Java实现的Sequence工具 - 1

Java实现的Sequence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.<br>

* <b>User</b>: leizhimin<br>

* <b>Date</b>: 2008-4-2 15:21:30<br>

* <b>Note</b>: Java实现的Sequence工具

*/

public class SequenceUtils {

private static SequenceUtils _instance = new SequenceUtils();

private Map<String, KeyInfo> keyMap = new HashMap<String, KeyInfo>(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.<br>

* <b>User</b>: leizhimin<br>

* <b>Date</b>: 2008-4-2 15:24:52<br>

* <b>Note</b>: 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