipher` object and waiting to be processed by it will not be written out. For example, if the encapsulated `Cipher` object is a block cipher, and the total number of bytes written using one of the `write` methods is less than the cipher's block size, no bytes will be written out.

    Specified by:
      `flush` in interface `Flushable`
    Overrides:
      `flush` in class `FilterOutputStream`
    Throws:
      `IOException` - if an I/O error occurs.
    See Also:
      - `FilterOutputStream.out`

  - ### close

    public void close() throws IOException
    Closes this output stream and releases any system resources associated with this stream.

    This method invokes the `doFinal` method of the encapsulated `Cipher` object, which causes any bytes buffered by the encapsulated `Cipher` object to be processed. The result is written out by calling the `flush` method of this output stream.

    This method resets the encapsulated `Cipher` object to its initial state and calls the `close` method of the underlying output stream.

    Specified by:
      `close` in interface `AutoCloseable`
    Specified by:
      `close` in interface `Closeable`
    Overrides:
      `close` in class `FilterOutputStream`
    Throws:
      `IOException` - if an I/O error occurs.
    See Also:
      - `FilterOutputStream.flush()`
      - `FilterOutputStream.out`