Java 数据库访问层

最近项目中需要对mysql进行操作，数据库的知识早在本科毕业那会就忘光了，这几年开发都没接触到数据库的操作。

借这个机会重新学习，数据库访问层是对数据库操作的一个封装，屏蔽底层的数据操作细节，通过使用DAO对数据库进行增删改查操作。

本文将以项目中的一小部分为例，介绍如何编写数据库访问层：

1. 实体类对象

 public class CheckInfo {
     private Integer id;
     private String userName;
     private Timestamp checkTime;
 
     public Integer getId() {
         return id;
     }
 
     public void setId(Integer id) {
         this.id = id;
     }
 
     public String getUserName() {
         return userName;
     }
 
     public void setUserName(String userName) {
         this.userName = userName;
     }
 
     public Timestamp getCheckTime() {
         return checkTime;
     }
 
     public void setCheckTime(Timestamp checkTime) {
         this.checkTime = checkTime;
     }
 
     @Override
     public String toString() {
         return "CheckInfo [id=" + id + ", userName=" + userName
                 + ", checkTime=" + checkTime + "]";
     }
 
 }

2. 获取数据库连接工具类ConnectionUtil

 public class ConnectionUtil {
 
     public Connection getConnection() {
         String username = "root";
         String password = "123456";
         String url="jdbc:mysql://localhost:3306/checkin";
         String driver="com.mysql.jdbc.Driver";
 
         try {
             Class.forName(driver);
             return DriverManager.getConnection(url, username, password);
         } catch (ClassNotFoundException e) {
             e.printStackTrace();
         } catch (SQLException e) {
             e.printStackTrace();
         }
         return null;
     }
 }

3. 数据访问层接口

 public interface CheckInfoDAO {
 
     public boolean save(CheckInfo checkInfo);
     public List<CheckInfo> listCheckInfo();
 
 }

4. 数据访问层实现

 public class CheckInfoDAOImpl implements CheckInfoDAO {
 
     @Override
     public boolean save(CheckInfo checkInfo) {
         boolean flag = false;
         ConnectionUtil connUtil = new ConnectionUtil();
         Connection conn = null;
 
         conn = connUtil.getConnection();
 
         PreparedStatement stmt = null;
         String sql = "insert into checkinfo values(name, time) values("
                 + checkInfo.getUserName() + "," + checkInfo.getCheckTime()
                 + ")";
         try {
             stmt = conn.prepareStatement(sql);
             flag = stmt.execute();
         } catch (SQLException e) {
             e.printStackTrace();
         }
 
         return flag;
     }
 
     @Override
     public List<CheckInfo> listCheckInfo() {
         List<CheckInfo> checkInfos = new ArrayList<CheckInfo>();
 
         ConnectionUtil connUtil = new ConnectionUtil();
         Connection conn = null;
 
         conn = connUtil.getConnection();
 
         PreparedStatement stmt = null;
         String sql = "select * from checkinfo";
         ResultSet resultSet = null;
 
         try {
             stmt = conn.prepareStatement(sql);
             resultSet = stmt.executeQuery();
             while(resultSet.next()) {
                 CheckInfo ci = new CheckInfo();
                 ci.setId(resultSet.getInt(1));
                 ci.setUserName(resultSet.getString(2));
                 ci.setCheckTime(resultSet.getTimestamp(3));
                 checkInfos.add(ci);
             }
         } catch (SQLException e) {
             e.printStackTrace();
         }
 
         return checkInfos;
     }
 
 }

mysql中的datetime类型对应于java的TimeStamp类型。

5.测试类

 public class TestCase {
 
     public static void main(String[] args) {
 
         testListCheckInfo();
     }
 
     private static void testListCheckInfo() {
         CheckInfoDAO checkInfoDAO = new CheckInfoDAOImpl();
         List<CheckInfo> checkInfos = checkInfoDAO.listCheckInfo();
 
         for (CheckInfo checkInfo : checkInfos) {
             System.out.println(checkInfo);
         }
     }
 
 }

数据库建表语句：

 create table if not exists checkinfo (
     id int(10) not null primary key auto_increment,
     userid varchar(40),
     time datetime
 );