精通从JavaScript到Jsp范例程序设计

				
				  package xbook.common ;
				
				  import java.lang.* ;
				  import java.sql.* ;
				  import java.util.* ;
				  import javax.servlet.* ;
				
				  public class ConnPool {
				    private static final int defaultMaxConnections=3 ;  
				
				    private Vector  freeConnections ;
				    private Hashtable  boundConnections ;
				    private String  driverName ;
				    private String  jdbcURL ;
				    private String  username ;
				    private String  password ;
				    private int maxConnections ;
				    
				// ------------------------------------ Constructot -------------------------------------
				    public ConnPool( int numConnections ) {
				      maxConnections=numConnections ;
				      boundConnections=null ;
				      freeConnections=null ;
				      driverName="" ;
				      jdbcURL="" ;
				      username="" ;
				      password="" ;
				    }
				
				// --------------------------------------------------------------------------------------
				    public ConnPool() {
				      this( defaultMaxConnections ) ;
				    }
				
				
				    public void closeDB() throws SQLException {
				      if( boundConnections!=null ) {
				        for( Enumeration e=boundConnections.elements() ; e.hasMoreElements() ; ) {
				      	  Connection conn=(Connection)e.nextElement() ;
				      	  conn.close() ;
				        }
				        boundConnections.clear() ;
				        boundConnections=null ;
				      }
				      
				      if( freeConnections!=null ) {
				        for( Enumeration e=freeConnections.elements() ; e.hasMoreElements() ; ) {
				      	  Connection conn=(Connection)e.nextElement() ;
				      	  conn.close() ;
				        }
				        freeConnections.removeAllElements() ;
				        freeConnections=null ;
				      }
				    }
				
				
				    public synchronized Connection getConnection()
				    throws SQLException {
				      if( freeConnections==null )
				        throw new SQLException( "The conection pool has not been established yet." ) ;
				      if( boundConnections.get( Thread.currentThread() )!=null )
				        throw new SQLException( "Cannot get connections over once for this current running thread." ) ;
				      try {
				        if( freeConnections.size()==0 )
				          wait() ;
				      }
				      catch( InterruptedException ex ) {
				      	throw new SQLException( ex.toString() ) ;
				      }
				      Connection conn=(Connection)freeConnections.firstElement() ;
				      freeConnections.removeElement( conn ) ;
				      boundConnections.put( Thread.currentThread(), conn ) ;
				
				      return conn ;
				    }
				    
				
				    public void openDB( String drvName, String url,
							String uname, String passwd )
				    throws SQLException {
				      try {
				        boundConnections=new Hashtable( maxConnections ) ;
				        freeConnections=new Vector( maxConnections ) ;
				        Class.forName( drvName ) ;
				        for( int i=0 ; i				          freeConnections.addElement( DriverManager.getConnection( url ,uname ,passwd ) ) ;
				      }
				      catch( Exception ex ) {
				      	boundConnections=null ;
				      	freeConnections=null ;
				       	throw new SQLException( ex.toString() ) ;
				      }
				    }
				
				
				    public synchronized void returnConnection()
				    throws SQLException {
				      Connection conn=(Connection)boundConnections.remove( Thread.currentThread() ) ;
				      if( conn==null )
				        throw new SQLException( "The connection which this current running thread got is not found." ) ;
				      freeConnections.addElement( conn ) ;
				      notify() ;
				    }
				    
				
				    public void setConnectionSwitch( String on_off ) throws ServletException {
				      try {
				      	if( on_off.equalsIgnoreCase( "ON" ) )
				          openDB( driverName, jdbcURL, username, password ) ;
				        else if( on_off.equalsIgnoreCase( "OFF" ) )
				          closeDB() ;
				      }
				      catch( SQLException ex ) {
				      	throw new ServletException( ex.toString() ) ;
				      }
				    }
				
				
				    public void setMaxConnections( int numConnections ) {
				      maxConnections=numConnections ;
				    }
				    
				
				    public void setDriverName( String drvName ) {
				      driverName=drvName ;
				    }
				
				
				    public void setJdbcURL( String url ) {
				      jdbcURL=url ;
				    }
				
				
				    public void setUserName( String uname ) {
				      username=uname ;
				    }
				
				
				    public void setPassword( String passwd ) {
				      password=passwd ;
				    }
				  }