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				一個ServiceLocator模式的實現
			
          
 			Posted on 2007-02-06 11:49 dennis 閱讀(3400) 評論(0)  編輯  收藏  所屬分類: 模式與架構 
			
			


		
          
		
          ?廢話不說，代碼說話：
          import?javax.naming.*;
          import?javax.naming.NamingException;
          import?javax.rmi.PortableRemoteObject;
          import?javax.ejb.EJBHome;
          import?javax.ejb.EJBLocalHome;
          import?javax.sql.DataSource;
          import?java.util.*;
          import?java.sql.*;

          /**
          ?*??實現?service?locater?模式，用于由客戶端來調用以通過JNDI查
          ?*??找相關的?ejb或是其它服務的入口.
          ?*?          */
          public?final?class?ServiceLocater?{

          ??          protected?static?ServiceLocater?inst?=?new?ServiceLocater();
          ??          private?InitialContext?ic?=?null;
          ??          private?Map?ejbHomeCache?=?null;
          ??          private?Map?dataSourceCache?=?null;
          ??          protected?ServiceLocater()?{
          ????          try?{
          ??????dataSourceCache?          =?Collections.synchronizedMap(new?HashMap());
          ??????ejbHomeCache?          =?Collections.synchronizedMap(new?HashMap());
          ??????ic?          =?new?InitialContext();
          ????}
          ????          catch?(Exception?e)?{
          ??????e.printStackTrace();
          ????}
          ??}

          ??          /**
          ???*?取得?servicelocater的單子實例.
          ???*?          */
          ??          synchronized?public?static?ServiceLocater?getInstance()?{
          ????          return?inst;
          ??}

          ??          /**
          ???*查找并返回一個數據源
          ???*?          @param?name?String?數據源名稱
          ???*?          @return?DataSource　，查找不到則拋出異常.
          ???*?          @throws?NamingException?，查找不到或是類型不對。
          ???*?          */
          ??          private?DataSource?lookUpDataSource(String?name)?throws?NamingException?{
          ????DataSource?tmpDS?          =?(DataSource)this.dataSourceCache.get(name);
          ????          if?(tmpDS?==?null)?{
          ??????          try?{
          ????????tmpDS?          =?(DataSource)this.ic.lookup(name);
          ????????          this.dataSourceCache.put(name,?tmpDS);
          ??????}
          ??????          catch?(NamingException?namE)?{
          ????????          throw?namE;
          ??????}
          ??????          catch?(Exception?otherE)?{
          ????????          throw?new?NamingException(otherE.getMessage());
          ??????}
          ????}
          ????          return?tmpDS;
          ??}

          ??          /**
          ???*?查找并返回一個遠程接口
          ???*?          @param?jndiHomeName?ebj名字
          ???*?          @param?className??ejb類名字
          ???*?          @return
          ???*?          @throws?ServiceLocatorException
          ???          */
          ??          public?EJBHome?getRemoteHome(String?jndiHomeName,?Class?className)?throws
          ??????ServiceLocatorException?          {
          ????EJBHome?home?          =?(EJBHome)this.ejbHomeCache.get(jndiHomeName);
          ????          if?(home?==?null)?{
          ??????          try?{
          ????????Object?objref?          =?ic.lookup(jndiHomeName);
          ????????Object?obj?          =?PortableRemoteObject.narrow(objref,?className);
          ????????home?          =?(EJBHome)?obj;
          ????????          this.ejbHomeCache.put(jndiHomeName,?home);
          ??????}
          ??????          catch?(NamingException?ne)?{
          ????????          throw?new?ServiceLocatorException(ne);
          ??????}
          ??????          catch?(Exception?e)?{
          ????????          throw?new?ServiceLocatorException(e);
          ??????}
          ????}
          ????          return?home;
          ??}

          ??          /**
          ???*?查找并返回一個本地接口
          ???*?          @param?jndiHomeName??jndiHomeName名字
          ???*?          @return?一個本地接口
          ???*?          @throws?ServiceLocatorException
          ???          */
          ??          public?EJBLocalHome?getLocalHome(String?jndiHomeName)?throws
          ??????ServiceLocatorException?          {
          ????EJBLocalHome?home?          =?null;
          ????          try?{
          ??????home?          =?(EJBLocalHome)?ic.lookup(jndiHomeName);
          ????}
          ????          catch?(NamingException?ne)?{
          ??????          throw?new?ServiceLocatorException(ne);
          ????}
          ????          catch?(Exception?e)?{
          ??????          throw?new?ServiceLocatorException(e);
          ????}
          ????          return?home;

          ??}

          ??          /**
          ???*查找一個數據源，并取得一個連接.
          ???*?          @param?name?String?數據源名稱
          ???*?          @return?DataSource　，查找不到則拋出異常.
          ???*?          @throws?NamingException?，查找不到或是類型不對。
          ???*?          */
          ??          public?Connection?getConnection(String?DataSourceJNDIName)?throws
          ??????SQLException?          {
          ????          try?{
          ??????Connection?conn?          =?this.lookUpDataSource(DataSourceJNDIName).getConnection();
          ??????conn.setAutoCommit(          false);
          ??????          //conn.setTransactionIsolation(Connection.TRANSACTION_READ_COMMITTED);
          ??????return?conn;
          ????}
          ????          catch?(Exception?e)?{
          ??????e.printStackTrace();
          ??????          throw?new?SQLException(e.getMessage());
          ????}
          ??}

          }
          
	
          
	


          
	    
    




          








          

				
			
          
		          		
	
          
	
          
		
			


		
	
          

          


    







          
        
	




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