JDBCUtils工具類創建和使用

先要導入mysql-connector的jar包，添加依賴關系。然后導入jdbc.properties配置文件

jdbc.properties的配置文件

url=jdbc:mysql://localhost:3306/數據庫名
user=root
password=root
driver=com.mysql.jdbc.Driver

下面是JDBCUtils工具類代碼實現

package util;

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

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

    /**
     * 文件讀取，只會執行一次，使用靜態代碼塊
     */
    static {
        //讀取文件，獲取值
        try {
            //1.創建Properties集合類
            Properties pro = new Properties();
            //獲取src路徑下的文件--->ClassLoader類加載器
            ClassLoader classLoader = JDBCUtils.class.getClassLoader();
            URL resource = classLoader.getResource("jdbc.properties");;
            String path = resource.getPath();
            //2.加載文件
            pro.load(new FileReader(path));
            //3獲取數據
            url = pro.getProperty("url");
            user = pro.getProperty("user");
            password = pro.getProperty("password");
            driver = pro.getProperty("driver");
            //4.注冊驅動
            Class.forName(driver);
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
    /**
     * 獲取連接
     * @return 連接對象
     */
    public static Connection getConnection() throws SQLException {
        Connection conn = DriverManager.getConnection(url, user, password);
        return conn;
    }

    /**
     * 釋放資源
     * @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();
            }
        }
    }
}

再創建一個數據庫表的類

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 + '\'' +
                '}';
    }
}

最后測試一下

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);
    }

    //定義一個方法，查詢user表的數據將其封裝為對象，然后裝載集合，返回。
    public static List<UserBean> findAll(){
        Connection conn = null;
        Statement st = null;
        ResultSet rs = null;
        List<UserBean> list = null;
        try {
            conn = JDBCUtils.getConnection();
            //定義sql
            String sql = "SELECT * FROM user";
            //獲取執行sql的對象
            st = conn.createStatement();
            //執行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