/*
	 * 静态代码块   类加载时完成数据初始化
	 */
	static {
		Properties p = new Properties();
		try {
			p.load(DbUtils.class.getClassLoader().getResourceAsStream("com/shanxi/properties/dbUtils.properties"));
			driverUrl = p.getProperty("driverUrl");
			url = p.getProperty("url");
			username = p.getProperty("username");
			password =  p.getProperty("password");
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

package com.shanxi.dbUtils;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.Types;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Properties;


/*
 * 数据库工具类
 */
public class DbUtils {
	//数据库连接对象  Connection
	private static Connection conn;
	//操作数据库对象Statement
	private static Statement sta;
	//操作数据库预编译对象Preparstatement
	private static PreparedStatement ps;
	//驱动类地址
	private static String driverUrl;
	//URL数据库连接
	private static String url;
	//用户名
	private static String username;
	//密码
	private static String password;
	/*
	 * 静态代码块   类加载时完成数据初始化
	 */
	static {
		Properties p = new Properties();
		try {
			p.load(DbUtils.class.getClassLoader().getResourceAsStream("com/shanxi/properties/dbUtils.properties"));
			driverUrl = p.getProperty("driverUrl");
			url = p.getProperty("url");
			username = p.getProperty("username");
			password =  p.getProperty("password");
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
	/*
	 * 获取Connection连接的方法
	 * @return conn
	 */
	public static  Connection getConnection() {
		try {
			Class.forName(driverUrl);
			conn = DriverManager.getConnection(url, username, password);
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		} catch (SQLException e) {
			e.printStackTrace();
		}
		return conn;
	}
	
	/*
	 * 不支持预编译的查询方法 
	 */
	public static List<Map<String,Object>> queryForList(String sql){
		List<Map<String,Object>> list =  new ArrayList<Map<String, Object>>();
		try {
			
			conn = getConnection();
			sta = conn.createStatement();
			ResultSet rs = sta.executeQuery(sql);
			list = rsToList(rs);
			close();
			
		} catch (SQLException e) {
			e.printStackTrace();
		}
		return list;
	}
	/*
	 * 不支持预编译的增删改方法
	 */
	public static int excuteUpdate(String sql){
		
		return 0;
	}
	
	/*
	 * 支持预编译的查询方法
	 */
	public static List<Map<String,Object>> queryForList(String sql,int[] type,Object[] obj){
		List<Map<String, Object>> list = new ArrayList<Map<String, Object>>();
		try {
			conn = getConnection();
			ps = conn.prepareStatement(sql);
			//循环遍历参数数组 并将数组中的值设置给预编译sql
			for (int i = 0; i < obj.length; i++) {
				switch (type[i]) {
				case Types.INTEGER:
					ps.setInt(i+1,Integer.parseInt(obj[i].toString()));
					break;
				case Types.VARCHAR:
					ps.setString(i+1,obj[i].toString());
					break;
				default:
					ps.setString(i+1,obj[i].toString());
				}
			}
			ResultSet rs = ps.executeQuery();
			list = rsToList(rs);
			close();
		
		} catch (SQLException e) {
			e.printStackTrace();
		}
		
		return list;
	}
	/*
	 * 支持预编译的增删改方法    
	 */
	public static int excuteUpdate(String sql,int[] type,Object[] obj){
		
		return 0;
	}
	
	/*
	 * 不支持预编译的计数查询方法    
	 */
	public static int queryForCount(String sql){
		
		
		return 0;
	}
	
	/*
	 * 支持预编译的计数查询方法
	 */
	
	public static int queryForCount(String sql,int[] type,Object[] obj){
		
		
		return 0;
	}
	
	/*
	 * 将resultSet结果集转换为List
	 * @param rs    封装数据的resultSet
	 * @return  	数据转换后的List
	 */
	private static List<Map<String, Object>> rsToList(ResultSet rs) {
		List<Map<String, Object>> list = new ArrayList<Map<String, Object>>();
		
		try {
			while(rs.next()){
				Map<String, Object>  map =  new HashMap<String,Object>();
				for (int i = 1; i <= rs.getMetaData().getColumnCount(); i++) {
					switch (rs.getMetaData().getColumnType(i)) {
					case Types.INTEGER:
						map.put(rs.getMetaData().getColumnName(i),rs.getInt(i));
						break;
					case Types.VARCHAR:
						map.put(rs.getMetaData().getColumnName(i),rs.getString(i));
						break;
					default:
						map.put(rs.getMetaData().getColumnName(i),rs.getObject(i));
					}
				}
				list.add(map);
			}
		} catch (SQLException e) {
			e.printStackTrace();
		}
		
		return list;
	}

	/*
	 * 关闭Connection连接的方法
	 */
	public static void close(){
		if(conn!=null){
			try {
				conn.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}finally {
				try {
					conn.close();
				} catch (SQLException e) {
					e.printStackTrace();
					System.gc();
				}
			}
		}
	}
	
	
	public static void main(String[] args) {
		
		List<Map<String, Object>> list =  new ArrayList<Map<String, Object>>();
		//测试非预编译方法
//		String sql ="select * from people";
//		list = DbUtils.queryForList(sql);
//		for (Map<String, Object> map : list) {
//			System.out.println(map.get("name")+"---"+map.get("age"));
//		}
		//测试预编译对象
		String sql1 ="select * from people where age = ? and sex= ? and salary >?";
		int [] type = {Types.INTEGER,Types.VARCHAR,Types.FLOAT};
		Object[] obj = {20,"男",3500};
		list = DbUtils.queryForList(sql1,type,obj);
		for (Map<String, Object> map : list) {
			System.out.println(map.get("name")+"---"+map.get("age"));
		}
	}
}