JDBCUtils工具类创建和使用

先要导入mysql-connector的jar包，添加依赖关系。然后导入jdbc.properties配置文件

jdbc.properties的配置文件

url=jdbc:mysql://localhost:3306/数据库名
user=root
password=root
driver=com.mysql.jdbc.Driver

下面是JDBCUtils工具类代码实现

package util;

import java.io.FileReader;
import java.io.IOException;
import java.net.URL;
import java.sql.*;
import java.util.Properties;

/**
 * JDBC 工具类
 */
public class JDBCUtils {
    private static String url;
    private static String user;
    private static String password;
    private  static String driver;

    /**
     * 文件读取，只会执行一次，使用静态代码块
     */
    static {
        //读取文件，获取值
        try {
            //1.创建Properties集合类
            Properties pro = new Properties();
            //获取src路径下的文件--->ClassLoader类加载器
            ClassLoader classLoader = JDBCUtils.class.getClassLoader();
            URL resource = classLoader.getResource("jdbc.properties");;
            String path = resource.getPath();
            //2.加载文件
            pro.load(new FileReader(path));
            //3获取数据
            url = pro.getProperty("url");
            user = pro.getProperty("user");
            password = pro.getProperty("password");
            driver = pro.getProperty("driver");
            //4.注册驱动
            Class.forName(driver);
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
    /**
     * 获取连接
     * @return 连接对象
     */
    public static Connection getConnection() throws SQLException {
        Connection conn = DriverManager.getConnection(url, user, password);
        return conn;
    }

    /**
     * 释放资源
     * @param rs
     * @param st
     * @param conn
     */
    public static void close(ResultSet rs, Statement st,Connection conn){
        if (rs != null){
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if(st != null){
            try {
                st.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (conn != null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

再创建一个数据库表的类

public class UserBean {
    private int id;
    private String username;
    private String password;
    public UserBean(int id, String username, String password){
        this.id = id;
        this.username = username;
        this.password = password;
    }

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

最后测试一下

import util.JDBCUtils;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

public class Demo01JDBCUtils {

    public static void main(String[] args) {
        List<UserBean> list = findAll();
        System.out.println("list = " + list);
    }

    //定义一个方法，查询user表的数据将其封装为对象，然后装载集合，返回。
    public static List<UserBean> findAll(){
        Connection conn = null;
        Statement st = null;
        ResultSet rs = null;
        List<UserBean> list = null;
        try {
            conn = JDBCUtils.getConnection();
            //定义sql
            String sql = "SELECT * FROM user";
            //获取执行sql的对象
            st = conn.createStatement();
            //执行sql
            rs = st.executeQuery(sql);
            UserBean bean = null;
            list = new ArrayList<UserBean>();
            while (rs.next()){
                int id = rs.getInt("id");
                String username = rs.getString("username");
                String password = rs.getString("password");
                bean = new UserBean(id,username,password);
                list.add(bean);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            JDBCUtils.close(rs,st,conn);
        }
        return list;
    }
    }

完成