package DBConnection ;

import java.lang.* ;
import java.sql.* ;
import java.util.* ;
import java.io.InputStream;

//本連接池技術不保持連接計數。無多個線程共用一個connection的情況
public class ConnPool {
    private static final int defaultMaxConnections=3 ;

    private Vector  freeConnections ; //空閑連接池
    private Hashtable  boundConnections ;    //已分配連接池
    private String  driverName ;
    private String  jdbcURL ;
    private String  username ;
    private String  password ;
    private int maxConnections ;

    private static ConnPool instance = null;

    public static ConnPool getInstance(){
        if (instance==null)
            instance = new ConnPool();
        return instance;
    }



// ------------------------------------ Constructot -------------------------------------
    public ConnPool( int numConnections ) {
        maxConnections=numConnections ;
        boundConnections=null ;
        freeConnections=null ;
        driverName="" ;
        jdbcURL="" ;
        username="" ;
        password="" ;
    }

// --------------------------------------------------------------------------------------
    public ConnPool() {
        this( defaultMaxConnections ) ;
        setPropsFileName("db.properties");
        try{
            setConnectionSwitch("ON");
        }catch (Exception e){
            e.printStackTrace();
        }
    }


    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( "ERROR : The conection pool still has not been established yet." ) ;
        if( boundConnections.get( Thread.currentThread() )!=null ){//同一線程不允許多次connect數據庫
            //Modifide by chenyuan 04-10
            System.err.println( "ERROR : Cannot get connections over once for this current running thread." ) ;
            returnConnection();
        }
        try {
            if( freeConnections.size()==0 )     //無空閑connect可分配了
                wait() ;
        }
        catch( InterruptedException ex ) {
            throw new SQLException( ex.toString() ) ;
        }
        //System.err.println("The free thread number is "+freeConnections.size());
        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<maxConnections ; i++ )//預先建立好max個連接放在空閑池中等待分配
                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( "ERROR : The connection which this current running thread got is not found." ) ;
        freeConnections.addElement( conn ) ;
        notify() ;
    }


    //public void setConnectionSwitch( String on_off ) throws ServletException {
    public void setConnectionSwitch( String on_off ) throws Exception {
        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() ) ;
            throw new Exception( 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 ;
    }

    public void setPropsFileName(String FileName){
        InputStream is = getClass().getResourceAsStream(FileName);
        Properties dbProps = new Properties();
        try {
            dbProps.load(is);
        }
        catch (Exception e) {
            System.err.println("ERROR : 不能讀取屬性文件. " +"請確保db.properties在CLASSPATH指定的路徑中");
            return;
        }
        String drvName=dbProps.getProperty("Drivers");
        String url=dbProps.getProperty("Url");
        String uName=dbProps.getProperty("UserName");
        String uPsw=dbProps.getProperty("PassWord");
        String maxconn = dbProps.getProperty("MaxConnectionNum", "0");
        int max;
        try {
            max = Integer.valueOf(maxconn).intValue();
        }
        catch (NumberFormatException e) {
            max = 0;
        }
        setDriverName(drvName);
        setJdbcURL(url);
        setUserName(uName);
        setPassword(uPsw);
        setMaxConnections(max);
    }
}