java连接数据库方式（一）：传统JDBC + 连接池

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用了太久的框架，传统的JDBC也不能忘记，以下是传统的JDBC实现连接数据库

使用传统的JDBC实现数据库连接，一般要DIY一个工具类，这个工具类中，最好使用连接池，数据库连接池有很多，JNDI，DBCP，C3P0等皆可以实现，这里我使用的是C3P0连接池。
C3P0连接池的配置文件c3p0-config.xml如下：

<?xml version="1.0" encoding="UTF-8"?>
<c3p0-config>

  <default-config>
    <property name="driverClass">com.mysql.jdbc.Driver</property>
	<property name="jdbcUrl">jdbc:mysql:///fruit</property>
	<property name="user">root</property>
	<property name="password">123456</property>
	<property name="initialPoolSize">50</property>
	<property name="maxPoolSize">100</property>
  </default-config>
  
  <named-config name="namedConfig"> 
    <property name="driverClass">com.mysql.jdbc.Driver</property>
	<property name="jdbcUrl">jdbc:mysql:///fruit</property>
	<property name="user">root</property>
	<property name="password">123456</property>
  </named-config>
  
</c3p0-config>

没有使用C3P0连接池之前，获取数据库连接对象是这样的（这是最原始的）：

// 获取数据库连接对象
public static Connection getConnection() {

	if (conn != null) {
		return conn;
	}

	try {

		// 加载驱动类，不同的数据库软件驱动类不同
		Class.forName(MYSQL_DRIVER);
		// 使用DriverManager获得连接对象，其中URL每个数据库不同
		conn = DriverManager.getConnection(MYSQL_URL, MYSQL_USER,
				MYSQL_PASS);
		
		System.out.println("数据库已连接...");

	} catch (ClassNotFoundException | SQLException e) {
		e.printStackTrace();
	}

	// 返回获得的连接对象
	return conn;
}

DIY封装的工具类加上C3P0连接池之后，获取数据库连接对象由C3P0连接池完成。
加上C3P0连接池后，DIY的工具类如下：

package com.fruitsys.dao;

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

import javax.sql.DataSource;

import com.mchange.v2.c3p0.ComboPooledDataSource;

/**
 *  These are data base utils
 * @author LIU
 * @version 1.0 2017-09-21
 */
public class BaseDao {

	/**
	 * Create Connection
	 */
	private static Connection conn = null;
	
	/**
	 * Create ResultSet
	 */
	private static ResultSet rs = null;
	
	/**
	 * Create PreparedStatement
	 */
	private static PreparedStatement pstmt = null;

	/**
	 * Create ComboPooledDataSource
	 */
	private static ComboPooledDataSource dataSource = new ComboPooledDataSource();
	
	/**
	 * Get dataSource
	 */
	public DataSource getDataSource(){
		return dataSource;
	}
	
	/**
	 * Get a Connection 
	 *TODO
	 *LIU
	 * @return Connection
	 * pm4:42:19
	 */
	public Connection getConnection(){
		try {
			return dataSource.getConnection();
		} catch (Exception e) {
			throw new RuntimeException(e);		
		}
	}
	
	
	/**
	 * Update information by sql
	 *TODO
	 *LIU
	 * @param sql
	 * @param objects
	 * @return int
	 * pm4:42:37
	 */
	public int updateBySql(String sql, Object ...objects){
		
		int result = 0;
		conn = getConnection();
		
		try {
			pstmt = conn.prepareStatement(sql);
			if (objects.length > 0) {
				for (int i = 0; i < objects.length; i++) {
					pstmt.setObject(i+1, objects[i]);
				}
			}
			
			result = pstmt.executeUpdate();
			
		} catch (Exception e) {
			e.printStackTrace();
		}

		return result;
	}
	
	
	
	/**
	 * Get information from database by sql
	 * TODO
	 * LIU
	 * @param sql
	 * @param objects
	 * @return ResultSet
	 * pm4:43:22
	 */
	public ResultSet selectBySql(String sql, Object ...objects){
		
		conn = getConnection();
		
		try {
			pstmt = conn.prepareStatement(sql);
			if (objects.length > 0) {
				for (int i = 0; i < objects.length; i++) {
					pstmt.setObject(i+1, objects[i]);
				}
			}
			
			rs = pstmt.executeQuery();
			
		} catch (Exception e) {
			e.printStackTrace();
		}

		return rs;
	}

	

	
	/**
	 * Close Connetion,ResultSet or PreparedStatement
	 *TODO
	 *LIU
	 *pm 11:16:00
	 */
	public void close() {
		try {
			if(rs != null){
				rs.close();
			}
			if(pstmt != null){
				pstmt.close();
			}
			if (conn != null) {
				conn.close();
				conn = null;
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

}

在数据访问实现类中使用DIY的工具类，实现对数据的增删改查。
数据访问实现类如下：

package com.fruitsys.dao.impl;

import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

import com.fruitsys.bean.Fruit;
import com.fruitsys.bean.Page;
import com.fruitsys.dao.BaseDao;
import com.fruitsys.dao.FruitDao;

/**
 * 水果信息数据访问实现类
 * @author LIU
 * @version 1.0 2017-10-17
 */
public class FruitDaoImpl extends BaseDao implements FruitDao {

	/**
	 * 获取总记录数
	 *TODO
	 *LIU
	 * @return
	 *下午4:06:37
	 */
	@Override
	public int getAllCount() {
		// TODO Auto-generated method stub
		String sql = "select count(id) from fruit";
		try {
			ResultSet rs = selectBySql(sql);
			if(rs.next()){
				return rs.getInt(1);
			}
		} catch (Exception e) {
			// TODO: handle exception
		}finally{
			close();
		}
		return 0;
	}

	
	/**
	 * 获取当前页的信息
	 *TODO
	 *LIU
	 * @param page
	 * @return
	 *下午4:09:03
	 */
	@Override
	public List<Fruit> showCurrList(Page page) {
		// TODO Auto-generated method stub
		String sql = "select id,type,breed,area,brief,weight,price from fruit limit ?,?";
		List<Fruit> fruitList = new ArrayList<Fruit>();
		
		try {
			ResultSet rs = selectBySql(sql, page.getStart(), page.getCurrCount());
			while(rs.next()){
				Fruit f = new Fruit();
				f.setId(rs.getInt("id"));
				f.setType(rs.getString("type"));
				f.setBreed(rs.getString("breed"));
				f.setArea(rs.getString("area"));
				f.setBrief(rs.getString("brief"));
				f.setWeight(rs.getInt("weight"));
				f.setPrice(rs.getDouble("price"));
			
				fruitList.add(f);
			}
		} catch (Exception e) {
			// TODO: handle exception
		}finally{
			close();
		}
		
		return fruitList;
	}

	
	/**
	 * 显示一条信息详情
	 *TODO
	 *LIU
	 * @return
	 *下午4:10:18
	 */
	@Override
	public Fruit showOne(int id) {
		// TODO Auto-generated method stub
		String sql = "select id,type,breed,area,brief,weight,price from fruit where id=?";
		
		try {
			ResultSet rs = selectBySql(sql, id);
			while(rs.next()){
				Fruit f = new Fruit();
				f.setId(rs.getInt("id"));
				f.setType(rs.getString("type"));
				f.setBreed(rs.getString("breed"));
				f.setArea(rs.getString("area"));
				f.setBrief(rs.getString("brief"));
				f.setWeight(rs.getInt("weight"));
				f.setPrice(rs.getDouble("price"));
			
				return f;
			}
		} catch (Exception e) {
			// TODO: handle exception
		}finally{
			close();
		}
		
		return null;
	}

	
	/**
	 * 删除一条信息
	 *TODO
	 *LIU
	 * @param id
	 * @return
	 *下午4:09:48
	 */
	@Override
	public int deleteFruit(int id) {
		// TODO Auto-generated method stub
		String sql = "delete from fruit where id=?";
		int result = updateBySql(sql, id);
		return result;
	}

}

项目目录结构如下：