JForum数据持久化

概述JForum“Support for several popular databases, including MySQL, PostgreSQL, Oracle and HSQLDB”。   JForum系统中用于持久化的实体类被放在net.jforum.entities包下，例如：User、UserSession、Post等。关于实体类的DAO *** 作被定义在多个接口中，例如：关于User的DAO

JForum“Support for several popular databases,including MysqL,Postgresql,Oracle and HsqlDB”。

JForum系统中用于持久化的实体类被放在net.jforum.entitIEs包下，例如：User、UserSession、Post等。关于实体类的DAO *** 作被定义在多个接口中，例如：关于User的DAO *** 作被定义在net.jforum.dao.UserDAO接口中。针对不同的数据库，有不同的UserDAO实现类。

如上图，GenericUserDAO是JForum的默认实现，对应的数据库是MysqL。GenericUserDAO、HsqldbUserDAO、OracleUserDAO和sqlServerUserDAO类都有public的无参数构造函数。JForum不是根据“配置文件 + if else”的方式决定初始化哪个UserDAO，而是新建了一个抽象类DataAccessDriver。

Java代码 publicabstractclassDataAccessDriver { privatestaticDataAccessDriverdriver; protectedDataAccessDriver(){} /** *Startstheengine. *ThismethodshouldbecalleDWhenthesystem *isstarting. * *@paramimplementationThedao.driverimplementation */ publicstaticvoIDinit(DataAccessDriverimplementation) { driver=implementation; } /** *Getsadriverimplementationinstance. *YouMUSTusethismethoDWhenyouwantainstance *ofavalID<code>DataAccessDriver</code>.Neveraccess *thedriverimplementationdirectly. * *@return<code>DataAccessDriver</code>instance */ publicstaticDataAccessDrivergetInstance() { returndriver; } publicabstractForumDAOnewForumDAO(); publicabstractGroupDAOnewGroupDAO(); publicabstractPostDAOnewPostDAO(); publicabstractPollDAOnewPollDAO(); publicabstractRankingDAOnewRankingDAO(); publicabstracttopicdaOnewtopicdaO(); publicabstractUserDAOnewUserDAO(); publicabstractcategoryDAOnewcategoryDAO(); publicabstractTreeGroupDAOnewTreeGroupDAO(); publicabstractSmilIEDAOnewSmilIEDAO(); publicabstractGroupSecurityDAOnewGroupSecurityDAO(); publicabstractPrivateMessageDAOnewPrivateMessageDAO(); publicabstractUserSessionDAOnewUserSessionDAO(); publicabstractConfigDAOnewConfigDAO(); publicabstractKarmaDAOnewKarmaDAO(); publicabstractBookmarkDAOnewBookmarkDAO(); publicabstractAttachmentDAOnewAttachmentDAO(); publicabstractModerationDAOnewModerationDAO(); publicabstractBannerDAOnewBannerDAO(); publicabstractSummaryDAOnewSummaryDAO(); publicabstractMailintegrationDAOnewMailintegrationDAO(); publicabstractAPIDAOnewAPIDAO(); publicabstractBanListDAOnewBanListDAO(); publicabstractModerationLogDAOnewModerationLogDAO(); publicabstractLuceneDAOnewLuceneDAO(); }

public abstract class DataAccessDriver {	private static DataAccessDriver driver;		protected DataAccessDriver() {}		/**	 * Starts the engine.	 * This method should be called when the system	 * is starting. 	 * 	 * @param implementation The dao.driver implementation	 */	public static voID init(DataAccessDriver implementation)	{		driver = implementation;	}		/**	 * Gets a driver implementation instance. 	 * You MUST use this method when you want a instance	 * of a valID <code>DataAccessDriver</code>. Never access	 * the driver implementation directly.  	 * 	 * @return <code>DataAccessDriver</code> instance	 */	public static DataAccessDriver getInstance()	{		return driver;	}		public abstract ForumDAO newForumDAO();	public abstract GroupDAO newGroupDAO();	public abstract PostDAO newPostDAO();	public abstract PollDAO newPollDAO();	public abstract RankingDAO newRankingDAO();	public abstract topicdaO newtopicdaO();	public abstract UserDAO newUserDAO();	public abstract categoryDAO newcategoryDAO();	public abstract TreeGroupDAO newTreeGroupDAO();	public abstract SmilIEDAO newSmilIEDAO();	public abstract GroupSecurityDAO newGroupSecurityDAO();	public abstract PrivateMessageDAO newPrivateMessageDAO();	public abstract UserSessionDAO newUserSessionDAO();	public abstract ConfigDAO newConfigDAO();	public abstract KarmaDAO newKarmaDAO();	public abstract BookmarkDAO newBookmarkDAO();	public abstract AttachmentDAO newAttachmentDAO();	public abstract ModerationDAO newModerationDAO();	public abstract BannerDAO newBannerDAO();        public abstract SummaryDAO newSummaryDAO();        public abstract MailintegrationDAO newMailintegrationDAO();	public abstract APIDAO newAPIDAO();	public abstract BanListDAO newBanListDAO();	public abstract ModerationLogDAO newModerationLogDAO();	public abstract LuceneDAO newLuceneDAO();}

init()方法仅在系统启动时被调用一次。JForum系统中有多处使用此类init()，有一点反向注入的味道。

系统启动时，初始化DataAccessDriver：

Java代码 publicstaticvoIDloadDaoImplementation() { //Startthedao.driverimplementation Stringdriver=SystemGlobals.getValue(ConfigKeys.DAO_DRIVER); logger.info("LoadingJDBCdriver"+driver); try{ Classc=Class.forname(driver); DataAccessDriverd=(DataAccessDriver)c.newInstance(); DataAccessDriver.init(d); } catch(Exceptione){ thrownewForumException(e); } }

	public static voID loadDaoImplementation()	{		// Start the dao.driver implementation		String driver = SystemGlobals.getValue(ConfigKeys.DAO_DRIVER);		logger.info("Loading JDBC driver " + driver);		try {			Class c = Class.forname(driver);			DataAccessDriver d = (DataAccessDriver)c.newInstance();			DataAccessDriver.init(d);		}		catch (Exception e) {			throw new ForumException(e);		}    }

如果是MysqL，String driver值为：net.jforum.dao.MysqL.MysqLDataAccessDriver

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