jdbc连接数据库单例预先初始化

package com.daqing.jdbc;

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

/**
 * 单例模式会有一个实例；会new一次
 * 单例模式不使用静态的
 * A0102JdbcUtilsSingletonBeforehand
 * 		意思：jdbc工具类，单例，预先初始化
 * @author Administrator
 *
 */
public final class A0102JdbcUtilsSingletonBeforehand {

	private String url = "jdbc:mysql://127.0.0.1:3306/jdbc";
	private String user = "root";
	private String password = "root";
	
	/**
	 * 预初始化
	 */
	private static A0102JdbcUtilsSingletonBeforehand instance = new A0102JdbcUtilsSingletonBeforehand();
	
	private A0102JdbcUtilsSingletonBeforehand(){
	}
	
	public static A0102JdbcUtilsSingletonBeforehand getInstacce(){
		return instance;
	}
	
	static {
		try {
			Class.forName("com.mysql.jdbc.Driver");
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
			throw new ExceptionInInitializerError(e);
		}
	}
	
	public Connection getConnection() throws SQLException{
		return DriverManager.getConnection(url, user, password);
	}
	
	public void free(ResultSet rs, PreparedStatement ps, Connection conn){
		try {
			if(rs!=null){
				rs.close();
			}
		} catch (SQLException e) {
			System.out.println("ResultSet关闭发生异常...");
		} finally {
			if(ps!=null){
				try {
					ps.close();
				} catch (SQLException e) {
					System.out.println("PreparedStatement关闭发生异常...");
				} finally {
					if(conn!=null){
						try {
							conn.close();
						} catch (SQLException e) {
							System.out.println("Connection关闭发生异常...");
						}
					}
				}
			}
		}
	}
}