嗨，我有一个要求，我需要生成类似 SessionID 的东西，但这也是同时发生的。我正在考虑从tomcat 7源“SessionIdGenerator”中获取代码。但我不确定它是否会在没有任何修改的情况下同时生成 uniqueID。
类本身在这里：
公共类 SessionIdGenerator {
private Logger logger = LoggerFactory.getLogger();
/**
* Queue of random number generator objects to be used when creating session
* identifiers. If the queue is empty when a random number generator is
* required, a new random number generator object is created. This is
* designed this way since random number generators use a sync to make them
* thread-safe and the sync makes using a a single object slow(er).
*/
private Queue<SecureRandom> randoms = new ConcurrentLinkedQueue<SecureRandom>();
/**
* The Java class name of the secure random number generator class to be
* used when generating session identifiers. The random number generator
* class must be self-seeding and have a zero-argument constructor. If not
* specified, an instance of {@link SecureRandom} will be generated.
*/
private String secureRandomClass = null;
/**
* The name of the algorithm to use to create instances of
* {@link SecureRandom} which are used to generate session IDs. If no
* algorithm is specified, SHA1PRNG is used. To use the platform default
* (which may be SHA1PRNG), specify the empty string. If an invalid
* algorithm and/or provider is specified the {@link SecureRandom} instances
* will be created using the defaults. If that fails, the {@link
* SecureRandom} instances will be created using platform defaults.
*/
private String secureRandomAlgorithm = "SHA1PRNG";
/**
* The name of the provider to use to create instances of
* {@link SecureRandom} which are used to generate session IDs. If
* no algorithm is specified the of SHA1PRNG default is used. If an invalid
* algorithm and/or provider is specified the {@link SecureRandom} instances
* will be created using the defaults. If that fails, the {@link
* SecureRandom} instances will be created using platform defaults.
*/
private String secureRandomProvider = null;
/** Node identifier when in a cluster. Defaults to the empty string. */
private String jvmRoute = "";
/** Number of bytes in a session ID. Defaults to 16. */
private int sessionIdLength = 16;
/**
* Specify a non-default @{link {@link SecureRandom} implementation to use.
*
* @param secureRandomClass The fully-qualified class name
*/
public void setSecureRandomClass(String secureRandomClass) {
this.secureRandomClass = secureRandomClass;
}
/**
* Specify a non-default algorithm to use to generate random numbers.
*
* @param secureRandomAlgorithm The name of the algorithm
*/
public void setSecureRandomAlgorithm(String secureRandomAlgorithm) {
this.secureRandomAlgorithm = secureRandomAlgorithm;
}
/**
* Specify a non-default provider to use to generate random numbers.
*
* @param secureRandomProvider The name of the provider
*/
public void setSecureRandomProvider(String secureRandomProvider) {
this.secureRandomProvider = secureRandomProvider;
}
/**
* Specify the node identifier associated with this node which will be
* included in the generated session ID.
*
* @param jvmRoute The node identifier
*/
public void setJvmRoute(String jvmRoute) {
this.jvmRoute = jvmRoute;
}
/**
* Specify the number of bytes for a session ID
*
* @param sessionIdLength Number of bytes
*/
public void setSessionIdLength(int sessionIdLength) {
this.sessionIdLength = sessionIdLength;
}
/**
* Generate and return a new session identifier.
*/
public String generateSessionId() {
byte random[] = new byte[16];
// Render the result as a String of hexadecimal digits
StringBuilder buffer = new StringBuilder();
int resultLenBytes = 0;
while (resultLenBytes < sessionIdLength) {
getRandomBytes(random);
for (int j = 0;
j < random.length && resultLenBytes < sessionIdLength;
j++) {
byte b1 = (byte) ((random[j] & 0xf0) >> 4);
byte b2 = (byte) (random[j] & 0x0f);
if (b1 < 10)
buffer.append((char) ('0' + b1));
else
buffer.append((char) ('A' + (b1 - 10)));
if (b2 < 10)
buffer.append((char) ('0' + b2));
else
buffer.append((char) ('A' + (b2 - 10)));
resultLenBytes++;
}
}
if (jvmRoute != null && jvmRoute.length() > 0) {
buffer.append('.').append(jvmRoute);
}
return buffer.toString();
}
private void getRandomBytes(byte bytes[]) {
SecureRandom random = randoms.poll();
if (random == null) {
random = createSecureRandom();
}
random.nextBytes(bytes);
randoms.add(random);
}
/**
* Create a new random number generator instance we should use for
* generating session identifiers.
*/
private SecureRandom createSecureRandom() {
SecureRandom result = null;
long t1 = System.currentTimeMillis();
if (secureRandomClass != null) {
try {
// Construct and seed a new random number generator
Class<?> clazz = Class.forName(secureRandomClass);
result = (SecureRandom) clazz.newInstance();
} catch (Exception e) {
logger.debug("exception:"+e);
}
}
if (result == null) {
// No secureRandomClass or creation failed. Use SecureRandom.
try {
if (secureRandomProvider != null &&
secureRandomProvider.length() > 0) {
result = SecureRandom.getInstance(secureRandomAlgorithm,
secureRandomProvider);
} else if (secureRandomAlgorithm != null &&
secureRandomAlgorithm.length() > 0) {
result = SecureRandom.getInstance(secureRandomAlgorithm);
}
} catch (NoSuchAlgorithmException e) {
logger.debug("exception:"+e);
} catch (NoSuchProviderException e) {
logger.debug("exception:"+e);
}
}
if (result == null) {
// Invalid provider / algorithm
try {
result = SecureRandom.getInstance("SHA1PRNG");
} catch (NoSuchAlgorithmException e) {
logger.debug("exception:"+e);
}
}
if (result == null) {
// Nothing works - use platform default
result = new SecureRandom();
}
// Force seeding to take place
result.nextInt();
long t2=System.currentTimeMillis();
if( (t2-t1) > 100 )
logger.debug("sessionIdGenerator algorithm:"+result.getAlgorithm()+"time taken:" +Long.valueOf(t2-t1));
return result;
}
}