用JDBC实现CRUD操作

定义

·· 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，同时，JDBC也是个商标名。

写一个实例类

package domain;

import java.util.Date;

public class User {
    private int id;
    private String username;
    private String password;
    private String email;
    private Date birthday;

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

    public void setUsername(String username) {
        this.username = username;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public void setEmail(String email) {
        this.email = email;
    }

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

    public int getId() {
        return id;
    }

    public String getUsername() {
        return username;
    }

    public String getPassword() {
        return password;
    }

    public String getEmail() {
        return email;
    }

    public Date getBirthday() {
        return birthday;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", email='" + email + '\'' +
                ", birthday=" + birthday +
                '}';
    }
}

定义一个工具类用于得到connection对象

package com.itheima.util;

import java.sql.*;
import java.util.ResourceBundle;

public class DBUtils {
    /**
     * 得到jdbc中connection的方法
     * @return
     * @throws ClassNotFoundException
     * @throws SQLException
     */
    private static String driverClass;
    private static String url;
    private static String username;
    private static String password;
    static{
        ResourceBundle dbinfo = ResourceBundle.getBundle("dbinfo");
        driverClass = dbinfo.getString(driverClass);
        url = dbinfo.getString(url);
        username = dbinfo.getString(username);
        password = dbinfo.getString(password);
        try {
            Class.forName(driverClass);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
    public static Connection getConnection() throws ClassNotFoundException, SQLException {
        return DriverManager.getConnection(url, username, password);
    }

    public static void closeAll(ResultSet resultSet, Statement statement,Connection connection){
        if(resultSet != null){
            try {
                resultSet.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
            resultSet = null;
        }
        if(statement != null){
            try {
                statement.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
            statement = null;
        }
        if(connection != null){
            try {
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
            connection = null;
        }
    }
}

设置配置文件

driverClass=com.mysql.jdbc.Driver
url=jdbc:mysql:///day12
username=root
password=abc

写一个测试类检查

package com.itheima.crud;

import com.itheima.util.DBUtils;
import domain.User;
import org.junit.Test;

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

public class TestCRUD {
    @Test
    public void testSelect(){
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;

        try {
            connection = DBUtils.getConnection();
            String sql = "select * from users";
            preparedStatement = connection.prepareStatement(sql);//使用预编译对象
            resultSet = preparedStatement.executeQuery();
            List<User> list = new ArrayList<>();
            while (resultSet.next()){
                User user = new User();
                user.setId(resultSet.getInt(1));
                user.setUsername(resultSet.getString(2));
                user.setPassword(resultSet.getString(3));
                user.setEmail(resultSet.getString(4));
                user.setBirthday(resultSet.getDate(5));
                list.add(user);
            }
            for (User user : list) {
                System.out.println(user);
            }
        }  catch (Exception e) {
            e.printStackTrace();
        } finally {
            DBUtils.closeAll(resultSet, preparedStatement, connection);
        }
    }

得到输出结果打印在控制台

User{id=1, username=’tom’, password=’123’, email=’[email protected]’, birthday=1992-08-02}