JDBC获取连接、关闭连接的简单工具类2

package com.adam.dev.utils;

import java.io.BufferedInputStream;
import java.io.FileInputStream;
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.util.Properties;

/**
 * @author adam.胡升阳
 * 
 */
public class JdbcByPropertiesUtil {
    private static String filePath = "jdbc.properties"; 
    private static JdbcByPropertiesUtil instance = null;
    
    public JdbcByPropertiesUtil() {
		super();
	}

	/**
     * 单例方式创建对象
     * @return
     */
    public static JdbcByPropertiesUtil getInstance() {
        if (instance == null) {
            synchronized (JdbcByPropertiesUtil.class) {
                if (instance == null) {
                    instance = new JdbcByPropertiesUtil();
                }
            }
        }
        return instance;
    }
       
    /**
     * 读取properties文件中 数据库连接信息
     * @param filePath
     * add 2012-4-17
     */
    public static Properties readPropertiesFile(){
    	String realFilePath = Thread.currentThread().getContextClassLoader().getResource("").getPath()+filePath; 
        Properties pros = new Properties();  
        try {  
            InputStream is = new BufferedInputStream(new FileInputStream(realFilePath));  
            pros.load(is); 
        } catch (Exception e) {  
            e.printStackTrace();
        }
        return pros;
    } 
    
    /**
     * 注册驱动
     * 静态代码块 用于启动web服务器时加载驱动
     */
    static{
        Properties pros = readPropertiesFile();
        String className = (String) pros.get("className");
        try {
            Class.forName(className).newInstance();
        } catch (Exception e) {
            e.printStackTrace();
        } 
    }
    
	/**
	 * 获取数据库连接
     * modify 2012-4-17
	 * @param con
	 * @return
	 */
	public Connection getConnection(){
        Properties pros = readPropertiesFile();
        String url = (String) pros.get("url");
        String user = (String) pros.get("user");
        String password = (String) pros.get("password");
        Connection conn = null;
		try {
			conn = DriverManager.getConnection(url,user,password);
		} catch (Exception e) {
			e.printStackTrace();
		}
		return conn;
	}
       
    /**
     *  依次关闭ResultSet、Statement、Connection
     *  若对象不存在则创建一个空对象
     * @param rs
     * @param st
     * @param pst
     * @param conn
     */
    public void close(ResultSet rs,Statement st,Connection conn){
        if(rs != null){
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            } finally{
                if(st != null){
                    try {
                        st.close();
                    } catch (SQLException e) {
                        e.printStackTrace();
                    } finally{
                        if(conn != null){
                            try {
                                conn.close();
                            } catch (SQLException e) {
                                e.printStackTrace();
                            }
                        }
                    }
                }
            }
        }
    }


    /**
     * 新增、修改、删除、查询记录(也可以改为有结果集ResultSet返回的查询方法)
     * @param sql
     * @throws  
     */
    public void execute(String sql){
        JdbcByPropertiesUtil jbpu = getInstance();
        Connection conn = null;
        PreparedStatement pst = null;
        try {
            conn = jbpu.getConnection();
            conn.setAutoCommit(false);
            pst = conn.prepareStatement(sql);
            pst.execute();
            conn.commit();
        } catch (Exception e) {
            try {
                conn.rollback();
            } catch (SQLException e1) {
                e1.printStackTrace();
            }
            e.printStackTrace();
        } finally{
            //Statement st = null;
            ResultSet rs = null;
            jbpu.close(rs, pst, conn); 
        }
    }
 
    /**
     * 新增、修改、删除记录
     * @param sql
     * @throws  
     */
    public void executeUpdate(String sql) {
        JdbcByPropertiesUtil jbpu = getInstance();
        Connection conn = null;
        PreparedStatement pst = null;
        try {
            conn = jbpu.getConnection();
            conn.setAutoCommit(false);
            pst = conn.prepareStatement(sql);
            pst.executeUpdate();
            conn.commit();
        } catch (Exception e) {
            try {
                conn.rollback();
            } catch (SQLException e1) {
                e1.printStackTrace();
            }
            e.printStackTrace();
        } finally{
            //Statement st = null;
            ResultSet rs = null;
            jbpu.close(rs, pst, conn); 
        }
    }
    
    
}