Posted on 2007-02-22 21:45
acooly 閱讀(686)
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Java開發 、
設計模式
??????多例模式Multiton基本特性同單例Singleton,由自己創建和管理自身實例，并向系統提供自身實例。不同之處是多例類在同一容器（類加載器）或JVM中可以存在多個實例。
應用實例：序列鍵值生成器本例采用hqldb作為演示數據庫。表結構如下：
CREATE?TABLE?KEYTABLE(
? KEYNAME?VARCHAR(32)?NOT?NULL?PRIMARY?KEY,
? KEYVALUE?int?NOT?NULL
)
package?pattern.multiton;
import?java.sql.Connection;
import?java.sql.Driver;
import?java.sql.DriverManager;
import?java.sql.ResultSet;
import?java.sql.Statement;
/**//*
?*?Key?service<br>
?*?table?strunction:<br/>
?*?CREATE?TABLE?KEYTABLE(<br/>
?*?KEYNAME?VARCHAR(32)?NOT?NULL?PRIMARY?KEY,<br/>
?*?KEYVALUE?int?NOT?NULL<br/>
?*?)<br>
?@author?ZhangPu
?Feb?22,?2007?4:30:47?PM
?*/
public?class?KeyService?
{
????private?int?cache;
????private?String?keyName;
????
????private?int?maxValue;
????private?int?nextValue;
????
????public?KeyService(int?cache,String?keyName)?{
??????this.cache?=?cache;
??????this.keyName?=?keyName;
??????retrieveKey();
????}
????/**?*//**
?????*?get?next?key?form?keyinfo
?????*?
?????*?@return
?????*/
????public?int?getNextKey()?{
????????if(nextValue?>=?maxValue){
????????????retrieveKey();
????????}
????????return?nextValue++;
????}
????
????/**?*//**
?????*?retrieve?current?value?form?db.
?????*?@return
?????*/
????private?void?retrieveKey(){
????????System.out.println("retrieve?database!");
????????
????????String?sqlUpdate?=?"update?KEYTABLE?set?KEYVALUE?=?KEYVALUE?+?"?+?cache?+?"?where?KEYNAME?=?'"+keyName+"'";?
????????String?sqlSelete?=?"select?KEYVALUE?from?KEYTABLE?where?KEYNAME?=?'"+keyName+"'";
????????
????????Connection?conn?=?null;
????????Statement?stmt?=?null;
????????int?keyFormDb?=?0;
????????try{
????????????Driver?driver?=?(Driver)Class.forName("org.hsqldb.jdbcDriver").newInstance();
????????????DriverManager.registerDriver(driver);
????????????
????????????String?url?=?"jdbc:hsqldb:hsql://localhost/pattern";
????????????String?user?=?"sa";
????????????String?passwd?=?"";
????????????conn?=?DriverManager.getConnection(url,user,passwd);
????????????stmt?=?conn.createStatement();
????????????stmt.executeUpdate(sqlUpdate);
????????????ResultSet?rs?=?stmt.executeQuery(sqlSelete);
????????????if(rs?!=?null?&&?rs.next()){
????????????????keyFormDb?=?rs.getInt(1);
????????????}
????????????
????????}catch(Exception?e){
????????????try?{
????????????????stmt.close();
????????????????conn.close();
????????????}?catch?(Exception?ex)?{
????????????????ex.printStackTrace();
????????????}
????????????e.printStackTrace();
????????}
????????maxValue?=?keyFormDb;
????????nextValue?=?keyFormDb?-?cache;
????}
????
}
package?pattern.multiton;
import?java.util.HashMap;
import?java.util.Map;
/*
?*?KeyGenerator?with?multiton?pattern
?@author?ZhangPu
?Feb?22,?2007?5:55:24?PM
?*/
public?class?KeyGenerator?{
????
????/**
?????*?save?keyServices
?????*/
????private?static?Map<String,KeyGenerator>?KeyGenerators?=?new?HashMap<String,KeyGenerator>();
????/**
?????*?the?current?instance.
?????*/
????private?KeyService?keyService;
????/**
?????*?cache?pool?size
?????*/
????private?static?final?int?KEY_CACHE?=?20;
????
????private?KeyGenerator(){}
????
????private?KeyGenerator(String?keyName){
?????????keyService?=?new?KeyService(KEY_CACHE,keyName);
????}
????
????/**
?????*?Multiton?instance
?????*?@param?keyName
?????*?@return
?????*/
????public?synchronized?static?KeyGenerator?getInstance(String?keyName){
????????
????????KeyGenerator?keyGenerator;
????????if(KeyGenerators.containsKey(keyName)){
????????????keyGenerator?=?KeyGenerators.get(keyName);
????????}else{
????????????keyGenerator?=?new?KeyGenerator(keyName);
????????????KeyGenerators.put(keyName,?keyGenerator);
????????}
????????return?keyGenerator;
????}
????
????/**
?????*?business?method.
?????*?@return
?????*/
????public?int?getNextKey(){
????????return?keyService.getNextKey();
????}
????
????
}
package?pattern.multiton;
/**//*
?@author?ZhangPu
?Feb?22,?2007?6:27:22?PM
?*/
public?class?Client?{
????public?static?void?main(String[]?args)?{
????????String?keyName?=?"SYS_RESOURCE";
????????KeyGenerator?keyGenerator?=?KeyGenerator.getInstance(keyName);
????????
????????for(int?i=0;i<20;i++){
????????????System.out.println("time"+(i+1)+":"+keyGenerator.getNextKey());
????????}
????}
}