java_jdbc_3层 解耦

Dao - 提供接口

DaoImpl - 实现

DaoFactory - 工厂模式获取实现

DaoExcetpion - jdbc异常处理 实现runtime exception类即可

TestDemo - 主函数

User - bean

daoconfig.properties - 配置文件

package cn.itcast.user;

public interface Dao {
	public User findById(int id);
}

package cn.itcast.user;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import cn.itcast.JdbcUtils;

public class DaoImpl implements Dao {

	@Override
	public User findById(int id) {
		Connection conn = null;
		PreparedStatement ps = null;
		ResultSet rs = null;
		User user=null;
		String sql = "select * from t_user where id=?";
		try{
		conn = JdbcUtils.getConnection();
		ps = conn.prepareStatement(sql);
		ps.setInt(1, id);
		rs=ps.executeQuery();
		while(rs.next()){
			user = new User();
			user.setId(rs.getInt("id"));
			user.setName(rs.getString("username"));
			user.setPassword(rs.getString("password"));
		}
		}catch(SQLException e){
			throw new DaoExcetpion(e.getMessage(),e);
		}finally{
			JdbcUtils.free(rs, ps, conn);
		}

		return user;
	}

}

package cn.itcast.user;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

public class DaoFactory {
	private static Dao dao = null;
	private static DaoFactory intance = new DaoFactory();

	private DaoFactory() {

		try {
			Properties prop = new Properties();
			InputStream inStream = DaoFactory.class.getClassLoader().getResourceAsStream("daoconfig.properties");
			prop.load(inStream);
			String userDaoClass = prop.getProperty("userDaoClass");
			dao=(Dao)Class.forName(userDaoClass).newInstance();
		} catch (Exception e) {
			// TODO Auto-generated catch block
			throw new ExceptionInInitializerError(e);
		}
	}

	public static DaoFactory getInstance() {
		return intance;
	}

	public Dao getUserDao() {
		return dao;
	}
}

package cn.itcast.user;

public class TestDemo {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
//		Dao dao = new DaoImpl();
		Dao dao = DaoFactory.getInstance().getUserDao();
		User user = dao.findById(2);
		System.out.println(user.getId());
		System.out.println(user.getName());
	}

}

//配置文件

userDaoClass=cn.itcast.user.DaoImpl