数据库主键生成器java代码

package com.aspboy.base.database.util;

import java.util.HashMap;

public class KeyGenerator
{
 private static KeyGenerator keygen=new KeyGenerator();
 private static final int POOL_SIZE=20;
 private HashMap keylist=new HashMap(10);
 private KeyGenerator()
 {}
 
 public static KeyGenerator getInstance()
 {
  return keygen;
 }
 public synchronized int  getNextKey(String keyName)
 {
  KeyInfo keyinfo;
  if (keylist.containsKey(keyName))
  {
   keyinfo=(KeyInfo)keylist.get(keyName);
   System.out.println("key found");
  }
  else
  {
   keyinfo=new KeyInfo(POOL_SIZE,keyName);
   keylist.put(keyName, keyinfo);
   System.out.println("new key created");
  }
  return keyinfo.getNextKey();
 }
 

}

package com.aspboy.base.database.util;

import com.aspboy.base.database.DBBean;

public class KeyInfo
{
 private int keyMax;
 private int Keymin;
 private int nextKey;
 private int poolSize;
 private String keyName;
 //private int times ;
 
 public KeyInfo(int poolSize,String keyName)
 {
  this.poolSize=poolSize;
  this.keyName=keyName;
  loadFromDB();
  //times++;
  //System.out.println("get keyvalue from db tiems=="+times);
  
 }

 public int getKeyMax() {
  return keyMax;
 }

 public int getKeymin() {
  return Keymin;
 }
 
 private void loadFromDB()
 {
  String sql1="update tb_key set KeyValue=KeyValue+"+poolSize+" where keyName='"+keyName+"'";
  DBBean.executeSql(sql1);
  String sql2="select KeyValue from  tb_key  where keyName='"+keyName+"'";
  int keyFromDB=DBBean.getIntSingle(sql2);
  keyMax=keyFromDB;
  Keymin=keyFromDB-poolSize+1;
  nextKey=Keymin;
 }

 public int getNextKey() {
  
  if (nextKey>keyMax)
  {
   loadFromDB();
   System.out.println("get keyvalue from db");
   
  }
  return nextKey++;
 }
 
 

}

调用 方法： KeyGenerator.getInstance().getNextKey(keyName);

keyName 为表名称

相关数据库结构：

表tb_key

字段如下：

 KeyValue：pk大小

keyName：表名