messagedigest_md5加密 java_java digest方法

This MessageDigest class provides applications the functionality of a message digest algorithm, such as MD5 or SHA. Message digests are secure one-way hash functions that take arbitrary-sized data and output a fixed-length hash value.

A MessageDigest object starts out initialized. The data is processed through it using the methods. At any point can be called to reset the digest. Once all the data to be updated has been updated, one of the 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 intece. 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.

See Also:

DigestInputStream, DigestOutputStream

Constructor Summary

Method Summary

(byte[]input,intoffset,intlen)

Updates the digest using the specified array of bytes, starting at the specified offset.

Methods inherited from class java.security.MessageDigestSpi

Methods inherited from class java.lang.Object

Constructor Detail

MessageDigest

protected MessageDigest(String algorithm)

Parameters:algorithm - the standard name of the digest algorithm. See Appendix A in the Java Cryptography Architecture API Specification & Reference for information about standard algorithm names.

Method Detail

getInstance

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 method.

Parameters:algorithm - the name of the algorithm requested. See Appendix A in the Java Cryptography Architecture API Specification & Reference for information about standard algorithm names.Returns:a Message Digest object that implements the specified algorithm.Throws:NoSuchAlgorithmException - if no Provider supports aMessageDigestSpi implementation for thespecified algorithm.See Also:Provider

getInstance

public static MessageDigest getInstance(String algorithm,
                                        String provider)
                                 throws NoSuchAlgorithmException,
                                        NoSuchProviderException

Returns a MessageDigest object that implements the specified digest algorithm.

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 method.

Parameters:algorithm - the name of the algorithm requested. See Appendix A in the Java Cryptography Architecture API Specification & Reference for information about standard algorithm names.provider - the name of the provider.Returns:a MessageDigest object that implements the specified algorithm.Throws:NoSuchAlgorithmException - if a MessageDigestSpiimplementation for the specified algorithm is notavailable from the specified provider.NoSuchProviderException - if the specified provider is notregistered in the security provider list.IllegalArgumentException - if the provider name is nullor empty.See Also:Provider

getInstance

public static MessageDigest getInstance(String algorithm,
                                        Provider provider)
                                 throws NoSuchAlgorithmException

Returns a MessageDigest object that implements the specified digest algorithm.

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.

Parameters:algorithm - the name of the algorithm requested. See Appendix A in the Java Cryptography Architecture API Specification & Reference for information about standard algorithm names.provider - the provider.Returns:a MessageDigest object that implements the specified algorithm.Throws:NoSuchAlgorithmException - if a MessageDigestSpiimplementation for the specified algorithm is not availablefrom the specified Provider object.IllegalArgumentException - if the specified provider is null.Since:

getProvider

public final Provider getProvider()

update

public void update(byte input)

update

public void update(byte[] input,
                   int offset,
                   int len)

Updates the digest using the specified array of bytes, starting at the specified offset.

Parameters: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.

update

public void update(byte[] input)

update

public final void update(ByteBuffer input)

Update the digest using the specified ByteBuffer. The digest is updated using the 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.

Parameters:input - the ByteBufferSince:

digest

public byte[] digest()

digest

public int digest(byte[] buf,
                  int offset,
                  int len)
           throws DigestException

digest

public byte[] digest(byte[] input)

Performs a final update on the digest using the specified array of bytes, then completes the digest computation. That is, this method first calls , passing the input array to the update method, then calls .

Parameters:input - the input to be updated before the digest is completed.Returns:the array of bytes for the resulting hash value.

toString

public String toString()

isEqual

public static boolean isEqual(byte[] digesta,
                              byte[] digestb)

Compares two digests for equality. Does a byte compare.

Parameters:digesta - one of the digests to compare.digestb - the other digest to compare.Returns:true if the digests are equal, false otherwise.

reset

public void reset()

getAlgorithm

public final String getAlgorithm()

Returns a string that identifies the algorithm, independent of implementation details. The name should be a standard Java Security name (such as "SHA", "MD5", and so on). See Appendix A in the Java Cryptography Architecture API Specification & Reference for information about standard algorithm names.

Returns:the name of the algorithm

getDigestLength

public final 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.

Returns:the digest length in bytes, or 0 if this operation is not supported by the provider and the implementation is not cloneable.Since:

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