Java实现的Sequence工具开发工具

  Sequence是数据库应用中很重要的一个特性，可是有些数据库没有这个特性，比如很流行的开源数据库MySQL就没有Sequence，利用自增主键感觉很不爽，每个表的ID都要设置，通用性也不好。因此考虑为这些不支持Sequence的数据做一个Sequence工具。自动为整个系统提供主键生成策略。

    下面是一个Sequence实现，以数据库MySQL为平台。源代码如下：

    一、Sequence工具类

package sequence;     import java.util.HashMap;     import java.util.Map;     import java.sql.SQLException;     /**     * Created by IntelliJ IDEA.     * User: leizhimin     * Date: 2008-4-2 15:21:30     * Note: Java实现的Sequence工具     */     public class SequenceUtils {         private static SequenceUtils _instance = new SequenceUtils();         private Map keyMap = new HashMap(20); //Sequence载体容器         private static final int POOL_SIZE = 10;      //Sequence值缓存大小         /**          * 禁止外部实例化          */         private SequenceUtils() {         }         /**          * 获取SequenceUtils的单例对象          * @return SequenceUtils的单例对象          */         public static SequenceUtils getInstance() {             return _instance;         }         /**          * 获取下一个Sequence键值          * @param keyName Sequence名称          * @return 下一个Sequence键值          */         public synchronized long getNextKeyValue(String keyName) {             KeyInfo keyInfo = null;             Long keyObject = null;             try {                 if (keyMap.containsKey(keyName)) {                     keyInfo = keyMap.get(keyName);                 } else {                     keyInfo = new KeyInfo(keyName, POOL_SIZE);                     keyMap.put(keyName, keyInfo);                 }                 keyObject = keyInfo.getNextKey();             } catch (SQLException e) {                 e.printStackTrace();             }             return keyObject;         }     }

 

 

 

    二、Sequence载体

package sequence;     import java.sql.*;     /**     * Created by IntelliJ IDEA.     * User: leizhimin     * Date: 2008-4-2 15:24:52     * Note: Sequence载体     */     public class KeyInfo {         private long maxKey;        //当前Sequence载体的最大值         private long minKey;        //当前Sequence载体的最小值         private long nextKey;       //下一个Sequence值         private int poolSize;       //Sequence值缓存大小         private String keyName;     //Sequence的名称         private static final String sql_update = "UPDATE KEYTABLE SET KEYVALUE = KEYVALUE + ? WHERE KEYNAME = ?";         private static final String sql_query = "SELECT KEYVALUE FROM KEYTABLE WHERE KEYNAME = ?";         public KeyInfo(String keyName, int poolSize) throws SQLException {             this.poolSize = poolSize;             this.keyName = keyName;             retrieveFromDB();         }         public String getKeyName() {             return keyName;         }         public long getMaxKey() {             return maxKey;         }         public long getMinKey() {             return minKey;         }         public int getPoolSize() {             return poolSize;         }         /**          * 获取下一个Sequence值          *          * @return 下一个Sequence值          * @throws SQLException          */         public synchronized long getNextKey() throws SQLException {             if (nextKey > maxKey) {                 retrieveFromDB();             }             return nextKey++;         }         /**          * 执行Sequence表信息初始化和更新工作          *          * @throws SQLException          */         private void retrieveFromDB() throws SQLException {             System.out.println("");             Connection conn = DBUtils.makeConnection();             //查询数据库             PreparedStatement pstmt_query = conn.prepareStatement(sql_query);             pstmt_query.setString(1, keyName);             ResultSet rs = pstmt_query.executeQuery();             if (rs.next()) {                 maxKey = rs.getLong(1) + poolSize;                 minKey = maxKey - poolSize + 1;                 nextKey = minKey;                 rs.close();                 pstmt_query.close();             } else {                 System.out.println("执行Sequence数据库初始化工作！");                 String init_sql = "INSERT INTO KEYTABLE(KEYNAME,KEYVALUE) VALUES('" + keyName + "',10000 + " + poolSize + ")";                 Statement stmt = conn.createStatement();                 stmt.executeUpdate(init_sql);                 maxKey = 10000 + poolSize;                 minKey = maxKey - poolSize + 1;                 nextKey = minKey;                 stmt.close();                 return;             }             //更新数据库             conn.setAutoCommit(false);             System.out.println("更新Sequence最大值！");             PreparedStatement pstmt_up = conn.prepareStatement(sql_update);             pstmt_up.setLong(1, poolSize);             pstmt_up.setString(2, keyName);             pstmt_up.executeUpdate();             pstmt_up.close();             conn.commit();             rs.close();             pstmt_query.close();             conn.close();         }     }

   

 

 

    三、简单的数据库连接工具

package sequence;     import java.sql.*;     /**     * 简单的数据连接工具     * File: DBUtils.java     * User: leizhimin     * Date: 2008-3-18 15:19:12     */     public class DBUtils {         public static final String url = "jdbc:mysql://127.0.0.1:3306/testdb";         public static final String username = "root";         public static final String password = "leizhimin";         public static final String driverClassName = "com.mysql.jdbc.Driver";         /**          * 获取数据库连接Connection          *          * @return 数据库连接Connection          */         public static Connection makeConnection() {             Connection conn = null;             try {                 Class.forName(driverClassName);             } catch (ClassNotFoundException e) {                 e.printStackTrace();             }             try {                 conn = DriverManager.getConnection(url, username, password);             } catch (SQLException e) {                 e.printStackTrace();             }             return conn;         }         public static void main(String args[]) {             testConnection();         }         /**          * 测试连接方法          */         public static void testConnection() {             Connection conn = makeConnection();             try {                 Statement stmt = conn.createStatement();                 ResultSet rs = stmt.executeQuery("SELECT * FROM mysql.user");                 while (rs.next()) {                     String s1 = rs.getString(1);                     String s2 = rs.getString(2);                     System.out.println(s1 + "/t" + s2);                 }                 rs.close();                 stmt.close();             } catch (SQLException e) {                 e.printStackTrace();             } finally {                 try {                     conn.close();                 } catch (SQLException e) {                     e.printStackTrace();                 }             }         }     }

   

 

    四、测试类（客户端）

package sequence;     /**     * Created by IntelliJ IDEA.     * User: leizhimin     * Date: 2008-4-2 15:31:30     * Company: LavaSoft(http://lavasoft.blog.51cto.com)     * Sequence测试(客户端)     */     public class TestSequence {         /**          * 测试入口          * @param args          */         public static void main(String args[]) {             test();         }         /**          * 测试Sequence方法          */         public static void test() {             System.out.println("----------test()----------");             for (int i = 0; i < 20; i++) {                 long x = SequenceUtils.getInstance().getNextKeyValue("sdaf");                 System.out.println(x);             }         }     }

   

 

    五、Sequence表的代码（for MySQL5）

-- SQL for MySQL5     -- http://lavasoft.blog.51cto.com     -- 2008年4月3日     -- 创建数据库testdb     create database if not exists testdb character set gbk collate gbk_chinese_ci;     -- 创建Sequence表     DROP TABLE IF EXISTS keytable;     CREATE TABLE keytable (       KEYNAME varchar(24) NOT NULL COMMENT 'Sequence名称',       KEYVALUE bigint(20) DEFAULT '10000' COMMENT 'Sequence最大值',       PRIMARY KEY (KEYNAME)     ) ENGINE=MyISAM DEFAULT CHARSET=gbk;

    数据库操作的截屏：

 

 

    六、运行测试类输出结果：

----------test()----------     更新Sequence最大值！     10061     10062     10063     10064     10065     10066     10067     10068     10069     10070     更新Sequence最大值！     10071     10072     10073     10074     10075     10076     10077     10078     10079     10080     Process finished with exit code 0

    说明：这个Sequence工具很智能，当请求一个不存在的Sequence时，会自动生成一个Sequence，保存到数据库 。当请求一个已经存在的Sequence时，会从Sequence载体的缓存中获取一个Sequence值返回，当Sequence载体的缓存值达到最大时，会自动重新初始化Sequence载体信息，并更新数据库记录信息 。