数据库访问JavaBean的设计

3.建立一个连接和释放资源的工具类JdbcUtil.java

package dbc;

import java.sql.*;
import java.util.Properties;  
public final class JdbcUtil {  
         
   private static String driver;  
   private static String user;  
   private static String password;  
   private static String url;  
   private static Properties pr=new Properties();
   private JdbcUtil(){} 
   //
   static{  
        try {  
            pr.load(JdbcUtil.class.getClassLoader().getResourceAsStream("db.properties"));    
            driver= pr.getProperty("driver"); 
            url = pr.getProperty("url");  
            user = pr.getProperty("username");  
            password = pr.getProperty("password");                                         
            Class.forName(driver);  
              
        } catch (Exception e) {            
            throw new ExceptionInInitializerError(e);  
        }          
    }  
    //  
    public static Connection getConnection()throws SQLException
    { 
        return DriverManager.getConnection(url, user, password);  
    }

        
     // 
    public static void free(ResultSet rs,Statement st,Connection conn)
    {  
        try
        { 
            if(rs!=null)              
                rs.close();                       
        }catch (SQLException e) 
        { 
            e.printStackTrace();  
        }finally{
                 try
                 {
                     if(st!=null)
                         st.close();                 
                 }catch (SQLException e) { e.printStackTrace();  
                 } finally{
                     if(conn!=null)                       
                         try
                     { 
                             conn.close();  
                     }
                     catch (SQLException e) {  
                         e.printStackTrace();  
                      }  
                     }   
                   }
        }
}

4.建立类User.java实现记录信息对象化，体现面向对象程序设计思想。

package vo;

public class User 
{
    private String userid,username,sex;
    public String getUserid(){return userid;}
    public void setUserid(String userid){this.userid=userid;}
    public String getUsername(){return username;}
    public void setUsername(String username){this.username=username;}
    public String getSex(){return sex;}
    public void setSex(String sex){this.sex=sex;}
}

5.在上面步骤的基础上建立类UserDao.java封装基本的数据库。

package dao;

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

import vo.User;
import dbc.JdbcUtil;
public class UserDao {
    public void add(User user)throws Exception{
        Connection conn=null;
        PreparedStatement ps=null;
        try{
            conn=JdbcUtil.getConnection();
            String sql="insert into user values(?,?,?)";
            ps=conn.prepareStatement(sql);
            ps.setString(1,user.getUserid());
            ps.setString(2,user.getUsername());
            ps.setString(3,user.getSex());
            ps.executeUpdate();            
        }finally{JdbcUtil.free(null,ps,conn);}
    }
    public void update(User user)throws Exception{
        Connection conn=null;
        PreparedStatement ps=null;
        try{
            conn=JdbcUtil.getConnection();
            String sql="update user set username=?,sex=? where userid=?";
            ps=conn.prepareStatement(sql);
            ps.setString(1,user.getUserid());
            ps.setString(2,user.getUsername());
            ps.setString(3,user.getSex());
            ps.executeUpdate();            
        }finally{JdbcUtil.free(null,ps,conn);}
    }

public void delete(String userId)throws Exception{
    Connection conn=null;
    PreparedStatement ps=null;
    try{
        conn=JdbcUtil.getConnection();
        String sql="delete from user where userid=?";
        ps=conn.prepareStatement(sql);
        ps.setString(1,userId);
        ps.executeUpdate();            
    }finally{JdbcUtil.free(null,ps,conn);}
}
    public User findUserById(String userId)throws Exception{
        Connection conn=null;
        PreparedStatement ps=null;
        ResultSet rs=null;
        User user=null;
        try{
            conn=JdbcUtil.getConnection();
            String sql="select* from user where userid=?";
            ps=conn.prepareStatement(sql);
            ps.setString(1,userId);
            rs=ps.executeQuery();        
            if(rs.next()){
                user=new User();
                user.setUserid(rs.getString(1));
                user.setUsername(rs.getString(2));
                user.setSex(rs.getString(3));
            }
        }finally{JdbcUtil.free(null,ps,conn);}
            return user;
    }
    public List<User> QueryAll()throws Exception{
        Connection conn=null;
        PreparedStatement ps=null;
        ResultSet rs=null;
        List<User>userList=new ArrayList<User>();
        try{
            conn=JdbcUtil.getConnection();
            String sql="select* from user";
            ps=conn.prepareStatement(sql);
            rs=ps.executeQuery();
            while(rs.next()){
                User user=new User();
                user.setUserid(rs.getString(1));
                user.setUsername(rs.getString(2));
                user.setSex(rs.getString(3));
                userList.add(user);
            }
        }finally{
            JdbcUtil.free(rs, ps, conn);
        }
        return userList;
        
        
        
    }
}

数据库访问JavaBean的设计

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