这个压缩包里的都是超级经典的java例子

				
				
				
				Generating a Message Authentication Code (MAC) (Java Developers Almanac Example)
				
				
				
				
				
				
				
				
				
				
				
				
				
				
				
				
				
				
				
				
				
				The Java Developers Almanac 1.4
				
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				  e469. Generating a Message Authentication Code (MAC)
				
				A MAC is like hash code for a sequence of bytes.  Unlike a hash code,
				a MAC uses a secret key to generate the hash code, or more
				specifically, the message digest.  A MAC is generally used to
				check the integrity or validity of information based on a secret key.
				
				
				    try {
				        // Generate a key for the HMAC-MD5 keyed-hashing algorithm; see RFC 2104
				        // In practice, you would save this key.
				        KeyGenerator keyGen = KeyGenerator.getInstance("HmacMD5");
				        SecretKey key = keyGen.generateKey();
				    
				        // Create a MAC object using HMAC-MD5 and initialize with key
				        Mac mac = Mac.getInstance(key.getAlgorithm());
				        mac.init(key);
				    
				        String str = "This message will be digested";
				    
				        // Encode the string into bytes using utf-8 and digest it
				        byte[] utf8 = str.getBytes("UTF8");
				        byte[] digest = mac.doFinal(utf8);
				    
				        // If desired, convert the digest into a string
				        String digestB64 = new sun.misc.BASE64Encoder().encode(digest);
				    } catch (InvalidKeyException e) {
				    } catch (NoSuchAlgorithmException e) {
				    } catch (UnsupportedEncodingException e) {
				    }
				
				
				
				
				             Related Examples
				
				
				
				
				e467. 
				    Listing All Available Message Authentication Code (MAC) Key Generators
				
				
				
				e468. 
				    Generating a Message Authentication Code (MAC) Key
				
				
				
				
				
				
				
				
				        See also: 
				
				    Encrypting and Decrypting
				  
				
				
				    Key Agreement
				  
				
				
				    Symmetric Keys
				  
				
				
				
				
				
				
				
				
				
				© 2002 Addison-Wesley.