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Android APIs
public class

CipherInputStream

extends FilterInputStream
java.lang.Object
   ↳ java.io.InputStream
     ↳ java.io.FilterInputStream
       ↳ javax.crypto.CipherInputStream

Class Overview

This class wraps an InputStream and a cipher so that read() methods return data that are read from the underlying InputStream and processed by the cipher.

The cipher must be initialized for the requested operation before being used by a CipherInputStream. For example, if a cipher initialized for decryption is used with a CipherInputStream, the CipherInputStream tries to read the data an decrypt them before returning.

Summary

[Expand]
Inherited Fields
From class java.io.FilterInputStream
Public Constructors
CipherInputStream(InputStream is, Cipher c)
Creates a new CipherInputStream instance for an InputStream and a cipher.
Protected Constructors
CipherInputStream(InputStream is)
Creates a new CipherInputStream instance for an InputStream without a cipher.
Public Methods
int available()
Returns an estimated number of bytes that can be read or skipped without blocking for more input.
void close()
Closes this CipherInputStream, also closes the underlying input stream and call doFinal on the cipher object.
boolean markSupported()
Returns whether this input stream supports mark and reset, which it does not.
int read()
Reads the next byte from this cipher input stream.
int read(byte[] buf, int off, int len)
Reads the next len bytes from this input stream into buffer buf starting at offset off.
long skip(long byteCount)
Skips byteCount bytes in this stream.
[Expand]
Inherited Methods
From class java.io.FilterInputStream
From class java.io.InputStream
From class java.lang.Object
From interface java.io.Closeable

Public Constructors

public CipherInputStream (InputStream is, Cipher c)

Since: API Level 1

Creates a new CipherInputStream instance for an InputStream and a cipher.

Warning: passing a null source creates an invalid CipherInputStream. All read operations on such a stream will fail.

Parameters
is the input stream to read data from.
c the cipher to process the data with.

Protected Constructors

protected CipherInputStream (InputStream is)

Since: API Level 1

Creates a new CipherInputStream instance for an InputStream without a cipher.

A NullCipher is created and used to process the data.

Parameters
is the input stream to read data from.

Public Methods

public int available ()

Since: API Level 1

Returns an estimated number of bytes that can be read or skipped without blocking for more input.

Note that this method provides such a weak guarantee that it is not very useful in practice.

Firstly, the guarantee is "without blocking for more input" rather than "without blocking": a read may still block waiting for I/O to complete — the guarantee is merely that it won't have to wait indefinitely for data to be written. The result of this method should not be used as a license to do I/O on a thread that shouldn't be blocked.

Secondly, the result is a conservative estimate and may be significantly smaller than the actual number of bytes available. In particular, an implementation that always returns 0 would be correct. In general, callers should only use this method if they'd be satisfied with treating the result as a boolean yes or no answer to the question "is there definitely data ready?".

Thirdly, the fact that a given number of bytes is "available" does not guarantee that a read or skip will actually read or skip that many bytes: they may read or skip fewer.

It is particularly important to realize that you must not use this method to size a container and assume that you can read the entirety of the stream without needing to resize the container. Such callers should probably write everything they read to a ByteArrayOutputStream and convert that to a byte array. Alternatively, if you're reading from a file, length() returns the current length of the file (though assuming the file's length can't change may be incorrect, reading a file is inherently racy).

The default implementation of this method in InputStream always returns 0. Subclasses should override this method if they are able to indicate the number of bytes available.

Returns
  • the estimated number of bytes available
Throws
IOException

public void close ()

Since: API Level 1

Closes this CipherInputStream, also closes the underlying input stream and call doFinal on the cipher object.

Throws
IOException if an error occurs.

public boolean markSupported ()

Since: API Level 1

Returns whether this input stream supports mark and reset, which it does not.

Returns
  • false, since this input stream does not support mark and reset.

public int read ()

Since: API Level 1

Reads the next byte from this cipher input stream.

Returns
  • the next byte, or -1 if the end of the stream is reached.
Throws
IOException if an error occurs.

public int read (byte[] buf, int off, int len)

Since: API Level 1

Reads the next len bytes from this input stream into buffer buf starting at offset off.

if buf is null, the next len bytes are read and discarded.

Parameters
buf the byte array in which to store the bytes read.
off the initial position in buffer to store the bytes read from this stream.
len the maximum number of bytes to store in buffer.
Returns
  • the number of bytes filled into buffer buf, or -1 of the of the stream is reached.
Throws
IOException if an error occurs.
NullPointerException if the underlying input stream is null.

public long skip (long byteCount)

Since: API Level 1

Skips byteCount bytes in this stream. Subsequent calls to read will not return these bytes unless reset is used. This implementation skips byteCount bytes in the filtered stream.

Parameters
byteCount the number of bytes to skip.
Returns
  • the number of bytes actually skipped.
Throws
IOException