public abstract class MessageDigest extends MessageDigestSpi
A MessageDigest object starts out initialized. The data is
processed through it using the update
methods. At any point reset
can be called
to reset the digest. Once all the data to be updated has been
updated, one of the digest
methods should
be called to complete the hash computation.
The digest
method can be called once for a given number
of updates. After digest
has been called, the MessageDigest
object is reset to its initialized state.
Implementations are free to implement the Cloneable interface. Client applications can test cloneability by attempting cloning and catching the CloneNotSupportedException:
MessageDigest md = MessageDigest.getInstance("SHA");
try {
md.update(toChapter1);
MessageDigest tc1 = md.clone();
byte[] toChapter1Digest = tc1.digest();
md.update(toChapter2);
...etc.
} catch (CloneNotSupportedException cnse) {
throw new DigestException("couldn't make digest of partial content");
}
Note that if a given implementation is not cloneable, it is still possible to compute intermediate digests by instantiating several instances, if the number of digests is known in advance.
Note that this class is abstract and extends from
MessageDigestSpi
for historical reasons.
Application developers should only take notice of the methods defined in
this MessageDigest
class; all the methods in
the superclass are intended for cryptographic service providers who wish to
supply their own implementations of message digest algorithms.
Every implementation of the Java platform is required to support
the following standard MessageDigest
algorithms:
MD5
SHA-1
SHA-256
DigestInputStream
,
DigestOutputStream
Modifier | Constructor | Description |
---|---|---|
protected |
MessageDigest(String algorithm) |
Creates a message digest with the specified algorithm name.
|
Modifier and Type | Method | Description |
---|---|---|
Object |
clone() |
Returns a clone if the implementation is cloneable.
|
byte[] |
digest() |
Completes the hash computation by performing final operations
such as padding.
|
byte[] |
digest(byte[] input) |
Performs a final update on the digest using the specified array
of bytes, then completes the digest computation.
|
int |
digest(byte[] buf,
int offset,
int len) |
Completes the hash computation by performing final operations
such as padding.
|
String |
getAlgorithm() |
Returns a string that identifies the algorithm, independent of
implementation details.
|
int |
getDigestLength() |
Returns the length of the digest in bytes, or 0 if this operation is
not supported by the provider and the implementation is not cloneable.
|
static MessageDigest |
getInstance(String algorithm) |
Returns a MessageDigest object that implements the specified digest
algorithm.
|
static MessageDigest |
getInstance(String algorithm,
String provider) |
Returns a MessageDigest object that implements the specified digest
algorithm.
|
static MessageDigest |
getInstance(String algorithm,
Provider provider) |
Returns a MessageDigest object that implements the specified digest
algorithm.
|
Provider |
getProvider() |
Returns the provider of this message digest object.
|
static boolean |
isEqual(byte[] digesta,
byte[] digestb) |
Compares two digests for equality.
|
void |
reset() |
Resets the digest for further use.
|
String |
toString() |
Returns a string representation of this message digest object.
|
void |
update(byte input) |
Updates the digest using the specified byte.
|
void |
update(byte[] input) |
Updates the digest using the specified array of bytes.
|
void |
update(byte[] input,
int offset,
int len) |
Updates the digest using the specified array of bytes, starting
at the specified offset.
|
void |
update(ByteBuffer input) |
Update the digest using the specified ByteBuffer.
|
engineDigest, engineDigest, engineGetDigestLength, engineReset, engineUpdate, engineUpdate, engineUpdate
protected MessageDigest(String algorithm)
algorithm
- the standard name of the digest algorithm.
See the MessageDigest section in the
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard algorithm names.public static MessageDigest getInstance(String algorithm) throws NoSuchAlgorithmException
This method traverses the list of registered security Providers, starting with the most preferred Provider. A new MessageDigest object encapsulating the MessageDigestSpi implementation from the first Provider that supports the specified algorithm is returned.
Note that the list of registered providers may be retrieved via
the Security.getProviders()
method.
jdk.security.provider.preferred
Security
property to determine
the preferred provider order for the specified algorithm. This
may be different than the order of providers returned by
Security.getProviders()
.algorithm
- the name of the algorithm requested.
See the MessageDigest section in the
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard algorithm names.MessageDigest
object that implements the
specified algorithmNoSuchAlgorithmException
- if no Provider
supports a
MessageDigestSpi
implementation for the
specified algorithmNullPointerException
- if algorithm
is null
Provider
public static MessageDigest getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException
A new MessageDigest object encapsulating the MessageDigestSpi implementation from the specified provider is returned. The specified provider must be registered in the security provider list.
Note that the list of registered providers may be retrieved via
the Security.getProviders()
method.
algorithm
- the name of the algorithm requested.
See the MessageDigest section in the
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard algorithm names.provider
- the name of the provider.MessageDigest
object that implements the
specified algorithmIllegalArgumentException
- if the provider name is null
or emptyNoSuchAlgorithmException
- if a MessageDigestSpi
implementation for the specified algorithm is not
available from the specified providerNoSuchProviderException
- if the specified provider is not
registered in the security provider listNullPointerException
- if algorithm
is null
Provider
public static MessageDigest getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException
A new MessageDigest object encapsulating the MessageDigestSpi implementation from the specified Provider object is returned. Note that the specified Provider object does not have to be registered in the provider list.
algorithm
- the name of the algorithm requested.
See the MessageDigest section in the
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard algorithm names.provider
- the provider.MessageDigest
object that implements the
specified algorithmIllegalArgumentException
- if the specified provider is
null
NoSuchAlgorithmException
- if a MessageDigestSpi
implementation for the specified algorithm is not available
from the specified Provider
objectNullPointerException
- if algorithm
is null
Provider
public final Provider getProvider()
public void update(byte input)
input
- the byte with which to update the digest.public void update(byte[] input, int offset, int len)
input
- the array of bytes.offset
- the offset to start from in the array of bytes.len
- the number of bytes to use, starting at
offset
.public void update(byte[] input)
input
- the array of bytes.public final void update(ByteBuffer input)
input.remaining()
bytes starting
at input.position()
.
Upon return, the buffer's position will be equal to its limit;
its limit will not have changed.input
- the ByteBufferpublic byte[] digest()
public int digest(byte[] buf, int offset, int len) throws DigestException
buf
- output buffer for the computed digestoffset
- offset into the output buffer to begin storing the digestlen
- number of bytes within buf allotted for the digestbuf
DigestException
- if an error occurs.public byte[] digest(byte[] input)
update(input)
,
passing the input array to the update
method,
then calls digest()
.input
- the input to be updated before the digest is
completed.public String toString()
public static boolean isEqual(byte[] digesta, byte[] digestb)
digesta
- one of the digests to compare.digestb
- the other digest to compare.public void reset()
public final String getAlgorithm()
public final int getDigestLength()
public Object clone() throws CloneNotSupportedException
clone
in class MessageDigestSpi
CloneNotSupportedException
- if this is called on an
implementation that does not support Cloneable
.Cloneable
Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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DRAFT 9-internal+0-adhoc.mlchung.jdk9-jdeps