请问如何自编函数生成唯一ID？

用下面的模式生成序列号：CREATE SEQUENCE "USER"."SEQ_TABLE_ID" INCREMENT BY 1 START WITH 1 MAXVALUE 999999999 MINVALUE 1 NOCYCLE CACHE 20 ORDER;其中“USER”指用户名，SEQ_TABLE_ID是根据你自己的需要确定的序列号的名字。（上面的序列号是从1到999999999，不循环的，当然也可以建成循环的，前面再自己加上日期之类的区分就行了）

thanks不过我不希望该ID与数据库类型有关
要适合常见的DB,such as oracle,mssql,sybase,db2,etc.Who knows how to generate GUID with program?

create table sequence_table(name varchar(20), value number);
一条记录一个sequence, 每select一次，立刻update一次value=value+1

请问谁知道怎么用JAVA生成GUID？

GUID，说太长，分开回复
/*
* RandomGUID
* @version 1.2 01/29/02
* @author Marc A. Mnich
*
* From www.JavaExchange.com, Open Software licensing
*
* 01/29/02 -- Bug fix: Improper seeding of nonsecure Random object
*             caused duplicate GUIDs to be produced.  Random object
*             is now only created once per JVM.
* 01/19/02 -- Modified random seeding and added new constructor
*             to allow secure random feature.
* 01/14/02 -- Added random function seeding with JVM run time
*
*/
import java.net.*;
import java.util.*;
import java.security.*;
/*
* In the multitude of java GUID generators, I found none that
* guaranteed randomness.  GUIDs are guaranteed to be globally unique
* by using ethernet MACs, IP addresses, time elements, and sequential
* numbers.  GUIDs are not expected to be random and most often are
* easy/possible to guess given a sample from a given generator.
* SQL Server, for example generates GUID that are unique but
* sequencial within a given instance.
*
* GUIDs can be used as security devices to hide things such as
* files within a filesystem where listings are unavailable (e.g. files
* that are served up from a Web server with indexing turned off).
* This may be desireable in cases where standard authentication is not
* appropriate. In this scenario, the RandomGUIDs are used as directories.
* Another example is the use of GUIDs for primary keys in a database
* where you want to ensure that the keys are secret.  Random GUIDs can
* then be used in a URL to prevent hackers (or users) from accessing
* records by guessing or simply by incrementing sequential numbers.
*
* There are many other possiblities of using GUIDs in the realm of
* security and encryption where the element of randomness is important.
* This class was written for these purposes but can also be used as a
* general purpose GUID generator as well.
*
* RandomGUID generates truly random GUIDs by using the system's
* IP address (name/IP), system time in milliseconds (as an integer),
* and a very large random number joined together in a single String
* that is passed through an MD5 hash.  The IP address and system time
* make the MD5 seed globally unique and the random number guarantees
* that the generated GUIDs will have no discernable pattern and
* cannot be guessed given any number of previously generated GUIDs.
* It is generally not possible to access the seed information (IP, time,
* random number) from the resulting GUIDs as the MD5 hash algorithm
* provides one way encryption.
*
* ----> Security of RandomGUID: <-----
* RandomGUID can be called one of two ways -- with the basic java Random
* number generator or a cryptographically strong random generator
* (SecureRandom).  The choice is offered because the secure random
* generator takes about 3.5 times longer to generate its random numbers
* and this performance hit may not be worth the added security
* especially considering the basic generator is seeded with a
* cryptographically strong random seed.
*
* Seeding the basic generator in this way effectively decouples
* the random numbers from the time component making it virtually impossible
* to predict the random number component even if one had absolute knowledge
* of the System time.  Thanks to Ashutosh Narhari for the suggestion
* of using the static method to prime the basic random generator.
*
* Using the secure random option, this class compies with the statistical
* random number generator tests specified in FIPS 140-2, Security
* Requirements for Cryptographic Modules, secition 4.9.1.
*
* I converted all the pieces of the seed to a String before handing
* it over to the MD5 hash so that you could print it out to make
* sure it contains the data you expect to see and to give a nice
* warm fuzzy.  If you need better performance, you may want to stick
* to byte[] arrays.
*
* I believe that it is important that the algorithm for
* generating random GUIDs be open for inspection and modification.
* This class is free for all uses.
*
*
* - Marc
*/

GUID part1 --License/*
* RandomGUID
* @version 1.2 01/29/02
* @author Marc A. Mnich
*
* From www.JavaExchange.com, Open Software licensing
*
* 01/29/02 -- Bug fix: Improper seeding of nonsecure Random object
*             caused duplicate GUIDs to be produced.  Random object
*             is now only created once per JVM.
* 01/19/02 -- Modified random seeding and added new constructor
*             to allow secure random feature.
* 01/14/02 -- Added random function seeding with JVM run time
*
*/
import java.net.*;
import java.util.*;
import java.security.*;
/*
* In the multitude of java GUID generators, I found none that
* guaranteed randomness.  GUIDs are guaranteed to be globally unique
* by using ethernet MACs, IP addresses, time elements, and sequential
* numbers.  GUIDs are not expected to be random and most often are
* easy/possible to guess given a sample from a given generator.
* SQL Server, for example generates GUID that are unique but
* sequencial within a given instance.
*
* GUIDs can be used as security devices to hide things such as
* files within a filesystem where listings are unavailable (e.g. files
* that are served up from a Web server with indexing turned off).
* This may be desireable in cases where standard authentication is not
* appropriate. In this scenario, the RandomGUIDs are used as directories.
* Another example is the use of GUIDs for primary keys in a database
* where you want to ensure that the keys are secret.  Random GUIDs can
* then be used in a URL to prevent hackers (or users) from accessing
* records by guessing or simply by incrementing sequential numbers.
*
* There are many other possiblities of using GUIDs in the realm of
* security and encryption where the element of randomness is important.
* This class was written for these purposes but can also be used as a
* general purpose GUID generator as well.
*
* RandomGUID generates truly random GUIDs by using the system's
* IP address (name/IP), system time in milliseconds (as an integer),
* and a very large random number joined together in a single String
* that is passed through an MD5 hash.  The IP address and system time
* make the MD5 seed globally unique and the random number guarantees
* that the generated GUIDs will have no discernable pattern and
* cannot be guessed given any number of previously generated GUIDs.
* It is generally not possible to access the seed information (IP, time,
* random number) from the resulting GUIDs as the MD5 hash algorithm
* provides one way encryption.
*
* ----> Security of RandomGUID: <-----
* RandomGUID can be called one of two ways -- with the basic java Random
* number generator or a cryptographically strong random generator
* (SecureRandom).  The choice is offered because the secure random
* generator takes about 3.5 times longer to generate its random numbers
* and this performance hit may not be worth the added security
* especially considering the basic generator is seeded with a
* cryptographically strong random seed.
*
* Seeding the basic generator in this way effectively decouples
* the random numbers from the time component making it virtually impossible
* to predict the random number component even if one had absolute knowledge
* of the System time.  Thanks to Ashutosh Narhari for the suggestion
* of using the static method to prime the basic random generator.
*
* Using the secure random option, this class compies with the statistical
* random number generator tests specified in FIPS 140-2, Security
* Requirements for Cryptographic Modules, secition 4.9.1.
*
* I converted all the pieces of the seed to a String before handing
* it over to the MD5 hash so that you could print it out to make
* sure it contains the data you expect to see and to give a nice
* warm fuzzy.  If you need better performance, you may want to stick
* to byte[] arrays.
*
* I believe that it is important that the algorithm for
* generating random GUIDs be open for inspection and modification.
* This class is free for all uses.
*
*
* - Marc
*/

//part2 bodypublic class RandomGUID extends Object {  public String valueBeforeMD5 = "";
  public String valueAfterMD5 = "";
  private static Random myRand;
  private static SecureRandom mySecureRand;  /*
   * Static block to take care of one time secureRandom seed.
   * It takes a few seconds to initialize SecureRandom.  You might
   * want to consider removing this static block or replacing
   * it with a "time since first loaded" seed to reduce this time.
   * This block will run only once per JVM instance.
   */  static {
    mySecureRand = new SecureRandom();
    long secureInitializer = mySecureRand.nextLong();    myRand = new Random(secureInitializer);
  }  /*
   * Default constructor.  With no specification of security option,
   * this constructor defaults to lower security, high performance.
   */
  public RandomGUID() {
    getRandomGUID(false);
  }  /*
   * Constructor with security option.  Setting secure true
   * enables each random number generated to be cryptographically
   * strong.  Secure false defaults to the standard Random function seeded
   * with a single cryptographically strong random number.
   */
  public RandomGUID(boolean secure) {
    getRandomGUID(secure);
  }  /*
   * Method to generate the random GUID
   */
  private void getRandomGUID(boolean secure) {
    MessageDigest md5 = null;
    StringBuffer sbValueBeforeMD5 = new StringBuffer();    try {
      md5 = MessageDigest.getInstance("MD5");
    } catch (NoSuchAlgorithmException e) {
      System.out.println("Error: " + e);
    }    try {
      InetAddress id = InetAddress.getLocalHost();
      long time = System.currentTimeMillis();
      long rand = 0;      if (secure) {
        rand = mySecureRand.nextLong();
      } else {
        rand = myRand.nextLong();
      }      // This StringBuffer can be a long as you need; the MD5
      // hash will always return 128 bits.  You can change
      // the seed to include anything you want here.
      // You could even stream a file through the MD5 making
      // the odds of guessing it at least as great as that
      // of guessing the contents of the file!
      sbValueBeforeMD5.append(id.toString());
      sbValueBeforeMD5.append(":");
      sbValueBeforeMD5.append(Long.toString(time));
      sbValueBeforeMD5.append(":");
      sbValueBeforeMD5.append(Long.toString(rand));      valueBeforeMD5 = sbValueBeforeMD5.toString();
      md5.update(valueBeforeMD5.getBytes());      byte[] array = md5.digest();
      StringBuffer sb = new StringBuffer();      for (int j = 0; j < array.length; ++j) {
        int b = array[j] & 0xFF;        if (b < 0x10) sb.append('0');
        sb.append(Integer.toHexString(b));
      }      valueAfterMD5 = sb.toString();    } catch (UnknownHostException e) {
      System.out.println("Error:" + e);
    }
  }  /*
   * Convert to the standard format for GUID
   * (Useful for SQL Server UniqueIdentifiers, etc.)
   * Example: C2FEEEAC-CFCD-11D1-8B05-00600806D9B6
   */
  public String toString() {
    String raw = valueAfterMD5.toUpperCase();
    StringBuffer sb = new StringBuffer();    sb.append(raw.substring(0, 8));
    sb.append("-");
    sb.append(raw.substring(8, 12));
    sb.append("-");
    sb.append(raw.substring(12, 16));
    sb.append("-");
    sb.append(raw.substring(16, 20));
    sb.append("-");
    sb.append(raw.substring(20));    return sb.toString();
  }

  /*
   * Demonstraton and self test of class
   */
  public static void main(String args[]) {
    RandomGUID myGUID = new RandomGUID();    System.out.println("Seeding String=" + myGUID.valueBeforeMD5);
    System.out.println("rawGUID=" + myGUID.valueAfterMD5);
    System.out.println("RandomGUID=" + myGUID.toString());
  }
}

/**
     *  Get the next available ID
     *  @param tablename The table name
     *  @param pkname The primary key column, must be Integer
     *  @param conn The database connection object
     *  @return int The new ID
     *  @throws SQLException
     */
    public static int getNextID( String tablename, String pkname, Connection conn )
    throws SQLException
    {
        int id = 1;
        String str = "Select MAX(" + pkname + ") As A From " + tablename;        Statement stmt = conn.createStatement( );
        ResultSet rs = stmt.executeQuery( str );
        if ( rs.next() )
        {
            id += rs.getInt( "A" );
        }        rs.close();
        stmt.close();        return id;
    }然后进行 insert 操作。但整个过程需要一个transaction以应付并发访问。

调试易

请问如何自编函数生成唯一ID？

解决方案 »