JDBC学习：工具集和主测试类的代码

import jdk.dynalink.beans.StaticClass;

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

public class JDBC_TEST {
    private static String url;
    private static String user;
    private static String password;
    private static String driver;

    static {
        Properties pro = new Properties();

        ClassLoader classLoader = JDBC_TEST.class.getClassLoader();
        URL res = classLoader.getResource("pro.properties");
        String path = res.getPath();
        //获取类加载器。类加载器调用getResource获取当前类所属的project下的src文件夹下某指定名字的文件资源（本质URL）。
        // URL调用getPath获取文件绝对路径。注意绝不能有中文

        try {
            pro.load(new FileReader(path));
            //加载配置文件，获取配置信息
            url = pro.getProperty("url");
            user = pro.getProperty("user");
            password = pro.getProperty("password");

            Class.forName(pro.getProperty("driver"));
        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        Connection connection = null;
        Statement stmt = null;
        ResultSet rs = null;

        try {
            connection = DriverManager.getConnection(url,user,password);
            String sql = "select * from balance";

            stmt = connection.createStatement();
            rs = stmt.executeQuery(sql);

            ArrayList<balance> list = new ArrayList<>();
            balance b = new balance();
            int a;
            String name;
            int balance;
            while(rs.next()){
                a = rs.getInt(1);
                name = rs.getString("Name");
                balance = rs.getInt("balance");

                b.setId(a);
                b.setName(name);
                b.setBalance(balance);

                list.add(b);
            }
            System.out.println(list);

        } catch (Exception e) {
            e.printStackTrace();
        }  finally {
            JDBC_UTILS.close(rs,stmt,connection);
            //调用工具类释放资源
        }
    }
}


工具类的代码：

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class JDBC_UTILS {

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

    public static void close(Statement stmt, Connection con){
        if(stmt != null){
            try {
                stmt.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
        if(con != null) {
            try {
                con.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
    }
}