sequencedao.java

一个简易的网上书店（jsp+sqlservler+struts）。

package com.webshop.db;
import java.sql.*;
import com.webshop.domain.Sequence;
import com.webshop.exception.ActionException;
/**
 * @author w
 *
 * To change this generated comment edit the template variable "typecomment":
 * Window>Preferences>Java>Templates.
 * To enable and disable the creation of type comments go to
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 */
public class SequenceDAO {

	Connection con;//数据库连接
	String getNextId="select * from Sequence where name=?";
	String updateNextId="update Sequence set nextid=nextid+1 where name=?";
	private static final SequenceDAO instance =new SequenceDAO();
	/**
	 * Constructor for SequenceDAO. 
	 */
	private SequenceDAO() {
		super();
	}
	public static SequenceDAO getInstance()
	{
		return instance;
	}
	public synchronized int getNextId(String name)
	{
		int ret=-1;
		try
		{
			con=DatabaseConnection.getConnection();
		}
		catch(Exception e)
		{
			throw new ActionException("不能获得连接，"+e.getMessage());
		}
		try
		{
			PreparedStatement pstmt=con.prepareStatement(getNextId);
			pstmt.setString(1,name);
			ResultSet rst=pstmt.executeQuery();
          
			if(rst.next())
			{
				ret=rst.getInt("nextid");
				PreparedStatement pstmt2=con.prepareStatement(updateNextId);
				pstmt2.setString(1,name);
				pstmt2.executeUpdate();								
			   
			}
				con.close();
		}
		catch(SQLException e)
		{
			 throw new ActionException("执行数据库操作发生错误，"+e.getMessage());
		}
		finally
		{
			try
			{
				if(con!=null)
				con.close();
			}
			catch(Exception e2)
			{
			}
		}
		return ret;
	}			
	


}