JDBC学习笔记——简单UerDao

　　JDBC(Java DataBase Connectivity,java数据库连接)是一种用于执行SQL语句的Java API，可以为多种关系数据库提供统一访问，它由一组用Java语言编写的类和接口组成。JDBC提供了一种基准，据此可以构建更高级的工具和接口，使数据库开发人员能够编写数据库应用程序，利用JDBC提供的接口，可以方便得对数据库进行操作。

　

1、JDBCUtils（产生Connection，关闭资源）

package com.sina.jdbc;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.FileNotFoundException;
import java.util.Properties;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class JDBCUtils {
    private JDBCUtils(){

    }

    public static JDBCUtils getInstance(){
        if(instance == null){
            synchronized(JDBCUtils.class){
                if(instance == null){       //二次判空, 防止多线程下多次创建实例对象
                    instance = new JDBCUtils();
                }
            }
        }
        return instance;
    }

    public Connection getConnection(){
        Connection connection = null;
        try {
            connection = DriverManager.getConnection(URL, USER_NAME, PASSWORD);
        } catch(SQLException e){
            e.printStackTrace();
        }
        return connection;
    }

    public void close(Connection connection, Statement stmt, ResultSet rs){
        if(rs != null){
            try {
                rs.close();
            } catch(SQLException e){
                e.printStackTrace();
            }
        }

        if(stmt != null){
            try {
                stmt.close();
            } catch(SQLException e){
                e.printStackTrace();
            }
        }

        if(connection != null){
            try {
                connection.close();
            } catch(SQLException e){
                e.printStackTrace();
            }
        }
    }

    private static JDBCUtils instance = null;
    //加载配置文件, 读取以下信息以建立Connection
    private static String DRIVER_NAME;
    private static String URL;
    private static String USER_NAME;
    private static String PASSWORD;
    static {
        FileInputStream fis = null;
        try {
            Properties p = new Properties();
            File file = new File("./src/config.properties");
            fis = new FileInputStream(file);
            p.load(fis);
            DRIVER_NAME = p.getProperty("DRIVER_NAME");
            URL = p.getProperty("URL");
            USER_NAME = p.getProperty("USER_NAME");
            PASSWORD = p.getProperty("PASSWORD");

            Class.forName(DRIVER_NAME);  //加载驱动
        } catch(ClassNotFoundException e) {
            System.out.println(DRIVER_NAME + "驱动类找不着.");
        } catch(FileNotFoundException e) {
            System.out.println("文件 config.properties 找不到.");
        } catch(IOException e){
            e.printStackTrace();
        } finally{
            if(fis != null){
                try {
                    fis.close();
                } catch(IOException e){
                    e.printStackTrace();
                }
            }
        }
    }
}

2、UserDao

package com.sina.jdbc.dao;

import com.sina.jdbc.orm.User;

//UserDao（User数据访问对象）利用接口实现，属面向接口编程，方便代码使用和管理，若实现类被修改，使用接口方法的程序不受影响，不需修改
public interface UserDao {
    void addUser(User user);
    void deleteUser(User user);
    void updateUser(User user);
    User getUser(Integer id);
    User findUser(String name, String gender);
}

3、UserDaoFactory

package com.sina.jdbc.dao;

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

//使用DAD工厂实现，若要改用其他方式实现的UserDao，则直接修改配置文件即可，程序用到UserDao的地方无需修改
public class UserDaoFactory {
    private UserDaoFactory(){

    }

    public static UserDaoFactory getInstance(){
        if(instance == null){
            synchronized(UserDaoFactory.class){
                if(instance == null){
                    instance = new UserDaoFactory();
                }
            }
        }
        return instance;
    }

    public UserDao getUserDao(){
        UserDao retVal = null;
        Properties p = new Properties();
        InputStream is = null;
        try {
           is = UserDaoFactory.class.getClassLoader().getResourceAsStream("config.properties");
           p.load(is);
           String daoClassName = p.getProperty("daoClassName");
           retVal = (UserDao)Class.forName(daoClassName).getConstructor().newInstance();
        } catch(Exception e){
            throw new ExceptionInInitializerError();
        } finally{
            if(is != null){
                try {
                    is.close();
                } catch(IOException e){
                    e.printStackTrace();
                }
            }
        }
        return retVal;
    }

    private static UserDaoFactory instance = null;
}

4、UserDao（增删改查）

package com.sina.jdbc.dao.imp;

import com.sina.jdbc.dao.UserDao;
import com.sina.jdbc.dao.DAOException;
import com.sina.jdbc.orm.User;
import com.sina.jdbc.JDBCUtils;
import java.sql.*;

public class UserDaoJdbcImp implements UserDao {
    @Override
    public void addUser(User user) {
        Connection connection = null;
        PreparedStatement pstmt = null;
        try {
            connection = JDBCUtils.getInstance().getConnection();
            pstmt = connection.prepareStatement("insert into t_user values(?, ?, ?, ?, ?)");
            setPstmt(pstmt, user);
            pstmt.execute();
        } catch(SQLException e){
            throw new DAOException(e.getMessage(), e);  //抛出异常给上级调用者, 让得知异常发生
        } finally{
            JDBCUtils.getInstance().close(connection, pstmt, null);
        }
    }

    @Override
    public void deleteUser(User user){
        Connection connection = null;
        PreparedStatement pstmt = null;
        try {
            connection = JDBCUtils.getInstance().getConnection();
            pstmt = connection.prepareStatement("delete from t_user where id = ? and name = ?");
            pstmt.setInt(1, user.getId());
            pstmt.setString(2, user.getName());
            pstmt.execute();
        } catch(SQLException e){
            throw new DAOException(e.getMessage(), e);
        } finally{
            JDBCUtils.getInstance().close(connection, pstmt, null);
        }
    }

    @Override
    public void updateUser(User user){
        Connection connection = null;
        PreparedStatement pstmt = null;
        try {
            connection = JDBCUtils.getInstance().getConnection();
            pstmt = connection.prepareStatement("update t_user set id = ?, name = ?, birthday = ?, gender = ?, property = ? where id = ?");
            setPstmt(pstmt, user);
            pstmt.setInt(6, user.getId());
            pstmt.execute();
        } catch(SQLException e){
            throw new DAOException(e.getMessage(), e);
        } finally{
            JDBCUtils.getInstance().close(connection, pstmt, null);
        }
    }

    @Override
    public User getUser(Integer id){
        Connection connection = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        User user = null;
        try {
            connection = JDBCUtils.getInstance().getConnection();
            pstmt = connection.prepareStatement("select id,name,birthday,gender,property from t_user where id = ?");
            pstmt.setInt(1, id);
            rs = pstmt.executeQuery();
            user = createUser(rs);
        } catch(SQLException e){
            throw new DAOException(e.getMessage(), e);
        } finally{
            JDBCUtils.getInstance().close(connection, pstmt, rs);
        }
        return user;
    }

    @Override
    public User findUser(String name, String gender){
        Connection connection = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        User user = null;
        try {
            connection = JDBCUtils.getInstance().getConnection();
            pstmt = connection.prepareStatement("select id,name,birthday,gender,property from t_user where name = ? and gender = ?");
            pstmt.setString(1, name);
            pstmt.setString(2, gender);
            rs =  pstmt.executeQuery();
            user = createUser(rs);
        } catch(SQLException e){
            throw new DAOException(e.getMessage(), e);
        } finally{
            JDBCUtils.getInstance().close(connection, pstmt, rs);
        }
        return user;
    }

    private User createUser(ResultSet rs) throws SQLException {
        User user = null;
        while(rs.next()){
            user = new User(rs.getInt("id"), rs.getString("name"), rs.getDate("birthday"), rs.getString("gender"), rs.getFloat("property"));
        }
        return user;
    }

    private static void setPstmt(PreparedStatement pstmt, User user) throws SQLException {
        pstmt.setInt(1, user.getId());
        pstmt.setString(2, user.getName());
        pstmt.setDate(3, new Date(user.getBirthday().getTime()));
        pstmt.setString(4, user.getGender());
        pstmt.setFloat(5, user.getProperty());
    }
}

5、User

package com.sina.jdbc.orm;

import java.util.Date;

//ORM（对象关系映射），数据二维表对应Java类，表字段对应类属性
public class User {
    public User(){

    }

    public User(Integer id, String name, Date birthday, String gender, Float property){
        this.id = id;
        this.name = name;
        this.birthday = birthday;
        this.gender = gender;
        this.property = property;
    }

    public void setId(Integer id){
        this.id = id;
    }

    public Integer getId(){
        return id;
    }

    public void setName(String name){
        this.name = name;
    }

    public String getName(){
        return name;
    }

    public void setBirthday(Date birthday){
        this.birthday = birthday;
    }

    public Date getBirthday(){
        return birthday;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public String getGender(){
        return gender;
    }

    public void setProperty(Float property){
        this.property = property;
    }

    public Float getProperty(){
        return property;
    }

    private Integer id;       //采用包装类，如果id为主键并自增长，在插入数据库时可不指定id，
    // 若以PreparedStatement返回主键并给相应的User对象赋值，就可以区别哪些个对象已经写到数据库中，因为已经保存过的对象会得到返回的主键并赋值给id，
    // 而没被操作的对象id属性将为null，而不是数字0，易于区分
    private String name;
    private Date birthday;
    private String gender;
    private Float property;
}

6、DAOException(给上级调用者抛出异常，让其得知异常产生地点)

package com.sina.jdbc.dao;

public class DAOException extends RuntimeException {
    public DAOException() {
    }

    public DAOException(String message) {
        super(message);
    }

    public DAOException(String message, Throwable cause) {
        super(message, cause);
    }

    public DAOException(Throwable cause) {
        super(cause);
    }
}

有无DAOException时报告异常对比.

DAOException:

SQLException:

7、Test

package com.sina.jdbc;

import com.sina.jdbc.dao.UserDao;
import com.sina.jdbc.dao.UserDaoFactory;
import com.sina.jdbc.orm.User;
import java.util.Date;

public class Test {
    public static void main(String[] args){
        UserDao userDao = UserDaoFactory.getInstance().getUserDao();
        User user = new User(10, "Tom", new Date(), "男", 230f);
        userDao.addUser(user);
//        User user = userDao.findUser("Tom", "男");
//        System.out.println(user.getId()+ " " + user.getBirthday());
//        userDao.deleteUser(user);
    }
}

　　以下代码为简单的UserDAO，本人为JAVA新人，发布出来方便以后复习。另外，其中可能存在一些不足的地方，如有建议，请告知。