JDBC技术

package com.yc.test1.dao;

import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import com.yc.test1.utils.LogUtil;

public class DBHelper {
    //让静态块保证数据库的驱动只加载一次
    static{
        try{                //因为只有一条语句需要调用Myproperties ，可以直接.getInstance(). 来直接调用
            Class.forName(MyProperties.getInstance().getProperty("driverclassname"));
        }catch(ClassNotFoundException e){
            LogUtil.log.error(e.toString());
            e.printStackTrace();
        }catch(IOException e){
            LogUtil.log.error(e.toString());
            e.printStackTrace();
        }
    }
    //获取与数据库的连接
    public Connection getCon() throws SQLException, IOException{
        //因为有三句语句需要Myproperties，所以getInstance 它，节省语句
        MyProperties mp=MyProperties.getInstance();
        Connection con=DriverManager.getConnection(mp.getProperty("url"),mp.getProperty("username"),mp.getProperty("password"));
        return con;
    }

    //查询数据
    public List<Map<String,String>> findAll(String sql,List<Object>params) throws SQLException, IOException{
        Connection con=getCon();
        PreparedStatement pstmt=con.prepareStatement(sql);
        setParams(pstmt,params);
        // 得到结果集
        ResultSet rs=pstmt.executeQuery();
        //取出所有的列名，存到list中
        //从结果集中取出列名
        ResultSetMetaData rsmd=rs.getMetaData();
        //取出列数
        int columnCount=rsmd.getColumnCount();
        List<String>cnlist=new ArrayList<String>();
        for(int i=1;i<=columnCount;i++){
            cnlist.add(rsmd.getColumnName(i));
        }
        List<Map<String,String>>list=new ArrayList<Map<String,String>>();
        //取出表中的数据
        while(rs.next()){
            Map<String,String>map=new HashMap<String,String>();
            //循环cnlist中所有的列名，再根据这个列名从rs 中取数据
            for(String cn:cnlist){
                map.put(cn, rs.getString(cn));
            }
            list.add(map);
        }
        closeAll(pstmt,con,rs);
        return list;
    }


    //查询聚合函数的方法： count  avg  max  min
    public double findDouble(String sql,List<Object>params) throws SQLException, IOException{
        double result=0;
        Connection con=getCon();
        PreparedStatement pstmt=con.prepareStatement(sql);
        setParams(pstmt,params);
        //得到结果集
        ResultSet rs=pstmt.executeQuery();
        if(rs.next()){
            result=rs.getDouble(1);
        }
        closeAll(pstmt,con,rs);
        return result;
    }


    //封装增删改
    public int doUpdate(String sql,List<Object>params) throws SQLException, IOException{
        Connection con=getCon();
        PreparedStatement pstmt=con.prepareStatement(sql);
        setParams(pstmt,params);
        int result=pstmt.executeUpdate();
        closeAll(pstmt,con,null);
        return result;
    }
    
    //封装事务的增删改
    public void doUpdate(List<String> sqls,List<List<Object>>listparams) throws SQLException, IOException{
        Connection con=getCon();
        PreparedStatement pstmt=null;
        //关闭隐式事务提交（一句sql语句提交一次）
        con.setAutoCommit(false);
        try{
            if(sqls!=null&&sqls.size()>0){
                for(int i =0 ; i<sqls.size();i++){
                    String sql=sqls.get(i);//取出每条sql 语句
                    pstmt=con.prepareStatement(sql);
                    setParams(pstmt,listparams.get(i));
                    pstmt.executeUpdate();
                }
            }
            con.commit();//提交事务
        }catch(Exception e){
            if(con!=null){
                con.rollback();
            }
            LogUtil.log.error(e.toString());
        }finally{
            con.setAutoCommit(true);//再次恢复事务为隐式事务
            closeAll(pstmt,con,null);
        }
    }


    //设置sql语句当中的参数，如果有的话
    private void setParams(PreparedStatement pstmt, List<Object> params) throws SQLException {
        if(params!=null&& params.size()>0){
            for(int i=1;i<=params.size();i++){
                pstmt.setObject(i, params.get(i-1));
            }
        }

    }
    //关闭连接
    private void closeAll(PreparedStatement pstmt,Connection con,ResultSet rs) throws SQLException{
        if(rs!=null){
            rs.close();
        }
        if(pstmt!=null){
            pstmt.close();
        }
        if(con!=null){
            con.close();
        }
    }

    public List<Map<String, String>> find(String sql, List<Object> params) throws SQLException, IOException {
        List<Map<String,String>> list=new ArrayList<Map<String,String>>();
        Connection con=getCon();
        PreparedStatement pstmt=con.prepareStatement(sql);
        setParams(pstmt,params);
        ResultSet rs=pstmt.executeQuery();

        List<String> cnames=new ArrayList<String>();
        ResultSetMetaData rsmd=rs.getMetaData();
        for(int i=0;i<rsmd.getColumnCount();i++){
            cnames.add(rsmd.getColumnName(i+1));
        }

        while(rs.next()){
            Map<String,String>map =new HashMap<String,String>();
            for(String cn:cnames){
                String value=rs.getString(cn);
                map.put(cn, value);
            }
            list.add(map);
        }
        closeAll(pstmt,con,rs);
        return list;
    }
}

package com.net.dao;

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

public class MyProperties extends Properties {
    private static MyProperties myproperties;
    //将这个类的构造方法设为私有，这样这个类就不能多次实例化了
    private MyProperties() throws IOException {
        InputStream iis = MyProperties.class.getClassLoader().getResourceAsStream("db.properties");
        super.load(iis);
    }
    
    //对外提供一个方法来猎取唯一的一个实例
    public static MyProperties getInstance() throws IOException {
        if ( myproperties == null) {
            myproperties = new MyProperties();
        }
        return myproperties;
    }
}

username=scott
password=a
driveclass=oracle.jdbc.driver.OracleDriver
url=jdbc:oracle:thin:@localhost:1521:orcl