stockdb.java

关系型数据库 Postgresql 6.5.2

package example.corba;

import java.sql.*;

/**
 * This class handles the JDBC side of things. It opens a connection to
 * the database, and performes queries on that database.
 *
 * In essence, you could use this class on it's own. The rest of the classes
 * in this example handle either the CORBA mechanism, or the frontend.
 *
 * Note: Before you ask, why perform a query on each call, you have to remember
 * that an object could be changed by another client, and we need to ensure that
 * the returned data is live and accurate.
 *
 * $Id: StockDB.java,v 1.1 1999/01/25 21:22:03 scrappy Exp $
 */
public class StockDB
{
    Connection con;
    Statement st;
    
    // the current stock number
    int id = -1;
    
    public void connect(String url,String usr,String pwd) throws Exception {
	Class.forName("postgresql.Driver");
	System.out.println("Connecting to "+url);
	con = DriverManager.getConnection(url,usr,pwd);
	st = con.createStatement();
    }
    
    public void closeConnection() throws Exception {
	con.close();
    }
    
    public void fetchItem(int id) throws Exception {
	this.id = id;
    }
    
    public int newItem() throws Exception {
	// tba
	return -1;
    }
    
    public String getDescription() throws SQLException {
	ResultSet rs = st.executeQuery("select description from stock where id="+id);
	if(rs!=null) {
	    rs.next();
	    String s = rs.getString(1);
	    rs.close();
	    return s;
	}
	throw new SQLException("No ResultSet");
    }
    
    public int getAvailable() throws SQLException {
	ResultSet rs = st.executeQuery("select avail from stock where id="+id);
	if(rs!=null) {
	    rs.next();
	    int v = rs.getInt(1);
	    rs.close();
	    return v;
	}
	throw new SQLException("No ResultSet");
    }
    
    public int getOrdered() throws SQLException {
	ResultSet rs = st.executeQuery("select ordered from stock where id="+id);
	if(rs!=null) {
	    rs.next();
	    int v = rs.getInt(1);
	    rs.close();
	    return v;
	}
	throw new SQLException("No ResultSet");
    }
    
    public boolean isItemValid() throws SQLException {
	ResultSet rs = st.executeQuery("select valid from stock where id="+id);
	if(rs!=null) {
	    rs.next();
	    boolean b = rs.getBoolean(1);
	    rs.close();
	    return b;
	}
	throw new SQLException("No ResultSet");
    }
    
    public void addNewStock(int amount) throws SQLException {
	st.executeUpdate("update stock set avail=avail+"+amount+
			 ", ordered=ordered-"+amount+
			 " where id="+id+" and ordered>="+amount);
    }
    
    public void removeStock(int amount) throws SQLException {
	st.executeUpdate("update stock set avail=avail-"+amount+
			 " where id="+id);
    }
    
    public void orderStock(int amount) throws SQLException {
	st.executeUpdate("update stock set ordered=ordered+"+amount+
			 " where id="+id);
    }
    
    public int getLastID() throws SQLException {
	ResultSet rs = st.executeQuery("select max(id) from stock");
	if(rs!=null) {
	    rs.next();
	    int v = rs.getInt(1);
	    rs.close();
	    return v;
	}
	throw new SQLException("No ResultSet");
    }
    
}